Impaired phenytoin bioavailability secondary to cisplatinum, vinblastine, and bleomycin.
A 24-year-old woman experienced grand mal seizures temporally related to cisplatin, vinblastine, and bleomycin (CVB) administration. A second episode of seizures occurred when the patient's phenytoin level was estimated to be in the range of 15 micrograms/ml. Her plasma phenytoin level at the time had dropped to 2 microgram/ml despite a recent dosage increase. To evaluate the cause of the subtherapeutic phenytoin levels, daily plasma phenytoin levels and 24-h urine collections were obtained during her next CVB cycle. Data revealed a mean phenytoin absorption of 32% (normal greater than 80%), establishing that phenytoin malabsorption occurred. The disruption of phenytoin absorption at a cellular level by CVB therapy is the proposed mechanism. Frequent monitoring of plasma phenytoin levels is recommended for patients receiving CVB.
D000328:Adult; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000009:adverse effects* / Q000627:therapeutic use; D001682:Biological Availability; D001761:Bleomycin / Q000008:administration & dosage / Q000009:adverse effects; D002945:Cisplatin / Q000008:administration & dosage / Q000009:adverse effects; D005260:Female; D006801:Humans; D010672:Phenytoin / Q000097:blood / Q000378:metabolism* / Q000627:therapeutic use / Q000652:urine; D011247:Pregnancy; D012640:Seizures / Q000139:chemically induced / Q000188:drug therapy*; D014747:Vinblastine / Q000008:administration & dosage / Q000009:adverse effects / Q000031:analogs & derivatives; D014751:Vindesine
D001761:Bleomycin; D014747:Vinblastine; D010672:Phenytoin; D002945:Cisplatin; D014751:Vindesine