Plasma Concentrations Of Midazolam Research Articles

The effect of piperine on midazolam plasma concentration in healthy volunteers, a research on the CYP3A-involving metabolism

Some studies showed that piperine (the alkaloid of piper nigrum) can change the activities of microsomal enzymes. Midazolam concentration is applied as a probe to determine the CYP3A enzyme activity. This study was done to determine piperine pretreatment role on midazolam plasma concentration.Twenty healthy volunteers (14 men and 6 women) received oral dose of piperine (15 mg) or placebo for three days as pretreatment and midazolam (10 mg) on fourth day of study and the blood samples were taken at 0.5, 2.5 and 5 h after midazolam administration. The midazolam plasma levels were assayed using HPLC method (C18 analytical column, 75:25 methanol:water as mobile phase, UV detector at 242 nm wavelength and diazepam as internal standard). Data were fit in a “one-compartment PK model” using P-Pharm 1.5 software and analyzed under statistical tests.The mean ±SD of the age and body mass index were 24.3 ± 1.83 years (range: 21–28 years) and 23.46± 2.85, respectively. The duration of sedation in piperine receiving group was greater that the placebo group (188±59 vs. 102±43 min, p<0.0001). Half-life and clearance of midazolam were higher in piperine pretreatment group compared to placebo [1.88±0.03 vs. 1.71± 0.04 h (p<0.0001) and 33.62 ± 0.4 vs. 37.09 ± 1.07 ml/min (p<0.0001), respectively].According to the results, piperine can significantly increases half-life and decreases clearance of midazolam compared to placebo. It is suggested that piperine can demonstrate those effects by inhibition CYP3A4 enzyme activity in liver microsomal system.

Effect of a Dietary Supplement Containing Raspberry Ketone on Cytochrome P450 3A Activity

Objective: Various herbal medicines and dietary supplements are known to alter the effects of drugs and cause severe complications. One of the most famous examples is St. John’s wort, which promotes an increase of cytochrome P450 2C9 (CYP2C9), CYP2C19, and CYP3A4 expression, and reduces the effects of a large number of drugs. Raspberry ketone, an aromatic ingredient extracted from raspberries, is sold in Japan as a herbal supplement with a claimed slimming effect; however, its effect on CYP activity is unknown. To clarify the risk of an interaction between raspberry ketone-related supplements and CYP3A substrates, we performed an in vivo pharmacokinetic study using rats. Methods: We investigated the effect of the oral administration of raspberry ketone on the pharmacokinetics of midazolam, a typical CYP3A substrate, in rats. St. John’s wort, as a positive control, and raspberry ketone tablets at a dose of 50 mg/kg were administered every 12 h for 7 days, and at 24 h after the final treatment, 10 mg/kg midazolam was administered orally. The plasma concentration of midazolam was analyzed by high-performance liquid chromatography. Results: Oral clearance of midazolam in the St. John’s wort-treated group increased to 161% of that observed in the control group. Conversely, there was no significant difference between the raspberry ketone-treated and control groups. The mean residence time was essentially the same in all groups. Conclusion: Because raspberry ketone is considered to suppress the accumulation of body fat, it is mainly taken by young healthy women for weight loss. Considering this population, information about the interaction of raspberry ketone with oral contraceptives, which are substrates of CYP3A, is of clinical importance. In this study, raspberry ketone was found to have little impact on CYP3A activity, unlike St. John’s wort. These data indicate the low risk of an interaction between raspberry ketone-related supplements and many drugs metabolized by CYP3A.

Response to “Ethnic-Specific In Vitro–In Vivo Extrapolation and Physiologically Based Pharmacokinetic Approaches to Predict Cytochrome P450-Mediated Pharmacokinetics in Chinese Population: Opportunities and Challenges”

We thank Dr Li and his colleagues for their comments, and agree that the development of population physiologically based pharmacokinetic models is always a work in progress pending the availability of additional data. The extra data that Li et al. [1] document relate to liver weight, cardiac output and cytochrome P450 (CYP) phenotype frequencies in Chinese subjects. The additional data on liver weight for 1,114 subjects obtained at autopsy suggest a 9 % higher mean value than the value from our meta-analysis of data from 342 subjects measured by computed tomography. Nevertheless, both values are lower than the mean value observed from our meta-analysis of Caucasian data. In contrast to our analysis, which found a lower mean cardiac output in Chinese than in Caucasians, the data of Cao [2] cited by Dr Li and colleagues suggest the reverse. This difference should primarily affect the accuracy of the prediction of systemic clearance after intravenous administration of drugs with relatively high hepatic extraction ratios. Our predictions for plasma concentrations of midazolam, which has a hepatic extraction ratio of about 0.5 after intravenous injection, were similar to the observed data. With the exception of the frequency of CYP2D6 ultrarapid metabolisers in Chinese (18 %), the CYP frequencies established from additional data by Li et al. [1] were similar to those that we reported. A review of the study of Guo et al. [3], quoted by Li et al. [1], indicates that their assessment was apparently not based on data for gene duplication but simply on the frequency of CYP2D6*10 alleles. Thus, the value of 18 % is markedly higher than the figure of 1–2 % documented for Asian populations in general [4, 5] and by our meta-analysis [6].

A randomised study of the effect of danoprevir/ritonavir or ritonavir on substrates of cytochrome P450 (CYP) 3A and 2C9 in chronic hepatitis C patients using a drug cocktail

The aim of this study was to evaluate the effects of danoprevir in combination with low-dose ritonavir (danoprevir/r) and placebo plus low-dose ritonavir on the pharmacokinetics of probe drugs for cytochrome P450 (CYP) 3A and CYP2C9, in patients with chronic hepatitis C. A total of 54 patients infected with hepatitis C virus genotype 1 received an oral drug cocktail (2 mg midazolam, 10 mg warfarin and 10 mg vitamin K) before and after 14 days of dosing with either danoprevir/r or placebo plus low-dose ritonavir (placebo/r). Serial pharmacokinetic samples were collected up to 24 (midazolam) and 72 (S-warfarin) h post-dose. Plasma concentrations of midazolam, α-hydroxymidazolam and S-warfarin were measured using validated assays. Pharmacokinetic parameters were estimated using non-compartmental analysis, and geometric mean ratios (GMRs) and 90 % confidence intervals (CIs) for the differences between baseline and post-dosing values were calculated. Danoprevir/r and placebo/r significantly increased midazolam area under the time-concentration curve (AUC0-∞) and reduced the midazolam metabolic ratio while S-warfarin AUC0-∞ was modestly decreased. When danoprevir data were pooled across doses, the midazolam GMR (90 % CI) AUC0-∞ was 9.41 (8.11, 10.9) and 11.14 (9.42, 13.2) following danoprevir/r and placebo/r dosing, respectively, and the S-warfarin GMR (90 % CI) AUC0-∞ was 0.72 (0.68, 0.76) and 0.76 (0.69, 0.85), respectively. The effects of danoprevir/r and placebo/r appeared to be qualitatively similar. Substantial inhibition of CYP3A- and modest induction of CYP2C9- activity were observed with danoprevir/r and low-dose ritonavir.

Opposite Effects of Single-Dose and Multidose Administration of the Ethanol Extract of Danshen on CYP3A in Healthy Volunteers.

The aim of this study was to investigate the effect of single- and multidose administration of the ethanol extract of danshen on in vivo CYP3A activity in healthy volunteers. A sequential, open-label, and three-period pharmacokinetic interaction study design was used based on 12 healthy male individuals. The plasma concentrations of midazolam and its metabolite 1-hydroxymidazolam were measured. Treatment with single dose of the extract caused the mean C max of midazolam to increase by 87% compared with control. After 10 days of the danshen extract intake, the mean AUC0–12, C max, and t 1/2 of midazolam were decreased by 79.9%, 66.6%, and 43.8%, respectively. The mean clearance of midazolam was increased by 501.6% compared with control. The in vitro study showed that dihydrotanshinone I in the extract could inhibit CYP3A, while tanshinone IIA and cryptotanshinone could induce CYP3A. In conclusion, a single-dose administration of the danshen extract can inhibit intestinal CYP3A, but multidose administration can induce intestinal and hepatic CYP3A.

