Analysis of midazolam and metabolites in plasma by high-performance liquid chromatography: probe of CYP3A

Pharmacokinetics and Safety of Letermovir and Midazolam Coadministration in Healthy Subjects

Letermovir is a human cytomegalovirus (CMV) terminase inhibitor for the prophylaxis of CMV infection and disease in allogeneic hematopoietic stem-cell transplant recipients. In vitro studies have identified letermovir as a potential cytochrome P450 (CYP) 3A inhibitor. Thus, the effect of letermovir on the CYP3A isoenzyme-specific probe drug midazolam was investigated in a phase 1 trial. Healthy female subjects received single-dose intravenous (IV; 1 mg) and oral (2 mg) midazolam on days -4 and -2, respectively. Letermovir 240 mg once daily was administered on days 1 to 6, and further single doses of midazolam 1 mg IV and oral midazolam 2 mg were administered on days 4 and 6, respectively. Pharmacokinetics, tolerability, and safety were monitored throughout the trial. Following coadministration with letermovir, the least square means ratio for maximum plasma concentration and area under the plasma concentration-time curve from time 0 to the last measurable concentration was 172.4% and 225.3%, respectively, for oral midazolam, and 105.2% and 146.6%, respectively, for midazolam IV. The area under the plasma concentration-time curve from time 0 to the last measurable concentration ratio of midazolam to 1-hydroxymidazolam increased slightly in the presence of letermovir following IV (8.8-13.1; 49% increase) and oral (3.3-5.3; 59% increase) midazolam. Letermovir reached steady state, on average, by days 5 to 6. All treatments were generally well tolerated. Letermovir demonstrated moderate CYP3A inhibition.

Validation of a HPLC method for quantification of midazolam in rat plasma: Application during a Maytenus ilicifolia-drug interaction study

Midazolam (MDZ) is routinely employed as a marker compound of cytochrome P450 3A (CYP3A) activity. Despite the many HPLC-UV methods described to quantify MDZ in plasma, all of them use acetonitrile (ACN) or a mixture of methanol-isopropanol as organic solvent of the mobile phase. Since the ACN shortage in 2008, efforts have been made to replace this solvent during HPLC analysis. A simple, sensitive, accurate and repeatable HPLC-UV method (220 nm) was developed and validated to quantify MDZ in rat plasma using methanol instead. The method was applied during a herb-drug interaction study involving Maytenus ilicifolia, a Brazilian folk medicine used to treat gastric disorders. Plasma samples were alkalinized and MDZ plus alprazolam (internal standard) were extracted with diethyl ether. After solvent removal, the residue was reconstituted with methanol-water (1:1). The analyte was eluted throughout a C₁₈ column using sodium acetate buffer (10 mm, pH 7.4)-methanol (40:60, v/v). The precision at the lower limit of quantification never exceeded 19.40%, and 13.86% at the higher levels of quality control standards, whereas the accuracy ranged from -19.81 to 14.33%. The analytical curve was linear from 50 to 2,000 ng/ml. The activity of the hepatic CYP3A enzymes was not affected by the extract.

Inhibition of CYP3A4 and CYP3A5 expression by scutellarin is not mediated via the regulation of hsa-miR-27a, 27b, 148a, 298 and 451a levels

1. Scutellarin is a flavonoid glycoside widely used in the treatment of cardio-cerebrovascular diseases in China. In this study, we investigated the effect of scutellarin on cytochrome P450 3A4 (CYP3A4) and CYP3A5 expression. Furthermore, we studied the expression of hsa-miR-27a, hsa-miR-27b, hsa-miR-148a, hsa-miR-298 and hsa-miR-451a in humans to determine whether scutellarin regulated CYP3A4 and CYP3A5 expression by altering levels of those micro-ribonucleic acids (miRNAs). 2. In vitro CYP3A4 and CYP3A5 expression was measured in Chang liver cells via quantitative real-time polymerase chain reaction (qPCR) and western blot. In vivo CYP3A4 and CYP3A5 expression was evaluated through the metabolism of their substrate midazolam (MID), and detected via ultra-performance liquid chromatography-mass spectrometry. The relative miRNA levels in the plasma of study participants were investigated via qPCR. 3. Results showed that scutellarin significantly inhibited the CYP3A4 and CYP3A5 expression both in vitro and in vivo. However, the levels of hsa-miR-27a, hsa-miR-27b, hsa-miR-148a, hsa-miR-298 and hsa-miR-451a in scutellarin group did not show significant changes when compared with those of the placebo group (p > 0.05), suggesting that the expression of these miRNAs is not relevant to the scutellarin-induced down-regulation of CYP3A4 and CYP3A5.

Elucidation of a CGP7930 in vitro metabolite by liquid chromatography/electrospray ionization quadrupole time-of-flight tandem mass spectrometry

RATIONALE

γ-Aminobutyric acid-B (GABAB ) receptors are widely expressed in the nervous system and have been implicated as targets for various neurological and psychiatric disorders. CGP7930 is a positive allosteric modulator of GABAB receptors. It has been demonstrated to reduce drug self-administration and has gained increased research as a potential psychotropic treatment.

METHODS

An in vitro metabolic system with liver microsomes of SD rats has been conducted and evaluated by probe drugs. The predominant in vitro metabolite of CGP7930 was identified and elucidated using liquid chromatography/electrospray ionization quadrupole time-of-flight tandem mass spectrometry (LC/ESI-QTOF-MS/MS). Its structure was determined by comparing the characteristic ions of CGP7930 and those of the metabolite, based on the accurate mass measurement by MS and the fragmentation pattern obtained by MS/MS.

RESULTS

We found that the main metabolic pathway of CGP7930 was via a monohydroxylation reaction and the hydroxylation site located at the terminal butyl-carbon. The collision-induced dissociation (CID) fragmentation of the hydroxylated metabolite underwent McLafferty rearrangement and α-cleavage.

CONCLUSIONS

This work provides an understanding of the in vitro metabolism of CGP7930, which is helpful for the further study of the development of potential drug candidates targeting GABAB receptors, for the treatment of depression. The work also demonstrates that the LC/ESI-QTOF-MS/MS method has the advantage of possibly determining the structures of drug metabolites without the use of standards.

Serum alanine transaminase total bilirubin concentrations predict CYP3A activity as measured by midazolam and 1'-hydroxylation

Background

Microsomal enzyme P450 (CYP450) plays an important role in metabolism of most xenobiotics. The activity of CYP3A decreases in patients with liver dysfunction. However, whether serum concentrations of liver enzymes reflect the activity of CYP3A is unclear. We aimed to search for a new clue to predict the activity of CYP3A and guide clinical medication.

Material/Methods

Forty-five patients undergoing surgery under general anesthesia were enrolled in the study, including 15 cases with normal liver function (Group N), 15 cases with moderate fatty liver according to both the results of ultrasonic diagnosis of moderate fatty liver and the laboratory results of elevated alanine transaminase less than 3 times the normal (Group M), and 15 cases with end-stage liver disease (Group S). Each patient received a single dose of 5 mg midazolam intravenously. CYP3A activity was measured by plasma 1′hydroxymidsazolam/midazolam (1′-OH-MDZ/MDZ) ratio at 2 h after administration of midazolam.

Results

They was no significant difference in CYP3A activity between the patients with normal liver function and moderate fatty liver (P=0.332). The activity of CYP3A in Group S was lower than in Group N and Group M (P=0.000). Multiple linear regression analysis showed a statistically significant linear relationship between the activity of CYP3A and alanine transaminase (ALT, R²=0.682, P=0.000), and total bilirubin (TB, R²=0.519, P=0.002). There were no other factors, including albumin (ALB, P=0.881) and alkaline phosphatase (ALP, P=0.497), correlated with the activity of CYP3A.

Conclusions

We conclude that the activity of CYP3A in patients with end-stage liver disease decreased. The decrease in the activity of CYP3A was determined by the increase in the serum concentration of ALT and TB and not by patient’s age or body weight. ALT and TB therefore might have predictive value for the activity of CYP3A. An abnormal liver function test likely gives the clinician a hint about dosage adjustment.

Rate of onset of inhibition of gut-wall and hepatic CYP3A by clarithromycin

AIMS

To determine the extent and time-course of hepatic and intestinal cytochrome P450 3A (CYP3A) inactivation due to the mechanism-based inhibitor clarithromycin.

