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# Final Guidance on Washout Periods in Cancer Clinical Trials
- URL: https://www.fdaweb.com/final-guidance-on-washout-periods-in-cancer-clinical-trials/
- Published: 2026-07-27T12:00:00.000Z
- Updated: 2026-09-14T13:43:46.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5161521

FDA has issued a final guidance encouraging cancer clinical trial sponsors to adopt more flexible eligibility criteria related to washout periods and concomitant medications, arguing that unnecessarily restrictive requirements can slow patient enrollment and limit the applicability of trial results to real-world populations.

The [guidance](https://www.fda.gov/media/178016/download?ref=fdaweb.com), “Cancer Clinical Trial Eligibility Criteria: Washout Periods and Concomitant Medications,” recommends that trial sponsors move away from standardized exclusion criteria that have been carried over from previous studies without scientific justification. Instead, the agency says eligibility criteria should be tailored to the specific investigational therapy, disease, and patient population. The agency notes that overly restrictive enrollment criteria can reduce access to clinical trials and produce study populations that do not adequately reflect the patients who will ultimately receive the therapy after approval.

A key focus of the guidance is the use of washout periods — the interval between a patient's previous cancer treatment and enrollment in a new clinical trial. Rather than relying on fixed, time-based washout periods, FDA recommends using relevant clinical and laboratory measures to determine when patients have sufficiently recovered from prior therapy. If time-based washout periods are used, sponsors should provide a clear scientific rationale based on the pharmacokinetic and pharmacodynamic characteristics of the previous treatment and any potential safety concerns.

The guidance also advises sponsors to avoid broadly excluding patients who are taking concomitant medications unless there is a clinically significant risk of drug-drug interactions or overlapping toxicities. Instead of excluding such patients, sponsors should consider adjusting the dosage or regimen of either the investigational therapy or the concomitant medication when appropriate, provided those modifications are clearly described in study protocols and communicated to participants. FDA says these approaches could improve enrollment and make cancer clinical trials more representative of patients treated in routine clinical practice, particularly older adults who often take multiple medications.