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Zusammenfassung: Arzneimittelwechselwirkungen sind bei der Behandlung von HIV-Infizierten häufig, da die hochaktive antiretrovirale Therapie immer mehrere Wirkstoffe beinhaltet. Dazu kommen oft Medikamente gegen opportunistische Infektionen und Begleiterkrankungen. Alle Proteaseinhibitoren führen zu einer Inhibition von CYP3A, das im Metabolismus von rund 50% aller Arzneistoffe wichtig ist, beispielsweise Simvastatin, Atorvastatin, Sildenafil und Clarithromycin. Ritonavir ist von allen Proteaseinhibitoren der stärkste Hemmstoff der CYP3A-Aktivität. Dies wird auch genutzt, um die Bioverfügbarkeit anderer Proteaseinhibitoren zu erhöhen. Durch die nichtnukleosidischen Reverse-Transkriptase-Inhibitoren Efavirenz und Nevirapin wird die CYP3A-Aktivität in der Dauertherapie gesteigert. Um Interaktionen vorzubeugen, müssen zu Beginn und bei Therapieende die Dosierungen von CYP3A-Substraten angepasst werden. Interaktionen können auch durch die Beeinflussung von glukuronidierenden Enzymen oder Transportproteinen entstehen. So wird P-Glykoprotein durch Ritonavir gehemmt, was zu einer Erhöhung der Exposition gegenüber vielen Chemotherapeutika führt

The pharmacokinetics of dextromethorphan (DM) is markedly influenced by cytochrome P450 2D6 (CYP2D6) enzyme polymorphisms. The aim of this study was to quantify the effects of the CYP2D6*1, *2, and *41 variants on DM metabolism in vivo and to identify other sources of pharmacokinetic variability. Concentrations of DM and dextrorphan (DO) in plasma and urine were evaluated in 36 healthy Caucasian men. These volunteers participated in three clinical studies and received a single oral dose of 30 mg DM-HBr. Data were modeled simultaneously using the population pharmacokinetics NONMEM software. A five-compartment model adequately described the data. The activity levels of the alleles assessed differed significantly. The clearance attributable to an individual CYP2D6*1 copy was 2.5-fold higher as compared with CYP2D6*2 (5,010 vs. 2,020 l/h), whereas the metabolic activity of CYP2D6*41 was very low (85 l/h). Urinary pH was confirmed as a significant covariate for DM renal clearance. These results refine genotype-based predictions of pharmacokinetics for DM and presumably for other CYP2D6 substrates as well.

Drug-drug interactions are frequently encountered in the therapy of HIV-infected patients, since the highly active antiretroviral therapy always contains several drugs. Drugs against opportunistic infections and concomitant diseases are added frequently. All protease inhibitors are inhibitors of CYP3A, which is important in the metabolism of approximately 50% of all drugs, e.g. simvastatin, atorvastatin, sildenafil, and clarithromycin. Among the protease inhibitors, ritonavir is the strongest inhibitor of CYP3A activity. This inhibition is also used to enhance ("boost") the bioavailability of other protease inhibitors. The nonnucleoside reverse transcriptase inhibitors (NNRTI) efavirenz and nevirapine lead to an increase in CYP3A activity during long-term treatment. To prevent interactions, doses of CYP3A substrates have to be adapted in the beginning and at the end of CYP3A activity-modifying treatments. Interactions can also be a result of modifications in the activities of glucuronosyltransferases and of transport proteins. Ritonavir is an inhibitor of P-glycoprotein, which leads to increased expositions towards many antineoplastic drugs.

BACKGROUND: In inflammation and infection, cytochrome P450 (CYP) enzyme activities are down-regulated. Information on possible discrepancies in activities of CYP enzymes and drug transporters between HIV-infected patients and healthy people is limited. METHODS: We used midazolam, dextromethorphan and digoxin as in vivo phenotyping probes for CYP3A (CYP3A4/5), CYP2D6 and P-glycoprotein activities, respectively, and compared these activities between 12 healthy Caucasian volunteers and 30 treatment-naive HIV-infected patients. RESULTS: Among the HIV-infected patients, the overall CYP3A activity (apparent oral midazolam clearance) was approximately 50% of the activity observed in healthy volunteers (point estimate 0.490, 90% confidence interval [CI] 0.377-0.638). The CYP2D6 activity (plasma ratio area under the curve [AUC]; AUC(dextromethorphan)/AUC(dextrorphan)) was essentially unchanged (point estimate 1.289, 90% CI 0.778-2.136). P-glycoprotein activity was slightly lower in patients (digoxin maximum concentration point estimate 1.304, 90% CI 1.034-1.644). CONCLUSIONS: The overall CYP3A activity was approximately 50% lower in HIV-infected patients than in healthy volunteers. The CYP2D6 activity was highly variable, but, on average was not different between groups, whereas a marginally lower P-glycoprotein activity was observed in treatment-naive HIV-infected patients.

The narrow therapeutic range and wide interpatient variability in dose requirement make anticoagulation response to coumarin derivatives unpredictable. As a result, patients require frequent monitoring to avert adverse effects and maintain therapeutic efficacy. Polymorphisms in VKORC1 and CYP2C9 jointly account for about 40% of the interindividual