Drug(s)/product	Enzyme inhibitor or inducer	Drug(s)	Metabolizing enzyme	Possible clinical effect
Amiodarone (Cordarone)	CYP2C9 and CYP3A4 inhibitor	Warfarin (Coumadin)	CYP2C9	Increased risk of bleeding caused by increased warfarin level19
Carbamazepine (Tegretol), phenobarbital, phenytoin (Dilantin)	CYP3A4 inducer	Ethinyl estradiol-containing contraceptives	CYP3A4	Unplanned pregnancy caused by reduced estradiol level20
Clarithromycin (Biaxin), erythromycin, telithromycin (Ketek)	CYP3A4 inhibitor	Simvastatin (Zocor), verapamil (Calan)	CYP3A4	Myopathy or rhabdomyolysis caused by increased simvastatin level21
				Hypotension and QT interval prolongation caused by increased verapamil level22
Diltiazem (Cardizem), verapamil	CYP3A4 inhibitor	Prednisone	CYP3A4	Immunosuppression caused by increased prednisolone serum levels23
Fluoxetine (Prozac), paroxetine (Paxil),	CYP2D6 inhibitor	Risperidone (Risperdal), tramadol (Ultram)	CYP2D6	Increased risk of extrapyramidal adverse effects caused by increased risperidone level24; decrease in analgesic effect caused by low level of active metabolite25
Grapefruit juice	CYP3A4 inhibitor	Buspirone (Buspar)	CYP3A4	Dizziness and serotonin syndrome caused by increased buspirone level26
Metronidazole (Flagyl)	CYP2C9 inhibitor	Warfarin	CYP2C9	Increased risk of bleeding caused by increased warfarin level27
Terbinafine (Lamisil)	CYP2D6 inhibitor	Amitriptyline	CYP2D6	Dry mouth, dizziness, and cardiac toxicity caused by prolonged increase in amitriptyline and nortriptyline (Pamelor) levels28