Cephalexin, an orally administered cephalosporin antibiotic, was used for the treatment of infectious syphilis in regimens of 15 and 30 gm. The former dose was inadequate whereas the latter schedule gave results comparable to those obtained with presently recommended doses of either erythromycin or tetracycline, which can be used as alternate antibiotics to parenterally administered penicillin. Whenever possible, penicillin therapy must remain the treatment of choice for all stages of syphilis.
Duncan WC, Knox JM. Cephalexin Therapy for Infectious Syphilis. Arch Dermatol. 1974;110(1):77-80. doi:10.1001/archderm.1974.01630070045008