Drug interactions between Combivent and fluphenazine

MONITOR: Beta-2 adrenergic agonists can cause dose-related prolongation of the QT interval and potassium loss. Theoretically, coadministration with other agents that can prolong the QT interval may result in elevated risk of ventricular arrhythmias, including ventricular tachycardia and torsade de pointes, because of additive arrhythmogenic potential related to their effects on cardiac conduction. In general, the risk of an individual agent or a combination of agents causing ventricular arrhythmia in association with QT prolongation is largely unpredictable but may be increased by certain underlying risk factors such as congenital long QT syndrome, cardiac disease, and electrolyte disturbances (e.g., hypokalemia, hypomagnesemia). In addition, the extent of drug-induced QT prolongation is dependent on the particular drug(s) involved and dosage(s) of the drug(s). Clinically significant prolongation of QT interval and hypokalemia occur infrequently 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 in combination with other drugs that prolong the QT interval, including class IA and III antiarrhythmic agents, certain neuroleptic agents, phenothiazines, tricyclic antidepressants, quinolones, ketolide and macrolide antibiotics, and cisapride. Patients should be advised to seek medical attention if they experience symptoms that could indicate the occurrence of torsades de pointes such as dizziness, palpitations, or syncope.

Theoretically, the potential exists for additive anticholinergic effects such as mydriasis, blurred vision, heat intolerance, fever, dry mouth, tachycardia, urinary retention, and constipation when ipratropium, oxitropium or tiotropium is used with each other or other agents with anticholinergic properties (e.g., antihistamines, antispasmodics, neuroleptics, phenothiazines, skeletal muscle relaxants, tricyclic antidepressants, class IA antiarrhythmics especially disopyramide). However, due to the poor systemic absorption of ipratropium, oxitropium, and tiotropium when administered locally, the interaction would be unlikely at regularly recommended dosages.