Background CDC guidelines recommend gentamicin for the treatment of gonorrhea in cephalosporin-allergic patients. The efficacy of gentamicin in the treatment of pharyngeal gonorrhea, which is often undiagnosed, is uncertain.

Methods Between September 2018 – March 2019, we enrolled MSM with NAAT-diagnosed pharyngeal gonorrhea in a single-arm, unblinded clinical trial. Men received a single 360 mg intramuscular (IM) dose of gentamicin at enrollment and underwent test-of-cure (TOC) by culture 4–7 days later. The study measured creatinine at enrollment and TOC, serum gentamicin concentration post-dose to establish peak concentration (Cmax), and standard antimicrobial minimal inhibitory concentrations (MIC). The trial was designed to establish a point estimate for the efficacy of gentamicin for pharyngeal gonorrhea. We planned to enroll 50 evaluable subjects; assuming that gentamicin was 80% efficacious, the trial would establish a 95% confidence interval of 66%-90%. We planned interim analyses at n=10 and n=25.

Results The study was stopped early due to poor efficacy. Of 13 enrolled men, 10 were evaluable, and only two (20%, 95%CI: 2.5% - 55.6%) were cured. Of 2 concomitant rectal infections, both were cured. Efficacy was not associated with gentamicin Cmax (p=0.809) or MIC (p= 0.429). No participants experienced renal insufficiency; average creatinine percent change was 5% (range: -7%, 21%). Six (46%) subjects experienced headache; all deemed unrelated to treatment. On a scale of 0–10, mean injection pain was 2 (range: 1–7). Among subjects with history of bicillin (n=7) and/or ceftriaxone (n=8) IM injections, 86% believed IM gentamicin to be less painful than bicillin and 75% believed it was more painful than ceftriaxone.

Conclusion 360 mg of gentamicin failed to eradicate N. gonorrhoeae from the pharynx. Caution should be used when using the CDC’s current alternative therapy (gentamicin 240 mg plus azithromycin 2g) given increases in azithromycin resistance and gentamicin’s poor efficacy at the pharynx.

Disclosure No significant relationships.