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A Urine Metabolic Ratio of Dextromethorphan and 3‐Methoxymorphinan as a Probe for CYP3A Activity and Prediction of Cyclosporine Clearance in Healthy Volunteers
Author(s) -
Min David I.,
Ku YiMin,
Vichiendilokkul Aungkana,
Fleckenstein Lawrence L.
Publication year - 1999
Publication title -
pharmacotherapy: the journal of human pharmacology and drug therapy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.227
H-Index - 109
eISSN - 1875-9114
pISSN - 0277-0008
DOI - 10.1592/phco.19.9.753.31536
Subject(s) - pharmacokinetics , urine , cyp3a , dextromethorphan , chemistry , high performance liquid chromatography , cyp3a4 , beagle , pharmacology , crossover study , cyp2d6 , chromatography , medicine , metabolism , cytochrome p450 , biochemistry , alternative medicine , pathology , placebo
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 (r 2 = 0.38, p<0.0001). The correlation was similar for metabolic ratios of DM:3‐MM with intravenous CsA clearance (r 2 = 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.