Use caution with history of severe anaphylaxis to allergens (patients taking β-blockers may become more sensitive to repeated challenges). Proarrhythmic effects might occur (QTc prolongation). Patients with bronchospastic disease should not receive β-blockers. Use with caution in diabetes mellitus (may potentiate hypoglycemia and/or mask signs and symptoms). Electrolyte imbalances should be corrected before initiating (especially hypokalemia and hypomagnesemia). Use with caution in compensated heart failure, in myasthenia gravis, within first 2 weeks post-myocardial infarct, and in peripheral vascular disease. In pheochromocytoma adequate α-blockade is required prior to use of any β-blocker. Use with caution in history of psychiatric illness (may cause or exacerbate CNS depression), in renal impairment, in patients receiving anesthetic agents which decrease myocardial function, and with calcium channel blockers (bradycardia or heart block can occur). Concurrent use with other QTc-prolonging drugs (including Class I and Class III antiarrhythmics) generally not recommended. β-Blocker therapy should not be withdrawn abruptly (particularly in coronary artery disease).