The effect of obesity on antibiotic treatment failure: a historical cohort study

Obesity, a major health issue, is also an important risk factor for infections. Evidence demonstrates that excess weight affects the disposition of antibiotics but little work has been done to explore if this results in antibiotic treatment failure (ATF). ATF has serious adverse health outcomes and may increase treatment resistance. Given that obese patients often have other health issues, it is important to determine if excess weight independently increases the likelihood of ATF.

Consenting patients (N = 18 014), randomly sampled from Santé Québec Health surveys (1992, 1998), were linked with administrative health databases. Patients were within the normal, overweight, and obese weight categories aged 20-79 years old, receiving at least one course of antibiotic therapy from the survey date until December 2005. ATF was defined as any additional antibiotic prescriptions or hospitalizations for infections within the 30 days after initial therapy. Logistic regression was used to assess the impact of excess weight on ATF after adjusting for patient characteristics, comorbidities, history of antibiotic use, antibiotic resistance, and flu season.

Of the final sample size (N = 6 179), 39.0% were overweight and 21.4% were obese. The most frequently prescribed antibiotics were amoxicillin (16.0%), ciprofloxacin (9.2%), phenoxymethylpenicillin (8.8%), trimethroprim/sulfamethoxazole (8.6%), and clarithromycin (8.5%). ATF occurred in 828 (13.4%) of the 6 179 study patients. Obesity was a significant predictor of ATF (adjusted OR 1.26; 95% CI 1.03-1.52).

Obesity is a significant risk factor for ATF, and this association may be due to the current "one size fits all" dosing strategy, which warrants further investigation.