Paradoxical bronchospasm might occur (rarely) with use of inhaled bronchodilating agents. Immediate hypersensitivity reactions (urticaria, angioedema, rash, bronchospasm) reported. Serious adverse events, including fatalities, associated with excessive use of inhaled sympathomimetics. Do not use as component of chronic therapy without an anti-inflammatory agent. Use with caution in cardiovascular disease (arrhythmia or hypertension or heart failure); β-agonists may cause elevation in blood pressure, heart rate and result in CNS stimulation/excitation. β~2~-Agonists may also increase risk of arrhythmias. Use with caution in diabetes mellitus (β~2~-agonists might increase serum glucose), in glaucoma (might elevate intraocular pressure), in hyperthyroidism (might stimulate thyroid activity), in hypokalemia (β~2~-agonists might decrease serum potassium), and in seizure disorders (β-agonists might result in CNS stimulation/excitation). Face masks should be used in children under 4 years of age. Oral use should be avoided (increased incidence of adverse effects). Metaproterenol has more β~1~ activity than β~2~-selective agents such as albuterol (may no longer be β-agonist of first choice).