(azithromycin) Tablets and Oral Suspension
ZITHROMAX (azithromycin tablets and oral suspension) contains the active ingredient azithromycin, a macrolide antibacterial drug , for oral administration. Azithromycin has the chemical name (2R,3S,4R,5R,8R,10R,11R,12S,13S,14R)-13-[(2,6-dideoxy-3-C-methyl-3-O-methyl-α-L-ribo-hexopyranosyl)oxy]-2-ethyl- 3,4,10-trihydroxy-3,5,6,8,10,12,14-heptamethyl-11-[[3,4,6- trideoxy-3-(dimethylamino)-β-D-xylo-hexopyranosyl]oxy]-1-oxa-6-azacyclopentadecan-15-one. Azithromycin is derived from erythromycin; however, it differs chemically from erythromycin in that a methyl-substituted nitrogen atom is incorporated into the lactone ring. Its molecular formula is C38H72N2O12, and its molecular weight is 749.0. Azithromycin has the following structural formula:
Azithromycin, as the dihydrate, is a white crystalline powder with a molecular formula of C38H72N2O12•2H2O and a molecular weight of 785.0.
ZITHROMAX tablets contain azithromycin dihydrate equivalent to 600 mg azithromycin. They also contain the following inactive ingredients: dibasic calcium phosphate anhydrous, pregelatinized starch, sodium croscarmellose, magnesium stearate, sodium lauryl sulfate, and an aqueous film coat consisting of hypromellose, titanium dioxide, lactose, and triacetin.
ZITHROMAX for oral suspension is supplied in a single-dose packet containing azithromycin dihydrate equivalent to 1 g azithromycin. It also contains the following inactive ingredients: colloidal silicon dioxide, sodium phosphate tribasic, anhydrous; spray dried artificial banana flavor, spray dried artificial cherry flavor, and sucrose.
To reduce the development of drug-resistant bacteria and maintain the effectiveness of ZITHROMAX and other antibacterial drugs, ZITHROMAX should be used only to treat infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.
ZITHROMAX is a macrolide antibacterial drug indicated for the treatment of patients with mild to moderate infections caused by susceptible strains of the designated microorganisms in the specific conditions listed below.
Sexually Transmitted Diseases
Prophylaxis of Disseminated Mycobacterium Avium Complex (MAC) Disease
ZITHROMAX, taken alone or in combination with rifabutin at its approved dose, is indicated for the prevention of disseminated MAC disease in persons with advanced HIV infection. [see DOSAGE AND ADMINISTRATION]
Treatment of Disseminated MAC Disease
ZITHROMAX, taken in combination with ethambutol, is indicated for the treatment of disseminated MAC infections in persons with advanced HIV infection [see Use in Specific Populations and Clinical Studies].
DOSAGE AND ADMINISTRATION
[see INDICATIONS AND USAGE]
ZITHROMAX for oral suspension (single dose 1 g packet) can be taken with or without food after constitution. However, increased tolerability has been observed when tablets are taken with food.
Zithromax for oral suspension (single dose 1 g packet) is not for pediatric use. For pediatric suspension see the prescribing information for ZITHROMAX (azithromycin for oral suspension) 100 mg/5 mL and 200 mg/5 mL bottles.
Directions for administration of ZITHROMAX for oral suspension in the single dose packet (1 g): The entire contents of the packet should be mixed thoroughly with two ounces (approximately 60 mL) of water. Drink the entire contents immediately; add an additional two ounces of water, mix, and drink to ensure complete consumption of dosage. The single dose packet should not be used to administer doses other than 1000 mg of azithromycin.
Sexually Transmitted Diseases
The recommended dose of ZITHROMAX for the treatment of non-gonococcal urethritis and cervicitis due to C. trachomatis is a single 1 gram (1000 mg) dose of ZITHROMAX. This dose can be administered as one single dose packet (1 g).
Prevention of Disseminated MAC Infections
The recommended dose of ZITHROMAX for the prevention of disseminated Mycobacterium avium complex (MAC) disease is: 1200 mg taken once weekly. This dose of ZITHROMAX may be combined with the approved dosage regimen of rifabutin.
Treatment of Disseminated MAC Infections
ZITHROMAX should be taken at a daily dose of 600 mg, in combination with ethambutol at the recommended daily dose of 15 mg/kg. Other antimycobacterial drugs that have shown in vitro activity against MAC may be added to the regimen of azithromycin plus ethambutol at the discretion of the physician or health care provider.
Dosage Forms And Strengths
ZITHROMAX 600 mg tablets (engraved on front with “PFIZER” and on back with “308”) are supplied as white, modified oval-shaped, film-coated tablets containing azithromycin dihydrate equivalent to 600 mg azithromycin. These are packaged in bottles of 30 tablets.
ZITHROMAX for oral suspension 1000 mg/5 mL is supplied in single-dose packets containing azithromycin dihydrate equivalent to 1 gram of azithromycin.
Storage And Handling
ZITHROMAX 600 mg tablets (engraved on front with “PFIZER” and on back with “308”) are supplied as white, modified oval-shaped, film-coated tablets containing azithromycin dihydrate equivalent to 600 mg azithromycin. These are packaged in bottles of 30 tablets. ZITHROMAX tablets are supplied as follows:
Bottles of 30 NDC 0069-3080-30
Tablets should be stored at or below 30°C (86°F).
ZITHROMAX for oral suspension is supplied in single-dose packets containing azithromycin dihydrate equivalent to 1 gram of azithromycin as follows:
Boxes of 10 single-dose packets (1 g) NDC 0069-3051-07
Boxes of 3 single-dose packets (1 g) NDC 0069-3051-75
Store single-dose packets between 5° and 30°C (41° and 86°F).
Distributed by: Pfizer Labs Division of Pfizer Inc., NY, NY 10017. Revised: Dec 2015
Clinical Trials Experience
Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.
In clinical trials, most of the reported adverse reactions were mild to moderate in severity and were reversible upon discontinuation of the drug. Approximately 0.7% of the patients from the multiple-dose clinical trials discontinued ZITHROMAX (azithromycin) therapy because of treatment-related adverse reactions. Serious adverse reactions included angioedema and cholestatic jaundice. Most of the adverse reactions leading to discontinuation were related to the gastrointestinal tract, e.g., nausea, vomiting, diarrhea, or abdominal pain. [see Clinical Studies]
Overall, the most common adverse reactions in adult patients receiving a multiple-dose regimen of ZITHROMAX were related to the gastrointestinal system with diarrhea/loose stools (5%), nausea (3%), and abdominal pain (3%) being the most frequently reported.
No other adverse reactions occurred in patients on the multiple-dose regimen of ZITHROMAX with a frequency greater than 1%. Adverse reactions that occurred with a frequency of 1% or less included the following:
Cardiovascular: Palpitations and chest pain.
Allergic: Rash, photosensitivity, and angioedema.
Chronic therapy with 1200 mg weekly regimen
The nature of adverse reactions seen with the 1200 mg weekly dosing regimen for the prevention of Mycobacterium avium infection in severely immunocompromised HIV-infected patients were similar to those seen with short-term dosing regimens. [see Clinical Studies]
Chronic Therapy With 600 mg Daily Regimen Combined With Ethambutol
The nature of adverse reactions seen with the 600 mg daily dosing regimen for the treatment of Mycobacterium avium complex infection in severely immunocompromised HIV-infected patients were similar to those seen with short term dosing regimens. Five percent of patients experienced reversible hearing impairment in the pivotal clinical trial for the treatment of disseminated MAC in patients with AIDS. Hearing impairment has been reported with macrolide antibiotics, especially at higher doses. Other treatment related adverse reactions occurring in > 5% of subjects and seen at any time during a median of 87.5 days of therapy include: abdominal pain (14%), nausea (14%), vomiting (13%), diarrhea (12%), flatulence (5%), headache (5%), and abnormal vision (5%). Discontinuations from treatment due to laboratory abnormalities or adverse reactions considered related to study drug occurred in 8 of 88 (9.1%) of subjects.
Single 1 Gram Dose Regimen
Overall, the most common adverse reactions in patients receiving a single-dose regimen of 1 gram of ZITHROMAX were related to the gastrointestinal system and were more frequently reported than in patients receiving the multiple-dose regimen.
Adverse reactions that occurred in patients on the single 1 gram dosing regimen of ZITHROMAX with a frequency of 1% or greater included diarrhea/loose stools (7%), nausea (5%), abdominal pain (5%), vomiting (2%), dyspepsia (1%), and vaginitis (1%).
The following adverse reactions have been identified during post approval use of azithromycin. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.
Adverse reactions reported with azithromycin during the postmarketing period in adult and/or pediatric patients for which a causal relationship may not be established include:
Genitourinary: Interstitial nephritis, acute renal failure, and vaginitis.
Psychiatric: Aggressive reaction and anxiety.
Significant abnormalities (irrespective of drug relationship) occurring during the clinical trials were reported as follows:
- With an incidence of 1-2%, elevated serum creatine phosphokinase, potassium, ALT (SGPT), GGT, and AST (SGOT).
- With an incidence of less than 1%, leukopenia, neutropenia, decreased platelet count, elevated serum alkaline phosphatase, bilirubin, BUN, creatinine, blood glucose, LDH, and phosphate.
When follow-up was provided, changes in laboratory tests appeared to be reversible.
In multiple-dose clinical trials involving more than 3000 patients, 3 patients discontinued therapy because of treatment-related liver enzyme abnormalities and 1 because of a renal function abnormality.
In a phase 1 drug interaction study performed in normal volunteers, 1 of 6 subjects given the combination of azithromycin and rifabutin, 1 of 7 given rifabutin alone, and 0 of 6 given azithromycin alone developed a clinically significant neutropenia ( < 500 cells/mm³).
Chronic therapy (median duration: 87.5 days, range: 1-229 days) that resulted in laboratory abnormalities in > 5% of subjects with normal baseline values in the pivotal trial for treatment of disseminated MAC in severely immunocompromised HIV-infected patients treated with azithromycin 600 mg daily in combination with ethambutol include: a reduction in absolute neutrophils to < 50% of the lower limit of normal (10/52, 19%) and an increase to five times the upper limit of normal in alkaline phosphatase (3/35, 9%). These findings in subjects with normal baseline values are similar when compared to all subjects for analyses of neutrophil reductions (22/75, 29%) and elevated alkaline phosphatase (16/80, 20%). Causality of these laboratory abnormalities due to the use of study drug has not been established.
Co-administration of nelfinavir at steady-state with a single oral dose of azithromycin resulted in increased azithromycin serum concentrations. Although a dose adjustment of azithromycin is not recommended when administered in combination with nelfinavir, close monitoring for known adverse reactions of azithromycin, such as liver enzyme abnormalities and hearing impairment, is warranted. [see ADVERSE REACTIONS]
Spontaneous post-marketing reports suggest that concomitant administration of azithromycin may potentiate the effects of oral anticoagulants such as warfarin, although the prothrombin time was not affected in the dedicated drug interaction study with azithromycin and warfarin. Prothrombin times should be carefully monitored while patients are receiving azithromycin and oral anticoagulants concomitantly.
Potential Drug-Drug Interaction With Macrolides
Interactions with the following drugs listed below have not been reported in clinical trials with azithromycin; however, no specific drug interaction studies have been performed to evaluate potential drug-drug interaction. However, drug interactions have been observed with other macrolide products. Until further data are developed regarding drug interactions when digoxin or phenytoin are used with azithromycin careful monitoring of patients is advised.
Included as part of the PRECAUTIONS section.
Serious allergic reactions, including angioedema, anaphylaxis, and dermatologic reactions including Stevens-Johnson Syndrome, toxic epidermal necrolysis, and Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) have been reported rarely in patients on azithromycin therapy. [see CONTRAINDICATIONS]
Fatalities have been reported. Despite initially successful symptomatic treatment of the allergic symptoms, when symptomatic therapy was discontinued, the allergic symptoms recurred soon thereafter in some patients without further azithromycin exposure. These patients required prolonged periods of observation and symptomatic treatment. The relationship of these episodes to the long tissue half-life of azithromycin and subsequent prolonged exposure to antigen is presently unknown.
If an allergic reaction occurs, the drug should be discontinued and appropriate therapy should be instituted. Physicians should be aware that allergic symptoms may reappear when symptomatic therapy is discontinued.
Abnormal liver function, hepatitis, cholestatic jaundice, hepatic necrosis, and hepatic failure have been reported, some of which have resulted in death. Discontinue azithromycin immediately if signs and symptoms of hepatitis occur.
Infantile Hypertrophic Pyloric Stenosis (IHPS)
Following the use of azithromycin in neonates (treatment up to 42 days of life), infantile hypertrophic pyloric stenosis (IHPS) has been reported. Parents and caregivers should be informed to contact their physician if vomiting or irritability with feeding occurs.
