Increased effect of metoprolol
amiodarone, cimetidine, diltiazem, nifedipine, nicardipine, verapamil, flecainide, hydralazine, MAO inhibitors, quinidine, ciprofloxacin, propafenone, oral contraeptives, fluoxetine, sertraline.
Decreased effect of metoprolol NSAIDS, salycylates, barbiturates, rifampin, clonidine.
The dosage and frequency depend upon the individuals metabolism and the drug being used.
There are no substitutes to beta-blockers.