Diltiazem treatment impairs theophylline elimination in patients with bronchospastic airway disease

Ther Drug Monit. 1994 Feb;16(1):49-52. doi: 10.1097/00007691-199402000-00008.


On the basis of reports that diltiazem may bind to the hepatic microsomal enzymes and inhibits the metabolism of some co-administered drugs, and to determine the effects of diltiazem on theophylline pharmacokinetics in patients with bronchospastic airway disease, we have investigated the effect of a 180-mg daily dose of oral diltiazem during 5 days on theophylline clearance in eight patients with that disease. Theophylline half-life increased 24%, from 5.7 +/- 1 to 7.5 +/- 1.8 h (p < 0.05), and total body theophylline clearance showed a decrease of 22%, from 87.3 +/- 20 to 68.3 +/- 18.6 ml/min (p < 0.05) after diltiazem therapy. The apparent volume of distribution was unchanged. This reduction in theophylline clearance is likely produced by inhibition of its metabolism by diltiazem. A clinically important drug interaction may occur with theophylline when diltiazem therapy is given concurrently in patients with bronchospastic airway disease.

MeSH terms

  • Aged
  • Bronchial Spasm / drug therapy
  • Bronchial Spasm / metabolism*
  • Diltiazem / adverse effects*
  • Drug Interactions
  • Female
  • Half-Life
  • Humans
  • Male
  • Middle Aged
  • Theophylline / pharmacokinetics*
  • Theophylline / therapeutic use


  • Theophylline
  • Diltiazem