Diazepam and methadone blood levels following concurrent administration of diazepam and methadone

Kenzie L. Preston, Roland R. Griffiths, Edward J. Cone, William D. Darwin, Charles W. Gorodetzky

Research output: Contribution to journalArticlepeer-review

36 Scopus citations


Results of a previous study indicated that the opioid effects of methadone were enhanced by the concurrent administration of diazepam in methadone-maintained subjects. To determine whether a pharmacokinetic interaction might account for this methadone-diazepam interaction, the plasma levels of methadone, diazepam and diazepam metabolites were determined in blood samples collected during that study. Five adult male patients on methadone maintenance (50-60 mg/day) were administrated single doses of placebo, diazepam (20 and 40 mg), methadone (100%, 150% and 200% of the maintenance dose), and four diazepam-methadone dose combinations (20 and 40 mg diazepam in combination with 100% and 150% of the maintenance dose). The results showed that the concurrent administration of methadone and diazepam did not significantly change the time-course or areas under the plasma concentration-time curve of methadone, diazepam or N-desmethyl-diazepam compared to the levels following the administration of either drug alone. Thus, plasma drug level analysis does not indicate a pharmacokinetic interaction between diazepam and methadone.

Original languageEnglish (US)
Pages (from-to)195-202
Number of pages8
JournalDrug and alcohol dependence
Issue number2
StatePublished - Oct 1986


  • Blood levels
  • Diazepam
  • Methadone

ASJC Scopus subject areas

  • Toxicology
  • Pharmacology
  • Psychiatry and Mental health
  • Pharmacology (medical)


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