Mechanism of Action
Levofloxacin is a member of the fluoroquinolone class of antibacterial agents.
Pharmacokinetics
The mean ±SD pharmacokinetic parameters of levofloxacin determined under single and steady-state conditions following oral tablet, oral solution, or intravenous (IV) doses of LEVAQUIN® are summarized in Table 10.
Table 10: Mean ±SD Levofloxacin PK Parameters
| Regimen |
Cmax
(mcg/mL) |
Tmax
(h) |
AUC
(mcg•h/mL) |
CL/F1
(mL/min) |
Vd/F2
(L) |
t1/2
(h) |
CLR
(mL/min) |
| Single dose |
| 250 mg oral tablet3 |
2.8 ± 0.4 |
1.6 ± 1.0 |
27.2 ± 3.9 |
156 ± 20 |
ND |
7.3 ± 0.9 |
142 ± 21 |
| 500 mg oral tablet3* |
5.1 ± 0.8 |
1.3 ± 0.6 |
47.9 ± 6.8 |
178 ± 28 |
ND |
6.3 ± 0.6 |
103 ± 30 |
| 500 mg oral solution12 |
5.8 ± 1.8 |
0.8 ± 0.7 |
47.8 ± 10.8 |
183 ± 40 |
112 ± 37.2 |
7.0 ± 1.4 |
ND |
| 500 mg IV3 |
6.2 ± 1.0 |
1.0 ± 0.1 |
48.3 ± 5.4 |
175 ± 20 |
90 ± 11 |
6.4 ± 0.7 |
112 ± 25 |
| 750 mg oral tablet5* |
9.3 ± 1.6 |
1.6 ± 0.8 |
101 ± 20 |
129 ± 24 |
83 ± 17 |
7.5 ± 0.9 |
ND |
| 750 mg IV5 |
11.5 ± 4.04 |
ND |
110 ± 40 |
126 ± 39 |
75 ± 13 |
7.5 ± 1.6 |
ND |
| Multiple dose |
|
| 500 mg every 24h oral tablet3 |
5.7 ± 1.4 |
1.1 ± 0.4 |
47.5 ± 6.7 |
175 ± 25 |
102 ± 22 |
7.6 ± 1.6 |
116 ± 31 |
| 500 mg every 24h IV3 |
6.4 ± 0.8 |
ND |
54.6 ± 11.1 |
158 ± 29 |
91 ± 12 |
7.0 ± 0.8 |
99 ± 28 |
| 500 mg or 250 mg every 24h IV, patients with bacterial infection6 |
8.7 ± 4.07 |
ND |
72.5 ± 51.27 |
154 ± 72 |
111 ± 58 |
ND |
ND |
| 750 mg every 24h oral tablet5 |
8.6 ± 1.9 |
1.4 ± 0.5 |
90.7 ± 17.6 |
143 ± 29 |
100 ± 16 |
8.8 ± 1.5 |
116 ± 28 |
| 750 mg every 24h IV5 |
12.1 ± 4.14 |
ND |
108 ± 34 |
126 ± 37 |
80 ± 27 |
7.9 ± 1.9 |
ND |
| 500 mg oral tablet single dose, effects of gender and
age: |
| Male8 |
5.5 ± 1.1 |
1.2 ± 0.4 |
54.4 ± 18.9 |
166 ± 44 |
89 ± 13 |
7.5 ± 2.1 |
126 ± 38 |
| Female9 |
7.0 ± 1.6 |
1.7 ± 0.5 |
67.7 ± 24.2 |
136 ± 44 |
62 ± 16 |
6.1 ± 0.8 |
106 ± 40 |
| Young10 |
5.5 ± 1.0 |
1.5 ± 0.6 |
47.5 ± 9.8 |
182 ± 35 |
83 ± 18 |
6.0 ± 0.9 |
140 ± 33 |
| Elderly11 |
7.0 ± 1.6 |
1.4 ± 0.5 |
74.7 ± 23.3 |
121 ± 33 |
67 ± 19 |
7.6 ± 2.0 |
91 ± 29 |
| 500 mg oral single dose tablet, patients with renal insufficiency:
|
| CLCR 50-80 mL/min |
7.5 ± 1.8 |
1.5 ± 0.5 |
95.6 ± 11.8 |
88 ± 10 |
ND |
9.1 ± 0.9 |
57 ± 8 |
| CLCR 20-49 mL/min |
7.1 ± 3.1 |
2.1 ± 1.3 |
182.1 ± 62.6 |
51 ± 19 |
ND |
27 ± 10 |
26 ± 13 |
| CLCR < 20 mL/min |
8.2 ± 2.6 |
1.1 ± 1.0 |
263.5 ± 72.5 |
33 ± 8 |
ND |
35 ± 5 |
13 ± 3 |
| Hemodialysis |
5.7 ± 1.0 |
2.8 ± 2.2 |
ND |
ND |
ND |
76 ± 42 |
ND |
| CAPD |
6.9 ± 2.3 |
1.4 ± 1.1 |
ND |
ND |
ND |
51 ± 24 |
ND |
1 clearance/bioavailability
2 volume of distribution/bioavailability
3 healthy males 18-53 years of age
4 60 min infusion for 250 mg and 500 mg doses, 90 min infusion
for 750 mg dose
5 healthy male and female subjects 18-54 years of age
6 500 mg every 48h for patients with moderate renal impairment
(CLCR 20-50 mL/min) and infections of the respiratory tract or skin
7 dose-normalized values (to 500 mg dose), estimated by
population pharmacokinetic modeling
8 healthy males 22-75 years of age
9 healthy females 18-80 years of age
10 young healthy male and female subjects 18-36 years of
age
11 healthy elderly male and female subjects 66-80 years of age
12 healthy males and females 19-55 years of age.
* Absolute bioavailability; F=0.99 ± 0.08 from a 500 mg tablet and
F=0.99 ± 0.06 from a 750 mg tablet;
ND=not determined. |
Absorption
Levofloxacin is rapidly and essentially completely absorbed after oral administration. Peak plasma concentrations are usually attained one to two hours after oral dosing. The absolute bioavailability of levofloxacin from a 500 mg tablet and a 750 mg tablet of LEVAQUIN® are both approximately 99%, demonstrating complete oral absorption of levofloxacin. Following a single intravenous dose of LEVAQUIN® to healthy volunteers, the mean ±SD peak plasma concentration attained was 6.2 ±1.0 mcg/mL after a 500 mg dose infused over 60 minutes and 11.5 ±4.0 mcg/mL after a 750 mg dose infused over 90 minutes. LEVAQUIN® Oral Solution and Tablet formulations are bioequivalent.
