M.tareq Junior 20171012 07:53 Posting: # 17890 Views: 2,761 

Dear all , I have a question about Tmax from clinical perspective. According to EMA guidance: "A statistical evaluation of tmax is not required. However, if rapid release is claimed to be clinically relevant and of importance for onset of action or is related to adverse events, there should be no apparent difference in median tmax and its variability between test and reference product." If a fast disintegrating tab has a tmax earlier than the conventional release, does it prove that it has an earlier onset of action? Thanks in advance and Best regards 
Helmut Hero Vienna, Austria, 20171012 13:22 @ M.tareq Posting: # 17891 Views: 2,425 

Hi M.tareq, » "A statistical evaluation of tmax is not required … Unfortunately the EMA is so allergic to a nonparametric test that it was removed from the GL. » … if rapid release is claimed to be clinically relevant and of importance for onset of action or is related to adverse events, … We had to accept that BE is seen a “quality measure”. Why the heck does clinical relevance come back here? » … there should be no apparent difference in median tmax and its variability between test and reference product." Oh dear! Apparent? Variability of the median? » If a fast disintegrating tab has a tmax earlier than the conventional release, does it prove that it has an earlier onset of action? Not the slightest idea. First of all, t_{max} is a very poor predictor of differences in the rate of absorption. Example: One compartment model; F_{T}=F_{R}=1, k_{el} 0.1733 h^{–1} (t_{½} 4 h), k_{abs,R} 1.3863 h^{–1} (t_{½} 30 min), k_{abs,T} 2.0794 h^{–1} (t_{½} 20 min), sigmoidal effect model identical for T and R; E_{max} 125, EC_{50} 50, γ 0.25.
Although T has a 50% (!) faster absorption than R, t_{max} of T is only 15 min earlier than the one of R (reflected both in concentrations and effects). The T/Rratio of C_{max} is 113% but the maximum effect increases by only 1.5%! Is that relevant? This is a very simple PK/PDlink model. With others (e.g., incorporating a delay in onset) the observed difference in PK may disappear completely in PD. If we have no data about the PK/PDrelationship we are left out in the dark. I’m aware of only a few studies (rapid onset for multiphasic products of zolpidem and methlyphenidate). — Cheers, Helmut Schütz The quality of responses received is directly proportional to the quality of the question asked. ☼ Science Quotes 
M.tareq Junior 20171022 00:36 @ Helmut Posting: # 17902 Views: 2,094 

Thanks alot Helmut for your reply and help. 
kumarnaidu Regular Mumbai, India, 20181101 14:01 @ Helmut Posting: # 19516 Views: 745 

Dear All, “According to the CHMP Guideline on the investigation of bioequivalence (CPMP/EWP/QWP/1401/98 Rev. 1/Corr**) “if rapid release is claimed to be clinically relevant and of importance for onset of action or is related to adverse events, there should be no apparent difference in median Tmax and its variability between test and reference product . For example if the therapeutic indication of the product is for shortterm symptomatic treatment of mild and moderate pain. Then, as such the rate of release is clinically relevant for this immediate release product. So for such product in BE study if the median Tmax is found to be lower for the test product (1.25 hours) than for the reference product (2.00 hours) although overall ranges were similar for Tmax but median is not comparable. So with a difference of 45 minutes in median Tmax, the absorption rates of Test product and Reference are not considered comparable. Considering T/R ratios is around 100 and the statistical comparison cannot be used as an argument because the study was not necessarily powered to detect a difference in Tmax. what would be the possible reasons for this difference and how we should justify why the difference is not clinically relevant? Thanks in advance Regards, Kumar — Kumar Naidu 