1) Estimate the behavior of this drug in the body during:a) Oral absorptionb) Liver passage (potential phase I + II reactions)a) Good (drug is generally lipophilic)b) Phase I: a. Ester hydrolysisb. Oxidationc. Demethylation Phase II:a. Glucoronidationb. Sulfation2) Which drug has the higher efficacy?Both drugs have the same efficacy (they achieve the same maximal response), however, drug A has the higher potency (less drug is required to achieve maximalefficacy).A 35 kg child in an ER on an i.v. infusion requires immediate treatment with the antiarrhythmic drug procainamide.The textbook lists the following pharmakokinetic values for procainamide in a 70 kg adult: Vd = 130 LClearance = 36 L / hrOral availability = 83%Therapeutic concentration = 5 mg/L1. What iv loading dose should be administered?2. What constant infusion rate is required to maintain the therapeutic concentration?3. What is the predicted half-life of the drug in the child?Answers:The patient is half the weight of the average adult => Vd and clearance witll be ~ one half the given values. Drug is given i.v. => oral availability irrelevant:1. Loading dose = Vd x Cp = 130L/2 x 5 mg/mL = 325 mg2. Infusion rate = Cl x Cp = (36 L / hr)/2 x 5 mg/mL = 90 mg/hr3. T1/2 = ln2 x Vd/Cl = 0.693 x 130 L / 36 L/hr = 2.5
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