Knowledge of Pharma

PHYSIOLOGIC MODEL o    Also called as Blood flow rate –limited models and perfusion rate limited models. o    Physiological models describe the drug disposition in terms of realistic physiological parameters such as blood flow and tissue partition co-efficient. o    The number of compartments to be included in the model depends upon the disposition characteristics of drug. o    Organs such as bone that have no drug penetration are excluded. o    Most physiologic models are based on the assumption that the drug movement within a body region is much more rapid than its rate of delivery to that region by the perfusion blood and, therefore the model is said to be perfusion rate limited. The assumption is however applicable to the highly membrane permeable drugs i.e. low molecular weight, poorly ionized and highly lipophilic drugs. o    For, highly polar, ionized and charged drugs, the model is referred to as membrane permeation rate limited. ADVANTAGES OF PHYSIOLOGIC MO

Also called as the model independent method, as does not require assumption of specific compartment model. Ø   Non – compartmental models describe the pharmacokinetics of drug disposition using time and concentration parameters. Ø   This method can however be applied to any compartment model provided the drugs or metabolites follow linear kinetics. Ø   The approach based on statistical moments theory, involves the collection of experimental data following a single dose of drug. Ø   If one considers the time course of drug concentration in plasma as a statistical distribution curve, then: MRT = AUMC                            AUC Where MRT= Mean residence time             AUMC= area under the first moment curve             AUC= area under the zero moment curve. AUMC is obtained from a plot of product of plasma concentration and time (C*t) versus time t from zero to infinity. Mathematically, it is expressed by equation: AUC is obtained from a plot of

COMPARTMENTAL MODELS ·          Here the body can be represented as series, or systems, of compartments that communicate reversibly with each other. A compartment is not a real physiologic or anatomic region but is considered as a tissue or group of tissues that have similar blood flow and drug affinity. Within each compartment, the drug is considered to be uniformly distributed. ·          Rate constants are used to represent the overall rate processes of drug entry into and exit from the compartment. The model is an open system since the drug can be eliminated from the system. ·          Depending upon whether the compartments are arranged parallel or in a series, compartmental models are divided in two categories- §   Mammillary model §   Caternary model.  MAMMILLARY MODEL : This model is the most common compartmental used in pharmacokinetics. It consists of one or more peripheral compartments connected to the central compartment in a manner similar to connec