Two metabolites of a new compound were identified after incubation with pooled human liver microsomes, a desmethyl metabolite and a ring hydroxylated metabolite. The new compound was incubated with samples from a human liver microsome bank, and the amount of metabolite formed was compared with activities for probe substrates. The data are available in the table on the next slide. Correlation with CYP probe substrates Metabolite CYP2A6 CYP2B6 CYP2C19 CYP2D6 CYP3A4 Desmethyl 0.22 NS 0.33 NS 0.87 *** 0.41 NS 0.52 * R-hydroxyl 0.41 * 0.79 *** 0.24 * 0.21 NS 0.44 * Data are correlation coefficients with associated P values (a) The metabolites were identified and quantified using liquid chromatography, coupled to mass spectrometry (triple quadrupole) using selected reaction monitoring. Give a brief explanation of selected reaction monitoring, including a description of how each of the quadrupole mass analysers contributes to detection. (b) What would be the appropriate units for metabolite formation and probe substrate activity for these correlation studies? (c) A significant P value (shown by the asterisks) shows that the gradient of the regression line is significantly different from what value? (d) What do the correlation data suggest about the enzyme responsible for metabolite formation? (e) What further studies would you carry out to gain further information and confirmation

During exercise, localised metabolites are produced from kidneys liver skeletal muscle

The most prevalent poor metabolizers (PM) variant genotypes of CYP2C19 are  Blank 1 Question 2 and  Blank 2 Question 2 in Asian

A drug that undergoes high first pass hepatic metabolism

Classify each of these drugs based on their ability to induce or inhibit CYP450 enzymes phenobarbital

The principal metabolic pathway of phenytoin and phenobarbital in human is aromatic hydroxylation, catalyzed by CYP2C9 and CYP2C19. The reactive intermediate, arene oxide is deactivated by either epoxide hydrolase to dihydrodiol or by the action of glutathione (GSH) and glutathione S-transferase. The pathways of phenytoin metabolism are depicted below. Valproate metabolism by P450 CYP2C9 CYP2A6  Hypersensitivity reactions (idiosyncratic toxicity) to the aromatic antiepileptic drugs in susceptible individuals are believed to stem from the reactions of these reactive intermediates (i.e., arene oxide catechol or o-quinone) with hepatic enzymes or other cellular proteins forming covalently bonded haptens. • Both phenytoin and phenobarbital are potent liver enzyme inducers. (i) Explain why co-administering valproate with phenytoin will increase their idiosyncratic toxicities. (ii) Explain why there are cross-sensitivities in terms of idiosyncratic reactions between phenytoin, phenobarbital, and carbamazepine? (iii) Pharmacogenetic factors determine susceptibility to idiosyncratic reactions to anti-epileptic drugs. What genes may be involved in these reactions and what is the mechanism involved?