Mechanism of Action

Cefixime is a semisynthetic cephalosporin antibacterial drug [see Microbiology].

Pharmacokinetics

Suprax chewable tablets are bioequivalent to oral suspension.

Suprax tablets and suspension, given orally, are about 40% to 50% absorbed whether administered with or without food; however, time to maximal absorption is increased approximately 0.8 hours when administered with food. A single 200 mg tablet of cefixime produces an average peak serum concentration of approximately 2 mcg/mL (range 1 to 4 mcg/mL); a single 400 mg tablet produces an average peak concentration of approximately 3.7 mcg/mL (range 1.3 to 7.7 mcg/mL). The oral suspension produces average peak concentrations approximately 25% to 50% higher than the tablets, when tested in normal adult volunteers. Two hundred and 400 mg doses of oral suspension produce average peak concentrations of 3 mcg/mL (range 1 to 4.5 mcg/mL) and 4.6 mcg/mL (range 1.9 to 7.7 mcg/mL), respectively, when tested in normal adult volunteers. The area under the time versus concentration curve (AUC) is greater by approximately 10% to 25% with the oral suspension than with the tablet after doses of 100 to 400 mg, when tested in normal adult volunteers. This increased absorption should be taken into consideration if the oral suspension is to be substituted for the tablet. Because of the lack of bioequivalence, tablets should not be substituted for oral suspension in the treatment of otitis media [See DOSAGE AND ADMINISTRATION]. Crossover studies of tablet versus suspension have not been performed in children.

The 400 mg capsule is bioequivalent to the 400 mg tablet under fasting conditions. However, food reduces the absorption following administration of the capsule by approximately 15% based on AUC and 25% based on Cmax.

Peak serum concentrations occur between 2 and 6 hours following oral administration of a single 200 mg tablet, a single 400 mg tablet or 400 mg of cefixime suspension. Peak serum concentrations occur between 2 and 5 hours following a single administration of 200 mg of suspension. Peak serum concentrations occur between 3 and 8 hours following oral administration of a single 400 mg capsule.

Distribution

Serum protein binding is concentration independent with a bound fraction of approximately 65%. In a multiple dose study conducted with a research formulation which is less bioavailable than the tablet or suspension, there was little accumulation of drug in serum or urine after dosing for 14 days. Adequate data on CSF levels of cefixime are not available.

Metabolism and Excretion

There is no evidence of metabolism of cefixime in vivo. Approximately 50% of the absorbed dose is excreted unchanged in the urine in 24 hours. In animal studies, it was noted that cefixime is also excreted in the bile in excess of 10% of the administered dose. The serum half-life of cefixime in healthy subjects is independent of dosage form and averages 3 to 4 hours but may range up to 9 hours in some normal volunteers.

Special Populations

Geriatrics: Average AUCs at steady state in elderly patients are approximately 40% higher than average AUCs in other healthy adults. Differences in the pharmacokinetic parameters between 12 young and 12 elderly subjects who received 400 mg of cefixime once daily for 5 days are summarized as follows:

Pharmacokinetic Parameters (mean ± SD) for Cefixime in Both Young & Elderly Subjects

However, these increases were not clinically significant [See DOSAGE AND ADMINISTRATION].

Renal Impairment: In subjects with moderate impairment of renal function (20 to 40 mL/min creatinine clearance), the average serum half-life of cefixime is prolonged to 6.4 hours. In severe renal impairment (5 to 20 mL/min creatinine clearance), the half-life increased to an average of 11.5 hours. The drug is not cleared significantly from the blood by hemodialysis or peritoneal dialysis. However, a study indicated that with doses of 400 mg, patients undergoing hemodialysis have similar blood profiles as subjects with creatinine clearances of 21 to 60 mL/min.

Microbiology

Mechanism of Action

Bactericidal action of cefixime results from inhibition of cell-wall synthesis.

Cefixime has been shown to be active against most isolates of the following bacteria both in vitro and in clinical infections [see INDICATIONS AND USAGE]:

Gram-positive bacteria

Streptococcus pneumoniae
Streptococcus pyogenes

Gram-negative bacteria

Haemophilus influenzae
Moraxella catarrhalis
Escherichia coli
Proteus mirabilis
Neisseria gonorrhoeae

The following in vitro data are available, but their clinical significance is unknown. Suprax exhibits in vitro MICs of 1 mcg/mL or less against most ( ≥ 90%) isolates of the following bacteria; however, the safety and effectiveness of Suprax in treating clinical infections due to these bacteria have not been established in adequate and well-controlled clinical trials.

