OLMESARTAN. ENTEROPATHY, A RARE SIDE EFFECT

Olmesartan belongs to a group of drugs we call the Angiotensin Receptor blocker or ARB for short. We use it to treat hypertension and it is also useful in the management of heart failure. Amongst the ARBs ( and there are many ), olmesartan is one of the newest, and so our experience is less then some of the others like losartan, and valsartan.
Mayo Clinic, the very famous medical clinic in Rochester, Minnesota, has just reported 22 cases of a severe enteropathy, in their June issue of the Mayo Clinic Proceedings. These cases were reported between Aug 2008 and Sept 2011. The patients wee all on olmesartan, and they presented with chronic diarrhea and other effects of a chronic enteropathy. They were investigated for all the common enteropathies like coeliac's disease and Crohn's and these all proved negative. The physician decided to stop the olmesartan, and the diarrhea subsided.
This report is interesting as we cannot understand how olmesartan can cause an enteropathy. It is certainly rare. What also comes to mind quickly is, is this a olmesartan issue, or an ARB issue. We do not hear of this problem with Losartan and Valsartan, which have been in the market longer. It is true that ARBs as a whole does have some effect on inflammation and the immune system. We have heard of some patients having diarrhea as with many drugs that we use, but this seemed to be a chronic allergic response through cell mediated immunity.
I wish to emphasise that this is an uncommon side effect and at the moment, we are not 100% certain that it is due to olmesartan. The exact mechanism has yet to be worked out. Just to depend on improvement with drug withdrawal, is a very crude way to hypothesize that it is due to the drug. Much more work needs to be done. Patients on olmesartan at the moment should not just stop the drug. Should they develop diarrhea ( and I hope not ), they should consult their doctor for advise. before taking further action.
In the meantime, we should continue to observe our own patients and also the worldwide medical literature, to see if there are other reports.
Certainly, control of blood presure is an important strategy to prevent coronary artery disease and stroke, and olmesartan is a good and effective agent for this. At the moment, from all available information, olmesartan does more good than harm, and so should be continued, unless otherwise advised by your own doctor.
I thought that you wish to know.