バイオアベイラビリティ試験デザイン：単回投与試験と多回投与試験

Single-dose studies are preferred because they offer a straightforward approach with reduced drug exposure for participants. They involve administering one dose and collecting blood samples over an extended period to determine key pharmacokinetic parameters like terminal half-life and total area under the plasma concentration-time curve (AUC). This simplicity minimizes study duration and complexity while reducing adverse reaction risk.

Single-dose studies do not reliably predict steady-state drug concentrations or account for interindividual variability observed during long-term drug use. This limits their predictive value for chronic dosing scenarios where patients receive repeated doses over extended periods. Consequently, they may not accurately reflect how a drug behaves in real clinical practice.

In multiple-dose studies, the drug is administered repeatedly over five to six elimination half-lives before blood sampling begins. This extended dosing period allows the drug to accumulate and reach steady-state concentrations, where the amount of drug entering the body equals the amount being eliminated. This approach closely mimics clinical drug usage and provides reliable steady-state predictions.

Multiple-dose studies can detect nonlinear pharmacokinetics, which may arise from saturation of metabolic pathways or changes in drug clearance with repeated dosing. Single-dose studies cannot identify these phenomena. Additionally, multiple-dose studies reduce interindividual variability and eliminate extended washout periods, providing more clinically relevant data for drugs used chronically.

Multiple-dose studies are resource-intensive and time-consuming, requiring prolonged participant monitoring and higher costs. Increased drug exposure over the extended study period raises the potential for adverse effects, which may impact participant compliance and safety. These factors make multiple-dose studies more challenging to implement than single-dose alternatives.

Single-dose studies involve collecting blood samples for extended periods after administering one dose to precisely determine terminal half-life and total AUC. Multiple-dose studies administer the drug repeatedly over five to six elimination half-lives, then collect samples once steady-state is achieved. The timing and duration of sampling differ significantly between these two study designs.

Multiple-dose studies better simulate real-world clinical drug usage because they involve administering the drug repeatedly over extended periods, mirroring how patients actually take medications chronically. This design provides reliable steady-state predictions and reduces interindividual variability, offering more clinically relevant pharmacokinetic data than single-dose studies.