METHODS

Intestinal and hepatic CYP3A inhibition was examined in 12 healthy volunteers following the administration of single and multiple doses of oral clarithromycin (500 mg). Intestinal biopsies were obtained under intravenous midazolam sedation at baseline and after the first dose, on days 2-4, and on days 6-8 of the clarithromycin treatment. The formation of 1'-hydroxymidazolam in biopsy tissue and the serum 1'-hydroxymidazolam:midazolam ratio were indicators of intestinal and hepatic CYP3A activity, respectively.

RESULTS

Intestinal CYP3A activity decreased by 64 % (p = 0.0029) following the first dose of clarithromycin, but hepatic CYP3A activity did not significantly decrease. Repeated dosing of clarithromycin caused a significant decrease in hepatic CYP3A activity (p = 0.005), while intestinal activity showed little further decline. The CYP3A5 or CYP3A4*1B genotype were unable to account for inter-individual variability in CYP3A activity.

CONCLUSIONS

Following the administration of clarithromycin, the onset of hepatic CYP3A inactivation is delayed compared to that of intestinal CYP3A. The time-course of drug-drug interactions due to clarithromycin will vary with the relative contribution of intestinal and hepatic CYP3A to the clearance and bioavailability of a victim substrate.

Benzodiazepines: sample preparation and HPLC methods for their determination in biological samples

Benzodiazepines (BDZs) belong to a group of substances known for their sedative, antidepressive, muscle relaxant, tranquilizer, hypnotic and anticonvulsant properties. Their determination in biological fluids is essential in clinical assays as well as in forensics and toxicological studies. Researchers focus on the development of rapid, accurate, precise and sensitive methods for the determination of BDZs and their metabolites. A large number of analytical methods using different techniques have been reported, but none can be considered as the method of choice. BDZs are usually present at trace levels (microgram or nanogram per milliliter) in a complex biological matrix and the potentially interfering compounds must be isolated by various extraction techniques before analysis. An extended and comprehensive review is presented herein, focusing on sample preparation (pretreatment and extraction) and HPLC conditions applied by different authors. These methods enable bioanalysts to achieve detection limits down to 1-2 ng/ml using UV/diode array detection, readily available in most laboratories, and better than 1 ng/ml using electron capture detection, which is lower than that obtained using a nitrogen phosphorus detector. MS interfaced with electrospray ionization offered a similar sensitivity, while negative chemical ionization MS or sonic spray ionization MS provided sensitivity down to 0.1 ng/ml.

A pharmacodynamic-pharmacokinetic (PD-PK) study on the effects of Danshen (Salvia miltiorrhiza) on midazolam, a model CYP3A probe substrate, in the rat

This study investigated the effect of Danshen on the pharmacodynamic-pharmacokinetic (PD-PK) effects of midazolam, a model CYP3A probe substrate. The effects of acute and 3-day Danshen treatment on the pharmacokinetics of a low dose midazolam (10 mg/kg, i.p.) were determined in vivo in the rat. Danshen (200 mg/kg, i.p.) treatment decreased midazolam clearance by 16%, with increases in the AUC by 22% and the half-life by 14%. 3-Day Danshen treatment (200 mg/kg/day, i.p.) for 3 days decreased the clearance, with increases in the T(1/2) and AUC. The effects of acute and 3-day Danshen on midazolam-induced hypnosis, serum 1'-hydroxy-midazolam to midazolam ratio and hepatic CYP3A protein expression were determined in the rat. Danshen treatments (100-200 mg/kg, i.p. and 200-500 mg/kg, p.o.) increased the sleeping time (p<0.001) produced by a hypnotic dose of midazolam (50 mg/kg, i.p.) without affecting the sleep latency. Serum 1'-hydroxy-midazolam to midazolam ratio after the hypnotic dose of midazolam was decreased after intraperitoneal Danshen treatment (200 mg/kg) but not after oral treatment at up to 500 mg/kg. All the treatment groups with Danshen, after intraperitoneal and oral administration, decreased hepatic CYP3A protein expression (p<0.05) by about 25%. The results confirmed that Danshen had no enzyme inducing effects on rat CYP3A.

Blood concentrations of midazolam in status epilepticus using an appropriate condition of HPLC

BACKGROUND

The aim of the present study was to determine an index to evaluate the efficacy and safety of midazolam (MDZ) to treat status epilepticus (SE). An original system was therefore developed to measure blood concentrations of MDZ and 1-hydroxymidazolam (1-OHMDZ) as the main metabolite on high-performance liquid chromatography.

METHODS

This system was established through inspection of chromatograms, calibration curves and coefficient of correlations of MDZ. The clinical course of 11 SE patients, ranging from 4 months to 10 years of age, are described. These patients were treated with MDZ and measured at each blood concentration of MDZ. Moreover, patients were evaluated on cranial computed tomography and magnetic resonance imaging and video electroencephalogram (EEG), and it was determined that their seizures disappeared in accordance with the disappearance of convulsions and interictal EEG findings.

RESULTS

Reproducibility was good with this system. The standard curves of MDZ and 1-OHMDZ were almost straight, and the correlation coefficients of MDZ and 1-OHMDZ were r = 0.9999 and r = 0.9998, respectively. The convulsions in nine of 11 SE patients disappeared without side-effects and the blood concentrations of MDZ in all the patients were measured. The mean peak blood concentrations of MDZ and 1-OHMDZ were higher than those reported in other studies.

CONCLUSIONS

The clinical utility of this system has been demonstrated. An index to evaluate the efficacy and safety of MDZ is necessary, and MDZ blood concentrations measured on the present original precise measuring system could help in establishing a plan to successfully treat SE.

Development and validation of a rapid and sensitive assay for simultaneous quantification of midazolam, 1'-hydroxymidazolam, and 4-hydroxymidazolam by liquid chromatography coupled to tandem mass-spectrometry

Midazolam is an ultra short acting benzodiazepine derivative and a specific probe for phenotyping cytochrome P450 (P450) 3A4/5 activity. A rapid, sensitive, and selective LC-MS/MS method was developed for simultaneous quantitation of midazolam and its metabolites (1'-hydroxymidazolam and 4-hydroxymidazolam). Deuterated (D5) analog of midazolam was utilized as an internal standard. Sample preparation either from human plasma (100 microL) or liver microsomal incubations involved a simple protein precipitation using acetonitrile (900 microL) with an average recovery of >90% for all compounds. The chromatographic separation was achieved using Zorbax-SB Phenyl, Rapid Resolution HT (2.1 mm x 100 mm, 3.5 microm) and a gradient elution with 10 mM ammonium acetate in 10% methanol (A) and acetonitrile (B). The flow rate was 0.25 mL/min and total run time was 5.5 min. Calibration curves were linear over the concentration range of 0.100-250 ng/mL. The lower limit of quantitation (LLOQ) was 0.1 ng/mL for all three analytes. The accuracy and precision, estimated at LLOQ and three concentration levels of quality control samples in six replicates, were within 85-115%. In conclusion, a robust, simple and highly sensitive analytical method was developed and validated for the analysis of midazolam and its metabolites. This method is suitable for characterizing the P450 3A4/5 activity in vitro or in human pharmacokinetic studies allowing administration of smaller doses of midazolam.

Association of genotypes of the CYP3A cluster with midazolam disposition in vivo

The genes that encode for CYP3A4 and CYP3A5 are located in the same region (CYP3A cluster) on chromosome 7. Midazolam (MDZ) is a substrate for both CYP3A4 and CYP3A5. We hypothesize that MDZ disposition in vivo is associated with genotypes of the CYP3A cluster. A meta-analysis of the pharmacokinetic (PK) parameters from seven clinical trials was carried out, in which MDZ was administered both intravenously and orally. DNA samples were available from 116 patients. There were significant ethnic differences in the allelic frequencies of these four common single-nucleotide polymorphisms (SNPs) in the CYP3A cluster. Significant linkage disequilibrium was found between CYP3A5(*)3 and CYP3A4(*)1A in Caucasians, and between CYP3A5(*)1 and CYP3A4(*)1B in African Americans. There were no differences in MDZ disposition in vivo between different genotypes, haplotypes and diplotypes in the CYP3A cluster (P>0.05). No significant differences in MDZ PK parameters were observed between Caucasians and African Americans. Women had higher weight-corrected systemic and oral clearance than men, but dose-adjusted AUC and bioavailability differences were not observed between sexes. The clinical importance of elevated CYP3A activity in women remains to be determined. The r(GC)'s of MDZ PK parameters were between 0.3 and 13.6%. In conclusion, the meta-analysis of seven studies suggests that environmental factors explain the majority of CYP3A activity variation. Further studies are necessary to define the functional significance of SNPs in the CYP3A cluster and the effects of CYP3A genotypes on MDZ disposition in vivo.

