The effect of zinc sulphate and of bicitropeptide on tetracycline absorption.

The interaction between tetracyclines and di- and trivalent ions such as are contained in aluminium, magnesium, calcium, iron and zinc-containing salts or complexes or antacids is well documented. The potential for interaction between tetracyclines and zinc and bismuth salts is often not realised, but is emphasised by the findings reported here. The absorption of 250 mg phosphate-potentiated tetracycline hydrochloride was reduced by 75% when administered concurrently with 220 mg zinc sulphate. The absorption of 250 mg phosphate-potentiated tetracycline hydrochloride was reduced by 50% when administered concurrently with 10 ml bicitropeptide, a bismuth-protein complex. Tetracyclines should thus not be administered concurrently with zinc salts or bicitropeptide.