Demeclocycline

How it works

In this setting it acts on the renal collecting ducts to reduce responsiveness to antidiuretic hormone, producing a reversible nephrogenic diabetes insipidus that promotes water excretion.

Prescribing in practice

• It can be nephrotoxic, particularly in hepatic impairment, so renal function must be monitored and it is avoided in significant liver disease.
• As a tetracycline it causes photosensitivity and is contraindicated in pregnancy and young children because of effects on teeth and bone.
• Absorption is reduced by dairy products and by calcium, iron or antacids, which should be separated from dosing.

Monitoring

Monitor serum sodium and renal function during treatment for SIADH.

Counselling the patient

• Avoid strong sun exposure and use sun protection because of photosensitivity.
• Take separately from milk, indigestion remedies and iron or calcium supplements.
• Attend for blood tests to check sodium and kidney function.

Evidence & guidelines

Demeclocycline is an established option for chronic SIADH where fluid restriction is insufficient; use should follow the SPC.