Prolonged cardiac repolarization and QT interval, imparting a risk of developing cardiac arrhythmia and torsades de pointes, have been seen with treatment with macrolides, including azithromycin. Cases of torsades de pointes have been spontaneously reported during postmarketing surveillance in patients receiving azithromycin. Providers should consider the risk of QT prolongation which can be fatal when weighing the risks and benefits of azithromycin for at-risk groups including:
- patients with known prolongation of the QT interval, a history of torsades de pointes, congenital long QT syndrome, bradyarrhythmias or uncompensated heart failure
- patients on drugs known to prolong the QT interval
- patients with ongoing proarrhythmic conditions such as uncorrected hypokalemia or hypomagnesemia, clinically significant bradycardia, and in patients receiving Class IA (quinidine, procainamide) or Class III (dofetilide, amiodarone, sotalol) antiarrhythmic agents.
Elderly patients may be more susceptible to drug-associated effects on the QT interval.
Clostridium Difficile-Associated Diarrhea (CDAD)
CDAD has been reported with use of nearly all antibacterial agents, including ZITHROMAX, and may range in severity from mild diarrhea to fatal colitis. Treatment with antibacterial agents alters the normal flora of the colon, leading to overgrowth of C. difficile.
C. difficile produces toxins A and B which contribute to the development of CDAD. Hypertoxin-producing strains of C. difficile cause increased morbidity and mortality, as these infections can be refractory to antibacterial therapy and may require colectomy. CDAD must be considered in all patients who present with diarrhea following antibiotic use. Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents.
If CDAD is suspected or confirmed, ongoing antibiotic use not directed against C. difficile may need to be discontinued. Appropriate fluid and electrolyte management, protein supplementation, antibiotic treatment of C. difficile, and surgical evaluation should be instituted as clinically indicated.
Exacerbation Of Myasthenia Gravis
Exacerbations of symptoms of myasthenia gravis and new onset of myasthenic syndrome have been reported in patients receiving azitrhromycin therapy.
Use In Sexually Transmitted Infections
Antibacterial agents used in high doses for short periods of time to treat non-gonococcal urethritis may mask or delay the symptoms of incubating gonorrhea or syphilis. All patients with sexually transmitted urethritis or cervicitis should have a serologic test for syphilis and appropriate cultures for gonorrhea performed at the time of diagnosis. Appropriate antibacterial therapy and follow-up tests for these diseases should be initiated if infection is confirmed.
Development Of Drug-Resistant Bacteria
Prescribing ZITHROMAX in the absence of a proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.
Carcinogenesis, Mutagenesis, Impairment Of Fertility
Long-term studies in animals have not been performed to evaluate carcinogenic potential. Azithromycin has shown no mutagenic potential in standard laboratory tests: mouse lymphoma assay, human lymphocyte clastogenic assay, and mouse bone marrow clastogenic assay. No evidence of impaired fertility due to azithromycin was found in rats given daily doses up to 10 mg/kg (approximately 0.2 times an adult daily dose of 600 mg based on body surface area).
Use In Specific Populations
Pregnancy Category B: Reproduction studies have been performed in rats and mice at doses up to moderately maternally toxic dose levels (i.e., 200 mg/kg/day). These daily doses in rats and mice, based on body surface area, are estimated to be 3.2 and 1.6 times, respectively, an adult daily dose of 600 mg. In the animal studies, no evidence of harm to the fetus due to azithromycin was found. There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, azithromycin should be used during pregnancy only if clearly needed.
Azithromycin has been reported to be excreted in breast milk in small amounts. Caution should be exercised when azithromycin is administered to a nursing woman.
In controlled clinical studies, azithromycin has been administered to pediatric patients ranging in age from 6 months to 12 years. For information regarding the use of ZITHROMAX (azithromycin for oral suspension) in the treatment of pediatric patients, [see INDICATIONS AND USAGE and DOSAGE AND ADMINISTRATION] of the prescribing information for ZITHROMAX (azithromycin for oral suspension) 100 mg/5 mL and 200 mg/5 mL bottles.
HIV-Infected Pediatric Patients: The safety and efficacy of azithromycin for the prevention or treatment of MAC in HIV-infected children have not been established. Safety data are available for 72 children 5 months to 18 years of age (mean 7 years) who received azithromycin for treatment of opportunistic infections. The mean duration of therapy was 242 days (range 3-2004 days) at doses of < 1 to 52 mg/kg/day (mean 12 mg/kg/day). Adverse reactions were similar to those observed in the adult population, most of which involved the gastrointestinal tract. Treatment-related reversible hearing impairment in children was observed in 4 subjects (5.6%). Two (2.8%) children prematurely discontinued treatment due to adverse reactions: one due to back pain and one due to abdominal pain, hot and cold flushes, dizziness, headache, and numbness. A third child discontinued due to a laboratory abnormality (eosinophilia). The protocols upon which these data are based specified a daily dose of 10-20 mg/kg/day (oral and/or IV) of azithromycin.
In multiple-dose clinical trials of oral azithromycin, 9% of patients were at least 65 years of age (458/4949) and 3% of patients (144/4949) were at least 75 years of age. No overall differences in safety or effectiveness were observed between these subjects and younger subjects, and other reported clinical experience has not identified differences in responses between the elderly and younger patients, but greater sensitivity of some older individuals cannot be ruled out.
Elderly patients may be more susceptible to development of torsades de pointes arrhythmias than younger patients. [see WARNINGS AND PRECAUTIONS]
ZITHROMAX 600 mg tablets contain 2.1 mg of sodium per tablet. ZITHROMAX for oral suspension 1 gram single-dose packets contain 37.0 mg of sodium per packet.
Geriatric Patients with Opportunistic Infections, Including (MAC) Disease
Safety data are available for 30 patients (65-94 years old) treated with azithromycin at doses > 300 mg/day for a mean of 207 days. These patients were treated for a variety of opportunistic infections, including MAC. The adverse reaction were generally similar to that seen in younger patients, except for a higher incidence of adverse reactions relating to the gastrointestinal system and to reversible impairment of hearing. [see DOSAGE AND ADMINISTRATION]
Adverse reactions experienced in higher than recommended doses were similar to those seen at normal doses. In the event of overdosage, general symptomatic and supportive measures are indicated as required.
ZITHROMAX is contraindicated in patients with a history of cholestatic jaundice/hepatic dysfunction associated with prior use of azithromycin.
Mechanism Of Action
Azithromycin is a macrolide antibacterial drug. [see Microbiology]
Azithromycin concentrates in phagocytes and fibroblasts as demonstrated by in vitro incubation techniques. Using such methodology, the ratio of intracellular to extracellular concentration was > 30 after one hr of incubation. In vivo studies suggest that concentration in phagocytes may contribute to drug distribution to inflamed tissues.
