Evaluation of cephalexin failure rates in morbidly obese patients with cellulitis

Identification of adequate antimicrobial dosing regimens for morbidly obese patients is essential given the simultaneous increase in morbid obesity and cellulitis prevalence in recent years. Insufficient data currently exist to describe the effectiveness of extrapolating traditional antibiotic dosing strategies to morbidly obese patients with cellulitis. The primary objective of this study was to compare therapeutic failure rates in non-obese and morbidly obese patients with cellulitis when treated with cephalexin at standard dosing.

This was a single-centre, retrospective cohort analysis. Adult patients hospitalized or under inpatient observation at a 1265-bed academic medical centre who received cephalexin monotherapy for non-purulent cellulitis from 2005 to 2015 were evaluated for inclusion. Patients were divided into two cohorts based on body mass index (BMI), where BMI <30 kg/m(2) was defined as non-obese and BMI ≥40 kg/m(2) as morbidly obese. Patients with critical risk factors for purulent or polymicrobial cellulitis were excluded. The primary outcome, therapeutic failure, was defined as a need for extended or additional antimicrobial therapy, surgical intervention, emergency department visit, or re-hospitalization within two to thirty days after cephalexin initiation.

A total of 94 patients (69 non-obese and 25 morbidly obese) met inclusion and exclusion criteria, which was below the estimated sample size needed to reach desired power. The rate of therapeutic failure in the morbidly obese group was similar to the non-obese group (20% vs. 14·5%, P = 0·53). Patients most commonly had extended or additional antibiotics prescribed in response to therapeutic failure with cephalexin.

Cephalexin failure rates for cellulitis did not differ statistically between morbidly obese and non-obese patients. The underpowered nature of this study is a limitation. Until further study with a larger sample size is completed, empiric adjustment of cephalexin dosing based solely on BMI may not be necessary.