No role for the CYP3A5*3 polymorphism in intestinal and hepatic metabolism of midazolam

Kharasch et al. [1] recently published a study in Clinical Pharmacology and Therapeutics on the role of CYP3A5 polymorphisms in the pharmacokinetics and pharmacodynamics of the CYP3A probe drugs alfentanil and midazolam, both CYP3A4 and CYP3A5 substrates. These researchers reported that there was no relevant impact of CYP3A5 alleles *3, *6 and *7 on systemic or apparent oral clearances of alfentanil and midazolam, although these polymorphisms did confer decreased CYP3A5 expression and activity. We have assessed data on midazolam pharmacokinetics following semi-simultaneous administration of midazolam orally and intravenously (i.v.) to 59 healthy male volunteers and 30 human immunodeficiency virus (HIV)-infected patients who had participated in six phenotyping studies performed earlier (see Table 1). Our methodology allowed for separate assessment of intestinal and hepatic CYP3A activity, and the results were related to the main CYP3A5 polymorphism CYP3A5*3. All studies were approved by the Ethics Committee of the Medical Faculty of the University of Cologne and conducted in accordance with the Declaration of Helsinki; all participants gave their written informed consent. In all studies, midazolam was given orally and i.v. as part of a phenotyping cocktail, whereas the other components of the cocktails varied between the respective studies (see Table 1). In study A, the cocktail was given only once, while in studies B–F (interaction studies), phenotyping was performed in two separate study periods, with and without co-medication. CYP3A5*3 genotyping was done by LightCycler melting curve analysis using Primer R5′ (TAgTTgTACgACACA CAgCAACC), Primer F5′ (TTTgCCTCTTTgTACTTCTT CATC), Sensor 5′ (gAgCTCTTTTgTCTTTCAATATCTCTFL) and Anchor 5′ (LC Red640-CCCTgTTTggACCACA TTACCCTT–PH). Midazolam in the plasma was quantified by liquid chromatography/tandem mass spectrometry [2] Total clearance (Cl) and intestinal availability (Fi) of midazolam, which were used as metrics of hepatic and intestinal CYP3A activity, respectively, were assessed by population analysis using NONMEM software ver. 1.1 (NONMEM Project Group, University of California at San Francisco, 1998). A two-compartment model gave the best fit, allowing for the determination of Cl and oral bioavailability, whereas for the calculation of Fi an additional equation was implemented [3]. The results of the pharmacokinetic evaluation sorted by study and CYP3A5 genotype are shown in Table 1. The Eur J Clin Pharmacol (2008) 64:1033–1035 DOI 10.1007/s00228-008-0503-9