Demeclocycline (marketed as Declomycin, Declostatin and Ledermycin) is a member of the tetracycline antibiotics group used in various types of bacterial infections. One of its other registered uses is the treatment of hyponatremia (low blood sodium concentration) due to the syndrome of inappropriate antidiuretic hormone (SIADH) where fluid restriction alone has been ineffective. It is derived from the Streptomyces aureofaciens actinomycete strain.

Mode of action

Its use as an antibiotic is particularly in Lyme disease, acne and bronchitis. Resistance is gradually becoming more common. As with related tetracycline antibiotics, demeclocycline acts by binding to the 30S- and 50S-RNA, which impairs protein synthesis by bacteria. It is therefore bacteriostatic (it impairs bacterial growth but does not kill bacteria directly). Demeclocycline is rarely used for infections.

The use in SIADH actually relies on a side-effect of tetracycline antibiotics; many may cause diabetes insipidus (dehydration due to the inability to concentrate urine). It is not completely understood why demeclocycline impairs the action of antidiuretic hormone, but it is thought that it blocks the binding of the hormone to its receptor.

Side-effects and interactions

These are similar to other tetracyclines. Hypersensitivity may occur. Skin reactions with sunlight have been reported. Demeclocycline is unique in that it is the only tetracycline known to cause nephrogenic diabetes insipidus.

Contraindications

As other tetracyclines, demeclocycline is contraindicated in children and pregnant or nursing women. All members of this class interfere with bone development and may discolour teeth. Tetracyclines bind with cations such as calcium and magnesium and becomes insoluble and inabsorbable for the GI tract. Tetracyclines should not be given with milk or antacids.

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