Crossover Study
A trial design where participants receive both the treatment and control at different times with a washout period between. Each participant serves as their own control, reducing variability. Crossover designs are most suitable for stable chronic conditions and drugs with short half-lives.
Technical Context
Crossover designs require: stable chronic condition (not progressive or self-limiting), drug effects that are fully reversible during the washout period (no carryover effect), and sufficient washout duration (typically 5-7 half-lives). Statistical analysis accounts for period effects (treatment may differ in first vs second period) and carryover effects (residual effect from first period). AB/BA designs (simplest crossover) randomly assign half to treatment A→washout→B and half to B→washout→A. For peptide drugs with very long half-lives (weekly semaglutide t1/2 ~1 week would require ~5-7 week washout), crossover designs may be impractical. Crossover designs are most commonly used in bioequivalence studies and PK comparisons.