Bioavailability

Bioavailability refers to the proportion of a drug or other substance that enters the circulation when introduced into the body and so is able to have an active effect. It is a key concept in pharmacokinetics and nutrition, as it determines the correct dosage for non-intravenous administration of a drug. When a medication is administered intravenously, its bioavailability is considered to be 100% since it directly enters the bloodstream and is completely available to act on target tissues. However, when substances are administered via other routes, such as orally, the bioavailability is generally lower due to incomplete absorption and first-pass metabolism. First-pass metabolism refers to the chemical alteration of a substance by the liver before it reaches systemic circulation. Bioavailability is an important measurement tool because it helps clinicians understand the dose necessary to achieve a therapeutic effect and can explain the variation in effectiveness among different formulations of the same medication. It is influenced by several factors including the physical and chemical properties of the drug, the formulation of the drug product, the route of administration, and individual patient factors such as age, gender, metabolism, and the presence of other medical conditions. Understanding bioavailability is crucial for developing new drugs and optimizing the use of existing drugs to ensure maximum therapeutic benefit with minimal side effects.