carryover effect in endogenous substances [Regulatives / Guidelines]
As per previous discussion. We con't directly assess the carry-over effect for endogenous substances. As per USFDA regulatory requirement we have to approach the concept of 5% cmax for endogenous substances also https://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM234960.pdf. but they are not clearly telling about how to approach these concept for endogenous substances.
Kindly share your suggestions about to below statements.
When dealing with endogenous substances, the presence of carry-over effects is very difficult to quantify. Therefore to find a proof of absence or presence of carryover effect in endogenous substances, the pre-dose (baseline) drug concentrations for Period 1 should compared to the pre-dose concentrations for Period 2. Thus, previous period average pre-dose concentration should be subtracted with subsequent period average pre-dose concentration after that the resulted values should compare with 5% of cmax. Based on this we can ensure the carry over effect occurred or not in period 1 or in subsequent period.