A urine metabolic ratio of dextromethorphan and 3-methoxymorphinan as a probe for CYP3A activity and prediction of cyclosporine clearance in healthy volunteers.
Dextromethorphan (DM) is metabolized in the body to dextrophan (DT) and 3-methoxymorphinan (3-MM) by cytochrome P450 (CYP) 2D6 and 3A4, respectively, and cyclosporine (CsA) is a known substrate of CYP3A4. We attempted to determine if the urine metabolic ratio of DM:3-MM at various time intervals during 24 hours is predictive of CsA clearance in 11 healthy volunteers. Each subject took DM 30 mg orally, and serial urine samples were collected at 0-4, 4, and 4-24, and 0-24 hours. Subjects then were randomly assigned to receive either oral microemulsion CsA 5 mg/kg or intravenous CsA 1.5 mg/kg in a crossover fashion in a two-sequence pharmacokinetic study with a wash-out period of at least 7 days. A total of 17 blood samples were collected from each subject in the CsA pharmacokinetic study over 24 hours. Urinary DM, DT, and 3-MM were quantified by high-performance liquid chromatography (HPLC) with a fluorescence detector, and blood CsA concentrations were analyzed by HPLC with ultraviolet detection. All subjects were extensive metabolizers of CYP2D6 as determined by metabolic ratios of DM:DT (mean+/-SD 0.0255+/-0.048). There was no correlation between CYP2D6 and CYP3A4 (p=0.38). The metabolic ratios of DM:3-MM in any urine samples during the 24-hour collection period did not predict CsA pharmacokinetics, although the 0-24 hour sample had an unexpected positive correlation with CsA clearance (r2 = 0.38, p<0.0001). The correlation was similar for metabolic ratios of DM:3-MM with intravenous CsA clearance (r2 = 0.5, p<0.0001). Metabolic ratios of DM:3-MM based on 24-hour cumulative urine collection did not appear to have clinical utility in predicting CYP3A activity measured by CsA clearance.
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Division of Clinical and Administrative Pharmacy, College of Pharmacy, University of Iowa, Iowa City 52242, USA.
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Vichiendilokkul
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Fleckenstein
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D000284:Administration, Oral; D000328:Adult; D000996:Antitussive Agents / Q000652:urine*; D019540:Area Under Curve; D001189:Aryl Hydrocarbon Hydroxylases; D002851:Chromatography, High Pressure Liquid; D018592:Cross-Over Studies; D016572:Cyclosporine / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003915:Dextromethorphan / Q000031:analogs & derivatives* / Q000652:urine*; D004655:Emulsions; D005260:Female; D006801:Humans; D007166:Immunosuppressive Agents / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D007275:Injections, Intravenous; D008297:Male; D008657:Metabolic Clearance Rate; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism*; D011237:Predictive Value of Tests; D012016:Reference Values
D000996:Antitussive Agents; D004655:Emulsions; D007166:Immunosuppressive Agents; C028657:3-methoxymorphinan; D003915:Dextromethorphan; D016572:Cyclosporine; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating