References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
Bacterial STIs are treated with antibiotics, but the “best” choice depends on the specific infection. Different bacteria need different drugs, and UK guidelines are updated as resistance patterns change. Here’s a clear overview of first-line treatments for common bacterial STIs, as recommended by BASHH (British Association for Sexual Health and HIV).
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First-Line Treatments
| STI | First-Line Treatment |
|---|---|
| Chlamydia | Doxycycline 100mg twice daily for 7 days |
| Gonorrhoea | Ceftriaxone 1g intramuscular injection |
| Syphilis (early) | Benzathine penicillin single injection |
| Syphilis (late or unknown duration) | Weekly benzathine penicillin injections for 3 weeks |
| Trichomoniasis | Metronidazole (5-7 days or single 2g dose) |
| LGV | Doxycycline 100mg twice daily for 21 days |
| Mycoplasma genitalium (no resistance) | Doxycycline then azithromycin |
| Mycoplasma genitalium (with resistance) | Doxycycline then moxifloxacin |
| Non-specific urethritis | Doxycycline 100mg twice daily for 7 days |
Why Guidelines Change
Treatment guidelines are regularly updated because bacteria evolve resistance. Examples:
- Gonorrhoea has developed resistance to multiple older antibiotics; ceftriaxone is the current mainstay
- Azithromycin is no longer recommended as a single dose for chlamydia — doxycycline is preferred
- Mgen increasingly resistant to azithromycin
What About Viral STIs?
Antibiotics don’t treat viral infections. Different medicines are used:
- HIV — antiretroviral drugs, lifelong treatment
- Herpes — antiviral drugs (aciclovir, valaciclovir)
- Hepatitis B — antiviral suppressive treatment
- Hepatitis C — direct-acting antivirals (cure in over 95%)
- HPV — no specific antiviral; treatment targets symptoms
Allergies and Alternatives
If you are allergic to first-line antibiotics, alternatives exist:
- Penicillin allergy — doxycycline or erythromycin for syphilis
- Doxycycline alternative — azithromycin or erythromycin
- Ceftriaxone alternatives — specialist advice needed
Always tell your clinician about allergies.
Completing the Course
- Always finish the prescribed course, even if you feel better
- Don’t share antibiotics with partners — they need their own prescription
- Avoid alcohol during metronidazole treatment
- Doxycycline can cause photosensitivity — use sunscreen
- Avoid sex during treatment and for 7 days afterwards
Partner Treatment
Partners from recent weeks or months should be notified and treated, even if they have no symptoms. Clinics can help with this confidentially.
Antibiotic Stewardship
Using antibiotics responsibly matters for everyone. Don’t:
- Use old leftover antibiotics
- Take antibiotics without a proper diagnosis
- Pressure doctors to prescribe when not needed
Read more: What is chlamydia? | What is gonorrhoea? | What is syphilis?
Frequently Asked Questions
Can one antibiotic cover all STIs?
No. Different bacteria need different antibiotics. A proper diagnosis is needed to guide treatment.
Is doxycycline used for most STIs?
Doxycycline is first-line for chlamydia, LGV, non-specific urethritis and part of Mgen treatment. Other STIs need different drugs.
Will antibiotics cure all STIs?
No. Viral STIs (HIV, herpes, HPV, hepatitis) don’t respond to antibiotics. Different treatments are needed.
Related reading
- Using Antibiotics to Prevent STIs: DoxyPEP Explained
- Azithromycin: Uses in Sexual Health
- Ciprofloxacin for STIs: Uses, Dosage, and Side Effects
- Clindamycin: Uses in Sexual Health
- Diflucan (Fluconazole): What It Does
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