The pharmacokinetics of midazolam after intravenous, intramuscular, and rectal administration in healthy dogs

Intravenous benzodiazepines are utilized as first-line drugs to treat prolonged epileptic seizures in dogs and alternative routes of administration are required when venous access is limited. This study compared the pharmacokinetics of midazolam after intravenous (IV), intramuscular (IM), and rectal (PR) administration. Six healthy dogs were administered 0.2 mg/kg midazolam IV, IM, or PR in a randomized, 3-way crossover design with a 3-day washout between study periods. Blood samples were collected at baseline and at predetermined intervals until 480 min after administration. Plasma midazolam concentrations were measured by high-pressure liquid chromatography with UV detection. Rectal administration resulted in erratic systemic availability with undetectable to low plasma concentrations. Arithmetic mean values ± SD for midazolam peak plasma concentrations were 0.86 ± 0.36 μg/mL (C0) and 0.20 ± 0.06 μg/mL (Cmax), following IV and IM administration, respectively. Time to peak concentration (Tmax ) after IM administration was 7.8 ± 2.4 min with a bioavailability of 50 ± 16%. Findings suggest that IM midazolam might be useful in treating seizures in dogs when venous access is unavailable, but higher doses may be needed to account for intermediate bioavailability. Rectal administration is likely of limited efficacy for treating seizures in dogs.

A PBPK Model to Predict Disposition of CYP3A‐Metabolized Drugs in Pregnant Women: Verification and Discerning the Site of CYP3A Induction

Besides logistical and ethical concerns, evaluation of safety and efficacy of medications in pregnant women is complicated by marked changes in pharmacokinetics (PK) of drugs. For example, CYP3A activity is induced during the third trimester (T3). We explored whether a previously published physiologically based pharmacokinetic (PBPK) model could quantitatively predict PK profiles of CYP3A-metabolized drugs during T3, and discern the site of CYP3A induction (i.e., liver, intestine, or both). The model accounted for gestational age-dependent changes in maternal physiological function and hepatic CYP3A activity. For model verification, mean plasma area under the curve (AUC), peak plasma concentration (Cmax), and trough plasma concentration (Cmin) of midazolam (MDZ), nifedipine (NIF), and indinavir (IDV) were predicted and compared with published studies. The PBPK model successfully predicted MDZ, NIF, and IDV disposition during T3. A sensitivity analysis suggested that CYP3A induction in T3 is most likely hepatic and not intestinal. Our PBPK model is a useful tool to evaluate different dosing regimens during T3 for drugs cleared primarily via CYP3A metabolism.

Effect of the ethinylestradiol/levonorgestrel combined oral contraceptive on the activity of cytochrome P4503A in obese women.

While it is known that CYP3A4/5 activity is decreased with combined oral contraceptive (COC) use and obesity suppresses CYP expression, the combined effects of obesity and COC use on CYP3A4/5 activity are unclear. Therefore, our aim was to examine the effect of COC usage on CYP3A4/5 activity in obese women. Thirty-four, obese (body mass index, BMI > 30 kg m(-2)) women of reproductive age (18-35 years old) were placed on a COC pill containing 20 µg ethinylestradiol/100 µg levonorgestrel for 21 days starting at the onset of menses. A midazolam pharmacokinetic study was conducted prior to initiation and after 21 days of COC treatment. Serial blood samples were collected and plasma concentrations of midazolam were measured using liquid chromatography tandem mass spectrometry. Pharmacokinetic parameters were estimated using a non-compartmental method. Midazolam clearance, a surrogate measure of CYP3A4/5 activity, was significantly decreased upon COC use (63.3 l h(-1) vs. 53.9 l h(-1), P < 0.05). A median decrease of 5.6 l h(-1) (95% CI -4.1, 13.3 l h(-1)) was observed. However, the magnitude of change was similar to that reported in women with normal BMI. Although we hypothesized that obesity might amplify the impact on CYP3A4/5 activity in COC users, we found that this was not the case. This finding is reassuring regarding potential additional drug-drug interactions in obese COC users as CYP3A4/5 is a major enzyme in the metabolism of many marketed drugs.

Evaluation of intravenous midazolam limited sampling models to determine area under the concentration time curve during cytochrome P450 3A baseline, inhibition and induction or activation

This study evaluated if previously published limited sampling models (LSMs) accurately predict midazolam area under the concentration time curve (AUC) during cytochrome P450 (CYP) 3A baseline, inhibition and induction/activation. Plasma midazolam concentrations (n = 108) were obtained where intravenous midazolam was co-administered alone or concomitantly with ketoconazole, itraconazole, aprepitant, rifampin, or pleconaril. Observed AUC was calculated using noncompartmental analysis. Predicted AUC was calculated from the LSMs. Bias and precision were determined by percent mean prediction error (%MPE), percent mean absolute error (%MAE), and percent root mean squared error (%RMSE). Contrasting results were observed for LSMs in predicting CYP3A baseline activity, with the majority of studies resulting in unacceptable bias and precision. During CYP3A inhibition, unacceptable bias and precision were observed from single- and 2-time point LSMs. %MAE and %RMSE values exceeded acceptable limits during CYP3A induction with rifampin. Contrasting results were observed with pleconaril. The contrasting results during CYP3A baseline and induction/activation, as well as the unacceptable bias and precision during CYP3A inhibition, limits the widespread use of the previously published LSMs.

