Injections of penicillin are the most effective treatment for syphilis. In fact, penicillin is a cure for syphilis. The amount of penicillin used to treat syphilis depends on the stage of infection. There are not sufficient studies to recommend alternatives to penicillin for people who are allergic to the drug. For such individuals, it is recommended that they undergo penicillin desensitization.
Primary and secondary syphilis: For HIV-positive and HIV-negative people, one injection of penicillin is all that's usually needed. However, some experts recommend one injection every week for three weeks (a total of three injections) for HIV-positive people. This often depends on the overall health of the immune system—the lower the CD4 cell count, the less likely it is that syphilis will be cured with just one injection. In either case, follow-up blood tests should be done to make sure the treatment successfully cured the syphilis.
Latent syphilis: HIV-negative and HIV-positive people with early latent syphilis are generally treated with one injection of penicillin (HIV-positive people with early latent syphilis should be tested for neurosyphilis first, to determine if intensified treatment is necessary). HIV-negative and HIV-positive people with late latent syphilis—or those who don't know how long they've been infected with syphilis—should received one penicillin injection every week for three weeks (a total of three injections).
Tertiary syphilis: HIV-negative and HIV-positive people with tertiary syphilis should received one penicillin injection every week for three weeks (a total of three injections). They should also be examined for signs and symptoms of neurosyphilis to determine if more aggressive antibiotic treatment is necessary.
Neurosyphilis: Treating neurosyphilis often requires hospitalization. The treatment consists of penicillin administered through an intravenous (IV) line every four hours for up to two weeks. Treatment guidelines from the Centers for Disease Control and Prevention (CDC) in Atlanta recommend that everyone diagnosed with syphilis should also be carefully evaluated for neurosyphilis with both a physical examination and tests of spinal fluid. People suspected of having neurosyphilis should be treated for it even if treponemal spinal fluid tests fail to confirm the diagnosis.
Penicillin injections are administered directly into the butt muscle. Your butt may feel sore for several days after each injection. If you have a known allergy to penicillin, make sure you tell your doctor before you receive an injection. There are other antibiotics that can be given if you are allergic to penicillin. Due to a higher rate of first-line treatment failures among pregnant women, some doctors recommend that pregnant women diagnosed with syphilis receive a second injection one week after the first.
Some people become ill after receiving their first penicillin injection. This is because of a "Herxheimer reaction," named after a German doctor who first noted it in 1895. Because penicillin injections are so fast-acting against the bacterium that causes syphilis, it can cause the bacteria to release high levels of toxins as they die. This can cause symptoms such as high fever, profuse sweating, night sweats, nausea, and vomiting. The symptoms of Herxheimer reactions usually end within a few hours, and can often be managed with the use of aspirin, NSAIDs (non-steroidal anti-inflammatory drugs), Benadryl, pain medication, muscle relaxers, or others remedies—you should talk with your doctor or a nurse about your options.