Levofloxacin pharmacokinetics are linear and predictable after single and multiple oral or IV dosing regimens. Steady-state conditions are reached within 48 hours following a 500 mg or 750 mg once-daily dosage regimen. The mean ±SD peak and trough plasma concentrations attained following multiple once-daily oral dosage regimens were approximately 5.7 ±1.4 and 0.5 ±0.2 mcg/mL after the 500 mg doses, and 8.6 ±1.9 and 1.1 ±0.4 mcg/mL after the 750 mg doses, respectively. The mean ±SD peak and trough plasma concentrations attained following multiple once-daily IV regimens were approximately 6.4 ±0.8 and 0.6 ±0.2 mcg/mL after the 500 mg doses, and 12.1 ±4.1 and 1.3 ±0.71 mcg/mL after the 750 mg doses, respectively. Oral administration of a 500 mg dose of LEVAQUIN® with food prolongs the time to peak concentration by approximately 1 hour and decreases the peak concentration by approximately 14% following tablet and approximately 25% following oral solution administration. Therefore, LEVAQUIN® Tablets can be administered without regard to food. It is recommended that LEVAQUIN® Oral Solution be taken 1 hour before, or 2 hours after eating.
The plasma concentration profile of levofloxacin after IV administration is
similar and comparable in extent of exposure (AUC) to that observed for LEVAQUIN®
Tablets when equal doses (mg/mg) are administered. Therefore, the oral and IV
routes of administration can be considered interchangeable (see Figure 2
and Figure 3).
Figure 2: Mean Levofloxacin Plasma Concentration vs. Time
Profile: 750 mg
Figure 3: Mean Levofloxacin Plasma Concentration vs. Time
Profile: 500 mg
Distribution
The mean volume of distribution of levofloxacin generally ranges from 74 to 112 L after single and multiple 500 mg or 750 mg doses, indicating widespread distribution into body tissues. Levofloxacin reaches its peak levels in skin tissues and in blister fluid of healthy subjects at approximately 3 hours after dosing. The skin tissue biopsy to plasma AUC ratio is approximately 2 and the blister fluid to plasma AUC ratio is approximately 1 following multiple once-daily oral administration of 750 mg and 500 mg doses of LEVAQUIN®, respectively, to healthy subjects. Levofloxacin also penetrates well into lung tissues. Lung tissue concentrations were generally 2- to 5- fold higher than plasma concentrations and ranged from approximately 2.4 to 11.3 mcg/g over a 24-hour period after a single 500 mg oral dose.
In vitro, over a clinically relevant range (1 to 10 mcg/mL) of serum/plasma
levofloxacin concentrations, levofloxacin is approximately 24 to 38% bound to
serum proteins across all species studied, as determined by the equilibrium
dialysis method. Levofloxacin is mainly bound to serum albumin in humans. Levofloxacin
binding to serum proteins is independent of the drug concentration.
Metabolism
Levofloxacin is stereochemically stable in plasma and urine and does not invert metabolically to its enantiomer, D-ofloxacin. Levofloxacin undergoes limited metabolism in humans and is primarily excreted as unchanged drug in the urine. Following oral administration, approximately 87% of an administered dose was recovered as unchanged drug in urine within 48 hours, whereas less than 4% of the dose was recovered in feces in 72 hours. Less than 5% of an administered dose was recovered in the urine as the desmethyl and N-oxide metabolites, the only metabolites identified in humans. These metabolites have little relevant pharmacological activity.
Excretion
Levofloxacin is excreted largely as unchanged drug in the urine. The mean terminal plasma elimination half-life of levofloxacin ranges from approximately 6 to 8 hours following single or multiple doses of levofloxacin given orally or intravenously. The mean apparent total body clearance and renal clearance range from approximately 144 to 226 mL/min and 96 to 142 mL/min, respectively. Renal clearance in excess of the glomerular filtration rate suggests that tubular secretion of levofloxacin occurs in addition to its glomerular filtration. Concomitant administration of either cimetidine or probenecid results in approximately 24% and 35% reduction in the levofloxacin renal clearance, respectively, indicating that secretion of levofloxacin occurs in the renal proximal tubule. No levofloxacin crystals were found in any of the urine samples freshly collected from subjects receiving LEVAQUIN®.
Geriatric
There are no significant differences in levofloxacin pharmacokinetics between
young and elderly subjects when the subjects' differences in creatinine clearance
are taken into consideration. Following a 500 mg oral dose of LEVAQUIN®
to healthy elderly subjects (66 - 80 years of age), the mean terminal plasma
elimination half-life of levofloxacin was about 7.6 hours, as compared to approximately
6 hours in younger adults. The difference was attributable to the variation
in renal function status of the subjects and was not believed to be clinically
significant. Drug absorption appears to be unaffected by age. LEVAQUIN®
dose adjustment based on age alone is not necessary [See Use
in Specific Populations].
Pediatrics
The pharmacokinetics of levofloxacin following a single 7 mg/kg intravenous
dose were investigated in pediatric patients ranging in age from 6 months to
16 years. Pediatric patients cleared levofloxacin faster than adult patients,
resulting in lower plasma exposures than adults for a given mg/kg dose. Subsequent
pharmacokinetic analyses predicted that a dosage regimen of 8 mg/kg every 12
hours (not to exceed 250 mg per dose) for pediatric patients 6 months to 17
years of age would achieve comparable steady state plasma exposures (AUC0-24
and Cmax) to those observed in adult patients administered 500 mg of levofloxacin
once every 24 hours.
Gender
There are no significant differences in levofloxacin pharmacokinetics between male and female subjects when subjects' differences in creatinine clearance are taken into consideration. Following a 500 mg oral dose of LEVAQUIN® to healthy male subjects, the mean terminal plasma elimination half-life of levofloxacin was about 7.5 hours, as compared to approximately 6.1 hours in female subjects. This difference was attributable to the variation in renal function status of the male and female subjects and was not believed to be clinically significant. Drug absorption appears to be unaffected by the gender of the subjects. Dose adjustment based on gender alone is not necessary.
Race
The effect of race on levofloxacin pharmacokinetics was examined through a covariate analysis performed on data from 72 subjects: 48 white and 24 non-white. The apparent total body clearance and apparent volume of distribution were not affected by the race of the subjects.
Renal Impairment
Clearance of levofloxacin is substantially reduced and plasma elimination half-life
is substantially prolonged in adult patients with impaired renal function (creatinine
clearance < 50 mL/min), requiring dosage adjustment in such patients to avoid
accumulation. Neither hemodialysis nor continuous ambulatory peritoneal dialysis
(CAPD) is effective in removal of levofloxacin from the body, indicating that
supplemental doses of LEVAQUIN® are not required following hemodialysis
or CAPD [see DOSAGE AND ADMINISTRATION, Use
in Specific Populations].
Hepatic Impairment
Pharmacokinetic studies in hepatically impaired patients have not been conducted.
Due to the limited extent of levofloxacin metabolism, the pharmacokinetics of
levofloxacin are not expected to be affected by hepatic impairment [See Use
in Specific Populations].
Bacterial Infection
The pharmacokinetics of levofloxacin in patients with serious community-acquired bacterial infections are comparable to those observed in healthy subjects.
Drug-Drug Interactions
The potential for pharmacokinetic drug interactions between LEVAQUIN® and
antacids, warfarin, theophylline, cyclosporine, digoxin, probenecid, and cimetidine
has been evaluated [see DRUG INTERACTIONS].
Microbiology
Mechanism of Action
Levofloxacin is the L-isomer of the racemate, ofloxacin, a quinolone antimicrobial agent. The antibacterial activity of ofloxacin resides primarily in the L-isomer. The mechanism of action of levofloxacin and other fluoroquinolone antimicrobials involves inhibition of bacterial topoisomerase IV and DNA gyrase (both of which are type II topoisomerases), enzymes required for DNA replication, transcription, repair and recombination.
Drug Resistance
Fluoroquinolone resistance can arise through mutations in defined regions of DNA gyrase or topoisomerase IV, termed the Quinolone-Resistance Determining Regions (QRDRs), or through altered efflux.
Fluoroquinolones, including levofloxacin, differ in chemical structure and mode of action from aminoglycosides, macrolides and β-lactam antibiotics, including penicillins. Fluoroquinolones may, therefore, be active against bacteria resistant to these antimicrobials.
Resistance to levofloxacin due to spontaneous mutationin vitro is a
rare occurrence (range: 10-9 to 10-10). Although cross-resistance
has been observed between levofloxacin and some other fluoroquinolones, some
microorganisms resistant to other fluoroquinolones may be susceptible to levofloxacin.
Activity in vitro and in vivo
Levofloxacin has in vitro activity against a wide range of Gram-negative
and Gram-positive microorganisms.
Levofloxacin is often bactericidal at concentrations equal to or slightly greater than inhibitory concentrations.
Levofloxacin has been shown to be active against most strains of the following
microorganisms both in vitro and in clinical infections as described
in INDICATIONS:
Aerobic Gram-Positive Microorganisms
Enterococcus faecalis (many strains are only moderately susceptible)
Staphylococcus aureus (methicillin-susceptible strains)
Staphylococcus epidermidis (methicillin-susceptible strains)
Staphylococcus saprophyticus
Streptococcus pneumoniae (including multi-drug resistant strains [MDRSP]*)
Streptococcus pyogenes
* MDRSP (Multi-drug resistant Streptococcus pneumoniae) isolates are strains resistant to two or more of the following antibiotics: penicillin (MIC ≥ 2 mcg/mL), 2nd generation cephalosporins, e.g., cefuroxime; macrolides, tetracyclines and trimethoprim/sulfamethoxazole.
Aerobic Gram-Negative Microorganisms
| Enterobacter cloacae |
Legionella pneumophila |
| Escherichia coli |
Moraxella catarrhalis |
| Haemophilus influenzae |
Proteus mirabilis |
| Haemophilus parainfluenzae |
Pseudomonas aeruginosa* |
| Klebsiella pneumoniae |
Serratia marcescens |
| * As with other drugs in this class, some strains of Pseudomonas
aeruginosa may develop resistance fairly rapidly during treatment with
LEVAQUIN®.
|
Other Microorganisms
Chlamydophila pneumoniae
Mycoplasma pneumoniae
Levofloxacin has been shown to be active against Bacillus anthracis
both in vitro and by use of plasma levels as a surrogate marker in a
rhesus monkey model for anthrax (post-exposure) [see INDICATIONS,
Clinical Studies].
The following in vitro data are available, but their clinical significance
is unknown:
Levofloxacin exhibits in vitro minimum inhibitory concentrations (MIC
values) of 2 mcg/mL or less against most ( ≥ 90%) strains of the following
microorganisms; however, the safety and effectiveness of LEVAQUIN® in treating
clinical infections due to these microorganisms have not been established in
adequate and well-controlled trials.
| Aerobic Gram-Positive Microorganisms |
| Staphylococcus haemolyticus |
Streptococcus agalactiae |
| β-hemolytic Streptococcus (Group C/F) |
Streptococcus milleri |
| β-hemolytic Streptococcus (Group G) |
Viridans group streptococci |
| Aerobic Gram-Negative Microorganisms |
| Acinetobacter baumannii |
Klebsiella oxytoca |
| Acinetobacter lwoffii |
Morganella morganii |
| Bordetella pertussis |
Pantoea agglomerans |
| Citrobacter koseri |
Proteus vulgaris |
| Citrobacter freundii |
Providencia rettgeri |
| Enterobacter aerogenes |
Providencia stuartii |
| Enterobacter sakazakii |
Pseudomonas fluorescens |
| Anaerobic Gram-Positive Microorganisms |
| Clostridium perfringens |
|
Susceptibility Tests
Susceptibility testing for levofloxacin should be performed, as it is the optimal predictor of activity.
Quantitative methods are used to determine antimicrobial minimal inhibitory concentrations (MIC values). These MIC values provide estimates of the susceptibility of bacteria to antimicrobial compounds. The MIC values should be determined using a standardized procedure. Standardized procedures are based on a dilution method1 (broth or agar) or equivalent with standardized inoculum concentrations and standardized concentrations of levofloxacin powder. The MIC values should be interpreted according to the criteria outlined in Table 11.
Quantitative methods that require measurement of zone diameters also provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. One such standardized procedure2 requires the use of standardized inoculum concentrations. This procedure uses paper disks impregnated with 5 mcg levofloxacin to test the susceptibility of microorganisms to levofloxacin.
