- Antacids
- Bile acid sequestrants
|
Reduced absorption |
- Antacids/tetracyclines
- Cholestryamine/digoxin
|
- Proton pump inhibitors
- H2-receptor blockers
|
Altered gastric pH |
Ketoconazole absorption decreased |
- Rifampin
- Carbamazepine
- Barbiturates
- Phenytoin
- St. John’s wort
- Glutethimide
|
Induction of hepatic metabolism |
Decreased concentration and effects of
- warfarin
- quinidine
- cyclosporine
- losartan
- oral contraceptives
- methadone
|
- Tricyclic antidepressants
- Fluoxetine
- Quinidine
|
Inhibitors of CYP2D6 |
- Increased
 -blockade
- Decreased codeine effect
|
| Cimetidine |
Inhibitor of multiple CYPs |
Increased concentration and effects of
- warfarin
- theophylline
- phenytoin
|
- Ketoconazole, itraconazole
- Erythromycin, clarithromycin
- Calcium channel blockers
- Ritonavir
|
Inhibitor of CYP3A |
Increased concentration and toxicity of
- some HMG-CoA reductase inhibitors
- cyclosporine
- cisapride, terfenadine (now withdrawn)
Increased concentration and effects of
- indinavir (with ritonavir)
Decreased clearance and dose requirement for cyclosporine (with calcium channel blockers) |
| Allopurinol |
Xanthine oxidase inhibitor |
Azathioprine and 6-mercaptopurine toxicity |
| Amiodarone |
Inhibitor of many CYPs and of P-glycoprotein |
Decreased clearance (risk of toxicity) for
- warfarin
- digoxin
- quinidine
|
| Gemfibrazol (and other fibrates) |
CYP3A inhibition |
Rhabdomyolysis when co-prescribed with some HMG-CoA reductase inhibitors |
- Quinidine
- Amiodarone
- Verapamil
- Cyclosporine
- Itraconazole
- Erythromycin
|
P-glycoprotein inhibition |
Risk of digoxin toxicity |
- Phenylbutazone
- Probenecid
- Salicylates
|
Inhibition of renal tubular transport |
Salicylates  increased risk of methotrexate toxicity |
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