Demeclocycline

Demeclocycline is a broad-spectrum tetracycline antibiotic used to treat various bacterial infections caused by susceptible organisms. It is a semi-synthetic derivative of tetracycline and has been employed for respiratory, urinary, and skin infections, among others. In modern practice it is less commonly first-line due to resistance and the availability of other agents, but it remains listed for certain indications and in some regions.

A notable non-antibiotic use is the off-label treatment of hyponatremia associated with the syndrome of inappropriate antidiuretic hormone secretion (SIADH). In this setting, demeclocycline can induce nephrogenic diabetes insipidus by antagonizing vasopressin action in the collecting ducts, thereby aiding in free water excretion.

Mechanism of action involves binding to the 30S ribosomal subunit of susceptible bacteria, inhibiting aminoacyl-tRNA attachment and thus blocking bacterial protein synthesis. This action is generally bacteriostatic rather than bactericidal. The drug is typically given by mouth, with absorption that can be reduced by food and dairy products. It is distributed widely in body tissues and fluids and is eliminated through both renal and hepatic pathways, with dose adjustments needed in renal impairment.

Common adverse effects include gastrointestinal upset and photosensitivity. Demeclocycline can cause esophageal irritation if not taken with adequate fluids and may lead to tooth discoloration and enamel hypoplasia in children. It is contraindicated in pregnancy (risk to the fetus) and in children under 8 years old due to effects on developing teeth and bones. Its use can interfere with the absorption of other minerals and drugs that chelate polyvalent cations; separate administration as appropriate.