Tolvaptan, a cost benefit analysis

I have a patient who is enrolled in the ongoing TEMPO 4:4 trial. This is another randomized placebo controlled trial of tolvaptan similar to the ground breaking Tempo 3:4 released at Kidney Week 2012. The principle differences seem to be, enrolling people with lower kidney function (GFR >30 versus > 60 ml/min in 3:4).

Recently, he told me about one of his 24-hour urine collections that he has to do as part of the study. He made 7.7 liters of urine in twenty-four hours. As I was pulling my chin off the floor, he asked me if I thought he was on placebo. No, probably not. He agreed.

He has been on "study-drug" for over a year and the polyuria is really disruptive. He is getting up 3-4 times a night and now he needs to take naps during the day because he isn't getting enough sleep at night.
The guy is on 120 mg of study drug/tolvaptan a day, polyuria is going to be inevitable. The conversation then progressed to how much time the drug may give him off dialysis compared to placebo. Here is the back-of-the-envelope calculation we did to determine if the drug was worth the inconvenience.

His mother reached ESRD at age 55, he seems to be doing a bit better than her, possibly due to the ARB, or just due to phenotypic variance, but we used 55 as the target, that gave him roughly a dozen years or tolvaptan. Using the change in GFR from the sensitivity analysis for males you get the following:

He felt that for him the over-under was about 5 years, and since this beat that handily he was satisfied.

The patient saw a draft of this post and consented to the release of this personal health information.