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Tetracycline antibiotic Pregnancy: Contraindicated (third trimester — fetal teeth/bone). Use alternatives in pregnancy.

Doxycycline

Brand names: Vibramycin-D, Periostat

Adult dose

Dose: 100 mg twice daily on day 1, then 100 mg once daily; or 100 mg twice daily throughout
Route: Oral
Frequency: Once or twice daily
Max: 200 mg/day
Community-acquired pneumonia (atypicals): 200 mg day 1 then 100 mg daily for 5–7 days. Chlamydia: 100 mg BD for 7 days. Malaria prophylaxis: 100 mg daily (start 1–2 days before travel, continue 4 weeks after). Lyme disease: 100–200 mg BD for 14–21 days. Acne: 100 mg daily (long-term).

Paediatric dose

Dose: 2.2 mg/kg
Route: Oral
Frequency: Once or twice daily
Max: 200 mg/day
Licensed ≥12 years only (avoid in children <8 years — dental staining and bone effects). 12–17 years: adult dose. Some specialist use in younger children for severe infections (e.g., cholera, Rocky Mountain spotted fever) where benefit outweighs risk.

Dose adjustments

Renal

Unlike other tetracyclines, no dose adjustment required (not renally cleared).

Hepatic

Use with caution in severe hepatic impairment.

Paediatric weight-based calculator

Licensed ≥12 years only (avoid in children <8 years — dental staining and bone effects). 12–17 years: adult dose. Some specialist use in younger children for severe infections (e.g., cholera, Rocky Mountain spotted fever) where benefit outweighs risk.

Clinical pearls

  • Take in upright position with full glass of water to prevent oesophageal ulceration
  • Photosensitivity common — use SPF50+ sunscreen (especially in summer/travel)
  • Excellent for atypical CAP, Lyme disease, chlamydia, malaria prophylaxis, acne, rosacea
  • Not suitable for <8 years except when alternatives absent and infection is life-threatening
  • Unlike other tetracyclines — safer in renal impairment (faecal excretion predominates)

Contraindications

  • Children under 8 years (dental staining, bone growth inhibition)
  • Pregnancy (second half — fetal teeth and bones)
  • Hypersensitivity to tetracyclines

Side effects

  • GI irritation and oesophagitis (take with plenty of water and remain upright)
  • Photosensitivity (use sunscreen)
  • Dental staining (children <8 years)
  • Yeast infections (vaginal/oral)
  • Headache and visual disturbance (raised intracranial pressure — rare)
  • Hepatotoxicity (high doses)

Interactions

  • Antacids, iron, calcium, milk — chelation reduces absorption (take 2 hours apart)
  • Warfarin — increased anticoagulant effect
  • Barbiturates, carbamazepine, phenytoin — reduce doxycycline levels
  • Oral isotretinoin — combined intracranial hypertension risk
  • Oral contraceptives — very small theoretical reduction in efficacy

Monitoring

  • LFTs (prolonged use)
  • Signs of oesophagitis
  • Photosensitivity

Reference: BNFc; BNF; PHE guidelines; BASHH STI guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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