Pharmacokinetics of intravenous and oral midazolam in plasma and saliva in humans: usefulness of saliva as matrix for CYP3A phenotyping

Abstract

Aims: To compare midazolam kinetics between plasma and saliva and to find out whether saliva is suitable for CYP3A phenotyping.

Methods: This was a two way cross-over study in eight subjects treated with 2 mg midazolam IV or 7.5 mg orally under basal conditions and after CYP3A induction with rifampicin.

Results: Under basal conditions and IV administration, midazolam and 1'-hydroxymidazolam (plasma, saliva), 4-hydroxymidazolam and 1'-hydroxymidazolam-glucuronide (plasma) were detectable. After rifampicin, the AUC of midazolam [mean differences plasma 53.7 (95% CI 4.6, 102.9) and saliva 0.83 (95% CI 0.52, 1.14) ng ml(-1) h] and 1'-hydroxymidazolam [mean difference plasma 11.8 (95% CI 7.9 , 15.7) ng ml(-1) h] had decreased significantly. There was a significant correlation between the midazolam concentrations in plasma and saliva (basal conditions: r = 0.864, P < 0.0001; after rifampicin: r = 0.842, P < 0.0001). After oral administration and basal conditions, midazolam, 1'-hydroxymidazolam and 4-hydroxymidazolam were detectable in plasma and saliva. After treatment with rifampicin, the AUC of midazolam [mean difference plasma 104.5 (95% CI 74.1, 134.9) ng ml(-1) h] and 1'-hydroxymidazolam [mean differences plasma 51.9 (95% CI 34.8, 69.1) and saliva 2.3 (95% CI 1.9, 2.7) ng ml(-1) h] had decreased significantly. The parameters separating best between basal conditions and post-rifampicin were: (1'-hydroxymidazolam + 1'-hydroxymidazolam-glucuronide)/midazolam at 20-30 min (plasma) and the AUC of midazolam (saliva) after IV, and the AUC of midazolam (plasma) and of 1'-hydroxymidazolam (plasma and saliva) after oral administration.

Conclusions: Saliva appears to be a suitable matrix for non-invasive CYP3A phenotyping using midazolam as a probe drug, but sensitive analytical methods are required.

Figure 1

Kinetics of MDZ and 1 ′-OHMDZ in plasma (left panel) and saliva (right panel) after IV administration of 2 mg MDZ in eight healthy volunteers. CYP3A induction by rifampicin is associated with a decrease in the concentrations of MDZ (plasma and saliva) and 1′-OHMDZ (plasma). The data are presented as mean ± SD. The results of the kinetic calculations are presented in Table 1

Figure 2

Correlation between MDZ concentrations in plasma and saliva. Single values and the 95% confidence interval are shown. After IV administration of 2 mg MDZ, there is a linear correlation between the MDZ concentrations determined in plasma and saliva both under basal conditions (left panel, r = 0.864) and after treatment with rifampicin (right panel, r = 0.842)

Figure 3

Plasma concentrations of 1′-OHMDZ and 1′-OHMDZ-glucuronide under basal conditions and after treatment with rifampicin in one subject. Surprisingly, CYP3A induction by rifampicin is associated with a decrease in the plasma concentrations of 1′-OHMDZ. The explanation for this finding is an increase in the plasma concentrations of 1′OHMDZ-glucuronide. The 1′-OHMDZ concentrations at 20 and 30 min are presented in Table 2. 1′-OH MDZ baseline, (•); 1′OH MDZ-glucuronide baseline, (▾); 1′-OH MDZ induced, (○); 1′-OH MDZ-glucuronide induced, (▿)

Figure 4

Markers of CYP3A induction after IV administration of MDZ. A) The AUC of MDZ under basal conditions and after treatment with rifampicin partially overlap in plasma, but not in saliva. B) The AUC of 1′-OHMDZ separates well between basal conditions and CYP3A induction in plasma, but could not be determined in saliva after treatment with rifampicin. C) A good separation between basal conditions and CYP3A induction in plasma was also obtained by the concentration of 1′OHMDZ-glucuronide or the ratio (1′OHMDZ + 1′-OHMDZ-glucuronide) : MDZ 20 or 30 min after administration of MDZ. (1′OHMDZ + 1′OHMDZ-glucuronide) = 1′OHMDZ_tot

Figure 5

Kinetics of MDZ and 1′-OH-MDZ in plasma (left panel) and saliva (right panel) after oral administration of 7.5 mg MDZ in eight healthy volunteers. Similar to IV administration, CYP3A induction is associated with a decrease in the plasma concentrations of MDZ (plasma) and 1′-OHMDZ (plasma and saliva). In saliva, MDZ cannot be detected after CYP3A induction. The data are presented as mean ± SD. The results of the kinetic calculations are presented in Table 1

Figure 6

Markers of CYP3A induction after oral administration of MDZ. In plasma, the drop in the AUC of MDZ (A) and in the AUC of 1′-OHMDZ (B) separate well between basal conditions and CYP3A induction. In saliva, the drop in the AUC of 1′-OHMDZ (C) shows an excellent separation between basal conditions and CYP3A induction