Which statement about steady-state drug levels is true?

The concept of steady-state drug levels refers to the condition where the overall intake of a drug is fairly in dynamic equilibrium with its elimination. This is particularly significant in pharmacokinetics when assessing how often a drug should be administered to maintain therapeutic levels in the body.

The correct statement is that oral dosing intervals produce peaks and troughs in the dose-response curve. This occurs because, with oral administration, drugs are absorbed into the system over time, leading to an initial rise in drug concentration until it reaches a peak. Following this peak, the drug concentration gradually decreases as the body metabolizes and excretes the drug, resulting in a trough. These fluctuations in drug levels are characteristic of oral dosing due to the absorption and elimination processes.

In contrast, continuous intravenous infusion results in a more stable drug concentration without the same peaks and troughs seen with oral dosing because the drug is delivered directly into the bloodstream. The other choices relate to different aspects of pharmacokinetics; for instance, the amount absorbed should equal the amount excreted at steady state, and steady state typically requires around four to five half-lives to be achieved, not just two.