Prevention or treatment of infections Routine empiric prophylaxis for STIs for adults and adolescents consists of the following: Ceftriaxone 500 mg IM in a single dose or for patients weighing ≥ 150 kg, 1 g of ceftriaxone (for gonorrhea and chlamydia infections) AND Doxycycline 100 mg orally 2 times a day for 7 days (for chlamydial infection) For females, metronidazole 500 mg orally twice a day for 7 days (for trichomoniasis and bacterial vaginosis) For hepatitis B, the Centers for Disease Control and Prevention (CDC) recommends hepatitis B vaccination unless the patient has been previously vaccinated and has documented immunity.