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Clinical pharmacokinetics

Clinical pharmacokinetics is the study of the relationship between the body's response to a drug and the concentration of that drug at various locations in the body.

Although this has been documented for many drugs, it is apparent for some drugs that a simple relationship does not exist between drug response and its concentration in plasma.

Generally, the amount of drug in the blood circulation will be related to the amount of drug at its site of action.

The pharmacological effect that results may be either the effect desired, a toxic effect, or in some cases, neither.

Clinical pharmacokinetics helps to decide the correct dose needed for effectiveness. This field of study is used to establish relationships among concentrations of drugs in body fluids or tissues and the spectrum of effects these drugs produce.

The variables that dictate adjustment of dosage in individual subjects are related to an understanding of pharmacokinetics.

Volume of distribution

This is a measure of the apparent space in the body available to contain the drug.

The volume of distribution relates the amount of drug in the whole body to the concentration of drug in the blood or plasma.

Steady state concentrations

A steady state concentration of a given drug in a specific body fluid such as blood or plasma will be achieved when a specific quantity of drug is administered at a constant rate. At steady state, drug elimination is about equal to the rate of drug availability.


The half-life is the time it takes for the concentration of drug in a given tissue or fluid to be reduced by 50%.

Although it can be a poor indicator for drug elimination, the half-life of a drug does provide a good estimate of the time required to reach steady-state concentration on the basis of a given dosage regimen, the time for a drug to be removed from the body, and a means to estimate an appropriate time interval between doses.

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