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The pharmacokinetic profiles of two products containing the same drug are often compared. Two formulations which give ‘essentially’ equivalent circulating concentrations of a drug at each point in time in a pharmacokinetic profile are likely to elicit equivalent therapeutic effects and therefore can be regarded as bioequivalent.

Bioequivalence studies are helpful to assess the pharmacokinetics of two drug products, for instance: originally formulated product versus a reformulated or modified drug product, two different dosage forms of the same product e.g., tablets versus oral liquid or comparison of the generic with innovator's original product. Biopharmaceutical considerations in early development help to achieve optimum absorption and bioavailability of a drug product or developing targeted delivery systems. The biopharmaceutical approaches in formulation design are discussed in detail in Chapter 8.

Figure 2.10 An illustration showing the calculation of AUC in a plasma drug concentration–time profile.

Bioequivalence studies usually compare the C_max, t_max and AUC of the two products and if found within tolerances as set by the regulatory agencies (e.g., MHRA, FDA and EMA), the products may be declared as bioequivalent. Chapter 10 provides a detailed account of regulatory perspectives in bioavailability and bioequivalence studies.