Abstract Number: Esoc2026a496 Blinding Assessment in Trident: Investigators’ Guesses of Intensive Treatment Allocation

Abstract Background and aims The Triple therapy prevention of Recurrent Intracerebral Disease EveNts Trial (TRIDENT) was a multinational, double-blind, randomized, placebo-controlled trial involving intracerebral hemorrhage (ICH) patients comparing a single antihypertensive Triple-Pill (telmisartan 20mg, amlodipine 2.5mg, indapamide 1.25mg) with matching placebo. The Triple-Pill significantly prevented recurrent stroke in relation to a between-group blood pressure (BP) difference of 9/4 mmHg over a mean 3-years of follow-up. We aimed to assess the success of blinding of treatment in relation to BP reduction by the Triple-Pill. Methods 1670 adults with clinically-stable spontaneous ICH and mild–moderate hypertension (SBP 130-160mmHg) were randomized to Triple-Pill or placebo at 57 sites in 10 countries during 2017-2025. After database lock, and before un-blinding of treatment assignment, investigators were asked to guess the treatment allocation of each participant at their site. Results Investigators provided pre-unblinding treatment guesses for 1,293 (77%) participants. Overall accuracy was 55% (95%CI 52–57), and broadly similar for the Triple-Pill (56%, 95%CI 52–60) and placebo (53%, 95%CI 49–57) (p=0.29). The Bang Blinding Indices for the Triple-Pill and placebo were 0.12 (95%CI 0.05 to 0.20) and 0.06 (95%CI -0.02 to 0.14), respectively. Conclusions Investigators were scarcely better than chance in guessing whether TRIDENT participants were allocated to the Triple-Pill or placebo, supporting successful blinding in the trial. Clinical judgment of BP response is limited because of the large natural variability in BP. Conflict of interest Ruth Freed: nothing to disclose; Craig Anderson: Dr Anderson has received grants from the National Health and Medical Research Council (NHMRC), and the Medical Research Foundation (MRF) of the UK,. He is a consultant to Auzone Biotechnology Shanghai, a Chair of the data and safety monitoring boards for several trials, President-elect of the World Stroke Organization, and the Editor-in-Chief of Cerebrovascular Diseases; Anthony Rodgers: Professor Rodgers is employed by The George Institute for Global Health (TGI) and Imperial College London. He is seconded part-time as the Chief Medical Officer of George Medicines Pty Ltd (GM); GM reimburses TGI for this secondment. GM is owned by George Health Enterprises Pty Ltd, which is partly owned by TGI’s social enterprise arm, George Institute Ventures Pty Ltd. TGI has submitted patent applications and has been granted patents for low-dose combination products in hypertension, on which Professor Rodgers is listed as an inventor. TGI has granted GM a licence to the patents and GM has received investment to develop single-pill cardiovascular therapies based on them. Professor Rodgers holds no shares in any of the aforementioned companies and will not receive any royalties from the commercialisation of the patents or sale of the products. Asita de Silva: Nothing to disclose; Lili Song: Nothing to disclose; Catharina Klijn: Nothing to disclose; Kolawole Wahab: Nothing to disclose; Rustam Al-Shahi Salman: Nothing to disclose; John Chalmers: Nothing to disclose; Katie Harris: Nothing to disclose.