[The effect of beta blockers combined with thiazides on serum electrolytes]

The case reports of a total of 9,670 patients admitted to a medical department were reviewed manually. From this material, all patients receiving treatment with beta-blockers alone, bendroflumethiazide alone or combinations of these were selected. In addition, a control group was selected. The patients should have received treatment for at least seven days and they should not be "ill". Patients receiving treatment with beta-blockers had higher S-K+ (4.2 mmol/l) and lower standard bicarbonate levels (23 mmol/l) than matched controls. Patients receiving treatment with bendroflumethiazide had low S-K+ (3.6 mmol/l) and high standard bicarbonate (26 mmol/l). Patients receiving treatment with both bendroflumethiazide and beta-blocker had low S-K+ (3.4 mmol/l) and the same standard bicarbonate as patients who received bendroflumethiazide alone. A more limited group chosen according to stricter criteria confirmed the above mentioned results. The investigation demonstrated that treatment with both beta-blocker and bendroflumethiazide caused deterioration of the hypokalaemia induced by bendroflumethiazide despite the higher S-K+ during beta-blockade. This may be due to renal excretion of potassium during beta-blockade.