Roger Jeffs Ph.D. - President, Chief Operating Officer, Director
Analyst · Phil Nadeau
Thanks for the question, Phil. I’ll make three comments about dropouts to hopefully give full clarity on the situation. So, as everybody knows, we started the trial initially with the 1 milligram tablet strength, and that was the only strength in the tablet. And there were some dropouts due to intolerance related to prostacyclin-like side effects. About last June we introduced a 0.5 milligram tablet, and since that time there has been very, very few dropouts due to prostacyclin-like side effects. And in most respects we’ve abated dropouts due to prostacyclin-like AEs altogether. The dropout rate as it currently stands is hovering between 10% and 15% of the population in the FREEDOM-C trial. So, that’s the trial that Martine mentioned that we have completed our target enrollment of 300 patients. We’ve announced two sites that we will close enrollment on May 16. So I don’t think the dropout rate over the next couple of weeks is going to change materially. So I think it’s pretty fair to say that the final dropout rate will be between 10% and 15%. And to give you some perspective on that, the dropout rate in the TRIUMPH trial was around 10% on a very well tolerated therapy by everyone’s agreement. So this is really I think, very, very good news that the dropout rate, while there is some dropouts due to prostacyclin-like side effects, it’s not over abundant and it’s probably less than people have been assuming. So, that’s two points. One is the dropout rate itself and two the actually the 0.5 milligram tablet has abated additional dropouts. I think the other thing to remember is that because we’ve met our 300 patient target, that any additional patients that we enroll above and beyond that add additional power to the study. And we think that we will probably over enroll in the 10% range, if everything goes according to what sites tell us in terms of who is in the queue, who they want to enroll through May 16. So when you do that that additional power should also provide further mitigation of those early dropouts that occurred due to AEs. So at the end of the day we’re hoping that the dropouts due to prostacyclin-like side effects, which probably did occur preferentially in the treatment group, will be mostly mitigated. So, then the other part of your question is, how are we handling the dropouts? We’re handling the dropouts in an intent to treat manner. So, all Phase III trials handle patients as randomized in an ITT basis. For patients that don’t complete the full observation period of the study there are well defined and pre-specified imputation strategies on how to impute a value for 12 week walk. For patients that drop out due to AE-like side effects, if they had a headache for example, they have lost observation carried forward. The only patients that have worse rank are patients that died or had clinical worsening and we would hope and perhaps expect but that would happen more commonly in the placebo group. And that is a bit more draconian way to handle that small subset of patients that have those types of effects. So I think the fact that it’s last observation carried forward for prostacyclin-like side effects is yet a further mitigating statistical circumstance that’s been employed in this trial, and is employed in every trial that happens in pulmonary hypertension.