Prediction of CYP3A4 enzyme activity using haplotype tag SNPs in African Americans

The CYP3A locus encodes hepatic enzymes that metabolize many clinically used drugs. However, there is marked interindividual variability in enzyme expression and clearance of drugs metabolized by these enzymes. We utilized comparative genomics and computational prediction of transcriptional factor binding sites to evaluate regions within CYP3A that were most likely to contribute to this variation. We then used a haplotype tagging single-nucleotide polymorphisms (htSNPs) approach to evaluate the entire locus with the fewest number of maximally informative SNPs. We investigated the association between these htSNPs and in vivo CYP3A enzyme activity using a single-point IV midazolam clearance assay. We found associations between the midazolam phenotype and age, diagnosis of hypertension and one htSNP (141689) located upstream of CYP3A4. 141689 lies near the xenobiotic responsive enhancer module (XREM) regulatory region of CYP3A4. Cell-based studies show increased transcriptional activation with the minor allele at 141689, in agreement with the in vivo association study findings. This study marks the first systematic evaluation of coding and noncoding variation that may contribute to CYP3A phenotypic variability.

Assessment of the hepatic and intestinal first-pass metabolism of midazolam in a CYP3A drug–drug interaction model rats

In the current study, to understand the characteristics of dexamethasone (DEX)-treated female rats as an animal model for drug-drug interactions, a double-cannulation method was applied and separately assessed for the intestinal and hepatic first-pass metabolism of midazolam. Midazolam was administered intravenously or orally to the animals, and midazolam concentrations in the portal and systemic plasma were simultaneously determined. Next, the rates of elimination from the intestine and liver were estimated using the AUC values. After oral administration of midazolam, the entire drug was absorbed without intestinal first-pass metabolism, and 93% of the administered midazolam was extracted in the liver of the DEX-treated female rats. Seven per cent of the midazolam administered reached the systemic circulation. When ketoconazole was given orally to the animals, in conjunction with midazolam, the extraction ratio in the liver decreased from 93% to 77% in the control rats, and the bioavailability of midazolam increased to 23%. On the other hand, after intravenous administration, the elimination half-life of midazolam was not changed by ketoconazole pretreatment. These results indicated that midazolam is only extracted in the liver of DEX-treated female rats and that ketoconazole inhibits the hepatic first-pass metabolism, but not the systemic metabolism. In conclusion, DEX-treated female rats can be used as a drug-drug interaction model via CYP3A4 enzyme inhibition, especially for the hepatic first-pass metabolism of orally administered drugs.

Changes in the expression of cytochrome P450 genes in hemin-induced differentiated K562 cells

We have previously reported the expression of CYP genes in human myeloblastic and lymphoid cell lines, and the induction of the CYP3A4 and GSTP1 genes by oxidative stress in the human erythroleukemia cell line, K562. To further elucidate the role of drug metabolizing enzymes in hematogenesis, we have characterized the expression of CYP genes in hemin-induced differentiated K562 cells. After incubation with 50 microM hemin for 3 d, the expression of CYP1A1 and CYP3A4 genes was induced by 2.5- and 3.5-fold, respectively. In contrast, the CYP1B1 and CYP2E1 genes were downregulated in these cells to below 10% of the control levels. Moreover, these changes correlated with the hemin dose and culture time. Metabolism of midazolam, a probe substrate for CYP3A4, in the differentiated K562 cells increased by 2-folds, suggesting that the induction of CYP3A4 activity is consistent with the mRNA level. If these changes in the CYP expression profile in hematopoietic cells occurred, the susceptibility to xenobiotics and/or the therapeutic drugs of the cells might be influenced, and it also affects the metabolism of endogenous substrates, such as steroids and prostaglandins.

Rifampicin-induced CYP3A4 activation in CTX patients cannot replace chenodeoxycholic acid treatment

Cerebrotendinous xanthomatosis (CTX) is a rare neurodegenerative disorder with cholestanol accumulation resulting from mutations in the sterol 27-hydroxylase gene (CYP27A). Conventional treatment includes chenodeoxycholic acid and HMG-CoA reductase inhibitors. Mice with disrupted Cyp27A (Cyp27 KO) do not show elevated cholestanol levels nor develop CTX manifestations. This phenomenon was proposed to be due to murine CYP3A overexpression leading to an alternative pathway for degradation of bile alcohols including cholestanol. Our objective was to examine the influence of CYP3A4 induction on cholestanol elimination in CTX patients. Rifampicin (600 mg/day x 7 days), known to induce the PXR, and thereby to increase CYP3A activity, was used. The degree of CYP3A4 induction was assessed by comparing midazolam pharmacokinetics before and after rifampicin treatment. Cholestanol levels and cholestanol/cholesterol ratios were assayed during the experimental period and compared to a 3 weeks period without treatment. The results show that despite 60% increase in CYP3A4 activity following rifampicin treatment, there is no significant change in cholestanol levels. We conclude that up-regulated expression of CYP3A affects cholestanol elimination in mice differently as compared to its effect in CTX patients. Therefore, CYP3A4 inducers cannot replace chenodeoxycholic acid for the treatment of CTX.

Clinical Pharmacokinetic Monitoring of Midazolam in Critically Ill Patients

Midazolam is a commonly used sedative in critically ill, mechanically ventilated patients in intensive care unit (ICU) settings worldwide. We used a nine-step decision-making algorithm to determine whether therapeutic monitoring of midazolam in the ICU is warranted. Midazolam has a higher clearance and shorter half-life than other benzodiazepines, and prolonged sedation is achieved with continuous infusion. There appears to be very good correlation between plasma concentrations of both midazolam and its active metabolite, alpha1-hydroxymidazolam, and the degree of sedation. However, due to high interpatient variability, it is not possible to predict the level of sedation in any given individual based on plasma concentration of midazolam or its metabolites. Moreover, no simple and practical assay is available to quantitate midazolam plasma concentrations in the acute ICU setting. Many scales are available to assess the sedative effects of midazolam. Because the plasma concentration of midazolam required to achieve a constant level of sedation is highly variable, it is usually more prudent for the clinician to monitor for sedation with a validated clinical scale than by plasma concentrations alone. Various physiologic parameters, including age-related effects, compromised renal function, and liver dysfunction affect the pharmacokinetics of midazolam and alpha1-hydroxymidazolam. Although routine drug monitoring for all critically ill patients receiving midazolam is not recommended, this practice is likely beneficial in patients with neurologic damage in whom sedation cannot be assessed and in patients who have renal failure with a prolonged time to awakening.

Simultaneous determination of midazolam and 1′-hydroxymidazolam in human plasma by liquid chromatography with tandem mass spectrometry

A sensitive and simple liquid chromatography-tandem mass spectrometry method for the determination of midazolam and 1'-hydroxymidazolam in human plasma has been developed and validated with a dynamic range of 0.1-250 ng/mL. The analysis was based on semi-automated liquid-liquid extraction followed by evaporation of the extraction solvent, reconstitution and chromatography on a reversed-phase C(18) column. The mobile phase consists of 5 mm ammonium acetate and methanol and runs in gradient at a flow rate of 0.25 mL/min with column temperature of approximately 20 degrees C. The entire column effluent was transferred into the LC-MS/MS interface operated in positive electrospray ionization mode. The chromatographic run time was 4.3 min per injection, with retention times for midazolam, 1'-hydroxymidazolaml and the internal standard, triazolam, of 2.5, 2.3 and 2.1 min, respectively. The intra-day and inter-day precision (RSD %) and accuracy (bias %) of the quality control samples were <15.0% and within +/-13%, respectively. The current method has been applied to a clinical drug-drug interaction study in human.

