Bactroban (Mupirocin Calcium Topical) - Clinical Pharmacology

CLINICAL PHARMACOLOGY

Pharmacokinetics

Systemic absorption of mupirocin through intact human skin is minimal. The systemic absorption of mupirocin was studied following application of BACTROBAN CREAM three times daily for 5 days to various skin lesions (greater than 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.

CLINICAL STUDIES

The efficacy of topical BACTROBAN CREAM for the treatment of secondarily infected traumatic skin lesions (e.g., lacerations, sutured wounds, and abrasions not more than 10 cm in length or 100 cm² in total area) was compared to that of oral cephalexin in 2 randomized, double-blind, double-dummy clinical trials. Clinical efficacy rates at follow-up in the per protocol populations (adults and pediatric patients included) were 96.1% for BACTROBAN CREAM (n = 231) and 93.1% for oral cephalexin (n = 219). Pathogen eradication rates at follow-up in the per protocol populations were 100% for both BACTROBAN CREAM and oral cephalexin.

Pediatrics: There were 93 pediatric patients aged 2 weeks to 16 years enrolled per protocol in the secondarily infected skin lesion studies, although only 3 were less than 2 years of age in the population treated with BACTROBAN CREAM. Patients were randomized to either 10 days of topical BACTROBAN CREAM three times daily or 10 days of oral cephalexin (250 mg four times daily for patients >40 kg or 25 mg/kg/day oral suspension in 4 divided doses for patients ≤40 kg). Clinical efficacy at follow-up (7 to 12 days post-therapy) in the per protocol populations was 97.7% (43/44) for BACTROBAN CREAM and 93.9% (46/49) for cephalexin. Only 1 adverse event (headache) was thought to be possibly or probably related to drug therapy with BACTROBAN CREAM in the intent-to-treat pediatric population of 70 children (1.4%).