Table 4.

Treatment of late latent syphilis and syphilis of unknown duration

Drug	Dose, administration	Treatment duration	Level of evidence
Benzathine penicillin	2.4 million units 1× week, IM	3 consecutive weeks	III
Procaine penicillin	600 000 units once daily, IM	17–21 days	III
Alternatives
Doxycycline	200 mg once daily, PO	21–28 days	IV
Tetracycline	500 mg 4× daily, PO	28 days	IV
Erythromycin	500 mg 4× daily, PO	28 days	IV