How are drug interactions with beta blockers?

1- Aluminum salts, Cholestyramine: decrease the absorption of β blockers. 2-Drugs such as phenytoin, rifampin, and phenobarbital, as well as smoking (enzymatic inducer) : Induce hepatic biotransformation enzymes and may decrease plasma concentrations of β receptor antagonists that are metabolized extensively (e.g., propranolol). 3-Cimetidine (enzymatic inhibitor) may increase the bioavailability of agents such as propranolol and metoprolol