Midazolam exhibits characteristics of a highly permeable P-glycoprotein substrate

Pharm Res. 2003 May;20(5):757-64. doi: 10.1023/a:1023433502647.


Purpose: The purpose of this study was to investigate whether midazolam exhibits characteristics of a highly permeable P-glycoprotein (P-gp) substrate and to evaluate the potential influence of P-gp inhibition on 1-OH midazolam formation during midazolam transport.

Methods: P-gp interaction was investigated by P-gp ATPase assay, efflux inhibition studies, and transport studies of midazolam across MDR1-MDCK and 1-alpha,25-dihydroxy vitamin D3-induced Caco-2 monolayers with and without the P-gp inhibitor GF120918.

Results: Midazolam was highly permeable and transport appeared essentially unpolarized. In MDR1-MDCK, the basolateral-to-apical (B-to-A) permeability was slightly higher (16%) than apical-to-basolateral (A-to-B) permeability (p = 0.04); GF120918 increased A-to-B permeability by 27% (p = 0.01), and increased cellular midazolam accumulation during A-to-B transport by 45% (p = 0.01). Midazolam (200 microM) decreased rhodamine123 and vinblastine B/A ratios 3-fold (p < 0.006), while increasing their cellular accumulation (p < 0.003). P-gp ATPase activation by midazolam was dose-dependent and saturable [Km = 11.5(+/- 4.0) microM; Vmax = 41.1(+/- 7.4) nmol/mg/min]. P-gp inhibition increased 1-OH midazolam formation in A-to-B studies 1.3-fold when midazolam donor > or = 10 microM (p < 0.03). In B-to-A studies, P-gp inhibition did not significantly increase metabolite formation (p = 0.06). Midazolam's extraction ratio was not influenced by P-gp (p = 0.2).

Conclusion: The results indicate that midazolam exhibited characteristics of a highly permeable P-gp substrate. 1-OH midazolam formation during A-to-B midazolam transport increased slightly when P-gp was inhibited.

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B, Member 1 / metabolism*
  • Animals
  • Biological Transport / drug effects
  • Biological Transport / physiology
  • Caco-2 Cells
  • Cell Line
  • Dogs
  • Humans
  • Midazolam / pharmacokinetics*
  • Midazolam / pharmacology
  • Permeability / drug effects
  • Substrate Specificity / drug effects
  • Substrate Specificity / physiology


  • ATP Binding Cassette Transporter, Subfamily B, Member 1
  • Midazolam