Penicillin is the main drug used to treat syphilis. The pathogen of syphilis is the pale spirochete, also known as syphilis spirochete. This microorganism is highly sensitive to penicillin, so penicillin is used clinically to treat all stages and all types of syphilis. There are three types of penicillin generally available: penicillin g, procaine penicillin G, and benzathine penicillin G. According to the length of their effects, they can be used in the treatment of different types of syphilis. For example, for early syphilis, procaine penicillin G is commonly used as a daily injection or benzathine penicillin G as a weekly injection.