Browsing by Subject "drug interaction"
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(2021)Cytochrome P450 (CYP) enzyme inhibition is one of the most common reasons for adverse drug-drug interactions. An especially harmful form of inhibition is time-dependent inhibition (TDI) in which the inhibition potency increases over time and persists even after discontinuation of the drug. Both direct and time-dependent inhibition can be efficiently screened with the so-called cocktail method containing several CYP-selective probe substrates in a single reaction mixture. This method is practical especially in ADME studies of drug development, as it offers lower costs, consumption of fewer reagents and faster implementation in comparison to conventional methods. In addition, the cocktail method can be used to establish new diagnostic CYP inhibitors in vitro. The aim of this Master’s thesis was to participate in the development and optimization of a new cocktail assay method. The method was developed for screening of major drug-metabolizing CYP enzymes in vitro both in a direct and time-dependent manner using pooled human liver microsomes. Based on preliminary testing, included probe substrates were divided into two cocktails to avoid significant inter-substrate interactions: cocktail I containing tacrine/CYP1A2, bupropion/CYP2B6, amodiaquine/CYP2C8, tolbutamide/CYP2C9 and midazolam/CYP3A4, and cocktail II containing coumarin/CYP2A6, (S)-mephenytoin/CYP2C19, dextromethorphan/CYP2D6 and astemizole/CYP2J2. First, cocktail incubation conditions were optimized, followed by the determination of probe reaction kinetics, kinetic parameters (Km, Vmax) and inter-substrate interactions with single- or dual-substrate incubations. Finally, suitable probe substrate concentrations and the composition of cocktails was evaluated based on the obtained results. As a result of assay optimization, optimal incubation conditions for yet unoptimized cocktail II were established. In optimized incubation conditions, all probe reactions exhibited saturable Michaelis-Menten kinetics except for tacrine 1-hydroxylation (CYP1A2), which exhibited biphasic kinetics instead (Km1: 7.36, Km2: 517). The selected probe substrate concentrations were all below or near their respective Km values except for (S)-mephenytoin 4’-hydroxylation (40 µM vs. Km of 12.5 µM); however, its concentration could not be reduced in order to maintain sufficient metabolite formation for UHPLC-MS/MS-analysis. Dual-substrate incubation assays demonstrated a need for the reduction of bupropion concentration below 100 µM due to its inhibitory effects on CYP2C8 and CYP3A4. In addition, chlorzoxazone/CYP2E1 and testosterone/CYP3A4 were tested as complementary probe substrates for the cocktails; however, they proved to be unsuitable for both cocktails due to significant interactions (>40% inhibition). Prior to the deployment of the method, some adjustments of probe substrate concentrations are still required in addition to consideration of the suitability of less commonly used CYP3A4 and CYP2E1 probe reactions to improve cocktail coverage. Lastly, validation of the method with known time-dependent model inhibitors should also be conducted. Besides to improvement of the cocktails, new information was generated on inter-cocktail probe-probe interactions and enzyme kinetics of probe reactions, especially for the less-studied astemizole O-demethylation (CYP2J2) and tacrine 1-hydroxylation (CYP1A2). Generated information can be used, for example, in the development of new cocktails.
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(2016)Adverse drug events (ADE) are a major problem which deteriorates the quality of drug therapy. They cause significant morbidity and mortality each year. ADEs are often caused by incompatible drug combinations, drug-drug interactions (DDIs). Interprosessional collaboration between health care professionals is important in improving medication safety and preventig drug interactions. The aim of this study was to investigate the most common clinically significant drug-drug interactions in outpatient care and the role of pharmacist in preventing them. The study material was an interaction data which was collected in Helsinki University Pharmacy during August 2015. DDIs and the action needed by presecribers or pharmacists to handle them were collected. Only clinically significant interactions of the SFINX interaction database i.e. D- and C-interactions were recorded. The most common D-interactions (interactions to be avoided) were fluoroquinolones or tetracyclines combined with metal ions (calcium, iron, magnesium, aluminium) (14.7 % of D-interactions) and codeine or tramadol combined with CYP2D6 enzyme inhibiting antidepressants (12.6 %). C-interactions concerned most commonly interactions between antihypertensive drugs and NSAIDs (26.2 % of C-interactions). 59.6 % of D-interactions were interactions that might result in adverse drug reactions and 40.4 % were interactions that might result in therapeutic failure. For C-interactions numbers were 49.4 % and 50.6 %, respectively. Only a few interactions (1.6 %) led to contact with the prescriber from the pharmacy, and more often (1.8 %) the pharmacist advised the patient to contact the prescriber. 32.6 % of the interactions led to pharmacist's advice. The most typical interactions which can be prevented by pharmacist's advice were chelation interactions which can be prevented by taking drugs many hours apart from each other. 59.7 % of the interactions produced no action in pharmacy. Those concerned situations where the prescriber had planned the treatment and weighed up the benefits and risks of the medication, or interactions where the drugs had been in contemporary use for a long time, and thus the pharmacist assumed that the prescriber had planned the treatment. Pharmacists should intervene in drug-drug interactions easier. To avoid unnecessary calls, communication between prescribers and community pharmacies should be developed. Pharmacists' role in preventing DDIs could be improved for example by education and by updating the operations models in collaboration with other health care. Safe and efficient drug treatment should be ensured with interprofessional collaboration, and the responsibility should not be shifted to the patient alone.
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