bioavailabilityd

Bioavailability refers to the fraction of an administered dose of an unchanged drug that reaches the systemic circulation. When a drug is administered orally, for example, it must first be absorbed from the gastrointestinal tract into the bloodstream. Factors such as solubility, dissolution rate, and permeability across the intestinal wall all influence this absorption process. Once absorbed, the drug can undergo first-pass metabolism in the liver or gut wall, which can reduce the amount of active drug reaching the systemic circulation. Intravenous administration bypasses absorption and first-pass metabolism, resulting in 100% bioavailability by definition. For other routes of administration, such as intramuscular or transdermal, bioavailability is typically less than 100% but generally higher than oral administration. Understanding bioavailability is crucial in pharmacology for determining appropriate drug dosages and predicting therapeutic effects. It influences the speed and extent to which a drug is available to exert its action at its target site.