Morbidly obese patients with cellulitis have the same rates of treatment failure with cephalexin as non-obese patients. Those are the findings of a new retrospective study of patients hospitalized or in inpatient observation from January 2005 through February 2015, at the Mayo Clinic Hospital-Rochester, Minnesota. The study is the first of its kind to compare rates of therapeutic failure with cephalexin between obese and non-obese patients.

Eligible cohort patients had to be treated with cephalexin monotherapy at an appropriate full or renal-adjusted dose for a cellulitis diagnosis. They were split into a morbidly obese and a non-obese group, defined by BMIs of ≥40 kg/mand <30kg/m2,respectively. Those with BMIs between 30kg/m2 and 40kg/m2 were excluded in order to avoid skewing the results by having similar BMI patients in two separate groups.

Using these parameters the researchers identified 94 patients, a figure the researchers admitted was an, “unexpectedly low number”. The median BMI for the morbidly obese group was 44.4km/m2 and 26.8kg/m2 for the non-obese. Both groups had a median duration of cephalexin therapy for 10 days, with the majority of the patients receiving a 500mg dose 4 times daily. 

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The rate of treatment failure was found to be not significant between both groups. The non-obese group’s failure rate was 14.5% while the obese group’s rate was 20% (P=0.53). Antibiotic substitution or addition was the leading result of failure (10.1%–16% transitioned to an alternate regimen).

The authors stress how the lack of significant difference in therapeutic failures should be viewed with the understanding that the study was underpowered. “It remains possible that morbidly obese patients are at increased risk of failing treatment with standard cephalexin dosing and that inadequate patient enrollment in the study prevented elucidation of this finding,” they wrote.

To optimize outcomes and prevent unnecessary escalation to broad-spectrum antibiotics, the authors of the study suggest more research into the therapeutic efficacy of cephalexin dosing. Until such research is conducted, the authors conclude that, “clinicians may continue to utilize traditional cephalexin dosing regimens in morbidly obese patients with cellulitis.”

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