Bioavailability drug administration routes

Parenteral administration of drugs by intravenous (IV), intramuscular (IM), or subcutaneous (SC) routes is now an established and essential part of medical practice. Advantages for parenterally administered drugs include the following rapid onset, predictable effect, predictable and nearly complete bioavailability, and avoidance of the gastrointestinal (GI) tract and, hence, the problems of variable absorption, drug inactivation, and GI distress. In addition, the parenteral route provides reliable drug administration in very ill or comatose patients. 

In recent years, much of the research work in the pharmaceutical sciences was focused on the development of effective vehicle systems, such as micelles, microemulsions, and liposomes, for drugs that are critical with respect to bioavailability. Knowledge of this subject is a prerequisite to developing vehicle systems for special administration routes, such as dermal, transdermal, intravenous, and nasal. 

Evaluate pharmacokinetics and bioavailability (drug delivery) in toxicology rodent and nonrodent animal species after I.V. and proposed route of administration. 

Dry powder formulations for nasal delivery of peptides and proteins have been investigated for the first time by Nagai and others [38], Since then, much research work has been done on dry powders containing bioadhesive polymers for nasal drug administration. The bioavailability and duration of action of drugs administered by the nasal route are increased by the use of the principle of mucoadhesion and dry powder formulations. Research work on dry powder formulation containing bioadhesive polymers is summarized in Table 1. 

Biopharmaceutic considerations in the design and manufacture of a drug product to deliver the active drug with the desired bioavailability characteristics include 1) the type of drug product (e.g., solution, suspension suppository) 2) the nature of the excipients in the drug product 3) the physicochemical properties of the drug molecule and 4) the route of drug administration. 

Bioavailablity has been defined as a measure of the rate and extent of absorption of a drug into the systemic circulation after administration of a dosage form. An intravenous i.v. dose is considered by definition to be 100% bioavailable. All other routes of administration will produce a total bioavailability less than or equal to that of the i.v. dose. Thus, only a drug that is completely absorbed into the systemic circulation can have the extent of bioavailability equal to the dose stated on the label. In addition to the extent... 

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