Reports from the laboratory providing results of the standard single-disk susceptibility test with a 5 mcg levofloxacin disk should be interpreted according the criteria outlined in Table 11. Interpretation involves correlation of the diameter obtained in the disk test with the MIC for levofloxacin.
Table 11: Susceptibility Interpretive Criteria for LEVAQUIN
| |
Minimum Inhibitory Concentrations (mcg/mL) |
Disk Diffusion
(zone diameter in mm) |
| Pathogen |
S |
I |
R |
S |
I |
R |
| Enterobacteriaceae |
≤ 2 |
4 |
≥ 8 |
≥ 17 |
14-16 |
≤ 13 |
| Enterococcus faecalis |
≤ 2 |
4 |
≥ 8 |
≥ 17 |
14-16 |
≤ 13 |
| Methicillin-susceptible Staphylococcus species |
≤ 2 |
4 |
≥ 8 |
≥ 17 |
14-16 |
≤ 13 |
| Pseudomonas aeruginosa |
≤ 2 |
4 |
≥ 8 |
≥ 17 |
14-16 |
≤ 13 |
| Haemophilus influenzae |
≤ 2a |
--b |
--b |
≥ 17c |
--b |
--b |
| Haemophilus parainfluenzae |
≤ 2a |
--b |
--b |
≥ 17c |
--b |
--b |
| Streptococcus pneumoniae |
≤ 2d |
4d |
≥ 8d |
≥ 17e |
14-16e |
≤ 13e |
| Streptococcus pyogenes |
≤ 2 |
4 |
≥ 8 |
≥ 17 |
14-16 |
≤ 13 |
S = Susceptible, I = Intermediate, R = Resistant
a These interpretive standards are applicable only to broth microdilution
susceptibility testing with Haemophilus influenzae and Haemophilus
parainfluenzae using Haemophilus Test Medium.1
b The current absence of data on resistant strains precludes
defining any categories other than “Susceptible.” Strains yielding MIC /zone
diameter results suggestive of a “nonsusceptible” category should be submitted
to a reference laboratory for further testing.
c These interpretive standards are applicable only to disk diffusion
susceptibility testing with Haemophilus influenzae and Haemophilus
parainfluenzae using Haemophilus Test Medium.2
d These interpretive standards are applicable only to broth microdilution
susceptibility tests using cation-adjusted Mueller-Hinton broth with 2-5%
lysed horse blood.
e These zone diameter standards for Streptococcus spp.
including S. pneumoniae apply only to tests performed using Mueller-Hinton
agar supplemented with 5% sheep blood and incubated in 5% CO2.
|
A report of Susceptible indicates that the pathogen is likely to be
inhibited if the antimicrobial compound in the blood reaches the concentrations
usually achievable. 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 implies possible clinical applicability in body sites where the drug
is physiologically concentrated or in situations where a high dosage of drug
can be used. 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 the pathogen is not likely to be
inhibited if the antimicrobial compound in the blood reaches the concentrations
usually achievable; other therapy should be selected.
Standardized susceptibility test procedures require the use of laboratory control microorganisms to control the technical aspects of the laboratory procedures. For dilution technique, standard levofloxacin powder should give the MIC values provided in Table 12. For diffusion technique, the 5 mcg levofloxacin disk should provide zone diameters provided in Table 12.
Table 12: Quality Control for Susceptibility Testing
| Microorganism |
Microorganism QC Number |
MIC (mcg/mL) |
Disk Diffusion
(zone diameter in mm) |
| Enterococcus faecalis |
ATCC 29212 |
0.25 – 2 |
Not applicable |
| Escherichia coli |
ATCC 25922 |
0.008 – 0.06 |
29 – 37 |
| Escherichia coli |
ATCC 35218 |
0.015 – 0.06 |
Not applicable |
| Haemophilus influenzae |
ATCC 49247 |
0.008 – 0.03a |
32 – 40b |
| Pseudomonas aeruginosa |
ATCC 27853 |
0.5 – 4 |
19 – 26 |
| Staphylococcus aureus |
ATCC 29213 |
0.06 – 0.5 |
Not applicable |
| Staphylococcus aureus |
ATCC 25923 |
Not applicable |
25 – 30 |
| Streptococcus pneumoniae |
ATCC 49619 |
0.5 – 2c |
20 – 25d |
a This quality control range is applicable to
only H. influenzae ATCC 49247 tested by a broth microdilution procedure
using Haemophilus Test Medium (HTM).1
b This quality control range is applicable to only H. influenzae
ATCC 49247 tested by a disk diffusion procedure using Haemophilus Test Medium
(HTM).2
c This quality control range is applicable to only S. pneumoniae
ATCC 49619 tested by a broth microdilution procedure using cation-adjusted
Mueller-Hinton broth with 2-5% lysed horse blood.
d This quality control range is applicable to only S. pneumoniae
ATCC 49619 tested by a disk diffusion procedure using Mueller-Hinton agar
supplemented with 5% sheep blood and incubated in 5% CO2. |
Animal Toxicology and/or Pharmacology
Levofloxacin and other quinolones have been shown to cause arthropathy in immature
animals of most species tested [see WARNINGS AND PRECAUTIONS].
In immature dogs (4-5 months old), oral doses of 10 mg/kg/day for 7 days and
intravenous doses of 4 mg/kg/day for 14 days of levofloxacin resulted in arthropathic
lesions. Administration at oral doses of 300 mg/kg/day for 7 days and intravenous
doses of 60 mg/kg/day for 4 weeks produced arthropathy in juvenile rats. Three-month
old beagle dogs dosed orally with levofloxacin at 40 mg/kg/day exhibited clinically
severe arthrotoxicity resulting in the termination of dosing at Day 8 of a 14-day
dosing routine. Slight musculoskeletal clinical effects, in the absence of gross
pathological or histopathological effects, resulted from the lowest dose level
of 2.5 mg/kg/day (approximately 0.2-fold the pediatric dose based upon AUC comparisons).
Synovitis and articular cartilage lesions were observed at the 10 and 40 mg/kg
dose levels (approximately 0.7-fold and 2.4-fold the pediatric dose, respectively,
based on AUC comparisons). Articular cartilage gross pathology and histopathology
persisted to the end of the 18-week recovery period for those dogs from the
10 and 40 mg/kg/day dose levels.
When tested in a mouse ear swelling bioassay, levofloxacin exhibited phototoxicity similar in magnitude to ofloxacin, but less phototoxicity than other quinolones.
