To the Editor.—
In his extensive and excellent review on muscle cramps, McGee1 includes several medications, among them β agonists, which induced muscle cramps. However, an important group of drugs has not been mentioned at all, ie, the β-blockers with intrinsic sympathomimetic activity (ISA) that also can induce muscle cramps.In our clinic, 14 (4.7%) of 300 patients treated with the β-blocker pindolol (a β-blocker with ISA properties) developed muscle cramps, severe in most cases. The time lapse between starting the medication and appearance of cramps varied and was between 3 and 34 months. No positive association between the daily dose of pindolol and the severity of the cramps was found. No other pathogenesis that could be suspected as a possible etiologic factor was found. The plasma levels of potassium, sodium, calcium, and magnesium were normal. In all patients, creatine phosphokinase levels and thyroid function test results were normal.
Zimlichman R, Krauss S, Paran E. Muscle Cramps Induced by ß-Blockers With Intrinsic Sympathomimetic Activity Properties: A Hint of a Possible Mechanism. Arch Intern Med. 1991;151(5):1021. doi:10.1001/archinte.1991.00400050151034