bioengineering Two drug candidates with similar chemistry but somewhat different

Question

bioengineering Two drug candidates with similar chemistry but somewhat different Pk/PD parameters are under consideration. The drug response correlates with AUC after a single dose as illustrated below and reported in the table that follows. Which drug candidate has a higher potency? Which drug candidate has a higher efficacy? Both drugs are metabolized and excreted according to first-order kinetics. Drug A has a plasma half-life of 7.0 h and Drug B a plasma half-life of 1.0 h. Which drug candidate is more rapidly metabolized? For each drug, estimate the single dose required (mg/kg) lo achieve an effective response in 90% of the population assuming rapid absorption and distribution of the single dose with metabolism as given in pan (c). Assume a specific volume of distribution of 0.6 1/kg.

Explanation / Answer

(a) Drug B has higher percentage effetive response at low concentration of the dose. Also lesser concentration of B is required to produce 50 % of maximum response. Hence drug B has higher potency. Also drug B has higher efficacy.

(b) Plasma half-life is the time required for the concentration of drug in blood to become one-half of initial concentration. Hence lower the plasma half-life more rapidly is the drug metabolised to reduce its concentration in blood. Hence drug-B having a smaller plasma half-life (1.0 h) is more rapidly metabolised.

(c) Given specific volume distribution = 0.6 L/Kg = 600 mL / Kg

For Drug-A: 90 % effective response occurs at 350 micro-mg-h/mL

Hence dose required in mg-h/Kg = 350 x 10-6 mg-h.mL-1 x (600 mL / Kg) = 0.21 mg-h / Kg

For Drug-B: 90 % effective response occurs at 45 micro-mg-h/mL

Hence dose required in mg-h/Kg = 45 x 10-6 mg-h.mL-1 x (600 mL / Kg) = 0.027 mg-h / Kg

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