A drug with an elimination half-life of 12 hours is administered at a dosing interval equal to its half-life. What is the approximate accumulation ratio at steady state?
- A 1.0
- B 1.5
- C 2.0 ✓
- D 4.0
Correct answer: C. 2.0
Explanation
When dosing interval equals half-life, the accumulation ratio is approximately 2.0. This is calculated as 1/(1 − e^(−kτ)) where k = 0.693/half-life and τ = half-life, giving 1/(1 − 0.5) = 2. Accumulation increases as dosing interval shortens relative to half-life. A ratio of 1.0 implies no accumulation, which occurs only with very long intervals relative to half-life.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
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