Washout Period
A defined interval in a crossover or sequential clinical trial during which the effects of a prior treatment are allowed to dissipate before the next treatment is administered.
Full Definition
The washout period is a protocol-specified interval between successive treatment phases in a crossover or sequential trial, designed to eliminate residual biological or pharmacological effects of the preceding intervention before the next is introduced. In dental research, washout periods are critical in studies investigating oral rinses, analgesics, topical anaesthetics, or desensitising agents, where carry-over effects could confound outcomes. The duration of the washout period should be justified by reference to the known biological half-life or mode of action of the intervention. Editors should verify that authors have stated the washout duration, justified its length, and reported whether carry-over effects were tested statistically. Omission of washout period information is a frequent reporting deficiency flagged during peer review.
Usage
Usage note: Do not confuse 'washout period' with 'run-in period'; a run-in precedes the start of a trial and may involve a placebo phase, whereas a washout separates sequential interventions within a trial.
In Context
- "A two-week washout period separated the two treatment phases to prevent carry-over of the antiseptic rinse." — Methods section of a crossover dental RCT
- "The washout period duration was determined based on the pharmacokinetic profile of the study agent." — Study rationale section of a clinical protocol