Tetracyclines Magnesium compounds

Because acid-pepsin disease rarely occurs in the absence of gastric acid and pepsin, antacids are highly effective in its overall management. Antacids consist of a mixture of magnesium, aluminum, and calcium compounds. Their efficacy is based on their inherent ability to react with and neutralize gastric acid. Sodium bicarbonate, which may leave the stomach rapidly, can cause alkalosis and sodium retention. Calcium salts may produce hypercalcemia, which can be detrimental in patients with impaired renal function. Aluminum salts may decrease the absorption of tetracyclines and anticholinergic drugs. 

Magnesium oxide is a basic compound and as such can react with acidic compounds in the solid state to form salts such as Mg(ibuprofen)2 or degrade alkaline-labile drugs. Adsorption of various drugs onto magnesium oxide has been reported, such as antihistamines, antibiotics (especially tetracyclines), salicylates, atropine sulfate, hyoscyamine hydrobromide, paracetamol, chloroquine, and anthranilic acid derivatives have been reported to adsorb onto the surface of magnesium... 

Aluminium hydroxide has a relatively slower action. AP ions form complexes with cenatn drugs (e.g. tetracyclines) and tend to cause constipation. Mixtures of magnesium and aluminium compounds may be used to minimize the effeci.s on motility. 

Food, dairy products and calcium compounds markedly reduce the absorption of strontium ranelate, and administration should be separated by at least 2 hours. Aluminium and magnesium antacids only slightly reduce strontium ranelate absorption. Strontium ranelate is predicted to reduce the absorption of the quinolones and the tetracyclines, and strontium should be stopped during courses of these antibacterials. Vitamin D does not affect strontium ranelate bioavailability. 

---