Determination of midazolam and its hydroxy metabolites in human plasma and oral fluid by liquid chromatography/electrospray ionization ion trap tandem mass spectrometry

Midazolam (MDZ), a short-acting benzodiazepine, is a widely accepted probe drug for CYP3A phenotyping. Published methods for its analysis have used either therapeutic doses of MDZ, or, if employing lower doses, were mostly unable to quantify the two hydroxy metabolites. In the present study, a sensitive and specific liquid chromatography/electrospray ionization tandem mass spectrometry method was developed and validated for the quantitative determination of MDZ and two of its metabolites (1'-hydroxymidazolam (1'-OHMDZ) and 4-hydroxymidazolam (4-OHMDZ)) in human plasma and oral fluid. After liquid-liquid extraction with hexane/dichloromethane (73:27, v/v), the analytes were separated on a Luna C18(2) (100 x 2.1 mm) analytical column using gradient elution. Detection was achieved using tandem mass spectrometry on an ion trap mass spectrometer. Midazolam-d6 was used as internal standard for quantification. The calibration curves were linear (R2 >0.998) between 0.05 and 20 ng/mL for MDZ and both metabolites in both matrices. Using 1 mL samples, the limit of detection was 0.025 ng/mL and the limit of quantification was 0.05 ng/mL for MDZ and the hydroxy metabolites in both matrices. Intra- and inter-day accuracies, determined at three different concentrations, were between 92.1 and 102.3% and the corresponding coefficients of variation were <7.3%. The average recoveries were 90.6%, 86.7% and 79.0% for MDZ, 1'-OHMDZ and 4-OHMDZ in plasma and 95.3%, 96.6% and 86.8% for MDZ, 1'-OHMDZ and 4-OHMDZ, respectively, in oral fluid. The method was successfully applied to a pharmacokinetic study, showing that MDZ and its hydroxy metabolites can be determined precisely in in vivo samples obtained following a single oral or intravenous dose of 2 mg MDZ. The method appears to be useful for CYP3A phenotyping in plasma using sub-therapeutic MDZ doses, but larger studies are needed to test this assumption.

A developed determination of midazolam and 1'-hydroxymidazolam in plasma by liquid chromatography-mass spectrometry: application of human pharmacokinetic study for measurement of CYP3A activity

This paper describes sensitive and reliable determination of midazolam (MDZ) and its major metabolite 1'-hydroxymidazolam (1-OHMDZ) in human plasma by liquid chromatography-mass spectrometry (LC-MS) with a sonic spray ionization (SSI) interface. MDZ, 1-OHMDZ and diazepam as an internal standard were extracted from 1ml of alkalinized plasma using n-hexane-chloroform (70:30, v/v). The extract was injected into an analytical column (YMC-Pak Pro C(18), 50mmx2.0mmi.d.). The mobile phase for separation consisted of 10mM ammonium acetate and methanol (50:50, v/v) and was delivered at a flow-rate of 0.2ml/min. The drift voltage was 100V. The sampling aperture was heated at 120 degrees C and the shield temperature was 260 degrees C. The total time for chromatographic separation was less than 16min. The validated concentration ranges of this method were 0.25-50ng/ml for both MDZ and 1-OHMDZ. Mean recoveries were 93.6% for MDZ and 86.6% for 1-OHMDZ. Intra- and inter-day coefficient variations were less than 6.5 and 5.5% for MDZ, and 6.1 and 5.7% for 1-OHMDZ at 0.3, 4, 20 and 40ng/ml. The limits of quantification were 0.25ng/ml for both MDZ and 1-OHMDZ. This method was sensitive and reliable enough for pharmacokinetic studies on healthy volunteers, and was applied for the measurement of CYP3A activity in humans after an intravenous (1mg) and a single-oral administration (2mg) of subtherapeutic MDZ dose.

Probe of CYP3A by a single-point blood measurement after oral administration of midazolam in healthy elderly volunteers

BACKGROUND

Midazolam (MDZ) is used as an assessment of human cytochrome P450 3A (CYP3A) activity. A single blood measurement is used as a marker of its activity based on an observed correlation between MDZ clearance and the 1'-hydroxymidazolam (1'-OH-MDZ): MDZ plasma ratio is assessed at 0.5 h followig the intake of a single 7.5 mg oral dose of MDZ in healthy young volunteers. In addition, a 4-h plasma MDZ measurement has been found to be an excellent predictor of AUC and CYP3A activity.

OBJECTIVES

The main aim of this study was to define a single-point blood sampling in healthy elderly volunteers. The secondary objective was to investigate the pharmacological effects of a low oral dose of MDZ (5 mg) and its potential psychometric changes.

METHODS

Eight healthy elderly Caucasian volunteers participated in a single-dose, open-label, non-comparative study. Each subject received a single 5 mg oral dose of MDZ. Plasma concentrations of MDZ and its major metabolite, 1'-OH-MDZ, were assayed over 12 h. Secondary assessments of critical flicker fusion (CFF), body sway and mini-mental state examination were also carried out during the 12-h post-administration period.

RESULTS

A moderate correlation was observed between MDZ clearance and the 1'-OH-MDZ: MDZ plasma concentration ratio at 9 h post-dosing (Rho=0.81; p=0.04), but an even better correlation (Rho=0.99; p<0.009) was found between MDZ AUC and MDZ plasma concentration at 6 h post-dosing, with the latter value corresponding approximately to the average mean residence time (MRT) determined in our trial. This study was well-tolerated despite a significant transitory decrease (relative to baseline) in cortical arousal at 1 h post-dosing, as assessed by CFF, and a non-significant decrease (relative to baseline) in balance and vigilance also measured at 1 h and assessed on body sway, compared to baseline values.

CONCLUSION

Despite the small sample size, based on the results of healthy, elderly volunteers, a single MDZ plasma measurement taken at 6 h post-oral administration may represent an accurate marker of CYP3A phenotype. This single-time-point method could be used safely for predicting drug-drug or diet interactions and identifying individuals with genetic polymorphism that affect CYP3A activity.

Effect of oral administration of clinically relevant doses of dexamethasone on regulation of cytochrome P450 subfamilies in hepatic microsomes from dogs and rats

OBJECTIVE

To evaluate the effect of oral administration of dexamethasone (DEX) at clinically relevant doses on metabolic activities of cytochrome P450 (CYP) isoenzymes in dogs and rats.

ANIMALS

15 healthy 1-year-old male Beagles and 20 healthy 10-week-old male Wistar rats.

PROCEDURE

Hepatic microsomes were harvested from dogs treated orally with DEX at 2.5 and 7.5 mg for 5 days and from rats treated orally with DEX at 0.75, 6, and 48 mg/kg for 5 days. 7-ethoxyresorufin, tolbutamide, bufuralol, and midazolam were used as CYP1A, CYP2C, CYP2D, and CYP3A substrates, respectively. Concentrations of metabolites formed by CYPs were measured by use of high-performance liquid chromatography, except for the resorufin concentrations measured by use of a fluorometric method. Reaction velocity-substrate concentration data were analyzed to obtain maximum reaction velocity (Vmax) and Michaelis-Menten constant (Km).

RESULTS

Values of Vmax for midazolam 4-hydroxylation were significantly decreased by treatment with DEX at 2.5 and 7.5 mg in dogs, although values of Km were not affected. Values of Vmax for bufuralol 1'-hydroxylation were also decreased by treatment with DEX. In rats, values of Vmax for midazolam 4- hydroxylation were significantly decreased by treatment with DEX at 0.75 and 6 mg/kg but significantly increased at 48 mg/kg. Other reactions were not affected by treatment with DEX.

CONCLUSIONS AND CLINICAL RELEVANCE

Our results indicate that DEX downregulates the CYP3A subfamily when administered at clinically relevant doses to dogs. The effect of downregulation of CYP3A in dogs treated with DEX should be considered to avoid adverse effects from coadministration of drugs.

A highly sensitive LC-MS-MS assay for analysis of midazolam and its major metabolite in human plasma: applications to drug metabolism

The present report describes a rapid, selective and a highly sensitive assay for midazolam (MDZ) and its major metabolite 1-hydroxymidazolam (1-OH-MDZ) in human plasma employing liquid chromatography-tandem mass spectrometry (LC-MS-MS) detection. The method involves liquid-liquid extraction sample clean-up, separation on a Purospher RP 18-e column and detection with an electrospray interface in the positive ion mode. The overall recoveries were about 100% and 80% for midazolam and 1-hydroxymidazolam, respectively. Accuracy, precision and linearity were acceptable for biological samples with quantitation limits of 0.1-100 ng mL(-1) plasma for both analytes. The validated method was successfully applied to quantify plasma concentration of midazolam and 1-hydroxymidazolam in authentic samples from a healthy volunteer following a single 15 mg oral dose of midazolam (apparent total clearance: 3.47 L h(-1)kg(-1) and AUC(0-alpha)IOH-MDZ/MDZ: 0.338).