Based on animal models of infection, the antibacterial activity of azithromycin appears to correlate with the ratio of area under the concentration-time curve to minimum inhibitory concentration (AUC/MIC) for certain pathogens (S. pneumoniae and S. aureus). The principal pharmacokinetic/pharmacodynamic parameter best associated with clinical and microbiological cure has not been elucidated in clinical trials with azithromycin.
QTc interval prolongation was studied in a randomized, placebo-controlled parallel trial in 116 healthy subjects who received either chloroquine (1000 mg) alone or in combination with oral azithromycin (500 mg, 1000 mg, and 1500 mg once daily). Coadministration of azithromycin increased the QTc interval in a dose- and concentration- dependent manner. In comparison to chloroquine alone, the maximum mean (95% upper confidence bound) increases in QTcF were 5 (10) ms, 7 (12) ms and 9 (14) ms with the co-administration of 500 mg, 1000 mg and 1500 mg azithromycin, respectively.
The pharmacokinetic parameters of azithromycin in plasma after dosing as per labeled recommendations in healthy young adults and asymptomatic HIV-positive adults (age 18-40 years old) are portrayed in the following chart:
MEAN (CV%) PK PARAMETER
|DOSE/DOSAGE FORM (serum, except as indicated)||Subjects||Day No.||Cmax (mcg/mL)||Tmax (hr)||C24 (mcg/mL)||AUC (mcg•hr/mL)||T½ (hr)||Urinary Excretion (% of dose)|
|500 mg/250 mg capsule||12||1||0.41||2.5||0.05||2.6a||-||4.5|
|and 250 mg on Days 2-5||12||5||0.24||3.2||0.05||2.1a||-||6.5|
|1200 mg/600 mg tablets||12||1||0.66||2.5||0.074||6.8b||40||-|
|600 mg tablet/day||7||1||0.33||2.0||0.039||2.4a|
|600 mg tablet/day (leukocytes)||7||22||252||10.9||146||4763a||82.8||-|
With a regimen of 500 mg on Day 1 and 250 mg/day on Days 2-5, Cmin and Cmax remained essentially unchanged from Day 2 through Day 5 of therapy. However, without a loading dose, azithromycin Cmin levels required 5 to 7 days to reach steady state.
In asymptomatic HIV-positive adult subjects receiving 600 mg ZITHROMAX tablets once daily for 22 days, steady state azithromycin serum levels were achieved by Day 15 of dosing.
The high values in adults for apparent steady-state volume of distribution (31.1 L/kg) and plasma clearance (630 mL/min) suggest that the prolonged half-life is due to extensive uptake and subsequent release of drug from tissues.
The 1 gram single-dose packet is bioequivalent to four 250 mg azithromycin capsule
When the oral suspension of azithromycin was administered with food, the Cmax increased by 46% and the AUC by 14%.
The absolute bioavailability of two 600 mg tablets was 34% (CV=56%). Administration of two 600 mg tablets with food increased Cmax by 31% (CV=43%) while the extent of absorption (AUC) was unchanged (mean ratio of AUCs=1.00; CV=55%).
The serum protein binding of azithromycin is variable in the concentration range approximating human exposure, decreasing from 51% at 0.02 μg/mL to 7% at 2 μg/mL.
The antibacterial activity of azithromycin is pH related and appears to be reduced with decreasing pH. However, the extensive distribution of drug to tissues may be relevant to clinical activity.
Azithromycin has been shown to penetrate into tissues in humans, including skin, lung, tonsil, and cervix. Extensive tissue distribution was confirmed by examination of additional tissues and fluids (bone, ejaculum, prostate, ovary, uterus, salpinx, stomach, liver, and gallbladder). As there are no data from adequate and well-controlled studies of azithromycin treatment of infections in these additional body sites, the clinical importance of these tissue concentration data is unknown.
Following oral administration of a single 1200 mg dose (two 600 mg tablets), the mean maximum concentration in peripheral leukocytes was 140 μg/mL. Concentration remained above 32 μg/mL, for approximately 60 hr. The mean half-lives for 6 males and 6 females were 34 hr and 57 hr, respectively. Leukocyte-to-plasma Cmax ratios for males and females were 258 (±77%) and 175 (±60%), respectively, and the AUC ratios were 804 (±31%) and 541 (±28%) respectively. The clinical relevance of these findings is unknown.
Following oral administration of multiple daily doses of 600 mg (1 tablet/day) to asymptomatic HIV-positive adults, mean maximum concentration in peripheral leukocytes was 252 μg/mL (±49%). Trough concentrations in peripheral leukocytes at steady-state averaged 146 μg/mL (±33%). The mean leukocyte-to-serum Cmax ratio was 456 (±38%) and the mean leukocyte to serum AUC ratio was 816 (±31%). The clinical relevance of these findings is unknown.
In vitro and in vivo studies to assess the metabolism of azithromycin have not been performed.
Plasma concentrations of azithromycin following single 500 mg oral and IV doses declined in a polyphasic pattern resulting in an average terminal half-life of 68 hr. Biliary excretion of azithromycin, predominantly as unchanged drug, is a major route of elimination. Over the course of a week, approximately 6% of the administered dose appears as unchanged drug in urine.
Azithromycin pharmacokinetics was investigated in 42 adults (21 to 85 years of age) with varying degrees of renal impairment. Following the oral administration of a single 1.0 g dose of azithromycin (4 x 250 mg capsules), the mean Cmax and AUC0-120 increased by 5.1% and 4.2%, respectively, in subjects with GFR 10 to 80 mL/min compared to subjects with normal renal function (GFR > 80 mL/min). The mean Cmax and AUC0-120 increased 61% and 35%, respectively, in subjects with end-stage renal disease (GFR < 10 mL/min) compared to subjects with normal renal function (GFR > 80 mL/min).
The pharmacokinetics of azithromycin in subjects with hepatic impairment has not been established.
There are no significant differences in the disposition of azithromycin between male and female subjects. No dosage adjustment is recommended on the basis of gender.
Pharmacokinetic parameters in older volunteers (65 to 85 years old) were similar to those in younger volunteers (18 to 40 years old) for the 5-day therapeutic regimen. Dosage adjustment does not appear to be necessary for older patients with normal renal and hepatic function receiving treatment with this dosage regimen. [see Geriatric Use]
For information regarding the pharmacokinetics of ZITHROMAX (azithromycin for oral suspension) in pediatric patients, see the prescribing information for ZITHROMAX (azithromycin for oral suspension) 100 mg/5 mL and 200 mg/5 mL bottles.
Drug interaction studies were performed with azithromycin and other drugs likely to be co-administered. The effects of coadministration of azithromycin on the pharmacokinetics of other drugs are shown in Table 1 and the effects of other drugs on the pharmacokinetics of azithromycin are shown in Table 2.
