Other antihypertensive agents: Since labetalol hydrochloride may be administered to patients already being treated with other medications, including other antihypertensive agents, careful monitoring of these patients is necessary to detect and treat promptly any undesired effect from concomitant administration.
Beta-agonist bronchodilators: Drugs possessing beta-blocking properties can blunt the bronchodilator effect of beta-receptor agonist drugs in patients with bronchospasm; therefore, doses greater than the normal anti-asthmatic dose of beta-agonist bronchodilator drugs may be required.
Cimetidine: Cimetidine has been shown to increase the bioavailability of labetalol hydrochloride administered orally. Special care should be used in establishing the dose required for blood pressure control in such patients.
Halothane: Synergism has been shown between halothane anesthesia and intravenously administered labetalol hydrochloride.
Nitroglycerin: Labetalol hydrochloride blunts the reflex tachycardia produced by nitroglycerin without preventing its hypotensive effect. If labetalol hydrochloride is used with nitroglycerin in patients with angina pectoris additional antihypertensive effects may occur.
Calcium channel blockers: Care should be taken if labetalol hydrochloride is used concomitantly with calcium antagonists of the verapamil type. Labetalol hydrochloride when administer with alkaline drugs, such as furosemide, and then a white precipitate has been noted. So avoid coadministration.