Drug Interactions between Duo-Medihaler and methacholine

MONITOR: Coadministration of beta-2 adrenergic agonists with other adrenergic agents may potentiate the risk of cardiovascular side effects. Beta-2 adrenergic agonists can produce clinically significant cardiovascular effects including increases in pulse rate and systolic or diastolic blood pressure as well as ECG changes such as flattening of the T wave, prolongation of the QTc interval, and ST segment depression. The risk is lower when beta-2 adrenergic agonists are inhaled at normally recommended dosages. However, these effects may be more common when the drugs are administered systemically or when recommended dosages are exceeded.

MANAGEMENT: Caution is advised if beta-2 adrenergic agonists are used concomitantly with other adrenergic agents, particularly in patients with cardiovascular disorders such as coronary insufficiency, cardiac arrhythmias, hypertrophic obstructive cardiomyopathy, or hypertension. Blood pressure and heart rate should be closely monitored.

ADJUST DOSING INTERVAL: Anticholinergics, beta-agonists, and theophylline may inhibit the bronchial airway response to methacholine. Methacholine is a cholinergic agonist that binds muscarinic receptors in bronchial smooth muscle, which leads to bronchoconstriction. Since patients with asthma exhibit greater sensitivity to induced bronchoconstriction than healthy subjects, methacholine is used to diagnose bronchial airway hyperreactivity in the absence of clinically apparent asthma. Bronchodilation caused by anticholinergics, beta-agonists, and theophylline may counteract methacholine-induced bronchoconstriction, possibly leading to diagnostic failure.

MANAGEMENT: Treatment with anticholinergics, beta-agonists, and theophylline should be interrupted before methacholine administration for the following durations:
--Short-acting anticholinergics (e.g., ipratropium): 12 hours
--Long-acting anticholinergics (e.g., tiotropium): At least 168 hours
--Short-acting beta-agonists (e.g., albuterol): 6 hours
--Long-acting beta-agonists (e.g., salmeterol): 36 hours (some authorities recommend 48 hours for ultra-long-acting beta-agonists [e.g., indacaterol, olodaterol, vilanterol])
--Oral theophylline: 12 to 48 hours