Co-administration of azithromycin at therapeutic doses had a modest effect on the pharmacokinetics of the drugs listed in Table 1. No dosage adjustment of drugs listed in Table 1 is recommended when co-administered with azithromycin.
Co-administration of azithromycin with efavirenz or fluconazole had a modest effect on the pharmacokinetics of azithromycin. Nelfinavir significantly increased the Cmax and AUC of azithromycin. No dosage adjustment of azithromycin is recommended when administered with drugs listed in Table 2. [see DRUG INTERACTIONS]
Table 1: Drug Interactions: Pharmacokinetic Parameters
for Co-administered Drugs in the Presence of Azithromycin
|Co-administered Drug||Dose of Co-administered Drug||Dose of Azithromycin||n||Ratio (with/without azithromycin) of Co-administered Drug Pharmacokinetic Parameters (90% CI); No Effect = 1.00|
|Mean Cmax||Mean AUC|
|Atorvastatin||10 mg/day for 8 days||500 mg/day orally on days 6-8||12||0.83
(0.63 to 1.08)
(0.81 to 1.25)
|Carbamazepine||200 mg/day for 2 days, then 200 mg twice a day for 18 days||500 mg/day orally for days 16-18||7||0.97
(0.88 to 1.06)
(0.88 to 1.06)
|Cetirizine||20 mg/day for 11 days||500 mg orally on day 7, then 250 mg/day on days 8-11||14||1.03
(0.93 to 1.14)
(0.92 to 1.13)
|Didanosine||200 mg orally twice a day for 21 days||1,200 mg/day orally on days 8-21||6||1.44
(0.85 to 2.43)
(0.83 to 1.57)
|Efavirenz||400 mg/day for 7 days||600 mg orally on day 7||14||1.04*||0.95*|
|Fluconazole||200 mg orally single dose||1,200 mg orally single dose||18||1.04
(0.98 to 1.11)
(0.97 to 1.05)
|Indinavir||800 mg three times a day for 5 days||1,200 mg orally on day 5||18||0.96
(0.86 to 1.08)
(0.81 to 1.00)
|Midazolam||15 mg orally on day 3||500 mg/day orally for 3 days||12||1.27
(0.89 to 1.81)
(1.01 to 1.56)
|Nelfinavir||750 mg three times a day for 11 days||1,200 mg orally on day 9||14||0.90
(0.81 to 1.01)
(0.78 to 0.93)
|Sildenafil||100 mg on days 1 and 4||500 mg/day orally for 3 days||12||1.16 (0.86 to 1.57)||0.92 (0.75 to 1.12)|
|Theophylline||4 mg/kg IV on days 1, 11, 25||500 mg orally on day 7, 250 mg/day on days 8-11||10||1.19
(1.02 to 1.40)
(0.86 to 1.22)
|Theophylline||300 mg orally BID x 15 days||500 mg orally on day 6, then 250 mg/day on days 7-10||8||1.09
(0.92 to 1.29)
(0.89 to 1.31)
|Triazolam||0.125 mg on day 2||500 mg orally on day 1, then 250 mg/day on day 2||12||1.06*||1.02*|
|Trimethoprim/ Sulfamethoxazole||160 mg/800 mg/day orally for 7 days||1,200 mg orally on day 7||12||0.85
(0.75 to 0.97)/ 0.90
(0.78 to 1.03)
(0.80 to 0.95/ 0.96
(0.88 to 1.03)
|Zidovudine||500 mg/day orally for 21 days||600 mg/day orally for 14 days||5||1.12
(0.42 to 3.02)
(0.52 to 1.70)
|Zidovudine||500 mg/day orally for 21 days||1,200 mg/day orally for 14 days||4||1.31
(0.43 to 3.97)
(0.69 to 2.43)
|* - 90% Confidence interval not reported|
Table 2: Drug Interactions: Pharmacokinetic Parameters
for Azithromycin in the Presence of Co-administered Drugs. [see DRUG
|Co-administered Drug||Dose of Coadministered Drug||Dose of Azithromycin||n||Ratio (with/without co-administered drug) of Azithromycin Pharmacokinetic Parameters (90% CI); No Effect = 1.00|
|Mean Cmax||Mean AUC|
|Efavirenz||400 mg/day for 7 days||600 mg orally on day 7||14||1.22
(1.04 to 1.42)
|Fluconazole||200 mg orally single dose||1,200 mg orally single dose||18||0.82
(0.66 to 1.02)
(0.94 to 1.22)
|Nelfinavir||750 mg three times a day for 11 days||1,200 mg orally on day 9||14||2.36
(1.77 to 3.15)
(1.80 to 2.50)
|* - 90% Confidence interval not reported|
Azithromycin has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections as described in [see INDICATIONS AND USAGE].
Aerobic Gram-Positive Microorganisms
NOTE: Azithromycin demonstrates cross-resistance with erythromycin-resistant gram-positive strains. Most strains of Enterococcus faecalis and methicillin-resistant staphylococci are resistant to azithromycin.
Aerobic Gram-Negative Microorganisms
Beta-lactamase production should have no effect on azithromycin activity.
Azithromycin has been shown to be active in vitro and in the prevention and treatment of disease caused by the following microorganisms:
Mycobacterium avium complex (MAC) consisting of:
The following in vitro data are available, but their clinical significance is unknown.
Azithromycin exhibits in vitro minimal inhibitory concentrations (MICs) of 2.0 μg/mL or less against most ( ≥ 90%) strains of the following microorganisms; however, the safety and effectiveness of azithromycin in treating clinical infections due to these microorganisms have not been established in adequate and well-controlled trials.
Aerobic Gram-Positive Microorganisms
Streptococci (Groups C, F, G)
Viridans group streptococci
Aerobic Gram-Negative Microorganisms
Susceptibility Testing of Bacteria Excluding Mycobacteria
The in vitro potency of azithromycin is markedly affected by the pH of the microbiological growth medium during incubation. Incubation in a 10% CO2 atmosphere will result in lowering of media pH (7.2 to 6.6) within 18 hr and in an apparent reduction of the in vitro potency of azithromycin. Thus, the initial pH of the growth medium should be 7.2-7.4, and the CO2 content of the incubation atmosphere should be as low as practical.
Azithromycin can be solubilized for in vitro susceptibility testing by dissolving in a minimum amount of 95% ethanol and diluting to working concentration with water.
