Pharmacokinetics

Systemic absorption of mupirocin through intact human skin is minimal. The systemic absorption of mupirocin was studied following application of BACTROBAN CREAM 3 times daily for 5 days to various skin lesions (>10 cm in length or 100 cm2 in area) in 16 adults (aged 29 to 60 years) and 10 children (aged 3 to 12 years). Some systemic absorption was observed as evidenced by the detection of the metabolite, monic acid, in urine. Data from this study indicated more frequent occurrence of percutaneous absorption in children (90% of patients) compared to adults (44% of patients); however, the observed urinary concentrations in children (0.07 - 1.3 mcg/mL [1 pediatric patient had no detectable level]) are within the observed range (0.08 - 10.03 mcg/mL [9 adults had no detectable level]) in the adult population. In general, the degree of percutaneous absorption following multiple dosing appears to be minimal in adults and children. Any mupirocin reaching the systemic circulation is rapidly metabolized, predominantly to inactive monic acid, which is eliminated by renal excretion.

Microbiology

Mupirocin is an antibacterial agent produced by fermentation using the organism Pseudomonas fluorescens. It is active against a wide range of gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA). It is also active against certain gram-negative bacteria. Mupirocin inhibits bacterial protein synthesis by reversibly and specifically binding to bacterial isoleucyl transfer-RNA synthetase. Due to this unique mode of action, mupirocin demonstrates no in vitro cross-resistance with other classes of antimicrobial agents.

Resistance occurs rarely; however, when mupirocin resistance does occur, it appears to result from the production of a modified isoleucyl-tRNA synthetase. High-level plasmid-mediated resistance (MIC >1024 mcg/mL) has been reported in some strains of Staphylococcus aureus and coagulase-negative staphylococci.

Mupirocin is bactericidal at concentrations achieved by topical application. The minimum bactericidal concentration (MBC) against relevant pathogens is generally 8-fold to 30-fold higher than the minimum inhibitory concentration (MIC). In addition, mupirocin is highly protein bound (>97%), and the effect of wound secretions on the MICs of mupirocin has not been determined.

Mupirocin has been shown to be active against most strains of S. aureus and Streptococcus pyogenes, both in vitro and in clinical studies. (See INDICATIONS AND USAGE.) The following in vitro data are available, BUT THEIR CLINICAL SIGNIFICANCE IS UNKNOWN. Mupirocin is active against most strains of Staphylococcus epidermidis and Staphylococcus saprophyticus.

General

As with other antibacterial products, prolonged use may result in overgrowth of nonsusceptible microorganisms, including fungi. (See DOSAGE AND ADMINISTRATION.)

BACTROBAN CREAM is not formulated for use on mucosal surfaces.

Information for Patients

• Use this medication only as directed by your healthcare provider. It is for external use only. Avoid contact with the eyes.

• The treated area may be covered by gauze dressing if desired.

• Report to your healthcare provider any signs of local adverse reactions. The medication should be stopped and your healthcare provider contacted if irritation, severe itching, or rash occurs.

• If no improvement is seen in 3 to 5 days, contact your healthcare provider.

Drug Interactions

The effect of the concurrent application of topical mupirocin calcium cream and other topical products has not been studied.

Carcinogenesis, Mutagenesis, Impairment of Fertility

Long-term studies in animals to evaluate carcinogenic potential of mupirocin calcium have not been conducted.

Results of the following studies performed with mupirocin calcium or mupirocin sodium in vitro and in vivo did not indicate a potential for mutagenicity: Rat primary hepatocyte unscheduled DNA synthesis, sediment analysis for DNA strand breaks, Salmonella reversion test (Ames), Escherichia coli mutation assay, metaphase analysis of human lymphocytes, mouse lymphoma assay, and bone marrow micronuclei assay in mice.

Fertility studies were performed in rats with mupirocin administered subcutaneously at doses up to 49 times a human topical dose of 1 gram/day (approximately 20 mg mupirocin per day) on a mg/m2 basis and revealed no evidence of impaired fertility from mupirocin sodium.

Pregnancy

Nursing Mothers

It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when BACTROBAN CREAM is administered to a nursing woman.

Pediatric Use

The safety and effectiveness of BACTROBAN CREAM have been established in the age groups 3 months to 16 years. Use of BACTROBAN CREAM in these age groups is supported by evidence from adequate and well-controlled studies of BACTROBAN CREAM in adults with additional data from 93 pediatric patients studied as part of the pivotal trials in adults. (See CLINICAL STUDIES.)

Geriatric Use

In 2 well-controlled studies, 30 patients older than 65 years were treated with BACTROBAN CREAM. No overall difference in the efficacy or safety of BACTROBAN CREAM was observed in this patient population when compared to that observed in younger patients.