Drug absorption

[Dorothey Allen]

Drug absorption is the movement of a drug into the bloodstream after administration.
Absorption affects bioavailability—how quickly and how much of a drug reaches its intended target (site) of action. Factors that affect absorption (and therefore bioavailability) include

The way a drug product is designed and manufactured
Its physical and chemical properties
Other ingredients it contains
The physiologic characteristics of the person taking the drug
How the drug is stored

A drug product is the actual dosage form of a drug—a tablet, capsule, suppository, transdermal patch, or solution. It consists of the drug (active ingredient) and additives (inactive ingredients). The active ingredient is the chemical substance (the drug) that is taken to produce the desired effect (such as lowering blood pressure). The additives (inactive ingredients such as diluents, stabilizers, disintegrants, and lubricants) are mixed with the drug to make it easier to swallow or help break it up in the gastrointestinal tract. For example, to make tablets, the active/inactive ingredient mixture may be formed into small grains and compressed into tablet form. The type and amount of additives and the degree of compression affect how quickly the tablet disintegrates and how quickly the drug is absorbed. Drug manufacturers adjust these variables to optimize absorption.
Because drug products that contain the same drug (active ingredient) may have different inactive ingredients, absorption of the drug from different products may vary. Thus, a drug’s effects, even at the same dose, may vary from one drug product to another. Drug products that not only contain the same active ingredient but also produce virtually the same blood levels at the same points in time are considered bioequivalent (see Bioequivalence and Interchangeability of Generic Drugs). Bioequivalence ensures therapeutic equivalence (that is, production of the same therapeutic effect), and bioequivalent products are interchangeable.