Assignment Task: Drug Metabolism and Toxicology

Section A: Pharmacokinetics and Metabolism

(a) Sketch idealized plots illustrating plasma concentration versus time for a drug administered intravenously and orally.

(b) Define clearance, volume of distribution, and bioavailability and elucidate how they are derived from the plotted data.

(c) Propose potential metabolites resulting from cytochrome P450 (CYP) mediated oxidation of compounds containing benzene rings, benzylic methyl groups, and alkenes.

(d) Provide mechanisms for the oxidation transformations facilitated by cytochrome P450 enzymes.

Upon oral dosing in rats, no detectable blood levels of compound 4 were observed.

(a) Explain potential reasons for this observation.

(b) Identify the most probable reasons among the options provided.

(c) Suggest additional experiments to discern the cause of the issue for each identified reason.

(d) Recommend two structural modifications to address the highlighted problems, justifying your choices.

Section B: Toxicology

(a) Define acute and chronic toxicity and outline their distinctions.

(b) Define LD50 and ED50, illustrating their roles in determining the therapeutic index and its significance.

(c) Illustrate a dose-response curve for a compound with an LD50 of 50 mg/kg and a therapeutic index of 5.

Examine the structural and physicochemical attributes of drug molecules influencing hERG binding. Considering this, explain loperamide 8`s channel-blocking mechanism and propose two structural alterations to mitigate its hERG activity, substantiating your selections. Additionally, analyze two potential causes of toxicity for compound 9 and propose structural modifications to mitigate toxicity for each identified cause.