Effect of Quercetin on CYP3A Activity in Chinese Healthy Participants

The aims of this study were to investigate the effect of quercetin on CYP3A activity in vivo. An open, randomized, 2-period crossover experiment was performed in 18 healthy male volunteers. Genotyped data were available from a total of 165 participants. The allelic frequency was 52.5%. Every volunteer ingested orally 500 mg quercetin or placebo once a day for 13 consecutive days. On day 14, a single 7.5-mg midazolam tablet was administrated orally. The plasma concentrations of midazolam and 1-OH-midazolam were determined over 24 hours. The results showed that coadministration of quercetin in CYP3A5*1/*1 and CYP3A5*1/*3 individuals significantly decreased the area under the curve (AUC(0-12 h)) of midazolam (160.88 ± 45.58 ng·h/mL vs 188.07 ± 65.75 ng·h/mL, P < .05), significantly decreased the AUC(0-∞) of midazolam (165.46 ± 47.15 ng·h/mL vs 211.84 ± 75.80 ng·h/mL, P < .01), shortened t(1/2) (2.06 ± 0.51 h vs 2.75 ± 0.89 h, P < .01), and decreased t(max) significantly (0.48 ± 0.36 h vs 1.06 ± 0.69 h, P < .01), respectively. In conclusion, quercetin significantly induced CYP3A activity to substrate midazolam, and the induction was partly related to the CYP3A5 genotype, being more prominent in CYP3A5*1/*1 and CYP3A5*1/*3 individuals.

Bioavailability of a novel midazolam gel after intranasal administration in dogs

To compare the pharmacokinetics of a novel bioadhesive gel formulation of midazolam after intranasal (IN) administration with that of midazolam solution after IN, IV, and rectal administration to dogs. 10 (5 males and 5 females) healthy adult Beagles. Dogs were assigned to 4 treatment groups for a crossover study design. Initially, midazolam solution (5 mg/mL) was administered (0.2 mg/kg) IV to group 1, rectally to group 2, and IN to group 3; a 0.4% hydroxypropyl methylcellulose midazolam gel formulation (50 mg/mL) was administered (0.2 mg/kg, IN) to group 4. Each dog received all 4 treatments; there was a 7-day washout period between subsequent treatments. Blood samples were collected before and after midazolam administration. Plasma concentration of midazolam was determined by use of high-performance liquid chromatography. The peak plasma concentration after IN administration of the gel formulation was significantly higher than that after IN and rectal administration of the solution. Mean ± SD time to peak concentration was 11.70 ± 2.63 minutes (gel IN), 17.50 ± 2.64 minutes (solution IN), and 39 ± 14.49 minutes (solution rectally). Mean bioavailability of midazolam was 70.4% (gel IN), 52.0% (solution IN), and 49.0% (solution rectally). Bioavailability after IN administration of the gel formulation was significantly higher than that after IN and rectal administration of the solution. IN administration of midazolam gel was superior to both IN and rectal administration of midazolam solution with respect to peak plasma concentration and bioavailability.

Effect of critical illness on the pharmacokinetics and dose-response relationship of midazolam

Critically ill patients require sedation to tolerate the interventions necessary to facilitate their care. There is growing evidence, however, that use of sedatives, such as the benzodiazepine midazolam, is associated with delirium and other complications that can lead to prolonged ICU stay and increased mortality. The pharmacokinetics of midazolam in healthy populations has been well characterized, and pharmacodynamic studies demonstrate a predictable dose-response relationship. However, in critical illness, where midazolam is often administered as a continuous infusion, the pharmacokinetic properties are often altered. We sought to investigate whether analysis of midazolam plasma concentrations in combination with electroencephalography (EEG) will better define the effect of critical illness on the pharmacokinetics and clinical response to midazolam, while providing a method to assess the adequacy of sedation thereby minimizing the risks associated with prolonged or over-sedation.

Effects of the CYP Oxidoreductase Ala503Val Polymorphism on CYP3A Activity In Vivo: A Randomized, Open-Label, Crossover Study in Healthy Chinese Men

Background Cytochrome P450 (CYP) oxidoreductase (POR) is the electron donor for microsomal CYP enzymes. The POR Ala503Val ( POR*28 C > T) polymorphism has been reported to influence CYP3A activity in vivo in a white population. The influence of this polymorphism on CYP3A activity in vivo in the Chinese population currently unknown. Objective This study was designed to assess the influence of the POR*28 polymorphism on the CYP3A activity in vivo in healthy Chinese men using midazolam (MID) as a probe drug. Methods The POR*28 polymorphism was genotyped in healthy Chinese men. A randomized, 2-phase, open-label, crossover study was performed to assess in vivo CYP3A activity after both oral and intravenous MID administration, which reflect both intestinal and hepatic CYP3A or only hepatic CYP3A activity, respectively. The plasma concentrations of MID and 1-hydroxy-midazolam (1-OH-MID) were determined by liquid chromatography–tandem mass spectrometry. Results A total of 73 healthy Chinese men were enrolled (CC genotype, 21 subjects; TT genotype, 11; CT genotype, 41), 22 of whom were selected for additional phenotyping of the CYP3A5*3 polymorphism (CC, 7; TT, 8; CT, 7). The mean (range) age, weight, height, and body mass index of the 22 subjects were 23 (20–28) years, 65.0 (57–75) kg, 1.74 (1.63–1.80) m, and 22.01 (19.27–24.46) kg/m 2, respectively. The frequency of the POR*28 T (503V) allele was 43.2%. No significant differences in the demographic characteristics of the subjects were observed between the POR*28 genotype groups. All of the POR*28 CC and TT homozygotes and 2 of the POR*28 CT heterozygotes carried the CYP3A5*3/*3 genotype (CYP3A5 low expressors); 6 CT heterozygotes carried the CYP3A5*1 allele (CYP3A5 expressors). The mean (SD) 1-OH-MID AUC 0–8 was significantly greater in the TT homozygotes compared with the CT heterozygotes after intravenous (86.15 [24.34] vs 53.21 [31.36] ng/mL/h; P = 0.026) but not oral (126.36 [31.60] vs 103.09 [31.00] ng/mL/h; P = 0.159) MID administration. Mean 1-OH-MID C max was significantly greater in the TT homozygotes (51.40 [10.72] ng/mL) compared with the CC homozygotes (31.47 [11.54] ng/mL; P = 0.002) and CT heterozygotes (30.12 [9.21] ng/mL; P = 0.001) after intravenous MID administration. After intravenous MID injection, the MID metabolic ratio was significantly greater in the TT homozygotes compared with carriers of the C allele ( P = 0.031). Based on these findings, no significantly differences in overall (hepatic plus intestinal) CYP3A in vivo activity were observed between the POR*28 genotypes. Conclusion These findings suggest that individuals with the POR*28 C > T polymorphism underwent an increase in 1-hydroxylation of MID after intravenous MID administration, and that the polymorphism was associated with increased hepatic, but not intestinal, CYP3A activity in these healthy Chinese volunteers.

Inhibitory Effects of Continuous Ingestion of Schisandrin A on CYP3A in the Rat

The objective of this study was to evaluate the ability of schisandrin A (SchA) to inhibit the P450 enzyme CYP3A in vivo. Male Sprague-Dawley rats were intragastrically administered with varied doses of SchA (8 mg/kg or 16 mg/kg or 32 mg/kg) or 75 mg/kg ketoconazole for three consecutive days. Ketoconazole, a chemical inhibitor of CYP3A, was used as positive control. Subsequently, changes in hepatic microsome CYP3A activity and the pharmacokinetic profiles of midazolam (MDZ), a specific CYP3A substrate, were studied as indicators of rat hepatic microsomal activity of CYP3A. Differences in the plasma concentrations of MDZ and its related metabolites and the hepatic microsome concentrations of 1'-hydroxymidazolam were analysed by high-performance liquid chromatography. The current results provide direct and explicit evidence that SchA produced concentration-dependent inhibition of MDZ metabolite formation in rat liver microsomes (p < 0.01 or p < 0.001). Regular SchA consumption also caused concentration-dependent increase in Cmax and area under the concentration-time curve (AUC0-t and AUC0-∞ ) of peroral MDZ (p < 0.05 or p < 0.01) compared to vehicle-treated rats, whereas those of its metabolites (1'-hydroxymidazolam) were reduced (p < 0.05 or p < 0.01). Analysis of the data suggests that changes in the pharmacokinetic profiles of peroral MDZ in the rat model were contributed mainly to SchA inhibition of CYP3A activity. These results suggest that SchA, as an inhibitor of CYP3A, possesses a clinically beneficial property of altering the disposition of drugs metabolized by CYP3A.

