Drug-Drug

• May ↑ the effect of warfarin .

• May ↓ effectiveness of estrogen-containing oral contraceptives .

• Antacids , calcium , iron , and magnesium form insoluble compounds (chelates) and ↓ absorption of tetracycline.

• Sucralfate may bind to tetracycline and prevent its absorption from the GI tract.

• Cholestyramine or colestipol ↓ absorption.

• Adsorbent antidiarrheal agents may ↓ absorption.

• Barbiturates , phenytoin , or carbamazepine may ↓ activity of doxycycline.

Drug-Food
Calcium in foods or dairy products ↓ absorption by forming insoluble compounds (chelates).