RETROPERITONEAL HEMATOMA IN A PATIENT TREATED WITH ACENOCOUMAROL, PHENYTOIN AND PAROXETINE

Coumarin anticoagulants must be strictly monitored because of their na rrow therapeutic index and their potential interactions with other dra gs, The high probability of interactions can be explained by two pharm acokinetic properties of coumarins: high binding to plasma albumin (99 %), being displaced by other drugs with greater affinity to this prote in, and metabolism by liver microsomal enzymes (cytochrome P450), whic h can be induced or inhibited by other compounds (Shinn & Shrewsbury 1 985). A case is reported of a clinically relevant drug interaction of phenytoin and acenocoumarol, possibly potentiated by concomitant treat ment with paroxetine, leading to a retroperitoneal haematoma.