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CHAPTER OBJECTIVES

  • Define biopharmaceutics and pharmacokinetics.

  • Define drug product performance and discuss how biopharmaceutics can affect drug product performance.

  • Describe how pharmacokinetic studies relate to clinical efficacy and drug toxicity.

  • Discuss how clinical pharmacokinetics is used to develop drug dosage regimens in patients.

  • Define a pharmacokinetic model and the assumptions that are used in developing a pharmacokinetic model.

  • Discuss how the prescribing information or approved labeling for a drug helps the practitioner to recommend an appropriate dosage regimen for a patient.

DRUG PRODUCT PERFORMANCE

Drugs are substances intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease. Drugs are given in a variety of dosage forms or drug products such as solids (tablets, capsules), semisolids (ointments, creams), solutions, suspensions, emulsions, etc, for systemic or local therapeutic activity. Drug products are drug delivery systems that release and deliver drug to the site of action to produce the desired therapeutic effect and minimize adverse toxicity. Drug products should be designed to meet the patient’s individual requirements including palatability, convenience, compliance, and safety.

Drug product performance is defined as the release of the drug substance from the drug product either for local drug action or for absorption into the plasma for systemic drug activity. Advances in pharmaceutical technology and manufacturing have improved the quality of drug products and improved drug delivery.

BIOPHARMACEUTICS

Biopharmaceutics examines the relationship of the physical and chemical properties of the drug, the dosage form (drug product) in which the drug is formulated, and the route of administration for the delivery of the drug to the site of action. In pharmacokinetics, bioavailability (F) is the fraction of the administered dose of a drug that reaches the systemic circulation. Bioavailability is a formulation parameter that enables clinicians to consider the proportion of the dose that will be systemically absorbed in the patient when changing dosage forms of the same drug. For example, the extent of systemic drug absorption (drug exposure) should be the same when changing from an intravenous (IV) drug formulation in a stabilized patient during hospitalization to an oral tablet formulation of the same drug when the patient is discharged. In regulatory science, bioavailability is defined as both the rate and extent of drug that reaches systemic circulation or to the site of action. The US FDA defines bioequivalence as “the absence of a significant difference in the rate and extent to which the active ingredient or active moiety in pharmaceutical equivalents or pharmaceutical alternatives becomes available at the site of drug action when administered at the same molar dose under similar conditions in an appropriately designed study.” Bioequivalence is a critical component for the approval of drug products, whether they are new or generic drug products. Regulatory agencies such as the US Food and Drug Administration (FDA) define bioavailability more broadly as both the rate and ...

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