Tetracycline antibiotic / off-label SIADH treatment Pregnancy: Contraindicated during pregnancy and lactation. Tetracyclines cross the placenta, are found in fetal tissues and can be toxic to the developing fetus (often retardation of skeletal development); embryotoxicity has been noted in animals treated early in pregnancy. Use during tooth development (the last half of pregnancy and in children up to 12 years) may cause permanent yellow-grey-brown tooth discolouration and enamel hypoplasia. Tetracyclines are found in the milk of lactating women, so demeclocycline should not be given to breast-feeding women. (US label: Pregnancy Category D.)

Demeclocycline hydrochloride

Brand names: Ledermycin

Used in: Hyponatraemia

A tetracycline antibiotic that, in endocrine practice, is used off-label to manage chronic hyponatraemia due to the syndrome of inappropriate antidiuretic hormone secretion (SIADH).

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Antibiotic use: 600 mg daily. Chronic hyponatraemia due to SIADH (adults only): initially 900 mg to 1,200 mg daily, maintenance 600 mg to 900 mg daily

Route: Oral — capsules swallowed whole with plenty of fluid while sitting or standing

Frequency: Antibiotic use: 600 mg daily in 2 or 4 divided doses. SIADH: in divided doses. Take doses one hour before or two hours after meals, as absorption is impaired by milk and food

Max: Patients with known liver disease should not receive more than 1 g daily

PRIMARY ATYPICAL PNEUMONIA: the average daily dose is 900 mg in 3 divided doses for 6 days. DURATION: antibiotic therapy should be continued for one to three days after characteristic symptoms of fever have subsided; streptococcal infections should be treated for 8 full days even if symptoms have subsided, because of the risk of rheumatic fever or glomerulonephritis. SIADH: demeclocycline therapy for chronic hyponatraemia should not be withdrawn without commencing other methods of control; treating chronic hyponatraemia may require high doses for prolonged periods, increasing the potential for nephrotoxicity (rising plasma urea and creatinine) and photoallergic reactions. PHOTOSENSITIVITY: demeclocycline has the greatest potential of the tetracycline analogues for causing photo-allergic reactions — warn patients to avoid direct natural or artificial sunlight and to stop at the first sign of skin discomfort. MONITORING: on long-term therapy, perform periodic laboratory evaluation of haematopoietic, renal and hepatic systems; serum level determinations are advisable if therapy is prolonged in renal impairment. Discontinue if there are signs of overgrowth of resistant organisms (candida, enteritis, glossitis, stomatitis, vaginitis, pruritus ani, staphylococcal enterocolitis). ELDERLY: use with caution. May increase muscle weakness in myasthenia gravis; exacerbation of pre-existing SLE has been reported with tetracyclines. PAEDIATRIC — CONFLICT BETWEEN SOURCES: the UK SPC states it is not recommended for children under 12 years and lists children under 12 as a contraindication (risk of permanent yellow-grey-brown tooth discolouration and enamel hypoplasia during tooth development). The US label instead permits use above eight years of age and gives a weight-based paediatric daily dose not exceeding the adult 600 mg per day. These are irreconcilable in this fetch — do not surface a paediatric dose; follow the UK SPC and verify any paediatric use against a children's formulary.

Dose adjustments

Renal

Renal impairment is a contraindication in the UK SPC. Where used with caution, lower doses are indicated in renal impairment to avoid excessive systemic accumulation, and serum level determinations are advisable if therapy is prolonged. The US label advises decreasing the total dosage by reducing individual doses and/or extending the dose interval in impaired renal function; the same approach is advised for impaired liver function, and patients with known liver disease should not receive more than 1 g daily.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to demeclocycline or to any of the excipients; history of hypersensitivity to tetracyclines
Acute porphyria
Pregnancy and breast-feeding
Children under 12 years of age
Renal impairment

Side effects

Gastrointestinal: nausea, vomiting, diarrhoea, dysphagia, oesophagitis and oesophageal ulceration (particularly when taken immediately before lying down or with inadequate fluid), candidiasis, pseudomembranous colitis, glossitis, stomatitis, pancreatitis
Photosensitivity — demeclocycline has the greatest photo-allergic potential of the tetracyclines; also erythematous and maculo-papular rashes, pruritus, bullous dermatoses, exfoliative dermatitis, skin discolouration and serious skin reactions
Renal dysfunction, especially with pre-existing renal impairment; acute renal failure or nephritis; reversible nephrogenic diabetes insipidus with prolonged and/or high-dose use; rise in BUN (dose-related)
Hypersensitivity reactions including urticaria, Stevens-Johnson syndrome, angioneurotic oedema, anaphylaxis, anaphylactoid purpura, pericarditis and exacerbation of SLE
Benign intracranial hypertension in juveniles and adults, bulging fontanelles in infants, headache, dizziness, myasthenia, visual disturbances, impaired hearing
Haematological: haemolytic anaemia, thrombocytopenia, neutropenia, agranulocytosis, aplastic anaemia and eosinophilia; hepatitis, jaundice and hepatic failure

Interactions

Penicillins — should not be used with demeclocycline (bacteriostatic drugs may interfere with the bactericidal action of penicillins)
Anticoagulants (coumarins, phenindione) — tetracyclines depress plasma prothrombin activity, so reduced anticoagulant doses may be required
Milk and dairy products, food, and iron, calcium, zinc, magnesium and particularly aluminium salts (antacids) — impair absorption; also possibly reduced by kaolin, quinapril tablets (which contain magnesium carbonate), strontium ranelate, sucralfate and tripotassium dicitratobismuthate
Methoxyflurane anaesthesia — concurrent use increases the risk of kidney failure and has been reported to result in fatal renal toxicity
Retinoids (acitretin, isotretinoin, tretinoin) — possible increased risk of benign intracranial hypertension; ergotamine and methysergide — increased risk of ergotism
Oral typhoid vaccine — inactivated by antibacterials; the US label also notes tetracyclines may render oral contraceptives less effective

Clinical monograph

How it works

Demeclocycline induces a reversible, nephrogenic diabetes-insipidus-like state by reducing renal collecting-duct responsiveness to antidiuretic hormone, thereby promoting free-water excretion and raising serum sodium.

Prescribing in practice

The most important safety point is dose-dependent, usually reversible nephrotoxicity, so renal function must be monitored and the drug avoided in significant renal or hepatic impairment.
As a tetracycline it causes photosensitivity and is contraindicated in pregnancy, breastfeeding, and young children owing to dental staining and effects on bone.
Absorption is reduced by calcium, antacids, iron, and dairy products, which should be separated from dosing.

Monitoring

Monitor serum sodium and renal function closely, titrating to avoid over-rapid sodium correction and detect rising urea or creatinine.

Counselling the patient

Avoid taking this with milk, antacids, or iron supplements; separate them by a few hours.
Use sun protection as your skin may burn more easily.
Report reduced urine output or worsening tiredness, which may indicate kidney effects.

Evidence & guidelines

Demeclocycline is a recognised option for persistent SIADH in standard endocrinology references, used where fluid restriction alone is insufficient.

Reference: Society for Endocrinology hyponatraemia guidance; RCP; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways