The interaction of diltiazem with simvastatin

Clin Pharmacol Ther. 2000 Mar;67(3):267-74. doi: 10.1067/mcp.2000.104609.


Background: Simvastatin is an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase that is used as a cholesterol-lowering agent and is metabolized by cytochrome P450 3A (CYP3A) enzymes. Diltiazem is a substrate and an inhibitor of CYP3A enzymes and is commonly coadministered with cholesterol-lowering agents such as simvastatin. The objective of this study was to quantify the effect of diltiazem on the pharmacokinetics of simvastatin.

Method: A fixed-order study was conducted in 10 healthy volunteers with a 2-week washout period between the phases. In one arm of the study, a single 20-mg dose of simvastatin was administered orally; the second arm entailed administration of a single 20-mg dose of simvastatin orally after 2 weeks of treatment with 120 mg diltiazem twice a day.

Results: Diltiazem significantly increased the mean peak serum concentration of simvastatin by 3.6-fold (P < .05) and simvastatin acid by 3.7-fold (P < .05). Diltiazem also significantly increased the area under the serum concentration-time curve of simvastatin 5-fold (P < .05) and the elimination half-life 2.3-fold (P < .05). There was no change in the time to peak concentration for simvastatin and simvastatin acid.

Conclusion: Diltiazem coadministration resulted in a significant interaction with simvastatin, probably by inhibiting CYP3A-mediated metabolism. Concomitant use of diltiazem or other potent inhibitors of CYP3A with simvastatin should be avoided, or close clinical monitoring should be used.

Publication types

  • Clinical Trial
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Cardiovascular Agents / administration & dosage
  • Cardiovascular Agents / pharmacology*
  • Diltiazem / administration & dosage
  • Diltiazem / pharmacology*
  • Drug Administration Schedule
  • Drug Interactions
  • Female
  • Humans
  • Hydroxymethylglutaryl-CoA Reductase Inhibitors / administration & dosage
  • Hydroxymethylglutaryl-CoA Reductase Inhibitors / blood
  • Hydroxymethylglutaryl-CoA Reductase Inhibitors / pharmacokinetics*
  • Male
  • Reference Values
  • Simvastatin / administration & dosage
  • Simvastatin / blood
  • Simvastatin / pharmacokinetics*


  • Cardiovascular Agents
  • Hydroxymethylglutaryl-CoA Reductase Inhibitors
  • Simvastatin
  • Diltiazem