Mike Ufer

Genetic polymorphisms of cytochrome P450 2C9 causing reduced phenprocoumon (S)-7-hydroxylation in vitro and in vivo

The effect of cytochrome P450 (CYP) 2C9 polymorphisms on the stereoselective biotransformation of the oral anticoagulant phenprocoumon (PPC) to inactive, monohydroxylated metabolites was studied in vitro and in vivo. In human liver microsomes, the (S)-7-hydroxylation — being the major metabolic pathway — was significantly compromised in a gene–dose-dependent manner in samples expressing the CYP2C9*2 or CYP2C9*3 allele. The CYP2C9*3/*3 genotype corresponded to an almost fourfold lower (S)-7-hydroxylation rate than CYP2C9*1/*1 (wild-type). The intrinsic clearance of human recombinant CYP2C9*2 and CYP2C9*3 for the (S)-7-hydroxylation was 28.9 and 50.9% lower than of CYP2C9*1, respectively. The area under the plasma concentration–time curve (AUC) of PPC metabolites after oral intake of 12 mg racemic PPC was significantly lower in volunteers expressing the CYP2C9*2 or CYP2C9*3 allele. Increasing plasma AUC metabolic ratios (parent compound/metabolite) in CYP2C9*2 and CYP2C9*3 variant allele carriers were found for each hydroxylation reaction and the CYP2C9*3/*3 genotype corresponded to an about 10-fold higher metabolic ratio of PPC (S)-7-hydroxylation relative to CYP2C9*1/*1. CYP2C9 polymorphisms cause a markedly compromised PPC (S)-7-hydroxylation. However, PPC metabolism appears overall less influenced by CYP2C9 genotype compared with other oral anticoagulants and it may thus be a valuable alternative for therapeutic anticoagulation of patients expressing CYP2C9 variant alleles.

Quantification of cortisol and 6 beta-hydroxycortisol in human urine by LC-MS/MS, and gender-specific evaluation of the metabolic ratio as biomarker of CYP3A activity

Drug-drug and food-drug interactions are often due to an inhibition or induction of drug-metabolizing cytochrome P450 (CYP) enzymes and may result in non-response or adverse reactions. Hence, phenotypic biomarkers of CYP activity appear as useful tools for individualized pharmacotherapy. The metabolic ratio (MR) of the concentration of 6beta-hydroxycortisol (6beta-OHC) to cortisol (MR 6beta-OHC/cortisol) in human urine had been proposed as an endogenous marker for CYP3A activity. Here, we report on the improvement of published LC-MS/MS methods for the simultaneous quantification of cortisol and 6beta-OHC, using on-line sample cleanup by column switching and isotope-labeled analogues as internal standards. [(2)H(2)]6beta-OHC was prepared by incubation of human recombinant CYP3A4 with commercially available [(2)H(2)]cortisol. Analytical sensitivity could be increased about 10-fold. The first morning urine of 69 female and 27 male healthy volunteers was analyzed for cortisol and 6beta-OHC. Concentrations ranged from 1.0 to 142 and 24 to 670ng/mL, respectively. Individual MR 6beta-OHC/cortisol varied more than 20-fold and we were able to show for the first time for a Caucasian population significantly higher MR values in females as compared to males. This non-invasive biomarker for CYP3A activity lends itself for the study of genetic differences as well as enzyme induction or inhibition in the clinical setting without the need of using a probe drug.

Off-label paediatric prescribing in Stockholm (Sweden): a response to a letter to the editor