Gram-positive bacteria

Streptococcus agalactiae

Gram-negative bacteria

Haemophilus parainfluenzae
Proteus vulgaris
Klebsiella pneumoniae
Klebsiella oxytoca
Pasteurella multocida
Providencia species
Salmonella species
Shigella species
Citrobacter amalonaticus
Citrobacter diversus
Serratia marcescens

Susceptibility Tests Methods

When available, the clinical microbiology laboratory should provide the results of in vitro susceptibility test results for antimicrobial drugs used in resident hospitals to the physician as periodic reports that describe the susceptibility profile of nosocomial and community-acquired pathogens. These reports should aid the physician in selecting an antibacterial drug product for treatment.

Dilution Techniques: Quantitative methods are used to determine the minimum inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of bacteria to antimicrobial compounds. The MICs should be determined using standardized test methods^1,2 (broth, and/or agar). The MIC values should be interpreted according to the criteria in Table 1.

Diffusion Techniques: Quantitative methods that require measurement of zone diameters can also provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. The zone size provides an estimate of the susceptibility of bacteria to antimicrobial compounds. The zone size should be determined using standardized method.^2,3 This procedure uses paper disks impregnated with 5 mcg of cefixime to test the susceptibility of bacteria to cefixime. The disk diffusion interpretive criteria are provided in Table 1.

Table 1: Susceptibility interpretive criteria for cefixime

A report of “Susceptible” indicates that the antimicrobial is likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentration at the infection site necessary to inhibit growth of the pathogen. 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. This category also provides a buffer zone that prevents small uncontrolled technical factors from causing major discrepancies in interpretation. A report of “Resistant” indicates that the antimicrobial is not likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentrations usually achievable at the infection site; other therapy should be selected.

Quality Control

Standardized susceptibility test procedures require the use of laboratory controls to monitor and ensure the accuracy and precision of supplies and reagents used in the assay, and the techniques of the individuals performing the test.^1,2,3 The standard cefixime powder should provide the following range of MIC values provided in Table 2. For the diffusion technique using the 5-mcg cefixime disk the criteria provided in Table 2 should be achieved.

Table 2: Acceptable Quality Control Ranges for Susceptibility Testing

Clinical Studies

Comparative clinical trials of otitis media were conducted in nearly 400 children between the ages of 6 months to 10 years. Streptococcus pneumoniae was isolated from 47% of the patients, Haemophilus influenzae from 34%, Moraxella catarrhalis from 15% and S. pyogenes from 4%.

The overall response rate of Streptococcus pneumoniae to cefixime was approximately 10% lower and that of Haemophilus influenzae or Moraxella catarrhalis approximately 7% higher (12% when beta-lactamase positive isolates of H. influenzae are included) than the response rates of these organisms to the active control drugs.

In these studies, patients were randomized and treated with either cefixime at dose regimens of 4 mg/kg twice a day or 8 mg/kg once a day, or with a comparator. Sixty-nine to 70% of the patients in each group had resolution of signs and symptoms of otitis media when evaluated 2 to 4 weeks post-treatment, but persistent effusion was found in 15% of the patients. When evaluated at the completion of therapy, 17% of patients receiving cefixime and 14% of patients receiving effective comparative drugs (18% including those patients who had Haemophilus influenzae resistant to the control drug and who received the control antibiotic) were considered to be treatment failures. By the 2 to 4 week follow-up, a total of 30%-31% of patients had evidence of either treatment failure or recurrent disease.

Bacteriological Outcome of Otitis Media at Two to Four Weeks Post-Therapy Based on Repeat Middle Ear Fluid Culture or Extrapolation from Clinical Outcome

REFERENCES

1. Clinical and Laboratory Standards Institute (CLSI) Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically: Approved Standard-9th Edition. CLSI Document M07-A9. CLSI, 950 West Valley Rd., Suite 2500, Wayne, PA 19087, 2012.

2. Clinical and Laboratory Standards Institute (CLSI). Performance Standards for Antimicrobial Susceptibility Testing 21st Informational Supplement, CLSI document M100-S22,CLSI, 2012.

3. CLSI. Performance Standards for Antimicrobial Disk Diffusion Susceptibility Tests. Approved Standard-11^th Edition, CLSI document M02-A11, 2012.

4. Faulkner RD, Bohaychuk W, Lanc RA, et al.: Pharmacokinetics of cefixime in the young and elderly. J Antimicrob Chemother 1988; 21(6): 787-794.

Last reviewed on RxList: 3/6/2013
This monograph has been modified to include the generic and brand name in many instances.