Mass Spectrometry in Drug Metabolism

When a dose of drug is administered, three main phases of drug action may be distingushed. In the "pharmaceutical" phase the dosage form disintegrates, the active substance dissolves and becomes available for absorption. The second phase ("pharmaco­ kinetic" phase) includes absorption, distribution, metabolism, and excretion. That fraction of the dose which finally reaches the circulation after absorption will be available for biological action in the third, or "pharmacodynamic" phase when ...