While crystalluria has been observed in some intravenous rat studies, urinary crystals are not formed in the bladder, being present only after micturition and are not associated with nephrotoxicity.
In mice, the CNS stimulatory effect of quinolones is enhanced by concomitant administration of non-steroidal anti-inflammatory drugs.
In dogs, levofloxacin administered at 6 mg/kg or higher by rapid intravenous injection produced hypotensive effects. These effects were considered to be related to histamine release.
In vitro and in vivo studies in animals indicate that levofloxacin
is neither an enzyme inducer nor inhibitor in the human therapeutic plasma concentration
range; therefore, no drug metabolizing enzyme-related interactions with other
drugs or agents are anticipated.
Clinical Studies
Nosocomial Pneumonia
Adult patients with clinically and radiologically documented nosocomial pneumonia were enrolled in a multicenter, randomized, open-label study comparing intravenous LEVAQUIN® (750 mg once daily) followed by oral LEVAQUIN® (750 mg once daily) for a total of 7-15 days to intravenous imipenem/cilastatin (500-1000 mg every 6-8 hours daily) followed by oral ciprofloxacin (750 mg every 12 hours daily) for a total of 7-15 days. LEVAQUIN®-treated patients received an average of 7 days of intravenous therapy (range: 1-16 days); comparator-treated patients received an average of 8 days of intravenous therapy (range: 1-19 days).
Overall, in the clinically and microbiologically evaluable population, adjunctive
therapy was empirically initiated at study entry in 56 of 93 (60.2%) patients
in the LEVAQUIN® arm and 53 of 94 (56.4%) patients in the comparator arm.
The average duration of adjunctive therapy was 7 days in the LEVAQUIN® arm
and 7 days in the comparator. In clinically and microbiologically evaluable
patients with documented Pseudomonas aeruginosa infection, 15 of 17 (88.2%)
received ceftazidime (N=11) or piperacillin/tazobactam (N=4) in the LEVAQUIN®
arm and 16 of 17 (94.1%) received an aminoglycoside in the comparator arm. Overall,
in clinically and microbiologically evaluable patients, vancomycin was added
to the treatment regimen of 37 of 93 (39.8%) patients in the LEVAQUIN® arm
and 28 of 94 (29.8%) patients in the comparator arm for suspected methicillin-resistant
S. aureus infection.
Clinical success rates in clinically and microbiologically evaluable patients at the posttherapy visit (primary study endpoint assessed on day 3-15 after completing therapy) were 58.1% for LEVAQUIN® and 60.6% for comparator. The 95% CI for the difference of response rates (LEVAQUIN® minus comparator) was [-17.2, 12.0]. The microbiological eradication rates at the posttherapy visit were 66.7% for LEVAQUIN® and 60.6% for comparator. The 95% CI for the difference of eradication rates (LEVAQUIN® minus comparator) was [-8.3, 20.3]. Clinical success and microbiological eradication rates by pathogen are detailed in Table 13.
Table 13: Clinical Success Rates and Microbiological Eradication
Rates (Nosocomial Pneumonia)
| Pathogen |
N |
LEVAQUIN®No. (%) of Patients Microbiologic/
Clinical Outcomes |
N |
Imipenem/Cilastatin No. (%) of Patients
Microbiologic/ Clinical Outcomes |
| MSSAa |
21 |
14 (66.7)/13 (61.9) |
19 |
13 (68.4)/15 (78.9) |
| P. aeruginosab |
17 |
10 (58.8)/11 (64.7) |
17 |
5 (29.4)/7 (41.2) |
| S. marcescens |
11 |
9 (81.8)/7 (63.6) |
7 |
2 (28.6)/3 (42.9) |
| E. coli |
12 |
10 (83.3)/7 (58.3) |
11 |
7 (63.6 )/8 (72.7) |
| K. pneumoniaec |
11 |
9 (81.8)/5 (45.5) |
7 |
6 (85.7)/3 (42.9) |
| H. influenzae |
16 |
13 (81.3)/10 (62.5) |
15 |
14 (93.3)/11 (73.3) |
| S. pneumoniae |
4 |
3 (75.0)/3 (75.0) |
7 |
5 (71.4)/4 (57.1) |
a Methicillin-susceptible S. aureus
b See above text for use of combination therapy
c The observed differences in rates for the clinical and microbiological
outcomes may reflect other factors that were not accounted for in the study
|
Community-Acquired Pneumonia: 7-14 day Treatment Regimen
Adult inpatients and outpatients with a diagnosis of community-acquired bacterial
pneumonia were evaluated in 2 pivotal clinical studies. In the first study,
590 patients were enrolled in a prospective, multi-center, unblinded randomized
trial comparing LEVAQUIN® 500 mg once daily orally or intravenously for
7 to 14 days to ceftriaxone 1 to 2 grams intravenously once or in equally divided
doses twice daily followed by cefuroxime axetil 500 mg orally twice daily for
a total of 7 to 14 days. Patients assigned to treatment with the control regimen
were allowed to receive erythromycin (or doxycycline if intolerant of erythromycin)
if an infection due to atypical pathogens was suspected or proven. Clinical
and microbiologic evaluations were performed during treatment, 5 to 7 days posttherapy,
and 3 to 4 weeks posttherapy. Clinical success (cure plus improvement) with
LEVAQUIN® at 5 to 7 days posttherapy, the primary efficacy variable in this
study, was superior (95%) to the control group (83%). The 95% CI for the difference
of response rates (LEVAQUIN® minus comparator) was [-6, 19]. In the second
study, 264 patients were enrolled in a prospective, multi-center, non-comparative
trial of 500 mg LEVAQUIN® administered orally or intravenously once daily
for 7 to 14 days. Clinical success for clinically evaluable patients was 93%.
For both studies, the clinical success rate in patients with atypical pneumonia
due to Chlamydophila pneumoniae, Mycoplasma pneumoniae, and Legionella
pneumophila were 96%, 96%, and 70%, respectively. Microbiologic eradication
rates across both studies are presented in Table 14.
