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Tetracycline antibiotic (with anti-ADH effect) Pregnancy: Contraindicated — tooth discolouration, skeletal growth inhibition (2nd half pregnancy); maternal hepatotoxicity (rare).

Demeclocycline

Brand names: Ledermycin

Adult dose

Dose: SIADH (chronic, when fluid restriction insufficient): 600–1200 mg/day in 2–4 divided doses. Titrate over 1 week; typical maintenance 600–900 mg/day. Antibiotic indications (rare today): 600–900 mg/day in divided doses.
Route: Oral
Frequency: BD–QDS
Max: 1200 mg/day
Take 1 hour before or 2 hours after food, milk, antacids, or iron (chelation reduces absorption). Effect on Na+ takes 5–14 days — not for acute hyponatraemia.

Dose adjustments

Renal

Avoid in significant renal impairment — accumulation, ↑ AKI risk via nephrogenic DI mechanism. Use tolvaptan or fluid restriction instead.

Hepatic

Avoid in severe impairment.

Clinical pearls

  • Mechanism in SIADH: induces nephrogenic diabetes insipidus by uncoupling collecting duct response to ADH → free water excretion → corrects hyponatraemia.
  • Onset 5–14 days — NOT for acute symptomatic hyponatraemia (use hypertonic saline, then fluid restriction; tolvaptan if available).
  • Largely superseded by tolvaptan and fluid restriction for chronic SIADH; demeclocycline use is now niche/legacy.
  • Risk of nephrotoxicity (especially in cirrhosis or pre-existing CKD) limits long-term use — check creatinine weekly initially.
  • Strict photosensitivity counselling — wide-brim hat, SPF 50+, long sleeves; reactions can be severe.
  • Antibiotic activity (doxycycline-similar) — historic use for chronic infections; now rarely first-line for any infection.

Contraindications

  • Children <12 years (tooth discolouration, inhibition of bone growth)
  • Pregnancy (especially 2nd half) and breastfeeding
  • Severe renal impairment
  • Severe hepatic impairment
  • Hypersensitivity to tetracyclines
  • Concurrent use of retinoids (intracranial hypertension risk)

Side effects

  • Photosensitivity (severe — tetracycline class effect; counsel about strict sun protection)
  • Nephrogenic diabetes insipidus (the THERAPEUTIC effect in SIADH — but can become symptomatic dehydration)
  • Hyperkalaemia, hypernatraemia (overshoot)
  • GI upset: nausea, diarrhoea
  • Tooth discolouration in young children (irreversible)
  • Vestibular: dizziness, vertigo (rare)
  • Benign intracranial hypertension (rare)
  • Hepatotoxicity
  • Renal impairment
  • Oesophagitis (take with full glass of water; do not lie down for 30 min)

Interactions

  • Antacids, iron, calcium, magnesium, dairy: chelate — separate by 2 hours
  • Warfarin: ↑ INR
  • Oral contraceptives: theoretical ↓ efficacy (limited evidence)
  • Retinoids (isotretinoin, acitretin): intracranial hypertension — avoid
  • Methoxyflurane: severe nephrotoxicity
  • Lithium: ↑ lithium levels
  • Other diuretics: additive volume depletion

Monitoring

  • Sodium daily during initiation, then weekly until stable
  • U&Es weekly initially, monthly maintenance
  • LFTs monthly
  • Body weight, fluid balance

Reference: BNF 90; SmPC Ledermycin; UK Hyponatraemia Guidance (Spasovski et al. ESE 2014); Verbalis et al. Am J Med 2013. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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