Trends in syphilis treatments and the impact of intramuscular injectable Benzathine penicillin G in Japan: A descriptive study using administrative claims data from April 2016 to September 2023.

Introduction: The incidence of syphilis is increasing in Japan. A new treatment, penicillin intramuscular injection, was launched in January 2022. This study aimed to determine syphilis treatments in Japan and investigate the impact of the new intramuscular penicillin formulation.

Materials and methods: Data from the Japanese Administrative Claims Database from January 2016 to September 2023 were used to identify patients diagnosed with syphilis, and the types and annual trends of antimicrobials prescribed were investigated. Furthermore, the characteristics of patients prescribed an intramuscular injection of benzathine penicillin G were compared with those of patients who were not.

Results: Overall, 7867 patients were included in the analysis (81 %, male; 5.4 % positive for human immunodeficiency virus). Seventy-five percent of patients were diagnosed with syphilis in facilities with 0-19 beds. Annual trends showed oral amoxicillin as the most prescribed drug to 80 % of patients throughout the study period. In 2023, 10.6 % of patients received a prescription for an intramuscular penicillin formulation. Compared with those who did not receive this treatment, those who received it tended to have fewer clinic visits over 1 month (p = 0.0256).

Conclusions: Oral amoxicillin is the primary treatment for syphilis in Japan; however, the number of patients receiving intramuscular injection of benzathine penicillin G is increasing. Prescribed mainly by clinics, an intramuscular injection of benzathine penicillin G may contribute to a decreased number of office visits.