Primary and secondary stage Syphilis are usually treated with 1 intra muscular
injection of Benzathyne Penicillin (24 million units), or, if a person is allergic to Penicillin, then Doxycycline is recommended (100 mg tablets, twice per day, each tablet 12 hours apart for 14 days).
That is, if the infection lasted for under 1 year.