Felodipine: May affect plasma conc w/ drugs that inhibit or induce CYP3A4. Increased metabolism w/ CYP450 inducers eg, carbamazepine, phenytoin, phenobarb, rifampicin & St. John's wort (Hypericum perforatum
). Increased Cmax
& AUC w/ CYP450 inhibitors eg, itraconazole, ketoconazole, erythromycin & HIV protease inhibitors; grapefruit juice; cyclosporin; cyclosporin & cimetidine. Increased conc of tacrolimus. Metoprolol: May affect plasma conc w/ drugs that inhibit CYP2D6 eg, quinidine, terbinafine, paroxetine, fluoxetine, sertraline, celecoxib, propafenone & diphenhydramine. Induced metabolism w/ barbiturates, rifampicin. Inhibits metabolism w/ propafenone, quinidine. Bradycardia & fall in BP w/ verapamil. Additive -ve inotropic effects w/ class I antiarrhythmics eg, disopyramide. Reduced clearance & potentiated effects w/ diphenhydramine. Potentiated effects w/ sudden withdrawal of clonidine. Pronounced bradycardia w/ diltiazem, amiodarone. Counteract the antihypertensive effect w/ NSAIDs. May cause paradoxical hypertensive reactions w/ high dose of phenylpropanolamine. Marked HTN & bradycardia w/ epinephrine. Pronounced sinus bradycardia w/ amiodarone. Potentiated cardiodepressive effects w/ inhalation anesth. Other β-receptor blockers (eg, eye drops) or MAO inhibitors.