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Tetracycline antibiotic Pregnancy: Avoid — particularly second and third trimesters (permanent tooth staining in fetus, inhibits fetal bone growth).

Doxycycline 100mg Capsules (Sinusitis — Penicillin Allergy)

Brand names: Vibramycin-D, Efracea (acne — different indication)

Adult dose

Dose: 200 mg on day 1 (loading dose), then 100 mg once daily for 4 days (total 5-day course)
Route: Oral
Frequency: Once daily (after loading dose)
Max: 200 mg/day
Acute sinusitis in penicillin allergy: 200 mg stat loading dose, then 100 mg OD for 4 more days (5 days total — NICE NG120). Swallow whole with plenty of water; remain upright for 30 min after dose (prevent oesophageal ulceration). Avoid dairy and antacids within 2 hours. Can be taken with food to reduce GI upset.

Paediatric dose

Route: Oral
Frequency: Once daily
Max: Not recommended in children under 12 years
Contraindicated under 12 years (teeth and bone development). 12–18 years: adult dose. Clarithromycin is the alternative for younger children with penicillin allergy.

Dose adjustments

Renal

No dose adjustment required (doxycycline is relatively safe in renal impairment — faecal excretion).

Hepatic

Use with caution in severe hepatic impairment — monitor LFTs.

Clinical pearls

  • Recommended alternative to amoxicillin for sinusitis in penicillin allergy by NICE NG120
  • Must be taken with a full glass of water and patient must remain upright for at least 30 minutes — oesophageal ulceration is a common and preventable complication
  • Photosensitivity is common — warn patient to use sun protection during treatment
  • Safer than amoxicillin in renal impairment due to predominantly faecal elimination
  • Doxycycline is not effective for streptococcal pharyngitis — resistance rates are high

Contraindications

  • Children under 12 years (tooth discolouration, inhibits bone growth)
  • Pregnancy (especially second and third trimesters)
  • Hypersensitivity to tetracyclines
  • Myasthenia gravis (exacerbation risk — rare)

Side effects

  • Nausea and vomiting
  • Oesophageal ulceration (if not taken with sufficient water in upright position)
  • Photosensitivity (sunburn more easily — use sunscreen)
  • Oral / vaginal candidiasis
  • Hepatotoxicity (rare — high doses)
  • Tooth discolouration (children under 12 only)

Interactions

  • Antacids, iron, calcium, dairy — chelation reduces absorption (separate by 2 hours)
  • Warfarin — increased anticoagulant effect
  • Oral retinoids (isotretinoin) — increased risk of benign intracranial hypertension; avoid combination
  • Oral contraceptives — theoretical interaction (advise barrier method)

Monitoring

  • Clinical response at 72 hours
  • Symptoms of oesophageal irritation

Reference: BNFc; BNF; NICE NG120 Sinusitis; PHE Antibiotic 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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