Determination of midazolam and its major metabolite 1'-hydroxymidazolam by high-performance liquid chromatography-electrospray mass spectrometry in plasma from children

We have developed a sensitive, selective and reproducible reversed-phase high-performance liquid chromatography method coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS) for the simultaneous quantification of midazolam (MDZ) and its major metabolite, 1'-hydroxymidazolam (1'-OHM) in a small volume (200 microl) of human plasma. Midazolam, 1'-OHM and 1'-chlordiazepoxide (internal standard) were extracted from alkalinised (pH 9.5) spiked and clinical plasma samples using a single step liquid-liquid extraction with 1-chlorobutane. The chromatographic separation was performed on a reversed-phase HyPURITY Elite C18 (5 microm particle size; 100 mm x 2.1mm i.d.) analytical column using an acidic (pH 2.8) mobile phase (water-acetonitrile; 75:25% (v/v) containing formic acid (0.1%, v/v)) delivered at a flow-rate of 200 microl/min. The mass spectrometer was operated in the positive ion mode at the protonated-molecular ions [M+l]+ of parent drug and metabolite. Calibration curves in spiked plasma were linear (r2 > or = 0.99) from 15 to 600 ng/ml (MDZ) and 5-200 ng/ml (1'-OHM). The limits of detection and quantification were 2 and 5 ng/ml, respectively, for both MDZ and 1'-OHM. The mean relative recoveries at 40 and 600 ng/ml (MDZ) were 79.4+/-3.1% (n = 6) and 84.2+/-4.7% (n = 8), respectively; for 1'-OHM at 30 and 200 ng/ml the values were 89.9+/-7.2% (n = 6) and 86.9+/-5.6% (n = 8), respectively. The intra-assay and inter-assay coefficients of variation (CVs) for MDZ were less than 8%, and for 1'-OHM were less than 13%. There was no interference from other commonly used antimalarials, antipyretic drugs and antibiotics. The method was successfully applied to a pharmacokinetic study of MDZ and 1'-OHM in children with severe malaria and convulsions following administration of MDZ either intravenously (i.v.) or intramuscularly (i.m.).

Mechanism-based inhibition of cytochrome P450 3A4 by therapeutic drugs

Consistent with its highest abundance in humans, cytochrome P450 (CYP) 3A is responsible for the metabolism of about 60% of currently known drugs. However, this unusual low substrate specificity also makes CYP3A4 susceptible to reversible or irreversible inhibition by a variety of drugs. Mechanism-based inhibition of CYP3A4 is characterised by nicotinamide adenine dinucleotide phosphate hydrogen (NADPH)-, time- and concentration-dependent enzyme inactivation, occurring when some drugs are converted by CYP isoenzymes to reactive metabolites capable of irreversibly binding covalently to CYP3A4. Approaches using in vitro, in silico and in vivo models can be used to study CYP3A4 inactivation by drugs. Human liver microsomes are always used to estimate inactivation kinetic parameters including the concentration required for half-maximal inactivation (K(I)) and the maximal rate of inactivation at saturation (k(inact)). Clinically important mechanism-based CYP3A4 inhibitors include antibacterials (e.g. clarithromycin, erythromycin and isoniazid), anticancer agents (e.g. tamoxifen and irinotecan), anti-HIV agents (e.g. ritonavir and delavirdine), antihypertensives (e.g. dihydralazine, verapamil and diltiazem), sex steroids and their receptor modulators (e.g. gestodene and raloxifene), and several herbal constituents (e.g. bergamottin and glabridin). Drugs inactivating CYP3A4 often possess several common moieties such as a tertiary amine function, furan ring, and acetylene function. It appears that the chemical properties of a drug critical to CYP3A4 inactivation include formation of reactive metabolites by CYP isoenzymes, preponderance of CYP inducers and P-glycoprotein (P-gp) substrate, and occurrence of clinically significant pharmacokinetic interactions with coadministered drugs. Compared with reversible inhibition of CYP3A4, mechanism-based inhibition of CYP3A4 more frequently cause pharmacokinetic-pharmacodynamic drug-drug interactions, as the inactivated CYP3A4 has to be replaced by newly synthesised CYP3A4 protein. The resultant drug interactions may lead to adverse drug effects, including some fatal events. For example, when aforementioned CYP3A4 inhibitors are coadministered with terfenadine, cisapride or astemizole (all CYP3A4 substrates), torsades de pointes (a life-threatening ventricular arrhythmia associated with QT prolongation) may occur.However, predicting drug-drug interactions involving CYP3A4 inactivation is difficult, since the clinical outcomes depend on a number of factors that are associated with drugs and patients. The apparent pharmacokinetic effect of a mechanism-based inhibitor of CYP3A4 would be a function of its K(I), k(inact) and partition ratio and the zero-order synthesis rate of new or replacement enzyme. The inactivators for CYP3A4 can be inducers and P-gp substrates/inhibitors, confounding in vitro-in vivo extrapolation. The clinical significance of CYP3A inhibition for drug safety and efficacy warrants closer understanding of the mechanisms for each inhibitor. Furthermore, such inactivation may be exploited for therapeutic gain in certain circumstances.

Fast, Simple, and Validated Gas Chromatographic-Mass Spectrometric Assay for Quantification of Drugs Relevant to Diagnosis of Brain Death in Human Blood Plasma Samples

In addition to total anamnesis, one of the important aspects in diagnosis of brain death is the exclusion of effective plasma concentrations of drugs that might mimic brain death. A minimum consensus for toxicological analysis in this context includes relevant analytes (thiopental, pentobarbital, methohexital, phenobarbital, diazepam, nordazepam, and midazolam) and proposes limits of quantification. Propofol is another relevant drug. After liquid-liquid extraction of 200 microL of plasma using 50 microL of a solution of deuterated internal standards in butyl acetate and 50 microL of butyl acetate, 2 microL of the organic phase was analyzed by gas chromatography-mass spectrometry using selected-ion monitoring mode. Validation included the parameters selectivity, calibration model, precision and accuracy, and extraction efficiency. Accuracy and precision data obtained using 6-point and 1-point calibration were compared. The abovementioned analytes were separated within 10 minutes and sensitively detected. No interfering peaks were observed in blank samples from 10 different sources. The linearity ranges were 0.5-6 mg/L for propofol, 0.25-10 mg/L for pentobarbital and thiopental, 0.125-10 mg/L for methohexital, 2.5-50 mg/L for phenobarbital, 0.05-2.5 mg/L for diazepam and nordazepam, and 0.01-0.5 mg/L for midazolam. Extraction efficiency ranged from 85% to 111%. The acceptance criterion for accuracy and precision (99% confidence interval of measured mean within +/-50% of target value) was fulfilled for all analytes, even with 1-point calibration using a calibrator close to the center of the linearity range. The assay was applied to analysis of real brain death cases. In conclusion, the described assay allowed fast and reliable determination of analytes relevant to diagnosis of brain death, and 1-point calibration kept the workload low.

CYP3A activity measured by the midazolam test is not related to 3435 C >T polymorphism in the multiple drug resistance transporter gene

A recent study with 69 Japanese liver transplants treated with tacrolimus found that the MDR13435 C >T polymorphism, but not the MDR12677 G >T polymorphism, was associated with differences in the intestinal expression level of CYP3A4 mRNA. In the present study, over 6 h, we measured the kinetics of a 75 microg oral dose of midazolam, a CYP3A substrate, in 21 healthy subjects genotyped for the MDR13435 C >T and 2677 G >T polymorphism. No statistically significant differences were found in the calculated pharmacokinetic parameters between the three 3435 C >T genotypes (TT, CT and CC group, respectively: Cmax (mean +/- SD: 0.30 +/- 0.08 ng/ml, 0.31 +/- 0.09 ng/ml and 0.31 +/- 0.11 ng/ml; Apparent clearance: 122 +/- 29 l/h, 156 +/- 92 l/h and 111 +/- 35 l/h; t1/2: 1.9 +/- 1.1 h, 1.6 +/- 0.90 h and 1.7 +/- 0.7 h). In addition, the 30-min 1'OH midazolam to midazolam ratio, a marker of CYP3A activity, determined in 74 HIV-positive patients before the introduction of antiretroviral treatment, was not significantly different between the three 3435 C >T genotypes (mean ratio +/- SD: 3.65 +/- 2.24, 4.22 +/- 3.49 and 4.24 +/- 2.03, in the TT, CT and CC groups, respectively). Similarly, no association was found between the MDR12677 G >T polymorphism and CYP3A activity in the healthy subjects or in the HIV-positive patients. The existence of a strong association between the activity of CYP3A and MDR13435 C >T and 2677 G >T polymorphisms appears unlikely, at least in Caucasian populations and/or in the absence of specific environmental factors.

