Drug combination effective with syphilis

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A daily combination of high-dose amoxicillin and probenecid was an effective syphilis treatment in patients with HIV infection, according to results of a retrospective, observational study.

“The efficacy of 3g oral amoxicillin plus 750mg probenecid daily was very high in early and late syphilis patients with HIV infection,” Dr Ryutaro Tanizaki, of the AIDS Clinical Centre in Tokyo, and colleagues found. “The regimen was also highly tolerable and required only a single hospital visit.”

The study included 286 men (median age, 36 years; median CD4 count, 389 cells/mm3) with HIV-1 infection who sought treatment for syphilis between January 2000 and June 2014. The syphilis diagnosis was based on serum rapid plasma reagin (RPR) titers of 8 or higher and a positive Treponema pallidum haemaglutination test.

Patients were treated with 3g oral amoxicillin plus probenecid, according to the researchers, who defined successful syphilis treatment as at least a fourfold decrease in RPR titer within 24 hours of treatment initiation. The overall treatment efficacy was 95.5% and was high in primary (93.8%), secondary (97.3%), early latent syphilis (100%), late latent syphilis (85.7%) and syphilis of unknown duration (92.4%).

“The high treatment efficacy is surprising considering that our study population could have included asymptomatic neurosyphilis, because neurosyphilis in HIV-infected patients could occur even in early syphilis without clinical symptoms,” Tanizaki and colleagues wrote.

Within 1 year, 96.3% of participants had a fourfold decrease in the RPR titer. Duration of treatment was typically 14 to 16 days (94.4% efficacy) or 28 to 30 days (95.9% efficacy). As a result, for patients with early syphilis, the researchers recommend 2 weeks of treatment with 3g oral amoxicillin plus 750mg probenecid; they recommend 4 weeks of therapy with the same dose for patients with late latent and syphilis of unknown duration.

The treatment was well tolerated; only 9.8% of patients experienced adverse events such as skin rash, fever, diarrhoea and elevated liver enzymes, according to the researchers. Despite these events, 89.3% of these patients were successfully treated.

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Open Forum Infectious Diseases abstract

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