thanks for the suggestions. I'm not sure what's happening as he had such a bad reaction last night. I just refuse to give Istin again for the moment as it brought back all the old demons. But crushing a 1/4 pill and then dividing into 3 or 4 vaguely equal portions (and storing them) is very tricky as the 1/4 is small anyhow. The vet would not believe that such a small dose could cause problems, but Swampy's on lots of pills so anything's possible I think. He wanted me to give it again to make sure it's the Istin, but I said no.
He also told me the co who make Fortekor sell a home bp tester but it costs £700
I somehow don't think the insurance would cover that one. It's so difficult though when you need to constantly monitor bp but he can't do vet clinic visits any more. Definite gap in the market as digital people bp measuring cuff machines are so easy and relatively cheap.