What was the first successful drug used to treat syphilis?

Salvarsan was the first successful drug used to treat syphilis.

Paul Ehrlich and Sahachiro Hata developed Salvarsan, also called arsphenamine, in 1909. Ehrlich tested hundreds of chemical compounds in search of a substance that would attack the syphilis bacterium while causing acceptable harm to the patient. Compound 606 became Salvarsan and was introduced clinically in 1910.

Salvarsan was an early example of systematic drug discovery and the idea of a “magic bullet,” a treatment aimed selectively at a disease-causing organism. It was administered by injection and required careful preparation, but it offered a major alternative to older mercury-based treatments.

Penicillin later replaced Salvarsan because it was safer, more effective, and easier to use. Salvarsan is therefore a landmark in antimicrobial chemotherapy, not the first antibiotic in the modern penicillin sense. Ehrlich received the 1908 Nobel Prize in Physiology or Medicine.