Sensitive determination of midazolam and 1′-hydroxymidazolam in plasma by liquid–liquid extraction and column-switching liquid chromatography with ultraviolet absorbance detection and its application for measuring CYP3A activity

This manuscript described a new sensitive determination of midazolam and its metabolite 1'-hydroxymidazolam by automated column-switching high-performance liquid chromatography. The test compounds were extracted from 2 ml of plasma using chloroform-hexane (30:70, v/v) and the extract was injected into a column I (TSK-PW precolumn, 10 microm, 35 mm x 4.6 mm i.d.) for clean-up and column II (C18 STR ODS-II analytical column (5 microm, 150 mm x 4.6 mm i.d.) for separation. The mobile phase for separation consisted of phosphate buffer (0.02 M, pH 4.6), perchloric acid (60%) and acetonitrile (57.9:0.1:42, v/v/v) and was delivered at a flow-rate of 0.6 ml/min. The peak was detected using a UV detector set at 254 nm. The method was validated for the concentration range 0.3-100 ng/ml, and good linearity (r > 0.998) was confirmed. Intra- and inter-day coefficient variations for midazolam and 1'-hydroxymidazolam were less than 8.5 and 6.1%, respectively, at the concentrations of 0.5, 5 and 50 ng/ml for the test compounds. Relative errors ranged from -14 to 6% and mean recoveries were 78-85%. The limit of quantification was 0.5 ng/ml for each compound. This method was sensitive enough for pharmacokinetic studies measuring CYP3A activity in human volunteers following an intravenous (1 mg) and a single-oral administration (2 mg) of a subtherapeutic midazolam dose.

The MDR1 (ABCB1) gene polymorphism and its clinical implications

There has been an increasing appreciation of the role of drug transporters in the pharmacokinetic and pharmacodynamic profiles of certain drugs. Among various drug transporters, P-glycoprotein, the MDR1 gene product, is one of the best studied and characterised. P-glycoprotein is expressed in normal human tissues such as liver, kidney, intestine and the endothelial cells of the blood-brain barrier. Apical (or luminal) expression of P-glycoprotein in these tissues results in reduced drug absorption from the gastrointestinal tract, enhanced drug elimination into bile and urine, and impeded entry of certain drugs into the central nervous system. The clinical relevance of P-glycoprotein depends on the localisation in human tissues (i.e. vectorial or directional movement), the therapeutic index of the substrate drug and the inherent inter- and intra-individual variability. With regard to the variability, polymorphisms of the MDR1 gene have recently been reported to be associated with alterations in disposition kinetics and interaction profiles of clinically useful drugs, including digoxin, fexofenadine, ciclosporin and talinolol. In addition, polymorphism may play a role in patients who do not respond to drug treatment. Moreover, P-glycoprotein is an important prognostic factor in malignant diseases, such as tumours of the gastrointestinal tract.A growing number of preclinical and clinical studies have demonstrated that polymorphism of the MDR1 gene may be a factor in the overall outcome of pharmacotherapy for numerous diseases. We believe that further understanding the physiology and biochemistry of P-glycoprotein with respect to its genetic variations will be important to establish individualised pharmacotherapy with various clinically used drugs.

Determination of picogram levels of midazolam, and 1- and 4-hydroxymidazolam in human plasma by gas chromatography–negative chemical ionization–mass spectrometry

Midazolam is a widely accepted probe for phenotyping cytochrome P4503A. A gas chromatography-mass spectrometry (GC-MS)-negative chemical ionization method is presented which allows measuring very low levels of midazolam (MID), 1-OH midazolam (1OHMID) and 4-OH midazolam (4OHMID), in plasma, after derivatization with the reagent N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide. The standard curves were linear over a working range of 20 pg/ml to 5 ng/ml for the three compounds, with the mean coefficients of correlation of the calibration curves (n = 6) being 0.999 for MID and 1OHMID, and 1.0 for 4OHMID. The mean recoveries measured at 100 pg/ml, 500 pg/ml, and 2 ng/ml, ranged from 76 to 87% for MID, from 76 to 99% for 1OHMID, from 68 to 84% for 4OHMID, and from 82 to 109% for N-ethyloxazepam (internal standard). Intra- (n = 7) and inter-day (n = 8) coefficients of variation determined at three concentrations ranged from 1 to 8% for MID, from 2 to 13% for 1OHMID and from 1 to 14% for 4OHMID. The percent theoretical concentrations (accuracy) were within +/-8% for MID and 1OHMID, within +/-9% for 4OHMID at 500 pg/ml and 2 ng/ml, and within +/-28% for 4OHMID at 100 pg/ml. The limits of quantitation were found to be 10 pg/ml for the three compounds. This method can be used for phenotyping cytochrome P4503A in humans following the administration of a very low oral dose of midazolam (75 microg), without central nervous system side-effects.

A sensitive HPLC-MS-MS assay for quantitative determination of midazolam in dog plasma

The clinical pharmacokinetics of midazolam have been extensively studied, due to its high clearance by CYP3A4 and sensitivity to drug-drug interactions. In order to investigate the potential to model drug-drug interactions with midazolam in the dog, a selective and sensitive high performance liquid chromatography-tandem mass spectroscopy (HPLC-MS-MS) method has been developed, with sufficient sensitivity to allow analysis of dog plasma samples generated following administration of a clinically relevant dose. The method involves extraction of midazolam and internal standard (flunitrazepam) from dog plasma, using 96-well Oasis MCX solid phase extraction plates. The assay has been validated over a concentration range of 0.1-10 ng/ml and its specificity, accuracy and precision demonstrated. The relative bias of the assay was within +/-15% for all standards with intra- and inter-assay precision (coefficient of variation-%CV) of less than 15%. The assay was applied to the analysis of plasma samples (0.2 ml), generated following intravenous or oral administration of midazolam to male beagle dogs, at a dose level of 0.05 mg/kg, and pharmacokinetic parameters were derived from the resulting data.

A sensitive, rapid and specific determination of midazolam in human plasma and saliva by liquid chromatography/electrospray mass spectrometry

A rapid, sensitive and selective liquid chromatography/electrospray mass spectrometry (LC/ES-MS) method was developed for the quantitative determination of the anaesthetic benzodiazepine midazolam (MID) in human saliva and plasma from patients undergoing anesthesia procedures. Biological samples spiked with diazepam-d5, the internal standard, were extracted into diethyl ether. Compounds were separated on a Xterra RP18 column using a mobile phase of acetonitrile/formic acid 0.1% at a flow rate of 0.25 mL/min under a linear gradient. Column effluents were analyzed using MS with an ES source in the positive ionization mode. Calibration curves were linear in the concentration ranges of 1-250 and 0.2-25 ng/mL in plasma and saliva, respectively. The limits of detection were 0.5 ng/mL in plasma and 0.1 ng/mL in saliva, using a 0.5-mL sample volume. The recoveries of the spiked samples were above 65%. The method was applied to ten real samples from patients undergoing midazolam treatment.

In-process control of midazolam synthesis by HPLC

A high-performance liquid chromatographic assay coupled with UV detection (239 nm) has been developed for the determination of midazolam and its synthesis precursors. The separation of the analytes was performed on a Kromasil C8 column (15 cm x 4.6 mm i.d., 5 microm) at 30 degrees C. The mobile phase [ammonium chloride (pH 5.5, 1 g l(-1))-methanolacetonitrile (45:22:33, v/v/v)] was pumped at a flow-rate of 1.5 ml min(-1). This method is rapid (less than 11 min), sensitive (limit of detection (LOD) ranged between 0.05 and 0.5 mg l(-1)) and selective for the determination of midazolam, and it could be used for monitoring different synthetic routes.

