Which process occurs first in the pharmacokinetic sequence of a drug?

The pharmacokinetic sequence of a drug involves several key processes: absorption, distribution, metabolism, and excretion. Absorption is the first step in this process, as it refers to the movement of a drug from its site of administration into the bloodstream. This initial phase is crucial because it determines how quickly and efficiently a drug enters systemic circulation, influencing the therapeutic effects and onset of action.

When a drug is administered, whether orally, intravenously, or via other routes, it must be absorbed into the body to exert any pharmacological effect. For instance, oral medications must dissolve in the gastrointestinal tract before being absorbed into the bloodstream, while intravenous medications bypass this step and enter circulation directly.

Following absorption, the drug is then distributed throughout the body, metabolized, and eventually excreted. Therefore, absorption is the cornerstone of pharmacokinetics, making it the first process in the sequence that dictates how a drug reaches its site of action and how effectively it performs its intended function.