April 09, 2015
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Amoxicillin/probenecid effectively treats syphilis in HIV patients

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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 3 g oral amoxicillin plus 750 mg probenecid daily was very high in early and late syphilis patients with HIV infection,” Ryutaro Tanizaki, MD, of the AIDS Clinical Center in Tokyo, and colleagues wrote in Open Forum Infectious Diseases. “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 hemagglutination test.

Patients were treated with 3 g oral amoxicillin plus probenecid, according to the researchers, who defined successful syphilis treatment as at least a fourfold decrease in RPR titer within 24 months 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 3 g oral amoxicillin plus 750 mg 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, diarrhea and elevated liver enzymes, according to the researchers. Despite these events, 89.3% of these patients were successfully treated. – by Colleen Owens

Disclosure: The researchers report no relevant financial disclosures.

Editors’ note: The article was updated to clarify that successful syphilis treatment was defined in the study as at least a fourfold decrease in rapid plasma reagin titer within 24 months of treatment initiation. The editors regret the error.