Hot weather, older people, antihypertensives and low potassium

Like you, I’ve sweated through a few duty doctor sessions during the latest heatwave. I’ve received some ‘frank and honest’ feedback from my colleagues that scrubs plus shorts is not a good look, but hey ho – needs must. 

I took a call on Monday from the daughter of Maeve, a delightful 85 year old lady with mild dementia and hypertension. Maeve is on amlodipine, thiazide and losartan. She is feeling weak, tired, more confused and dizzy. You arrange for her obs to be checked (BP 118/68 and HR 90) and some simple bloods. It’s likely she is dehydrated, but is it safe to stop her BP meds?

Our frail, elderly patients like Maeve have been really suffering in the hot weather. Totally to be expected of course as they have less physiological reserve, drink less water due to a reduced thirst drive and are on lots of meds with potential with iatrogenic harm. They have been more dizzy, having more falls, getting more tired and weak, more confused, more constipation, frequent UTIs. The list goes on, all potential consequences of dehydration and orthostatic hypotension potentially exacerbated by antihypertensive medication and may lead to emergency hospital admissions. And then, you get Maeve’s potassium result of 2.3. Is that real, or could it be spurious pseudohypokalaemia?

The concept of ‘seasonal pseudohypokalaemia’, with spurious low K in U&E samples taken from primary care in hot weather is well reported in the literature Clin Biochem 2009. But in a patient on diuretics, it could of course also be real and contributing to their weakness and fatigue. Older people are at the greatest risk of adverse drug reactions, but they are of course also at the greatest risk of stroke if we stop their antihypertensives. So, is it safe to suspend antihypertensives in this vulnerable group if they have symptoms or signs of dehydration and/or hypokalaemia?

With Maeve in mind, I was pleased to read an excellent commentary in the DTB August 2022 on the short-term effects of deprescribing antihypertensives in older people. It was based on the results from the OPTIMISE Trial JAMA2020, which looked at adults aged over 80 on ≥ 2 antihypertensives and with a SBP < 150. They compared a strategy of antihypertensive medication reduction versus continuation on BP control over the next 12 weeks. The findings? There was a small increase in systolic BP of 3.4mmHg in the intervention group, and the authors conclude that overall medication reduction was ‘non-inferior’ to usual care and not associated with substantial change in BP over 12 weeks.

Like most studies, you can pick holes in OPTIMISE and GPs always have to make nuanced, individualised decisions for patients. But this study did give me the confidence to suspend Maeve’s antihypertensives in the short term whilst we continue to monitor her with the evidence suggesting that there is unlikely to be an unsafe, clinically significant increase in her BP over the next few weeks. Deprescribing always feels good, and I suspect Maeve will feel better for it.