The major part of the basic properties of a chemical entity can be extrapolated from single-dose studies if the pharmacokinetics of the drug are linear. Linear pharmacokinetics is described by an increase in dose that is followed by a proportional increase in exposure of the drug (e.g., the area under the plasma concentration-time curve), over the anticipated therapeutic dose interval. The basic pharmacokinetic parameters of a drug from the single-dose studies can then be used for predictions of drug exposure after repeated doses, after various dosing regimens .
Indications of nonlinear pharmacokinetics should be investigated early to determine if the cause is related to absorption, distribution, metabolism, or excretion processes. It is generally recommended that the pharmacokinetic studies are performed in fasting subjects (overnight fast), to reduce the influence of potentially confounding factors elicited by concomitant food intake. On the other hand, it is most desirable that potential influence of food on the pharmacokinetics of the drug also is investigated early on in the drug development program. This information facilitates appropriate recommendations as how the drug should be administered in the Phase II or Phase III trials in the target patient populations.
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