PMID: 9533548May 14, 1998Paper

Phenytoin alters the disposition of topotecan and N-desmethyl topotecan in a patient with medulloblastoma

Clinical Cancer Research : an Official Journal of the American Association for Cancer Research
W C ZamboniC F Stewart

Abstract

Topotecan undergoes both renal and hepatic elimination, with topotecan urinary recovery ranging from 60 to 70%. We evaluated the potential of phenytoin to alter the disposition of topotecan and its N-desmethyl metabolite. A 5-year-old child with high-risk medulloblastoma received the first course of topotecan with phenytoin and the second course without phenytoin. For both courses, topotecan doses were adjusted to achieve a target topotecan lactone plasma area under the curve (AUC). Serial plasma samples were obtained, and lactone and total plasma concentrations of topotecan, as well as total plasma and cerebrospinal fluid concentrations of N-desmethyl topotecan, were measured by high-performance liquid chromatography. Phenytoin coadministration increased lactone and total topotecan clearance from 43.4 +/- 1.9 L/h/m2 to 62.9 +/- 6.4 L/h/m2, and 20.8 +/- 2.8 L/h/m2 to 30.6 +/- 4.1 L/h/m2, respectively (P < 0.05). Concomitant phenytoin increased the plasma AUC of total N-desmethyl topotecan from 7.5 +/- 0.68 ng/ml x h to 16.3 +/- 0.53 ng/ml x h (P < 0.05) at plasma AUC of total topotecan of 226.0 +/- 5.5 ng/ml x h and 240.9 +/- 39.8 ng/ml x h, respectively. N-Desmethyl topotecan penetrated into the cerebrospinal fluid (0.12 +/- 0...Continue Reading

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