The extent of a drug's absorption into the bloodstream is known as?

• A. Purity
• B. Bioavailability
• C. Assay
• D. Generic drugs

Answer: (B)

Bioavailability is the proportion of an administered dose that reaches the bloodstream in active form and is available to exert an effect. This concept explains why medications given by different routes don't produce the same level of effect: intravenous administration delivers the entire dose into circulation, so bioavailability is effectively 100%, while oral or other routes involve incomplete absorption and possible first-pass metabolism, reducing the amount that reaches systemic circulation. Purity refers to how free the drug is from impurities, assay is a lab test to measure drug amount, and generic drugs describe formulations that are the same active ingredient and strength but not about how much drug enters the blood. Factors such as solubility, permeability, stability in the GI tract, and first-pass metabolism influence bioavailability, along with formulation and patient-specific factors.