Treatment

Last Updated: June 2026

Syphilis treatment is delivered in prefilled syringes of benzathine benzylpenicillin 1.2 million units/2.3mL per syringe.
Inject a prefilled syringe into each ventrogluteal or dorsogluteal site
A complete dose of 2.4 million units IM requires 2 injections per treatment.

Bicillin L-A benzathine benzylpenicillin packaging and prefilled syringes

Syphilis treatment depends on the stage of infection:

Stage	Treatment
Primary, secondary and early latent	Benzathine benzylpenicillin injection 2.4 million units (1.8 gm) IM stat, given as two injections containing 1.2 MU (0.9g)*
Late latent and unknown duration	Benzathine benzylpenicillin 2.4 million units IMI weekly for three weeks*
Allergy to penicillin	Alternate treatment available- Doxycycline. Discuss with a specialist.

*Up to 14 days is an acceptable interval between multiple doses of benzathine penicillin, providing all three injections are given over a period not exceeding 28 days.

Reference: Melbourne Sexual Health Centre. Syphilis treatment guidelines [Internet]. Carlton (VIC): Melbourne Sexual Health Centre; 2021 [cited 17 April 2026]. Available from: https://www.mshc.org.au/health-professionals/treatment-guidelines/syphilis-treatment-guidelines

Treatment side effects

Mild pain at injection site

Jarisch-Herxheimer reaction is a common reaction to treatment in patients with primary and secondary syphilis. It occurs 6-12 hours after commencing treatment and is an unpleasant reaction of varying severity with fever, headache, malaise, rigors and joint pains, and lasts for several hours. Symptoms are controlled with analgesics and rest. Patients should be alerted to the possibility of this reaction and reassured accordingly.