Demeclocycline Antacids

Concomitant therapy - Absorpi on is impaired by antacids containing aluminum, calcium, or magnesium, and by preparations containing iron. Take demeclocycline at least 1 hour before or 2 hours after these products. 

The oral dosage for rapidly excreted tetracyclines, equivalent to tetracycline hydrochloride, is 0.25-0.5 g four times daily for adults and 20-40 mg/kg/d for children (8 years of age and older). For severe systemic infections, the higher dosage is indicated, at least for the first few days. The daily dose is 600 mg for demeclocycline or methacycline, 100 mg once or twice daily for doxycycline, and 100 mg twice daily for minocycline. Doxycycline is the oral tetracycline of choice because it can be given as a once-daily dose and its absorption is not significantly affected by food. All tetracyclines chelate with metals, and none should be orally administered with milk, antacids, or ferrous sulfate. To avoid deposition in growing bones or teeth, tetracyclines should be avoided in pregnant women and children less than 8 years of age. 

Tetracyclines mainly differ in their absorption after oral administration and their elimination. Absorption after oral administration is approximately 30% for chiortetracycline 60-70% for tetracycline, oxytetracycline, demeclocycline, and methacycline and 95-100% for doxycycline and minocycline. A portion of an orally administered dose of tetracycline remains in the gut lumen, modifies intestinal flora, and is excreted in the feces. Absorption occurs mainly in the upper small intestine and is impaired by food (except doxycycline and minocycline) by divalent cations (Ca2+, Mg2+, Fe2+) or Al3+ by dairy products and antacids, which contain multivalent cations and by alkaline pH. Specially buffered tetracycline solutions are formulated for intravenous administration. 

Because of their chelating action, tetracycline drugs are inactivated in the patient s bowel by any dietary calcium or magnesium ions, whether from milk or from antacid medication. Through such mishaps, many patients have lost the potential benefit of these antibiotics. Tetracyclines are usually given orally. Tetracycline, itself, is still much prescribed, but there are also lower-dose forms available demeclocycline and methacycline, and a sub-class of these which require less frequent dosing doxycycline and minocycline. 

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