Bioavailability of a drug is defined as the fraction of the administered dose that reaches the systemic circulation unchanged. The bioavailability of an intravenous drug is taken as what value?

• A 50%
• B 75%
• C Depends on first-pass metabolism
• D 100% ✓

Explanation

By definition, intravenous administration delivers the entire dose directly into systemic circulation, bypassing absorption barriers and first-pass metabolism. IV bioavailability is therefore 100% (F = 1). This serves as the reference against which oral bioavailability is calculated. First-pass metabolism reduces oral bioavailability but does not apply to IV drugs.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

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