Timed-release formulation to avoid drug-drug interaction between diltiazem and midazolam

The purpose of this study was to investigate whether the use of a timed-release (TR) drug formulation can avoid unfavorable pharmacokinetic drug-drug interactions in vivo. First, the effects of the time interval between administration of midazolam and diltiazem on the known drug-drug interaction between these drugs were investigated in dogs. When dogs were given midazolam orally at the same time they were orally given an aqueous diltiazem solution, the area under the plasma concentration-time curves of midazolam increased significantly compared with that of midazolam given orally in the absence of diltiazem. However, there was no significant difference in pharmacokinetics of midazolam when the diltiazem solution was administered 1-2 h after midazolam. Tests on a TR formulation containing diltiazem demonstrated that the first appearance of diltiazem in plasma occurs at 2.6 +/- 0.5 h in dogs. Subsequent tests showed that the plasma concentration-time profile of midazolam after concurrent oral administration of the diltiazem TR formulation was almost the same as that of midazolam administered alone. These results demonstrate that a TR formulation of diltiazem can avoid the interaction between diltiazem and midazolam by creating a time interval between absorption of drugs in vivo, without the need for closely controlling the time of drug administration.

The distribution and gender difference of CYP3A activity in Chinese subjects

AIMS

To investigate the distribution of CYP3A activity in the Chinese population, and to test for gender-related differences in CYP3A activity.

METHODS

Using midazolam as a probe drug, CYP3A activity in 202 Chinese healthy subjects (104 men) was measured by plasma 1'-hydroxymidazolam:midazolam (1'-OH-MDZ:MDZ) ratio at 1 h after oral administration of 7.5 mg midazolam. The different phases of the menstrual cycle including preovulatory, ovulatory and luteal phases of 66 women phenotyped with midazolam were recorded. The concentrations of 1'-OH-MDZ and MDZ in plasma were measured by HPLC RESULTS: A 13-fold variation of CYP3A activity (log1'-OH-MDZ:MDZ: range -0.949-0.203) was shown. The CYP3A activity was normally distributed as indicated by the frequency distribution histogram, the probit plot and the Kolmogorov-Smirnov test (P > 0.05). The CYP3A activity of women was higher than that of men (median: -0.36 vs -0.43, P < 0.05; 95% CI for difference: -0.127, -0.012). There was a significant difference in CYP3A activity between the three phases of the menstrual cycle. The activity was highest in the preovulatory phase and decreased sequentially in the ovulatory and luteal phases (P < 0.05).

CONCLUSIONS

A normal distribution of CYP3A activity was observed in the Chinese population. The CYP3A activity is higher in female subjects than in males. CYP3A activity differed across the phases of the menstrual cycle.

Determination of midazolam and 1'-hydroxymidazolam by liquid chromatography-mass spectrometry in plasma of patients undergoing methadone maintenance treatment

A rapid, sensitive and selective LC-MS method was developed for the simultaneous determination of midazolam (MDZ) and 1'-hydroxymidazolam (1'-OHMDZ) in plasma taken from 54 patients undergoing methadone maintenance therapy, most of whom were multidrug users. Samples spiked with prazepam, the internal standard, and were extracted into diethyl ether. Compounds were separated on a Phenomenex Luna C(18) column and a mobile phase of acetonitrile-ammonium acetate buffer (10 mM, pH 4.7) (52:48, v/v) at a flow-rate of 1 ml/min. The limit of detection was 0.65 and 0.68 (ng/ml) for MDZ and 1'-OHMDZ, respectively. Within-day relative standard deviations were less than 8%.

[Sedation induced by midazolam in intensive care: pharmacologic and pharmacokinetic aspects]

OBJECTIVE

Review on midazolam in order to optimize drug utilisation and therapeutic monitoring.

DATA SOURCES

Research of English or French articles published until August 2001, using Medline database. The key words were: midazolam, pharmacokinetics, pharmacodynamic, sedation, drug interaction.

STUDY SELECTION

Original articles, clinical cases and letters to the Editor were selected. Animal studies were excluded.

DATA EXTRACTION

The articles were analysed according to their interest in midazolam clinical practice.

DATA SYNTHESIS

Midazolam is a benzodiazepine widely used in intensive care unit, as a sedative, anxiety-relieving, and amnesic drug. Midazolam could be used in patients with cardiac, or respiratory failure, and in neurosurgery. A great interindividual variability on pharmacokinetic and pharmacodynamic response was observed. In intensive care patients, elimination half-life is known to be widely increased. Midazolam is metabolised by hepatic microsomes. The major metabolite is the 1-hydroxymidazolam, which is pharmacologically active. A prolonged sedation due to an accumulation of conjugated metabolite was observed in renal failure patients. Enzymatic inductors or inhibitors could influence pharmacokinetics and pharmacodynamic effects of midazolam.

CONCLUSION

According to midazolam pharmacokinetic and pharmacodynamic variability, an individual dosage adjustment is essential for long-term sedation. Target controlled sedation could be a mean to limit the variability and to reach quickly the pharmacodynamic effect.

Enzyme and plasma protein induction by multiple oral administrations of phenobarbital at a therapeutic dosage regimen in dogs

In dogs effects of phenobarbital (PB) on hepatic cytochrome P450 (CYP) activities and on concentrations of plasma alpha 1-acid glycoprotein (AGP) were examined. Total body clearance (Cl(B)) of antipyrine and plasma AGP concentrations were monitored during oral PB treatment at a therapeutic dose for 35 days. Cl(B) of antipyrine, which reflects hepatic CYP activities, gradually increased and was maintained at about threefold concentrations compared with that before treatment, suggesting that PB induced CYP activities at a large extent even in a therapeutic dose, necessary for an antiepileptic effect. Plasma AGP concentrations also increased significantly (about fourfold). Dogs were killed at the 35th day of the PB treatment, and hepatic CYP content and enzyme kinetics of several CYPs were determined using liver microsomes. CYP content was about twofold higher than that from untreated dogs. The V(max) values for CYP1A-like activity (ethoxyresorufin O-deethylation), 2B-like activity (ethoxycoumarin O-deethylation), 2C-like activity (tolbutamide hydroxylation) and 3A-like activity (midazolam 4-hydroxylation) were higher (2-4-fold) than that in untreated dogs. In summary, a therapeutic dose of PB for antiepileptic therapy significantly induced hepatic CYPs and plasma AGP in dogs. Therefore, during antiepileptic therapy with PB, special attention must be paid to the pharmacokinetics of drugs simultaneously administered.

Analysis of certain tranquilizers in biological fluids

A review with 282 references is presented that deals with the reported methods of analysis of phenothiazines, thioxanthenes, and benzodiazepine derivatives of pharmaceutical interest. The review includes the methods adapted in biological fluids.

Response to antiretroviral treatment in HIV-1-infected individuals with allelic variants of the multidrug resistance transporter 1: a pharmacogenetics study

BACKGROUND

HIV-1-infected patients vary considerably by their response to antiretroviral treatment, drug concentrations in plasma, toxic events, and rate of immune recovery. This variability could have a genetic basis. We did a pharmacogenetics study to analyse the association between response to antiretroviral treatment and allelic variants of several genes.

METHODS

In 123 patients, we did PCR analyses of the gene for the multidrug-resistance transporter (MDR1), which codes for P-glycoprotein, of genes coding for isoenzymes of cytochrome P450, CYP3A4, CYP3A5, CYP2D6, and CYP2C19, and of the gene for the chemokine receptor CCR5. We measured concentrations in plasma of the antiretroviral agents efavirenz and nelfinavir by high-performance liquid-chromatography, and measured levels of P-glycoprotein expression, CD4-cell count, and HIV-1 viraemia.

FINDINGS

Median drug concentrations in patients with the MDR1 3435 TT, CT, and CC genotypes were at the 30th, 50th, and 75th percentiles, respectively (p=0.0001). In patients with CYP2D6 extensive-metaboliser or poor-metaboliser alleles, median drug concentrations were at percentiles 45 and 62.5, respectively (p=0.04). Patients with the MDR1 TT genotype 6 months after starting treatment had a greater rise in CD4-cell count (257 cells/microL) than patients with the CT (165 cells/microL) and CC (121 cells/microL) genotype (p=0.0048), and the best recovery of naïve CD4-cells.

INTERPRETATION

The polymorphism MDR1 3435 C/T predicts immune recovery after initiation of antiretroviral treatment. This finding suggests that P-glycoprotein has an important role in admittance of antiretroviral drugs to restricted compartments in vivo.

