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Pharmacokinetics

Pharmacokinetics. Objective is to model the time course of the drug in plasma. One way to do this is through compartmental analysis . Compartments:

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Pharmacokinetics

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  1. Pharmacokinetics • Objective is to model the time course of the drug in plasma. One way to do this is through compartmental analysis. • Compartments: • systems that are continuous and nonhomogeneous are replaced with compartments that are discrete and in which concentrations, and so on, are homogeneous. tissue, lymph intravenous excretion blood plasma bound  free drug in dosage form metabolism liver oral site of action CHEE 440

  2. CHEE 440

  3. Open one-compartment model • process of distribution to each compartment is much faster than absorption into blood and elimination • drug concentration everywhere in the compartment is equal (CSTR) • elimination processes are pseudo-1st order Vd ka kel DB D Cp CHEE 440

  4. Example • A proprietary drug in clinical trials is injected in human volunteers in order to determine the elimination constant which was 0.02 min-1. The company wants to use this information to develop a tablet formulation which must have a Tmax of 20 minutes. Find the absorption rate constant that the drug must have, assuming that all the drug is absorbed and the initial mass of drug in the tablet is 580 mg. If the volume of distribution of the drug is 58 L, calculate the the zero order release rate required from a controlled release device that achieves the same Cmax as achieved with the tablet. CHEE 440

  5. Bioavailability • absolute bioavailability • any drug delivered extravascularly has the potential of being bound or eliminated before reaching bloodstream • amount of drug reaching bloodstream is equal to the area under the Cp vs t curve, AUC • relative bioavailability • some drugs cannot be given by iv • bioavailability determined by comparison to standard dosage form CHEE 440

  6. Therapeutic Index • not all individuals respond in same manner no. of individuals minimum dose for response (mg/kg) therapeutic index (TI) CHEE 440

  7. Cp time Bioequivalence • comparison of amounts of same drug that are absorbed from 2 different formulations of the same dosage form (generics) • the two formulations are considered equivalent if there is no significant difference between any of Cmax, Tmax, AUC CHEE 440

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