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Original research
Clinical efficacy and tolerability of 1.5 g/day oral amoxicillin therapy without probenecid for the treatment of syphilis
  1. Kazuhiko Ikeuchi,
  2. Kazuaki Fukushima,
  3. Masaru Tanaka,
  4. Keishiro Yajima,
  5. Akifumi Imamura
  1. Department of Infectious Diseases, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Bunkyo-ku, Japan
  1. Correspondence to Dr Kazuaki Fukushima, Infectious Diseases, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Bunkyo-ku 113-8677, Japan; fukushima-ngi{at}umin.ac.jp

Abstract

Objectives Intramuscular benzathine penicillin G is not available in certain countries. In a previous report, 3 g/day amoxicillin with probenecid was shown to be effective in treating syphilis in patients with HIV; however, 7.3% of patients changed their therapy owing to adverse events. The objective of this study was to assess the clinical efficacy and tolerability of 1.5 g/day amoxicillin without probenecid for the treatment of syphilis.

Methods The routine clinical records of patients diagnosed with syphilis and treated with 1.5 g/day amoxicillin at a tertiary care hospital between 2006 and 2018 were retrospectively analysed. Syphilis was diagnosed if serum rapid plasma reagin (RPR) titres were ≥8 RU and the Treponema pallidum latex-agglutination test was positive. Serological cure was defined as a ≥fourfold decrease in the RPR titre within 12 months in symptomatic early syphilis and within 24 months in latent syphilis.

Results Overall, 138 patients (112 with HIV) were analysed. The percentages of primary, secondary, early latent, late latent and latent syphilis of unknown duration were 8.0%, 50.0%, 25.4%, 5.8% and 10.9%, respectively. The median treatment duration was 4.5 weeks (IQR 4–8 weeks), which was not related to the stage of syphilis. Two patients (1.5%) changed treatment due to skin rash. The rate of serological cure was 94.9% (131/138; 95% CI 89.8% to 97.9%) overall; 93.8% (105/112; 95% CI 87.5% to 97.5%) in patients with HIV and 100% (26/26; 95% CI 86.8% to 100%) in patients without HIV. Treatment duration was not related to the treatment efficacy.

Conclusion The regimen of 1.5 g/day amoxicillin without probenecid is highly effective with a low switch rate in patients with and without HIV.

  • syphilis
  • therapeutics
  • serologic tests
  • HIV

Data availability statement

Data are available on reasonable request. Our data were collected from routine clinical records. Study dataset with deidentified participant data is available from fukushima-ngi@umin.ac.jp.

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Data availability statement

Data are available on reasonable request. Our data were collected from routine clinical records. Study dataset with deidentified participant data is available from fukushima-ngi@umin.ac.jp.

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Footnotes

  • Handling editor Jason J Ong

  • Contributors KI and KF conceived this research, extracted clinical data and drafted the manuscript. All authors were responsible for the clinical management of the patients, revised the draughts and approved the final manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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