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M. R. Flicker, MD, PhD; M. A. Quigley, PhD; E. G. Caldwell, MD
Marion Laboratories Inc Kansas City, Mo

JAMA. 1987;258(14):1891.

	Since this article does not have an abstract, we have provided the first 150 words of the full text PDF and any section headings.

To the Editor.—

In his Letter,¹ Dr Hoyt speculates that therapy with the calcium antagonist diltiazem may have exacerbated hyperkalemia in a 70-year-old patient treated with metoprolol who was consuming massive quantities of potassium as salt substitute. We wish to suggest that there is insufficient evidence to postulate a role for diltiazem therapy in such a clinical setting.

Metoprolol treatment is likely to have contributed to the patient's hyperkalemia. Although the author argues against this possibility on the basis of metoprolol's β1-specificity, loss of such specificity has been well described² at daily doses of 100 mg or more (the patient was receiving 200 mg/d). Administration of 100-mg doses of metoprolol has been shown to parallel propranolol's tendency to augment the exercise-induced rise in serum potassium level,³ while administration of 200mg daily doses of metoprolol may cause a significant rise in the resting serum potassium level.⁴

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