Table 14: Microbiologic Eradication Rates Across 2 Community
Acquired nPneumonia Clinical Studies
| Pathogen |
No. Pathogens |
Microbiologic Eradication Rate (%) |
| H. influenzae |
55 |
98 |
| S. pneumoniae |
83 |
95 |
| S. aureus |
17 |
88 |
| M. catarrhalis |
18 |
94 |
| H. parainfluenzae |
19 |
95 |
| K. pneumoniae |
10 |
100.0 |
Community-Acquired Pneumonia Due to Multi-Drug Resistant Streptococcus pneumoniae
LEVAQUIN® was effective for the treatment of community-acquired pneumonia caused by multi-drug resistant Streptococcus pneumoniae (MDRSP). MDRSP isolates are strains resistant to two or more of the following antibacterials: penicillin (MIC ≥ 2 mcg/mL), 2nd generation cephalosporins (e.g., cefuroxime, macrolides, tetracyclines and trimethoprim/sulfamethoxazole). Of 40 microbiologically evaluable patients with MDRSP isolates, 38 patients (95.0%) achieved clinical and bacteriologic success at post-therapy. The clinical and bacterial success rates are shown in Table 15.
Table 15: Clinical and Bacterial Success Rates for LEVAQUIN®-Treated
MDRSP in Community Acquired Pneumonia Patients (Population Valid for Efficacy)
| Screening Susceptibility |
Clinical Success |
Bacteriological Successc |
| n/Na |
% |
n/Nb |
% |
| Penicillin-resistant |
16/17 |
94.1 |
16/17 |
94.1 |
| 2nd generation Cephalosporin resistant |
31/32 |
96.9 |
31/32 |
96.9 |
| Macrolide-resistant |
28/29 |
96.6 |
28/29 |
96.6 |
| Trimethoprim/ Sulfamethoxazole resistant |
17/19 |
89.5 |
17/19 |
89.5 |
| Tetracycline-resistant |
12/12 |
100 |
12/12 |
100 |
a n=the number of microbiologically evaluable patients
who were clinical successes; N=number of microbiologically evaluable patients
in the designated resistance group.
b n=the number of MDRSP isolates eradicated or presumed eradicated
in microbiologically evaluable patients; N=number of MDRSP isolates in a
designated resistance group.
c One patient had a respiratory isolate that was resistant to
tetracycline, cefuroxime, macrolides and TMP/SMX and intermediate to penicillin
and a blood isolate that was intermediate to penicillin and cefuroxime and
resistant to the other classes. The patient is included in the database
based on respiratory isolate. |
Not all isolates were resistant to all antimicrobial classes tested. Success and eradication rates are summarized in Table 16.
Table 16: Clinical Success and Bacteriologic Eradication
Rates for Resistant Streptococcus pneumoniae (Community Acquired Pneumonia)
| Type of Resistance |
Clinical Success |
Bacteriologic Eradication |
| Resistant to 2 antibacterials |
17/18 (94.4%) |
17/18 (94.4%) |
| Resistant to 3 antibacterials |
14/15 (93.3%) |
14/15 (93.3%) |
| Resistant to 4 antibacterials |
7/7 (100%) |
7/7 (100%) |
| Resistant to 5 antibacterials |
0 |
0 |
| Bacteremia with MDRSP |
8/9 (89%) |
8/9 (89%) |
Community-Acquired Pneumonia: 5-Day Treatment Regimen
To evaluate the safety and efficacy of higher dose and shorter course of LEVAQUIN®, 528 outpatient and hospitalized adults with clinically and radiologically determined mild to severe community-acquired pneumonia were evaluated in a double-blind, randomized, prospective, multicenter study comparing LEVAQUIN® 750 mg, IV or orally, every day for five days or LEVAQUIN® 500 mg IV or orally, every day for 10 days.
Clinical success rates (cure plus improvement) in the clinically evaluable population were 90.9% in the LEVAQUIN® 750 mg group and 91.1% in the LEVAQUIN® 500 mg group. The 95% CI for the difference of response rates (LEVAQUIN® 750 minus LEVAQUIN® 500) was [-5.9, 5.4]. In the clinically evaluable population (31-38 days after enrollment) pneumonia was observed in 7 out of 151 patients in the LEVAQUIN® 750 mg group and 2 out of 147 patients in the LEVAQUIN® 500 mg group. Given the small numbers observed, the significance of this finding cannot be determined statistically. The microbiological efficacy of the 5-day regimen was documented for infections listed in Table 17.
Table 17: Microbiological Eradication Rates (Community-Acquired
Pneumonia)
| Penicillin susceptible S. pneumoniae |
19/20 |
| Haemophilus influenzae |
12/12 |
| Haemophilus parainfluenzae |
10/10 |
| Mycoplasma pneumoniae |
26/27 |
| Chlamydophila pneumoniae |
13/15 |
Acute Bacterial Sinusitis: 5-day and 10-14 day Treatment Regimens
LEVAQUIN® is approved for the treatment of acute bacterial sinusitis (ABS) using either 750 mg by mouth x 5 days or 500 mg by mouth once daily x 10-14 days. To evaluate the safety and efficacy of a high dose short course of LEVAQUIN®, 780 outpatient adults with clinically and radiologically determined acute bacterial sinusitis were evaluated in a double-blind, randomized, prospective, multicenter study comparing LEVAQUIN® 750 mg by mouth once daily for five days to LEVAQUIN® 500 mg by mouth once daily for 10 days.
Clinical success rates (defined as complete or partial resolution of the pre-treatment signs and symptoms of ABS to such an extent that no further antibiotic treatment was deemed necessary) in the microbiologically evaluable population were 91.4% (139/152) in the LEVAQUIN® 750 mg group and 88.6% (132/149) in the LEVAQUIN® 500 mg group at the test-of-cure (TOC) visit (95% CI [-4.2, 10.0] for LEVAQUIN® 750 mg minus LEVAQUIN® 500 mg).
Rates of clinical success by pathogen in the microbiologically evaluable population who had specimens obtained by antral tap at study entry showed comparable results for the five- and ten-day regimens at the test-of-cure visit 22 days post treatment.
Table 18: Clinical Success Rate by Pathogen at the TOC in
Microbiologically Evaluable Subjects Who Underwent Antral Puncture (Acute Bacterial
Sinusitis)
| Pathogen |
LEVAQUIN®
750 mg x 5 days |
LEVAQUIN®
500 mg x 10 days |
| Streptococcus pneumoniae* |
25/27 (92.6%) |
26/27 (96.3%) |
| Haemophilus influenzae* |
19/21 (90.5%) |
25/27 (92.6%) |
| Moraxella catarrhalis* |
10/11 (90.9%) |
13/13 (100%) |
| * Note: Forty percent of the subjects in this trial had specimens
obtained by sinus endoscopy. The efficacy data for subjects whose specimen
was obtained endoscopically were comparable to those presented in the above
table |
Complicated Skin and Skin Structure Infections
Three hundred ninety-nine patients were enrolled in an open-label, randomized, comparative study for complicated skin and skin structure infections. The patients were randomized to receive either LEVAQUIN® 750 mg once daily (IV followed by oral), or an approved comparator for a median of 10 ± 4.7 days. As is expected in complicated skin and skin structure infections, surgical procedures were performed in the LEVAQUIN® and comparator groups. Surgery (incision and drainage or debridement) was performed on 45% of the LEVAQUIN®-treated patients and 44% of the comparator treated patients, either shortly before or during antibiotic treatment and formed an integral part of therapy for this indication.
Among those who could be evaluated clinically 2-5 days after completion of study drug, overall success rates (improved or cured) were 116/138 (84.1%) for patients treated with LEVAQUIN® and 106/132 (80.3%) for patients treated with the comparator.
Success rates varied with the type of diagnosis ranging from 68% in patients with infected ulcers to 90% in patients with infected wounds and abscesses. These rates were equivalent to those seen with comparator drugs.
Chronic Bacterial Prostatitis
Adult patients with a clinical diagnosis of prostatitis and microbiological
culture results from urine sample collected after prostatic massage (VB3)
or expressed prostatic secretion (EPS) specimens obtained via the Meares-Stamey
procedure were enrolled in a multicenter, randomized, double-blind study comparing
oral LEVAQUIN® 500 mg, once daily for a total of 28 days to oral ciprofloxacin
500 mg, twice daily for a total of 28 days. The primary efficacy endpoint was
microbiologic efficacy in microbiologically evaluable patients. A total of 136
and 125 microbiologically evaluable patients were enrolled in the LEVAQUIN®
and ciprofloxacin groups, respectively. The microbiologic eradication rate by
patient infection at 5-18 days after completion of therapy was 75.0% in the
LEVAQUIN® group and 76.8% in the ciprofloxacin group (95% CI [-12.58, 8.98]
for LEVAQUIN® minus ciprofloxacin). The overall eradication rates for pathogens
of interest are presented in Table 19.
Table 19: Microbiological Eradication Rates (Chronic Bacterial
Prostatitis)
| |
LEVAQUIN® (N=136) |
Ciprofloxacin (N=125) |
| Pathogen |
N |
Eradication |
N |
Eradication |
| E. coli |
15 |
14 (93.3%) |
11 |
9 (81.8%) |
| E. faecalis |
54 |
39 (72.2%) |
44 |
33 (75.0%) |
| S. epidermidis* |
11 |
9 (81.8%) |
14 |
11 (78.6%) |
| * Eradication rates shown are for patients who had a sole
pathogen only; mixed cultures were excluded. |
Eradication rates for S. epidermidis when found with other co-pathogens
are consistent with rates seen in pure isolates.
Clinical success (cure + improvement with no need for further antibiotic therapy) rates in microbiologically evaluable population 5-18 days after completion of therapy were 75.0% for LEVAQUIN®-treated patients and 72.8% for ciprofloxacin-treated patients (95% CI [-8.87, 13.27] for LEVAQUIN® minus ciprofloxacin). Clinical long-term success (24-45 days after completion of therapy) rates were 66.7% for the LEVAQUIN®-treated patients and 76.9% for the ciprofloxacin-treated patients (95% CI [-23.40, 2.89] for LEVAQUIN® minus ciprofloxacin).
Complicated Urinary Tract Infections and Acute Pyelonephritis: 5-day Treatment
Regimen
To evaluate the safety and efficacy of the higher dose and shorter course of LEVAQUIN®, 1109 patients with cUTI and AP were enrolled in a randomized, double-blind, multicenter clinical trial conducted in the US from November 2004 to April 2006 comparing LEVAQUIN® 750 mg IV or orally once daily for 5 days (546 patients) with ciprofloxacin 400 mg IV or 500 mg orally twice daily for 10 days (563 patients). Patients with AP complicated by underlying renal diseases or conditions such as complete obstruction, surgery, transplantation, concurrent infection or congenital malformation were excluded. Efficacy was measured by bacteriologic eradication of the baseline organism(s) at the post-therapy visit in patients with a pathogen identified at baseline. The post-therapy (test-of-cure) visit occurred 10 to 14 days after the last active dose of LEVAQUIN® and 5 to 9 days after the last dose of active ciprofloxacin.
The bacteriologic cure rates overall for LEVAQUIN® and control at the test-of-cure (TOC) visit for the group of all patients with a documented pathogen at baseline (modified intent to treat or mITT) and the group of patients in the mITT population who closely followed the protocol (Microbiologically Evaluable) are summarized in Table 20.
Table 20: Bacteriologic Eradication at Test-of-Cure
| |
LEVAQUIN® 750 mg orally or IV once daily
for 5 days |
Ciprofloxacin 400 mg IV/500 mg orally twice
daily for 10 days |
Overall Difference [95% CI] |
| n/N |
% |
n/N |
% |
LEVAQUIN®-
Ciprofloxacin |
| mITT Populationa |
| Overall (cUTI or AP) |
252/333 |
75.7 |
239/318 |
75.2 |
0.5 (-6.1, 7.1) |
| cUTI |
168/230 |
73.0 |
157/213 |
73.7 |
|
| AP |
84/103 |
81.6 |
82/105 |
78.1 |
|
| Microbiologically Evaluable Populationb
|
| Overall (cUTI or AP) |
228/265 |
86.0 |
215/241 |
89.2 |
-3.2 [-8.9, 2.5] |
| cUTI |
154/185 |
83.2 |
144/165 |
87.3 |
|
| AP |
74/80 |
92.5 |
71/76 |
93.4 |
|
a The mITT population included
patients who received study medication and who had a positive ( ≥ 105
CFU/mL) urine culture with no more than 2 uropathogens at baseline. Patients
with missing response were counted as failures in this analysis.
b The Microbiologically Evaluable population included patients
with a confirmed diagnosis of cUTI or A P, a causative organism(s) at
baseline present at ≥ 105 CFU/mL, a valid test-of-cure urine
culture, no pathogen isolated from blood resistant to study drug, no premature
discontinuation or loss to follow-up, and compliance with treatment (among
other criteria). |
Microbiologic eradication rates in the Microbiologically Evaluable population at TOC for individual pathogens recovered from patients randomized to LEVAQUIN® treatment are presented in Table 21.
