Alprazolam as a probe for CYP3A using a single blood sample: pharmacokinetics of parent drug, and of alpha- and 4-hydroxy metabolites in healthy subjects.

Author(s): Wennerholm A, Allqvist A, Svensson JO, Gustafsson LL, Mirghani RA, Bertilsson L

Affiliation(s): Division of Clinical Pharmacology C1:68, Karolinska University Hospital, Huddinge, 141 86, Stockholm, Sweden.

Publication date & source: 2005-04, Eur J Clin Pharmacol., 61(2):113-8. Epub 2005 Apr 2.

Publication type: Clinical Trial; Research Support, N.I.H., Extramural ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, P.H.S.

OBJECTIVES: (1) To determine the pharmacokinetic parameters of alprazolam and its two metabolites in plasma from healthy volunteers; (2) to identify a suitable single time point to take a plasma sample for CYP3A phenotyping. METHODS: Twelve healthy Swedish volunteers received a single oral dose of 1 mg alprazolam. Blood samples were collected before drug intake and frequently up to 72 h thereafter. A liquid-chromatography/mass-spectrometry (LC/MS) method was used for the quantification of alprazolam, and 4- and alpha-hydroxyalprazolam. RESULTS: The interindividual variation in the area under the concentration-time curve (AUC) was two, three and fourfold for alprazolam, 4-hydroxyalprazolam and alpha-hydroxyalprazolam, respectively. Plasma concentration ratios collected between 1 h and 48 h for both alprazolam/4-hydroxyalprazolam and alprazolam/alpha-hydroxyalprazolam correlated significantly to the corresponding AUC0-infinity ratios. CONCLUSIONS: The metabolic ratios of alprazolam to respective metabolite in a single plasma sample at 3-24 h are suggested to reflect the alprazolam 4- and alpha-hydroxylation activities. In future, it will be important to study these activities in populations where CYP3A5, in addition to CYP3A4, is expressed at a high frequency and to clarify the relative importance of the two enzymatic pathways for in vivo clearance of alprazolam.