Antibiotic — Tetracycline Pregnancy: CONTRAINDICATED in pregnancy — all trimesters. Use azithromycin or erythromycin as alternative for chlamydia treatment

Doxycycline

Brand names: Vibramycin, Doxycycline Hyclate

Adult dose

Dose: 100 mg

Route: Oral

Frequency: Twice daily (7–14 days depending on indication)

Max: 200 mg/24h

Used for chlamydia (100 mg BD × 7 days — BASHH 2018), PID (100 mg BD × 14 days with ceftriaxone + metronidazole), endometriosis-associated infection. CONTRAINDICATED in pregnancy (fetal tooth discolouration and bone growth inhibition).

Paediatric dose

Dose: Seek specialist opinion mg/kg

Route: Oral

Frequency: N/A

Max: N/A

BNFc: generally avoid in children <12 years — causes permanent yellow-brown tooth staining and reduced bone growth. Specialist use only (e.g. Lyme disease in penicillin-allergic children >12 years)

Dose adjustments

Renal

No dose adjustment required — hepatic excretion

Hepatic

Use with caution in severe hepatic impairment — avoid if possible

Paediatric weight-based calculator

Patient weight (kg)

BNFc: generally avoid in children <12 years — causes permanent yellow-brown tooth staining and reduced bone growth. Specialist use only (e.g. Lyme disease in penicillin-allergic children >12 years)

Clinical pearls

CONTRAINDICATED in pregnancy — all trimesters. Causes permanent yellow-brown staining of developing teeth (mineralised from 14 weeks) and inhibits fetal bone growth
BASHH 2018 Chlamydia: doxycycline 100 mg BD × 7 days is first-line (superior to azithromycin 1 g stat for rectal and pharyngeal infection)
In pregnancy, chlamydia is treated with azithromycin 1 g stat or erythromycin — doxycycline avoided
Take with full glass of water sitting upright — risk of oesophageal ulceration if taken lying down
Photosensitivity: counsel to avoid prolonged sun exposure; use sunscreen
PID regimen: ceftriaxone 500 mg IM stat + doxycycline 100 mg BD × 14 days + metronidazole 400 mg BD × 14 days

Contraindications

Pregnancy — all trimesters (CONTRAINDICATED)
Children <12 years (routine use)
Hypersensitivity to tetracyclines
Breastfeeding (fetal/infant tooth and bone effects)

Side effects

Photosensitivity
Nausea
Oesophagitis (if taken without adequate fluid)
GI disturbance
Fetal tooth discolouration (in utero)
C. difficile (low risk)
Intracranial hypertension (rare)

Interactions

Antacids, iron, calcium, milk — significantly reduce absorption; take 2 hours apart
Warfarin — enhanced anticoagulant effect
OCP — no clinically significant interaction (current guidance)
Isotretinoin — increased intracranial hypertension risk

Monitoring

Symptom response
LFTs (prolonged use)
Intracranial pressure (headache or visual symptoms)

Reference: BNFc; BNF 90; BNFc; BASHH Chlamydia Guidelines (2018); BASHH PID Guidelines (2019); RCOG (2022). Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators