Deep surgical site infections following double-dose perioperative antibiotic prophylaxis in adult obese orthopedic patients

•Obesity is a risk factor associated with orthopedic surgical site infections (SSI).•Many centers apply weight- or body mass index-related antibiotic prophylaxis to reduce deep SSIs.•The clinical benefit of the double-dose adapted antibiotic prophylaxis is unknown.•This prophylactic dose-doubling failed to reduce SSIs among the obese patients in this study. Obesity is a risk factor for surgical site infections (SSI). Based on retrospective comparisons and pharmacology, many orthopedic centers have adopted weight- or body mass index (BMI)-related antibiotic prophylaxis. Double-dose prophylaxis was introduced in March 2017 for patients weighting >80 kg. The period April 2014 to March 2017 (‘before’) was compared to the period March 2017 to June 2019 (‘after’) regarding the impact on deep SSIs. A total of 9318 surgeries ‘before’ were compared to 7455 interventions ‘after’ the introduction of double-dose prophylaxis. Baseline demographic characteristics (age, sex, BMI, American Society of Anesthesiologists score, and duration of surgery) were similar. In the period ‘after’, 3088 cases (3088/16 773; 18%) received double-dose prophylaxis. Overall, 82 deep SSIs were observed (0.5%). The pathogens were resistant to the standard cefuroxime prophylaxis in 30 cases (30/82; 37%). Excluding these prophylaxis-resistant cases and all of the five hematogenous SSIs, the remaining 47 SSIs (57%) could have been prevented by the preceding prophylaxis. Double-dosing of parenteral cefuroxime from 1.5 g to 3.0 g in obese patients did not reduce deep SSIs (hazard ratio 0.7, 95% confidence interval 0.3–1.6). In the direct group comparison among obese patients >80 kg, the double-dose prophylaxis equally failed to alter the SSI risk (3088/16 726 non-infections vs 8/47 SSI despite double-dose prophylaxis; Chi-square test, P = 0.78). In this single-center before-and-after study with almost 17 000 orthopedic surgeries in adult patients, systemic doubling of the perioperative antibiotic prophylaxis in obese patients clinically failed to reduce the overall deep SSI risk.