Table 21: Microbiological Eradication Rates for Individual
Pathogens Recovered From Patients Randomized to LEVAQUIN® 750 mg QD for
5 Days Treatment
| Pathogen |
Microbiologic Eradication Rate
(n/N) |
% |
| Escherichia coli* |
155/172 |
90 |
| Klebsiella pneumoniae |
20/23 |
87 |
| Proteus mirabilis |
12/12 |
100 |
| * The predominant organism isolated from patients
with AP was E. coli: 91% (63/69) eradication in AP and 89% (92/103)
in patients with cUTI. |
Complicated Urinary Tract Infections and Acute Pyelonephritis: 10-day Treatment
Regimen
To evaluate the safety and efficacy of the 250 mg dose, 10 day regimen of LEVAQUIN®, 567 patients with uncomplicated UTI, mild-to-moderate cUTI, and mild-to-moderate AP were enrolled in a randomized, double-blind, multicenter clinical trial conducted in the US from June 1993 to January 1995 comparing LEVAQUIN® 250 orally once daily for 10 days (285 patients) with ciprofloxacin 500 mg orally twice daily for 10 days (282 patients). Patients with a resistant pathogen, recurrent UTI, women over age 55 years, and with an indwelling catheter were initially excluded, prior to protocol amendment which took place after 30% of enrollment. Microbiological efficacy was measured by bacteriologic eradication of the baseline organism(s) at 1-12 days post-therapy in patients with a pathogen identified at baseline.
The bacteriologic cure rates overall for LEVAQUIN® and control at the test-of-cure (TOC) visit for the group of all patients with a documented pathogen at baseline (modified intent to treat or mITT) and the group of patients in the mITT population who closely followed the protocol (Microbiologically Evaluable) are summarized in Table 22.
Table 22. Bacteriologic Eradication Overall (cUTI or AP)
at Test-Of-Curea
| |
LEVAQUIN®
250 mg once daily for 10 days |
Ciprofloxacin
500 mg twice daily for 10 days |
| n/N |
% |
n/N |
% |
| mITT Populationb |
174/209 |
83.3 |
184/219 |
84.0 |
| Microbiologically Evaluable Populationc |
164/177 |
92.7 |
159/171 |
93.0 |
a 1-9 days posttherapy for 30%
of subjects enrolled prior to a protocol amendment; 5-12 days posttherapy
for 70% of subjects.
b The mITT population included patients who had a pathogen
isolated at baseline. Patients with missing response were counted as failures
in this analysis.
c The Microbiologically Evaluable population included mITT
patients who met protocol-specified evaluability criteria. |
Inhalational Anthrax (Post-Exposure)
The effectiveness of LEVAQUIN® for this indication is based on plasma concentrations
achieved in humans, a surrogate endpoint reasonably likely to predict clinical
benefit. LEVAQUIN® has not been tested in humans for the post-exposure prevention
of inhalation anthrax. The mean plasma concentrations of LEVAQUIN® associated
with a statistically significant improvement in survival over placebo in the
rhesus monkey model of inhalational anthrax are reached or exceeded in adult
and pediatric patients receiving the recommended oral and intravenous dosage
regimens [see INDICATIONS; DOSAGE
AND ADMINISTRATION].
Levofloxacin pharmacokinetics have been evaluated in adult and pediatric patients.
The mean (± SD) steady state peak plasma concentration in human adults
receiving 500 mg orally or intravenously once daily is 5.7 ± 1.4 and
6.4 ± 0.8 mcg/mL, respectively; and the corresponding total plasma exposure
(AUC024) is 47.5 ± 6.7 and 54.6 ± 11.1 mcg.h/mL, respectively.
The predicted steady-state pharmacokinetic parameters in pediatric patients
ranging in age from 6 months to 17 years receiving 8 mg/kg orally every 12 hours
(not to exceed 250 mg per dose) were calculated to be comparable to those observed
in adults receiving 500 mg orally once daily [see CLINICAL PHARMACOLOGY].
In adults, the safety of LEVAQUIN® for treatment durations of up to 28 days is well characterized. However, information pertaining to extended use at 500 mg daily up to 60 days is limited. Prolonged LEVAQUIN® therapy in adults should only be used when the benefit outweighs the risk.
In pediatric patients, the safety of levofloxacin for treatment durations of
more than 14 days has not been studied. An increased incidence of musculoskeletal
adverse events (arthralgia, arthritis, tendonopathy, gait abnormality) compared
to controls has been observed in clinical studies with treatment duration of
up to 14 days. Long-term safety data, including effects on cartilage, following
the administration of levofloxacin to pediatric patients is limited [see WARNINGS
AND PRECAUTIONS, Use
in Specific Populations].
A placebo-controlled animal study in rhesus monkeys exposed to an inhaled mean
dose of 49 LD50 (~2.7 X 106) spores (range 17 - 118 LD50)
of B. anthracis (Ames strain) was conducted. The minimal inhibitory concentration
(MIC) of levofloxacin for the anthrax strain used in this study was 0.125 mcg/mL
In the animals studied, mean plasma concentrations of levofloxacin achieved
at expected Tmax (1 hour post-dose) following oral dosing to steady state ranged
from 2.79 to 4.87 mcg/mL. Steady state trough concentrations at 24 hours post-dose
ranged from 0.107 to 0.164 mcg/mL. Mean (SD) steady state AUC0-24
was 33.4 ± 3.2 mcg.h/mL (range 30.4 to 36.0 mcg.h/mL). Mortality due
to anthrax for animals that received a 30 day regimen of oral LEVAQUIN®
beginning 24 hrs post exposure was significantly lower (1/10), compared to the
placebo group (9/10) [P=0.0011, 2-sided Fisher's Exact Test]. The one levofloxacin
treated animal that died of anthrax did so following the 30-day drug administration
period.
REFERENCES
1. Clinical and Laboratory Standards Institute. Methods for Dilution Antimicrobial
Susceptibility Tests for Bacteria That Grow Aerobically Approved Standard -Seventh
Edition. Clinical and Laboratory Standards Institute document M7-A7, Vol. 26,
No. 2, CLSI, Wayne, PA, January 2006.
2. Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial
Disk Susceptibility Tests. Approved Standard - Ninth Edition. Clinical and Laboratory
Standards Institute document M2-A9, Vol. 26, No. 1, CLSI, Wayne, PA, January
2006.
Last updated on RxList: 6/9/2009