One treatment option for a syphilis rash is penicillin, according to Cleveland Clinic. The drug is injected and acts to kill the bacteria that causes the disease.
The type of penicillin specifically needed for a syphilis rash is benzathine penicillin G, according to the Centers for Disease Control and Prevention. The patient and his sex partner need to take the medication for some time to make sure that the infection is cleared up, says Cleveland Clinic. This means that the patient takes the penicillin even after the rash is gone.
Alternatives to penicillin include tetracycline and doxycycline, according to the CDC. The efficacy of these drugs is uncertain, but the patient who takes them must be closely monitored by his physician.