Randomized Controlled Trial of Prophylactic Antibiotics for Dog Bites with Refined Cost Model

OBJECTIVE The aim of this study was to determine the rate of infection at which it is cost-effective to treat dog bite wounds with antibiotics. METHODS Our study was composed of two parts. First we performed a randomized, double-blind controlled trial (RCT) to compare the infection rates of dog bite wounds in patients given amoxicillin-clavulanic acid versus placebo. Subjects were immunocompetent patients presenting to the emergency department (ED) with dog bite wounds less than 12 hours old without suspected neurovascular, tendon, joint or bone injury, and who had structured follow-up after two weeks. Second, we developed a cost model with sensitivity analysis to determine thresholds for treatment. RESULTS In the RCT, primary outcomes were obtained in 94 patients with dog bites. The overall wound infection rate at two weeks was 2% [95% CI 0 to 7%]. Two of 46 patients (4%) receiving no antibiotics developed infections, while none of the 48 patients (0%) receiving prophylactic antibiotics developed an infection (absolute reduction 4% [95% CI -1.0 to 4.5%]). Using a sensitivity analysis across a rate of infections from 0-10%, our cost model determined that prophylactic antibiotics were cost effective if the risk of wound infection was greater than 5% and antibiotics could decrease that risk by greater than 3%. CONCLUSION Our wound infection rate was lower than older studies and more in line with current estimates. Assuming that prophylactic antibiotics could provide an absolute risk reduction (ARR) of 3%, it would not be cost effective to treat wounds with an infection rate of less than 3% and unlikely that the ARR would be achievable unless the baseline rate was greater than 5%, suggesting that only wounds with greater than 5% risk of infection should be treated. Future work should focus on identifying wounds at high-risk of infection that would benefit from antibiotic prophylaxis.