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Prescribing Advice for GPs

An NHS Prescribing Advisers' Blog

Electrolytes and Diuretics

The British Journal of Clinical Pharmacology has published the results of a retrospective observational study into the effects of thiazide diuretics on electrolytes1. This study has also been reported by the BBC.

The study concludes that thiazides should be prescribed at low dose and the risk of electrolyte abnormalities should be managed by monitoring, especially in older patients.

Closer scrutiny of the study reveals that there are several confounders in the data. The data collected may not reflect current practice because it was time limited to a twelve year period between 1990 and 2002. Of the 32,000 patients identified detailed prescribing data was only available for 2942. Perhaps most importantly no details of co-morbidities or co-prescriptions were collected or analysed.

Current guidelines in Hypertension, like the NICE Guideline, recommend thiazides as first line drug. The Prescribing Formulary area of this site has made recommendations for first line drug choice that included a low dose thiazide.

Perhaps the only area of concern raised by this study is the finding that monitoring was not carried out in approximately two thirds of patients prescribed thiazides. The implementation of new contractual arrangements for GPs may have improved this recently but systematic monitoring is clearly an issue that still needs to be tackled.

Action: Media reporting of this publication may cause patients to report to their GP. Clinicians should be aware of the limitations of the study but take the opportunity to carry out routine monitoring, especially in those patients who are more prone to electrolyte abnormalities such as those prescribed other medicines and the elderly.


  1. Clayton JA et al. Thiazide diuretic prescription and electrolyte abnormalities in primary care. Br J Clin Pharmacol;61:87-95

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