Quantitative methods are used to determine minimal inhibitory concentrations that provide reproducible estimates of the susceptibility of bacteria to antibacterial compounds. One such standardized procedure uses a standardized dilution method1 (broth, agar or microdilution) or equivalent with azithromycin powder. The MIC values should be interpreted according to the following criteria:
|< 2||Susceptible (S)|
|> 8||Resistant (R)|
A report of “Susceptible” indicates that the pathogen is likely to respond to monotherapy with azithromycin. A report of “Intermediate” indicates that the result should be considered equivocal, and, if the microorganism is not fully susceptible to alternative, clinically feasible drugs, the test should be repeated. This category also provides a buffer zone which prevents small uncontrolled technical factors from causing major discrepancies in interpretation. A report of “Resistant” indicates that usually achievable drug concentrations are unlikely to be inhibitory and that other therapy should be selected.
Measurement of MIC or minimum bacterial concentration (MBC) and achieved antibacterial compound concentrations may be appropriate to guide therapy in some infections. [see CLINICAL PHARMACOLOGY] section for further information on drug concentrations achieved in infected body sites and other pharmacokinetic properties of this antibacterial drug product.)
Standardized susceptibility test procedures require the use of laboratory control microorganisms. Standard azithromycin powder should provide the following MIC values:
|Escherichia coli ATCC 25922||2.0-8.0|
|Enterococcus faecalis ATCC 29212||1.0-4.0|
|Staphylococcus aureus ATCC 29213||0.25-1.0|
Quantitative methods that require measurement of zone diameters also provide reproducible estimates of the susceptibility of bacteria to antibacterial compounds. One such standardized procedure2 that has been recommended for use with disks to test the susceptibility of microorganisms to azithromycin uses the 15 μg azithromycin disk. Interpretation involves the correlation of the diameter obtained in the disk test with the MIC for azithromycin.
Reports from the laboratory providing results of the standard single-disk susceptibility test with a 15 μg azithromycin disk should be interpreted according to the following criteria:
|Zone Diameter (mm)||Interpretation|
|≥ 18||Susceptible (S)|
|≤ 13||Resistant (R)|
Interpretation should be as stated above for results using dilution techniques.
As with standardized dilution techniques, diffusion methods require the use of laboratory control microorganisms. The 15 μg azithromycin disk should provide the following zone diameters in these laboratory test quality control strains:
|Microorganism||Zone Diameter (mm)|
|Staphylococcus aureus ATCC 25923||21-26|
In Vitro Activity of Azithromycin Against Mycobacteria
Azithromycin has demonstrated in vitro activity against MAC organisms. While gene probe techniques may be used to distinguish between M. avium and M. intracellulare, many studies only reported results on MAC isolates. Azithromycin has also been shown to be active against phagocytized MAC organisms in mouse and human macrophage cell cultures as well as in the beige mouse infection model.
Various in vitro methodologies employing broth or solid media at different pHs, with and without oleic acid-albumindextrose- catalase (OADC), have been used to determine azithromycin MIC values for MAC strains. In general, azithromycin MIC values decreased 4-8 fold as the pH of Middlebrook 7H11 agar media increased from 6.6 to 7.4. At pH 7.4, azithromycin MIC values determined with Mueller-Hinton agar were 4 fold higher than that observed with Middlebrook 7H12 media at the same pH. Utilization of oleic OADC in these assays has been shown to further alter MIC values. The relationship between azithromycin and clarithromycin MIC values has not been established. In general, azithromycin MIC values were observed to be 2-32 fold higher than clarithromycin independent of the susceptibility method employed.
The ability to correlate MIC values and plasma drug levels is difficult as azithromycin concentrates in macrophages and tissues. [see CLINICAL PHARMACOLOGY]
Complete cross-resistance between azithromycin and clarithromycin has been observed with MAC isolates. In most isolates, a singlepoint mutation at a position that is homologous to the Escherichia coli positions 2058 or 2059 on the 23S rRNA gene is the mechanism producing this cross-resistance pattern.3,4 MAC isolates exhibiting cross-resistance show an increase in azithromycin MICs to ≥ 128 μg/mL with clarithromycin MICs increasing to ≥ 32 μg/mL. These MIC values were determined employing the radiometric broth dilution susceptibility testing method with Middlebrook 7H12 medium. The clinical significance of azithromycin and clarithromycin cross-resistance is not fully understood at this time but preclinical data suggest that reduced activity to both agents will occur after MAC strains produce the 23S rRNA mutation.
Susceptibility Testing for MAC
The disk diffusion techniques and dilution methods for susceptibility testing against gram-positive and gram-negative bacteria should not be used for determining azithromycin MIC values against mycobacteria. In vitro susceptibility testing methods and diagnostic products currently available for determining MIC values against MAC organisms have not been standardized or validated. Azithromycin MIC values will vary depending on the susceptibility testing method employed, composition and pH of media, and the utilization of nutritional supplements. Breakpoints to determine whether clinical isolates of M. avium or M. intracellulare are susceptible or resistant to azithromycin have not been established.
The clinical relevance of azithromycin in vitro susceptibility test results for other mycobacterial species, including Mycobacterium tuberculosis, using any susceptibility testing method has not been determined.
Phospholipidosis (intracellular phospholipid accumulation) has been observed in some tissues of mice, rats, and dogs given multiple doses of azithromycin. It has been demonstrated in numerous organ systems (e.g., eye, dorsal root ganglia, liver, gallbladder, kidney, spleen, and/or pancreas) in dogs and rats treated with azithromycin at doses which, expressed on the basis of body surface area, are similar to or less than the highest recommended adult human dose. This effect has been shown to be reversible after cessation of azithromycin treatment. Based on the pharmacokinetic data, phospholipidosis has been seen in the rat (50 mg/kg/day dose) at the observed maximal plasma concentration of 1.3 mcg/mL (1.6 times the observed Cmax of 0.821 mcg/mL at the adult dose of 2 g.) Similarly, it has been shown in the dog (10 mg/kg/day dose) at the observed maximal serum concentration of 1 mcg/mL (1.2 times the observed Cmax of 0.821 mcg/mL at the adult dose of 2 g).
Phospholipidosis was also observed in neonatal rats dosed for 18 days at 30 mg/kg/day, which is less than the pediatric dose of 60 mg/kg based on the surface area. It was not observed in neonatal rats treated for 10 days at 40 mg/kg/day with mean maximal serum concentrations of 1.86 mcg/mL, approximately 1.5 times the Cmax of 1.27 mcg/mL at the pediatric dose. Phospholipidosis has been observed in neonatal dogs (10 mg/kg/day) at maximum mean whole blood concentrations of 3.54 mcg/mL, approximately 3 times the pediatric dose Cmax. The significance of the finding for animals and for humans is unknown.