O-Dealkylation of fluoxetine in relation to CYP2C19 gene dose and involvement of CYP3A4 in human liver microsomes

This work evaluated the kinetic behavior of fluoxetine O-dealkylation in human liver microsomes from different CYP2C19 genotypes and identified the isoenzymes of cytochrome P450 involved in this metabolic pathway. The kinetics of the rho-trifluoromethylphenol (TFMP) formation from fluoxetine was determined in human liver microsomes from three homozygous (wt/wt) and three heterozygous (wt/m1) extensive metabolizers (EMs) and three poor metabolizers (PMs) with m1 mutation (m1/m1) with respect to CYP2C19. The formation rate of TFMP was determined by gas chromatograph with electron-capture detection. The kinetics of TFMP formation was best described by the two-enzyme and single-enzyme Michaelis-Menten equation for liver microsomes from CYP2C19 EMs and PMs, respectively. The mean intrinsic clearance (V(max)/K(m)) for the high- and low-affinity component was 25.2 microl/min/nmol and 3.8 microl/min/nmol of cytochrome P450 in the homozygous EMs microsomes and 12.8 microl/min/nmol and 2.9 microl/min/nmol of cytochrome P450 in the heterozygous EMs microsomes, respectively. Omeprazole (a CYP2C19 substrate) at a high concentration and triacetyloleandomycin (a selective inhibitor of CYP3A4) substantially inhibited O-dealkylation of fluoxetine. Furthermore, fluoxetine O-dealkylation was correlated significantly with S-mephenytoin 4'-hydroxylation at a low substrate concentration and midazolam 1'-hydroxylation at a high substrate concentration in liver microsomes of 11 Chinese individuals, respectively. Moreover, there were obvious differences in the O-dealkylation of fluoxetine in liver microsomes from different CYP2C19 genotypes and in microsomal fractions of different human-expressed lymphoblast P450s. The results demonstrated that polymorphic CYP2C19 and CYP3A4 enzymes were the major cytochrome P450 isoforms responsible for fluoxetine O-dealkylation, whereas CYP2C19 catalyzed the high-affinity O-dealkylation of fluoxetine, and its contribution to this metabolic reaction was gene dose-dependent.

Effect of multiple dosing of ketoconazole on pharmacokinetics of midazolam, a cytochrome P-450 3A substrate in beagle dogs

To evaluate effects of multiple dosing of ketoconazole (KTZ) on hepatic CYP3A, the pharmacokinetics of intravenous midazolam (MDZ, 0.5 mg/kg) before and during multiple dosing of KTZ were investigated in beagle dogs. KTZ tablets were given orally to dogs (n = 4) for 30 days (200 mg b.i.d.). With coadministration of KTZ, t(1/2beta) of MDZ were significantly increased both on day 1 (2-fold) and on day 30 (3-fold). Total body clearance (CL(tot)) of MDZ declined gradually during the first 5 days after the start of KTZ treatment, and thereafter CL(tot) appeared to reach a plateau phase (one-fourth), depending on plasma KTZ concentrations. The effects of KTZ on the biotransformation of MDZ were also investigated using dog liver microsomes (n = 5). The K(i) values of KTZ for MDZ 1'-hydroxylation and 4-hydroxylation were 0.0237 and 0.111 microM, respectively, indicating that KTZ extensively inhibits hepatic CYP3A activity in dogs. CL(tot) values estimated from in vitro K(i) values corrected by unbound fraction of KTZ and unbound concentrations of the drug in plasma were consistent with in vivo CL(tot) of MDZ. The results in this study suggest that KTZ treatment is necessary until plasma concentrations of the drug reach a steady state to evaluate the effect of multiple dosing of the drug on hepatic CYP3A in vivo. In addition, it is suggested that K(i) values corrected by unbound fraction of KTZ and unbound concentrations of the drug in plasma enable precise in vitro-in vivo scaling.

Determination of midazolam in human plasma by solid-phase microextraction and gas chromatography/mass spectrometry

A new method is described for the qualitative and quantitative analysis of midazolam, a short-acting 1,4-imidazole benzodiazepine, in human plasma. It involves a plasma deproteinization step, solid-phase microextraction (SPME) of midazolam using an 85-microm polyacrylate fiber, and its detection by gas chromatography/mass spectrometry (GC/MS) in selected ion monitoring (SIM) mode, using pinazepam as internal standard. The assay is linear over a midazolam plasma range of 1.5-300 ng/mL, relative intra- and inter-assay standard deviations at 5 ng/mL are below 7%, and the limit of detection is 1 ng/mL. The method is simple, fast and sufficiently sensitive to be applied in clinical and forensic toxicology as well as for purposes of therapeutic drug monitoring.

Clinically significant pharmacokinetic interactions between dietary caffeine and medications

Caffeine from dietary sources (mainly coffee, tea and soft drinks) is the most frequently and widely consumed CNS stimulant in the world today. Because of its enormous popularity, the consumption of caffeine is generally thought to be safe and long term caffeine intake may be disregarded as a medical problem. However, it is clear that this compound has many of the features usually associated with a drug of abuse. Furthermore, physicians should be aware of the possible contribution of dietary caffeine to the presenting signs and symptoms of patients. The toxic effects of caffeine are extensions of their pharmacological effects. The most serious caffeine-related CNS effects include seizures and delirium. Other symptoms affecting the cardiovascular system range from moderate increases in heart rate to more severe cardiac arrhythmia. Although tolerance develops to many of the pharmacological effects of caffeine, tolerance may be overwhelmed by the nonlinear accumulation of caffeine when its metabolism becomes saturated. This might occur with high levels of consumption or as the result of a pharmacokinetic interaction between caffeine and over-the-counter or prescription medications. The polycyclic aromatic hydrocarbon-inducible cytochrome P450 (CYP) 1A2 participates in the metabolism of caffeine as well as of a number of clinically important drugs. A number of drugs, including certain selective serotonin reuptake inhibitors (particularly fluvoxamine), antiarrhythmics (mexiletine), antipsychotics (clozapine), psoralens, idrocilamide and phenylpropanolamine, bronchodilators (furafylline and theophylline) and quinolones (enoxacin), have been reported to be potent inhibitors of this isoenzyme. This has important clinical implications, since drugs that are metabolised by, or bind to, the same CYP enzyme have a high potential for pharmacokinetic interactions due to inhibition of drug metabolism. Thus, pharmacokinetic interactions at the CYP1A2 enzyme level may cause toxic effects during concomitant administration of caffeine and certain drugs used for cardiovascular, CNS (an excessive dietary intake of caffeine has also been observed in psychiatric patients), gastrointestinal, infectious, respiratory and skin disorders. Unless a lack of interaction has already been demonstrated for the potentially interacting drug, dietary caffeine intake should be considered when planning, or assessing response to, drug therapy. Some of the reported interactions of caffeine, irrespective of clinical relevance, might inadvertently cause athletes to exceed the urinary caffeine concentration limit set by sports authorities at 12 mg/L. Finally, caffeine is a useful and reliable probe drug for the assessment of CYP1A2 activity, which is of considerable interest for metabolic studies in human populations.

Sensitive and specific determination of midazolam and 1-hydroxymidazolam in human serum by liquid chromatography-electrospray mass spectrometry

A liquid chromatographic-mass spectrometric technique was designed for the determination of the anaesthetic benzodiazepine midazolam (MID) and its active metabolite 1-hydroxymidazolam (1-OHM), with the aim of conducting pharmacokinetic/pharmacodynamic studies. MID and 1-OHM were extracted from alkalinised (pH 9.5) spiked and clinical serum samples using a single step, liquid-liquid extraction procedure with diethyl ether-2-propanol (98:2, v/v). The chromatographic separation was performed on a Nucleosil C18, 5 microm (150x1 mm I.D.) column, using a gradient of acetonitrile in 5 mM ammonium formate, pH 3.0 as the mobile phase, delivered at a flow-rate of 50 microl/min. The compounds were ionised in the ionspray source of an atmospheric pressure mass spectrometer, fragmented by in-source collisions and the pseudomolecular and fragment ions detected in the selected ion monitoring mode. The recovery was between 79 and 87% for MID, between 83 and 87% for 1-OHM and 81.5% for methylclonazepam. The limit of detection was 0.2 microg/l for MID and 0.5 microg/l for 1-OHM, the limit of quantitation (LOQ) was 0.5 microg/l for both. Linearity was verified from these LOQs up to 2000 microg/l and the method was found accurate and precise over this range. It was successfully applied to a preliminary study to establish the concentration versus time curve of MID and 1-OHM in a patient administered midazolam by continuous infusion.