Demeclocycline (marketed as Declomycin, Declostatin, and Ledermycin) is a tetracycline antibiotic derived from a strain of Streptomyces aureofaciens.
Uses
It is officially indicated for the treatment of various types of bacterial infections. It is used as an antibiotic in the treatment of Lyme disease, acne, and bronchitis. Resistance, though, is gradually becoming more common, and demeclocycline is now rarely used for infections.
It is widely used (though off-label in many countries) in the treatment of hyponatremia (low blood sodium concentration) due to the syndrome of inappropriate antidiuretic hormone (SIADH) when fluid restriction alone has been ineffective. Physiologically, this works by reducing the responsiveness of the collecting tubule cells to ADH.
The use in SIADH actually relies on a side effect; demeclocycline induces nephrogenic diabetes insipidus (dehydration due to the inability to concentrate urine). The use of demeclocycline in SIADH was first reported in 1975, and, in 1978, a larger study found it to be more effective and better tolerated than lithium carbonate, the only available treatment at the time. Demeclocycline has since been the drug of choice for treating SIADH, although it may be superseded as vasopressin receptor antagonists, such as tolvaptan, become available.
Contraindications
Like 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.
Side effects and interactions
These are similar to those of other tetracyclines. Skin reactions with sunlight have been reported. Demeclocycline is unique in that it is the only tetracycline known to cause nephrogenic diabetes insipidus.
Tetracyclines bind to cations, such as calcium, iron (when given orally), and magnesium, rendering them insoluble and inabsorbable for the gastrointestinal tract. Demeclocycline should not be taken with food (particularly milk and other dairy products) or antacids.
Mechanism of action
As with related tetracycline antibiotics, demeclocycline acts by binding to the 30S ribosomal subunit to inhibit binding of aminoacyl tRNA which impairs protein synthesis by bacteria. It is bacteriostatic (it impairs bacterial growth, but does not kill bacteria directly).
It is not completely understood why demeclocycline impairs the action of antidiuretic hormone, but is thought to block the binding of the hormone from its receptor.
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