Biopharmaceutics is the study of the in-vitro impact of the physicochemical properties of drugs and drug products on drug delivery to the body under normal or pathologic conditions. A primary concern in biopharmaceutics is the bioavailability of drugs. Bioavailability refers to the measurement of the rate and extent of active drug that becomes available at the site of action. Because the systemic blood circulation delivers therapeutically active drug to the tissues and to the site of action of the drug, changes in bioavailability affect changes in the pharmacodynamics and toxicity of a drug. The aim of biopharmaceutics is to adjust the delivery of drug from the drug product in such a manner as to provide optimal therapeutic activity and safety for the patient.
Biopharmaceutic studies allow for the rational design of drug products based on
(1) the physical and chemical properties of the drug substance;
(2) the route of drug administration, including the anatomic and physiologic nature of the application site (eg, oral, topical, injectable, implant, transdermal patch, etc); and
(3) desired pharmacodynamic effect (eg, immediate or prolonged activity);
(4) toxicologic properties of the drug;
(5) safety of excipients; and
(6) effect of excipients and dosage form on drug delivery.
[wp_ad_camp_4]For example, some drugs are intended for topical or local therapeutic action at the site of administration. For these drugs, systemic absorption is undesirable. Drugs intended for local activity are designed to have a direct pharmacodynamic action without affecting other body organs. These drugs may be applied topically to the skin, nose, eye, mucous membranes, buccal cavity, throat, or rectum. A drug intended for local activity may be given intravaginally, into the urethral tract, intranasally, into the ear, on the eye, or orally. Examples of drugs used for local action include anti-infectives, antifungals, local anesthetics, antacids, astringents, vasoconstrictors, antihistamines, and corticosteroids. However, some systemic drug absorption may occur with drugs used for local activity.