Tetracycline Magnesium sulfate

Electrolyte imbalance, and diseases that lead to electrolyte imbalance, such as adrenal cortical insufficiency, alter neuromuscular blockade. Depending on the nature of the imbalance, either enhancement or inhibition may be expected. Magnesium sulfate, used in the management of toxemia of pregnancy, enhances the skeletal-muscle-relaxing effects of pancuronium. Antibiotics such as aminoglycosides, tetracyclines, clindamycin, lincomycin, colistin, and sodium colistimethate augment the pancuronium-induced neuromuscular blockade. Anesthetics such as halothane, enflurane, and isoflurane enhance the action of pancuronium, whereas azathioprine will cause a reversal of neuromuscular blockade. 

Magnesium sulfate certainly interacts with tetracycline, but in the only clinical study available the amount of magnesium was much higher than would normally be found in the usual dose of antacid. 

Harcourt RS, Hamburger M. The effect of magnesium sulfate in lowering tetracycline blood levels. JLab Clin Med (1957) 50, 464-8. 

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... 

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