28-09-2013, 03:18 PM
MULTI COMPARTMENT MODEL
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INTRODUCTION
One compartment model adequately describes pharmacokinetics of many drugs.
The body is composed of heterogeneous group of tissues each with different degree of blood flow and affinity for drug and different rates of equilibration.
Multi compartment model based on some assumptions
1. Blood/plasma and the highly perfused tissues such as brain, heart, lung, liver and kidneys constitute the central compartment.
2. Other tissues with similar distribution characteristics are pooled together to constitute peripheral compartment tissues on the basis of similarly in their distribution characteristics
3.Intravenously administered medications are introduced directly in to the central compartment
4. Irreversible drug elimination, either by hepatic biotransformation or renal excretion, takes place only from central compartment
5. Reversible distribution occurs between central and peripheral compartments
6. After drug equilibration between central and peripheral compartments, elimination of drug follows first order kinetics.
7. The peripheral compartment is usually inaccessible to direct measurement and is not a site of drug elimination or clearance.
ADVANTAGES
It is a simple and flexible approach.
visual representation of various rate processes involved in drug disposition.
It shows how many rate constants are necessary to describe these processes.
It is useful in predicting drug concentration-time profile in both normal physiologic and in pathologic conditions.
It is important in the development of dosage regimens.
DISADVANTAGES OF COMPARTMENT MODEL
No relationship with the physiologic functions or the anatomic structure of the species.
Extensive efforts are required in the development of an exact model.
The model is based on curve fitting of plasma concentration with complex multi exponential mathematical equations.
The model may vary within a study population.
Compartment model may change with route of administration
Difficulties generally arised when using model to interpret the differences between results from human and animal experiments.