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Macrolide Antibiotic — STI Treatment

Azithromycin (Chlamydia / STI in Pregnancy)

Brand names: Zithromax

This page concerns azithromycin, a macrolide antibiotic, used to treat genital chlamydia and certain other sexually transmitted infections in pregnancy, where it is a preferred option.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

It binds the bacterial 50S ribosomal subunit and inhibits protein synthesis, giving a bacteriostatic effect against susceptible organisms including Chlamydia trachomatis.

Prescribing in practice

  • It is regarded as a suitable choice in pregnancy for chlamydia where tetracyclines are contraindicated, making it a key option for treating infection safely in this population.
  • It can prolong the QT interval, so caution is needed with other QT-prolonging drugs or relevant cardiac risk factors.
  • Test of cure and partner notification and treatment are important parts of management, and re-testing is advised in pregnancy.

Monitoring

Monitor for resolution with test of cure where indicated and for gastrointestinal tolerance rather than routine laboratory monitoring.

Counselling the patient

  • Complete the prescribed course and avoid sexual contact until you and your partner have completed treatment and follow-up advice.
  • Ensure partners are tested and treated to prevent reinfection.
  • Report severe or persistent diarrhoea or palpitations.

Evidence & guidelines

National sexual health and antenatal guidance support azithromycin as an effective treatment for chlamydia in pregnancy, with recommended test of cure.

Reference: BASHH Chlamydia Guidelines 2018; BASHH Gonorrhoea Guidelines 2019; MHRA QT alert 2013; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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