We welcome the opportunity to respond to a comment regarding our recent publication [1]. As pointed out by Gleiter et al., we report on proportions of off-label prescribing for paediatric outpatients in Sweden that are essentially similar to their results obtained in Germany [2, 3]. Our assessment was done with respect to age, formulation and route of administration in nine different gender-specific age groups, whereas the German study was restricted to age, formulation and ‘dose unit’—the latter being a somewhat misleading term, as it does not reflect on the actually prescribed daily dose (PDD). Similarities between the German and Swedish results were not necessarily to be expected, and cross-national comparisons in this regard appear vital due to country-specific legal aspects, reimbursement schemes, and not at last population characteristics and therapeutic traditions that substantially differ among European countries [4, 5, 6, 7]. Moreover, our original approach to compare the proportion of off-label drug use with a quality of prescribing indicator was chosen in an attempt to investigate to what extent such drug use may eventually still be evidence-based [1]. The use of this indicator has been extensively described in a previous study [8]. We identified the proportion of prescription items corresponding to drugs recommended in the commonly used therapeutic guideline (‘The Wise List’) issued by the Drug and Therapeutics Committee (LÄKSAK) of the Stockholm County Council [9]. About 20 expert groups annually update this guideline according to the current scientific knowledge, and the appreciation of its usefulness is high among general practitioners in Stockholm [8]. The large overlap between off-label and recommended drug use argues in favour of the prescribing physician that has preferentially chosen the appropriate drug in the child’s best interest. We do not consider the lack of information about the respective indications as a serious limitation, since most of the recommended drugs are used for a single major indication. Moreover, any reader should not have been fooled, since we explicitly state in the paper that our assessment is restricted to the appropriate drug selection rather than prescribing for the correct indication or at an adequate dose. Nevertheless, we agree with Gleiter et al. that a lack of paediatric labelling may contribute to an impaired drug quality and safety. We have therefore also addressed the issue of drug safety as influenced by the extent of off-label prescribing for paediatric outpatients in a separate study [10]. From our two studies it appears crucial to consider both the benefits as well as the risks of off-label drug use and correct for administrative obstacles that hinder an appropriate use of drugs—even outside the terms of the product licence. Two such unfortunate administrative problems have actually been pointed out by Gleiter et al. regarding the liability of the prescribing physician for adverse drug reactions arising from off-label drug use and the missing reimbursement for off-label prescribed drugs in some European countries. Thus, off-label drug prescribing remains indeed a major public health concern, and clinical trials in children as well as a careful postmarketing surveillance of drugs commonly prescribed for paediatric patients are highly warranted. However, under the current circumstances, it may eventually be recommended or even required to prescribe off-label and a restriction to the use of properly labelled drugs appears neither practical nor ethical. Eur J Clin Pharmacol (2003) 59: 493–494 DOI 10.1007/s00228-003-0644-9

Clinical Pharmacology of the Reversible and Potent P2Y12 Receptor Antagonist ACT‐246475 After Single Subcutaneous Administration in Healthy Male Subjects

ACT‐246475 is a selective and reversible P2Y12 receptor antagonist inducing inhibition of platelet aggregation (IPA). A randomized, double‐blind, placebo‐controlled, parallel‐design study was performed to investigate the safety, tolerability, pharmacokinetics, and pharmacodynamics of escalating single subcutaneous doses of ACT‐246475 (1, 2, 4, 8, 16, or 32 mg) in healthy male subjects (N = 8 per dose, 3:1 active:placebo ratio). Pharmacodynamic effects were assessed based on maximum platelet aggregation and P2Y12 reaction units using light transmission aggregometry and VerifyNow® assays, respectively. ACT‐246475 was safe and well tolerated up to 32 mg based on adverse event data and absence of clinically relevant changes in hematology, biochemistry, vital signs, and electrocardiogram variables. Median time to reach maximum plasma concentration was 0.5–0.75 hours, and geometric mean terminal half‐life ranged from 1.3 to 9.2 hours across the tested dose range. Exposure to ACT‐246475 was dose proportional across all dose groups. The maximal %IPA was reached within 30 minutes after subcutaneous administration of ACT‐246475. A dose‐dependent duration and extent of effect were observed based on area under the effect curve and maximum effect data. Similar results were observed for maximum platelet aggregation and P2Y12 reaction units. The %IPA was ≥85% at doses ≥2 mg. This level of %IPA was extended to at least 12 hours in the 32‐mg dose group. The safety and pharmacokinetic/pharmacokinetic profile with quick onset and adequate duration of IPA support further investigation in patients with coronary artery disease.