ANTACIDS, ZINC, BISMUTH, CALCIUM, MAGNESIUM AND IRON REDUCED ABSORPTION. THE METABOLISM OF DOXYCYCLINE MAY BE ACCELERATED BY DRUGS THAT INDUCE HEPATIC ENZYMES SUCH AS ALCOHOL, CARBAMAZEPINE, PHENOBARBITONE, PHENYTOIN, PRIMIDONE AND RIFAMPICIN. IT MAY INTERFERE WITH BACTERICIDAL ACTION OF PENICILLINS. TETRACYCLINES HAVE BEEN SHOWN TO DEPRESS PLASMA PROTHROMBIN ACTIVITY, PATIENTS WHO ARE ON ANTICOAGULANT THERAPY MAY REQUIRE LOWER DOSE OF ANTICOAGULANTS. MILK AND FOOD HAS LESS EFFECT ON ABSORPTION. CONCURRENT USE OF TETRACYCLINES WITH ORAL CONTRACEPTIVES MAY RENDER ORAL CONTRACEPTIVES LESS EFFECTIVE. NEPHROTOXIC EFFECTS ARE POTENTIATED BY DIURETICS, METHOXYFLURANE AND OTHER NEPHROTOXIC DRUGS. WITH RETINOIDS INCIDENCE OF BENIGN INTRACRANIAL HYPERTENSION IS INCREASED. CONCENTRATION OF LITHIUM, DIGOXIN, THEOPHYLLIN, ORAL ANTICOAGULANTS IS INCREASED. SUCRALFATE & CIMETIDINE HAS NO EFFECT ON ABSORPTION.