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PHARMACOECONOMICS

Analysis of Empiric Antimicrobial Strategies for Cellulitis in the Era of Methicillin-Resistant Staphylococcus aureus

PharmD/PhD Student, Department of Pharmacy, School of Pharmacy, Virginia Commonwealth University, Richmond, VA

Conan MacDougall, PharmD BCPS

Assistant Professor of Clinical Pharmacy, Department of Clinical Pharmacy, School of Pharmacy, University of California—San Francisco, San Francisco, CA

David A Holdford, PhD

Associate Professor of Pharmacy, Department of Pharmacy, School of Pharmacy, Virginia Commonwealth University

Reprints: Dr. MacDougall, Department of Clinical Pharmacy, University of California— San Francisco, 521 Parnassus Ave., C-152, Box 0622, San Francisco, CA 94143, fax 415/476-6632, macdougallc{at}pharmacy.ucsf.edu

BACKGROUND: The rise in community-onset methicillin-resistant Staphylococcus aureus (MRSA) infections potentially complicates the empiric management of cellulitis. The threshold at which drugs active against MRSA, such as clindamycin and trimethoprim/sulfamethoxazole (TMP/SMX), should be incorporated into empiric therapy is unknown.

OBJECTIVE: To evaluate the cost-effectiveness of using cephalexin, TMP/SMX, or clindamycin for outpatient empiric therapy of cellulitis, given various likelihoods of infection due to MRSA.

METHODS: A decision analysis of the empiric treatment of cellulitis was performed from the perspective of a third-party payer. The model included initial therapy with cephalexin, clindamycin, or TMP/SMX, followed by treatment with linezolid in cases of clinical failure. Probability and cost estimates were obtained from clinical trials, epidemiologic data, and publicly available cost data and were subjected to sensitivity analysis.

RESULTS: Under the base-case scenario (37% probability of infection by S. aureus and a 27% MRSA prevalence), cephalexin was the most cost-effective option. Clindamycin became a more cost-effective therapy at MRSA probabilities from 41–80% when the probability of staphylococcal infection was greater than 40%. TMP/SMX was cost-effective only at very high likelihoods of MRSA infection. Variables with the most influence in the model were probability of S. aureus being methicillin-resistant, cost of linezolid, probability of a cure with cephalexin for a non-MRSA infection, and probability of infection due to S. aureus.

CONCLUSIONS: Cephalexin remains a cost-effective therapy for outpatient management of cellulitis at current estimated MRSA levels. Cephalexin was the most cost-effective choice over most of the modeled range of probabilities, with clindamycin becoming more cost-effective at high likelihoods of MRSA infection. TMP/SMX is unlikely to be cost-effective for treatment of simple cellulitis. Further studies of the microbiology of cellulitis, the epidemiology of MRSA, and the clinical effectiveness of clindamycin and TMP/SMX in skin and soft tissue infections are needed.

Key Words: cellulitis, cost-effectiveness, methicillin-resistant Staphylococcus aureus

Published Online, January 2, 2007. www.theannals.com, DOI 10.1345/aph.1H452