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 C
max & AUC w/ CYP450 inhibitors eg, azole antifungal agents (eg, itraconazole, ketoconazole), macrolide antibiotics (eg, erythromycin) & HIV PIs; grapefruit juice; cyclosporine; 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. Increased plasma conc & inhibited 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 hypertensive reaction of sudden w/drawal of clonidine. Pronounced bradycardia w/ diltiazem. Counteract the antihypertensive effect w/ NSAIDs. May cause paradoxical hypertensive reactions w/ high dose of phenylpropanolamine. Marked HTN & bradycardia w/ epinephrine. Increased plasma levels & β-blockade w/ quinidine. Pronounced sinus bradycardia w/ amiodarone. Potentiated cardiodepressive effects w/ inhalation anesth. Other β-receptor blockers (eg, eye drops) or MAO inhibitors; antidiabetic drugs.