Clinical Studies In Patients With Advanced HIV Infection For The Prevention And Treatment Of Disease Due To Disseminated Mycobacterium avium Complex (MAC)
[see INDICATIONS AND USAGE]
Prevention of Disseminated MAC Disease
Two randomized, double-blind clinical trials were performed in patients with CD4 counts < 100 cells/μL. The first trial (Study 155) compared azithromycin (1200 mg once weekly) to placebo and enrolled 182 patients with a mean CD4 count of 35 cells/mcgL. The second trial (Study 174) randomized 723 patients to either azithromycin (1200 mg once weekly), rifabutin (300 mg daily), or the combination of both. The mean CD4 count was 51 cells/mcgL. The primary endpoint in these trials was disseminated MAC disease. Other endpoints included the incidence of clinically significant MAC disease and discontinuations from therapy for drug-related side effects.
In Study 155, 85 patients randomized to receive azithromycin and 89 patients randomized to receive placebo met the entrance criteria. Cumulative incidences at 6, 12, and 18 months of the possible outcomes are in the following table:
|Cumulative Incidence Rate, %: Placebo (n=89)|
|Month||MAC Free and Alive||MAC||Adverse Experience||Lost to Follow-up|
|Cumulative Incidence Rate, %: Azithromycin (n=85)|
|Month||MAC Free and Alive||MAC||Adverse Experience||Lost to Follow-up|
The difference in the one-year cumulative incidence rates of disseminated MAC disease (placebo – azithromycin) is 10.9%. This difference is statistically significant (p=0.037) with a 95% confidence interval for this difference of 0.8%, 20.9%. The comparable number of patients experiencing adverse events and the fewer number of patients lost to follow-up on azithromycin should be taken into account when interpreting the significance of this difference.
In Study 174, 223 patients randomized to receive rifabutin, 223 patients randomized to receive azithromycin, and 218 patients randomized to receive both rifabutin and azithromycin met the entrance criteria. Cumulative incidences at 6, 12, and 18 months of the possible outcomes are recorded in the following table:
|Cumulative Incidence Rate, %: Rifabutin (n=223)|
|Month||MAC Free and Alive||MAC||Adverse Experience||Lost to Follow-up|
|Cumulative Incidence Rate, %: Azithromycin (n=223)|
|Month||MAC Free and Alive||MAC||Adverse Experience||Lost to Follow-up|
|Cumulative Incidence Rate, %: Azithromycin/Rifabutin Combination (n=218)|
|Month||MAC Free and Alive||MAC||Adverse Experience||Lost to Follow-up|
Comparing the cumulative one-year incidence rates, azithromycin monotherapy is at least as effective as rifabutin monotherapy. The difference (rifabutin – azithromycin) in the one-year rates (7.6%) is statistically significant (p=0.022) with an adjusted 95% confidence interval (0.9%, 14.3%). Additionally, azithromycin/rifabutin combination therapy is more effective than rifabutin alone. The difference (rifabutin – azithromycin/rifabutin) in the cumulative one-year incidence rates (12.5%) is statistically significant (p < 0.001) with an adjusted 95% confidence interval of 6.6%, 18.4%. The comparable number of patients experiencing adverse events and the fewer number of patients lost to follow-up on rifabutin should be taken into account when interpreting the significance of this difference.
In Study 174, sensitivity testing5 was performed on all available MAC isolates from subjects randomized to either azithromycin, rifabutin, or the combination. The distribution of MIC values for azithromycin from susceptibility testing of the breakthrough isolates was similar between trial arms. As the efficacy of azithromycin in the treatment of disseminated MAC has not been established, the clinical relevance of these in vitro MICs as an indicator of susceptibility or resistance is not known.
Clinically Significant Disseminated MAC Disease
In association with the decreased incidence of bacteremia, patients in the groups randomized to either azithromycin alone or azithromycin in combination with rifabutin showed reductions in the signs and symptoms of disseminated MAC disease, including fever or night sweats, weight loss, and anemia.
Discontinuations from Therapy for Drug-Related Side Effects
In Study 155, discontinuations for drug-related toxicity occurred in 8.2% of subjects treated with azithromycin and 2.3% of those given placebo (p=0.121). In Study 174, more subjects discontinued from the combination of azithromycin and rifabutin (22.7%) than from azithromycin alone (13.5%; p=0.026) or rifabutin alone (15.9%; p=0.209).
As these patients with advanced HIV disease were taking multiple concomitant medications and experienced a variety of intercurrent illnesses, it was often difficult to attribute adverse reactions to study medication. Overall, the nature of adverse reactions seen on the weekly dosage regimen of azithromycin over a period of approximately one year in patients with advanced HIV disease were similar to that previously reported for shorter course therapies.
INCIDENCE OF ONE OR MORE TREATMENT-RELATEDa
ADVERSE REACTIONSb IN HIV INFECTED PATIENTS RECEIVING PROPHYLAXIS
FOR DISSEMINATED MAC OVER APPROXIMATELY 1 YEAR
|Study 155||Study 174|
|Azithromycin 1200 mg weekly
|Azithromycin 1200 mg weekly
|Rifabutin 300 mg daily
|Azithromycin + Rifabutin
|Mean Duration of Therapy (days)||303.8||402.9||315||296.1||344.4|
|Discontinuation of Therapy||2.3||8.2||13.5||15.9||22.7|
|Autonomic Nervous System|
|Central Nervous System|
|Skin & Appendages|
|a Includes those reactions considered possibly
or probably related to study drug
b > 2% adverse reaction rates for any group (except uveitis)
Adverse reactions related to the gastrointestinal tract were seen more frequently in patients receiving azithromycin than in those receiving placebo or rifabutin. In Study 174, 86% of diarrheal episodes were mild to moderate in nature with discontinuation of therapy for this reason occurring in only 9/233 (3.8%) of patients.
Changes in Laboratory Values
In these immunocompromised patients with advanced HIV infection, it was necessary to assess laboratory abnormalities developing on trial with additional criteria if baseline values were outside the relevant normal range.
