Drugs and Pharmacokinetic interactions

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cisapride, terfenadine (now withdrawn)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

Leave a Reply

 Master Of Medicine proudly uses PHP Speedy

%d bloggers like this: