May reduce serum levels w/ anticonvulsants (e.g. phenytoin, barbiturates, carbamazepine). May enhance the anticoagulant effect of warfarin and other coumarins w/ prolonged use. Accelerated absorption w/ metoclopramide and domperidone. May increase serum levels w/ probenecid. May increase serum levels of chloramphenicol. May reduce absorption w/ colestyramine w/in 1 hr of admin. May cause severe hypothermia w/ phenothiazine.