PROPHYLAXIS AGAINST DISSEMINATED MAC ABNORMAL
|Placebo||Azithromycin 1200 mg weekly||Rifabutin 300 mg daily||Azithromycin & Rifabutin|
|Hemoglobin||< 8 g/dL||1/51||2%||4/170||2%||4/114||4%||8/107||8%|
|Platelet Count||< 50 x 103/mm³||1/71||1%||4/260||2%||2/182||1%||6/181||3%|
|WBC Count||< 1 x 103/mm³||0/8||0%||2/70||3%||2/47||4%||0/43||0%|
|SGOT||> 5 x ULNb||1/41||2%||8/158||5%||3/121||3%||6/114||5%|
|SGPT||> 5 x ULN||0/49||0%||8/166||5%||3/130||2%||5/117||4%|
|Alk Phos||> 5 x ULN||1/80||1%||4/247||2%||2/172||1%||3/164||2%|
|aexcludes subjects outside of the relevant
normal range at baseline
bUpper Limit of Normal
Treatment of Disseminated MAC Disease
One randomized, double-blind clinical trial (Study 189) was performed in patients with disseminated MAC. In this trial, 246 HIV infected patients with disseminated MAC received either azithromycin 250 mg daily (N=65), azithromycin 600 mg daily (N=91), or clarithromycin 500 mg twice a day (N=90), each administered with ethambutol 15 mg/kg daily, for 24 weeks. Blood cultures and clinical assessments were performed every 3 weeks through week 12 and monthly thereafter through week 24. After week 24, patients were switched to any open-label therapy at the discretion of the investigator and followed every 3 months through the last follow-up visit of the trial. Patients were followed from the baseline visit for a period of up to 3.7 years (median: 9 months). MAC isolates recovered during treatment or post-treatment were obtained whenever possible.
The primary endpoint was sterilization by week 24. Sterilization was based on data from the central laboratory, and was defined as two consecutive observed negative blood cultures for MAC, independent of missing culture data between the two negative observations. Analyses were performed on all randomized patients who had a positive baseline culture for MAC.
The azithromycin 250 mg arm was discontinued after an interim analysis at 12 weeks showed a significantly lower clearance of bacteremia compared to clarithromycin 500 mg twice a day . Efficacy results for the azithromycin 600 mg daily and clarithromycin 500 mg twice a day treatment regimens are described in the following table:
RESPONSE TO THERAPY OF PATIENTS TAKING ETHAMBUTOL AND
EITHER AZITHROMYCIN 600 MG DAILY OR CLARITHROMYCIN 500 MG TWICE A DAY
|Azithromycin 600 mg daily||Clarithromycin 500 mg twice a day||a95.1% CI on difference|
|Patients with positive culture at baseline||68||57|
|Two consecutive negative blood culturesb||31/68 (46%)||32/57 (56%)||[-28, 7]|
|Mortality||16/68 (24%)||15/57 (26%)||[-18, 13]|
|a [95% confidence interval] on difference in
b Primary endpoint
The primary endpoint, rate of sterilization of blood cultures (two consecutive negative cultures) at 24 weeks, was lower in the azithromycin 600 mg daily group than in the clarithromycin 500 mg twice a day group.
Sterilization by Baseline Colony Count
Within both treatment groups, the sterilization rates at week 24 decreased as the range of MAC cfu/mL increased.
|Azithromycin 600 mg
|Clarithromycin 500 mg twice a day
|groups stratified by MAC colony counts at baseline||no. (%) subjects in stratified group sterile at week 24||no. (%) subjects in stratified group sterile at week 24|
|≤ 10 cfu/mL||10/15 (66.7%)||12/17 (70.6%)|
|11-100 cfu/mL||13/28 (46.4%)||13/19 (68.4%)|
|101-1,000 cfu/mL||7/19 (36.8%)||5/13 (38.5%)|
|1,001-10,000 cfu/mL||1/5 (20.0%)||1/5 (20%)|
|> 10,000 cfu/mL||0/1 (0.0%)||1/3 (33.3%)|
Susceptibility Pattern of MAC Isolates
Susceptibility testing was performed on MAC isolates recovered at baseline, at the time of breakthrough on therapy or during posttherapy follow-up. The T100 radiometric broth method was employed to determine azithromycin and clarithromycin MIC values. Azithromycin MIC values ranged from < 4 to > 256 μg/mL and clarithromycin MICs ranged from < 1 to > 32 μg/mL. The individual MAC susceptibility results demonstrated that azithromycin MIC values could be 4 to 32-fold higher than clarithromycin MIC values.
During treatment and post-treatment follow-up for up to 3.7 years (median: 9 months) in Study 189, a total of 6/68 (9%) and 6/57 (11%) of the patients randomized to azithromycin 600 mg daily and clarithromycin 500 mg twice a day respectively, developed MAC blood culture isolates that had a sharp increase in MIC values. All twelve MAC isolates had azithromycin MICs ≥ 256 μg/mL and clarithromycin MICs > 32 μg/mL. These high MIC values suggest development of drug resistance. However, at this time, specific breakpoints for separating susceptible and resistant MAC isolates have not been established for either macrolide.
1. Clinical and Laboratory Standards Institute (CLSI). Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically; Approved Standard - Ninth Edition. CLSI document M07-A9, Clinical and Laboratory Standards Institute, 950 West Valley Road, Suite 2500, Wayne, Pennsylvania 19087, USA, 2012.
2. Clinical and Laboratory Standards Institute (CLSI). Performance Standards for Antimicrobial Disk Diffusion Susceptibility Tests; Approved Standard – Eleventh Edition CLSI document M02-A11, Clinical and Laboratory Standards Institute, 950 West Valley Road, Suite 2500, Wayne, Pennsylvania 19087, USA, 2012.
4. Meier A, Kirshner P, Springer B, et al. Identification of mutations in 23S rRNA gene of clarithromycin-resistant Mycobacterium intracellulare. Antimicrob Agents Chemother. 1994;38:381-384.
5. Methodology per Inderlied CB, et al. Determination of In Vitro Susceptibility of Mycobacterium avium Complex Isolates to Antimicrobial Agents by Various Methods. Antimicrob Agents Chemother. 1987;31:1697-1702.
ZITHROMAX tablets may be taken with or without food. However, increased tolerability has been observed when tablets are taken with food.
ZITHROMAX for oral suspension in single 1 g packets can be taken with or without food after constitution.
Patients should also be cautioned not to take aluminum- and magnesium-containing antacids and azithromycin simultaneously.
The patient should be directed to discontinue azithromycin immediately and contact a physician if any signs of an allergic reaction occur.
Patients should be counseled that antibacterial drugs, including ZITHROMAX, should only be used to treat bacterial infections. They do not treat viral infections (e.g., the common cold). When ZITHROMAX is prescribed to treat bacterial infection, patients should be told that although it is common to feel better early in the course of therapy, the medication should be taken exactly as directed. Skipping doses or not completing the full course of therapy may (1) decrease the effectiveness of the immediate treatment and (2) increase the likelihood that bacteria will develop resistance and will not be treatable by ZITHROMAX or other antibacterial drugs in the future.
Diarrhea is a common problem caused by antibacterial which usually ends when the antibiotic is discontinued. Sometimes after starting treatment with antibacterials, patients can develop watery and bloody stools (with or without stomach cramps and fever) even as late as two or more months after having taken the last dose of the antibacterial. If this occurs, patients should contact their physician as soon as possible.
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