COMPOUNDS CONTAINING CALCIUM AND MAGNESIUM, INCLUDING ANTACIDS AND MINERAL SUPPLEMENTS, AND BICARBONATES, CARBONATES, OXALATES OR PHOSPHATES. MAY ALSO IMPAIR THE ABSORPTION OF IRON BY THE FORMATION OF INSOLUBLE COMPLEXES. SIMILARLY THE ABSORPTION OF BOTH IRON SALTS AND TETRACYCLINES IS DIMINISHED WHEN THEY ARE TAKEN CONCOMITANTLY BY MOUTH. IF TREATMENT WITH BOTH DRUGS IS REQUIRED, A TIME INTERVAL OF ABOUT 2 TO 3 HOURS SHOULD BE ALLOWED BETWEEN THEM. A SUITABLE INTERVAL IS ALSO ADVISED IF AN IRON SUPPLEMENT IS REQUIRED IN PATIENTS RECEIVING TRIENTINE. ZINC SALTS MAY DECREASE THE ABSORPTION OF IRON. SOME AGENTS, SUCH AS ASCORBIC ACID AND CITRIC ACID. MAY ACTUALLY INCREASE THE ABSORPTION OF IRON. THE RESPONSE TO IRON MAY BE DELAYED IN PATIENTS RECEIVING CONCOMITANT PARENTERAL CHLORAMPHENICOL THERAPY. IRON SALTS CAN ALSO DECREASE THE ABSORPTION OF OTHER DRUGS AND THUS REDUCE THEIR BIOAVAILABILITY AND CLINICAL EFFECT. DRUGS SO AFFECTED INCLUDED BISPHOSPHONATES, FLUOROQUINOLONES, LEVODOPA, METHYLDOPA, PENICILLAMINE AND TETRACYCLINE. IRON SALTS MAY REDUCE THE EFFICACY OF THYROXINE. THERE IS SOME EVIDENCE THAT ENALAPRIL MAY POTENTIATE SYSTEMIC ADVERSE EFFECTS SEEN WITH INTRAVENOUS IRON THERAPY.