Quick Answer

The STI antibiotic map: azithromycin or doxycycline for chlamydia; ceftriaxone injection for gonorrhea; benzathine penicillin for syphilis; metronidazole or tinidazole for trichomoniasis and bacterial vaginosis — with moxifloxacin reserved for resistant mycoplasma genitalium.

  • Doxycycline 100mg twice daily × 7 days: current first-line chlamydia monotherapy.
  • Ceftriaxone 500mg IM single dose: gonorrhea's last reliable first-line agent as resistance climbs.
  • Penicillin G benzathine IM: syphilis gold standard — one dose early stages, three weekly for late.
  • Metronidazole 2g single dose: trichomoniasis and BV share this therapy.
  • Amoxicillin does NOT treat standard STIs reliably — a persistent myth from dental-prescribing confusion.

The Landscape

Each antibiotic targets specific organism vulnerabilities: cell-wall synthesis (penicillins/cephalosporins), protein assembly (doxycycline), DNA processes (metronidazole's radical mechanism). Matching drug-to-bug determines success — broad-spectrum guessing loses to targeted precision.

Resistance watch

Gonococcus developed resistance to every prior first-line agent sequentially — penicillin, then fluoroquinolones, then azithromycin. Ceftriaxone remains effective but surveillance continues; resistance-aware prescribing isn't optional.

Allergy accommodations

Penicillin-allergic syphilis patients receive doxycycline alternatives with enhanced follow-up; true anaphylactic histories deserve allergist consultation since 90% of 'penicillin allergies' test negative.

Treatment Windows by Infection

Bacterial infections clear with antibiotics measured in days: single-dose azithromycin or a ceftriaxone shot for gonorrhea, seven days of doxycycline for chlamydia, penicillin injections for syphilis staged by duration. Viral infections play a longer game — suppressive antivirals for herpes, daily ART driving HIV to undetectable, and 8–12-week antiviral courses curing over 95% of hepatitis C cases.

⚕️ This page is educational and does not replace advice from a licensed clinician. If you may have been exposed to an STI, get tested — most infections are manageable, and many are fully curable.

Sources & Further Reading

Figures reflect CDC surveillance and WHO estimates; they are population statistics, not personal risk predictions.