Late syphilis and recurrent secondary syphilis in patients allergic to penicillin tetracycline (or erythromycin) 500 mg qid for 30 days doxycyline 100 mg bid for 30 days may be given.Late syphilis and recurrent secondary syphilis • in patients allergic to penicillin - tetracycline (or erythromycin) 500 mg qid for 30 days - doxycyline 100 mg bid for 30 days may be given