The effect of midazolam on the end-tidal concentration of isoflurane necessary to prevent movement in dogs

ObjectiveTo determine the possible additive effect of midazolam, a GABAA agonist, on the end-tidal concentration of isoflurane that prevents movement (MACNM) in response to noxious stimulation. Study designRandomized cross-over experimental study. AnimalsSix healthy, adult intact male, mixed-breed dogs. MethodsAfter baseline isoflurane MACNM (MACNM-B) determination, midazolam was administered as a low (LDS), medium (MDS) or high (HDS) dose series of midazolam. Each series consisted of two dose levels, low and high. The LDS was a loading dose (Ld) of 0.2 mg kg−1 and constant rate infusion (CRI) (2.5 μg kg−1 minute−1) (LDL), followed by an Ld (0.4 mg kg−1) and CRI (5 μg kg−1 minute−1) (LDH). The MDS was an Ld (0.8 mg kg−1) and CRI (10 μg kg−1 minute−1) (MDL) followed by an Ld (1.6 mg kg−1) and CRI (20 μg kg−1 minute−1) (MDH). The HDS was an Ld (3.2 mg kg−1) and CRI (40 μg kg−1 minute−1) (HDL) followed by an Ld (6.4 mg kg−1) and CRI (80 μg kg−1 minute−1) (HDH). MACNM was re-determined after each dose in each series (MACNM-T). ResultsThe median MACNM-B was 1.42. MACNM-B did not differ among groups (p > 0.05). Percentage reduction in MACNM was significantly less in the LDS (11 ± 5%) compared with MDS (30 ± 5%) and HDS (32 ± 5%). There was a weak correlation between the plasma midazolam concentration and percentage MACNM reduction (r = 0.36). Conclusion and clinical relevanceMidazolam doses in the range of 10–80 μg kg−1 minute−1 significantly reduced the isoflurane MACNM. However, doses greater than 10 μg kg−1 minute−1 did not further decrease MACNM indicating a ceiling effect.

Assessment of oral midazolam limited sampling strategies to predict area under the concentration time curve (AUC) during cytochrome P450 (CYP) 3A baseline, inhibition and induction or activation

A previous study reported a 2- and 3-timepoint limited sampling strategy (LSS) model accurately predicted oral midazolam area under the concentration time curve (AUC), and thus cytochrome P450 (CYP) 3A activity. This study evaluated whether the LSS models predict midazolam AUC during CYP3A baseline, inhibition and induction/activation. Plasma midazolam concentrations from 106 healthy adults from 6 published studies were obtained where oral midazolam was co-administered alone or with ketoconazole, double-strength grapefruit juice, Ginkgo biloba extract, pleconaril, or rifampin. Observed and predicted midazolam AUCs were determined. Bias and precision of the LSS models were determined. Contrasting results were observed for the 2- and 3-timepoint LSS models in accurately predicting midazolam AUC during baseline CYP3A conditions. With the exception of 1 study (single dose, double-strength grapefruit juice), the 2- and 3-timepoint LSS models did not accurately predict midazolam AUC during conditions of CYP3A inhibition and induction/activation. The previously reported 2- and 3-timepoint oral midazolam LSS models are not applicable to the evaluated conditions of CYP3A baseline, inhibition, and induction/ activation.

Evaluation of the pharmacokinetic interaction of midazolam with ursodeoxycholic acid, ketoconazole and dexamethasone by brain benzodiazepine receptor occupancy

To clarify whether alterations in midazolam pharmacokinetics resulting from changes in cytochrome P450 3A (CYP3A) activity lead to changes in its pharmacodynamic effects, benzodiazepine receptor occupancy was measured in the brain of rats after oral administration of midazolam. Receptor occupancy was measured by radioligand binding assay in rats pretreated with ursodeoxycholic acid (UDCA), ketoconazole and dexamethasone, and the plasma concentration of midazolam was simultaneously determined. There was a significant increase in the apparent dissociation constant and decrease in the maximum number of binding sites for specific [(3) H]flunitrazepam binding after oral administration of midazolam at pharmacologically relevant doses, suggesting that midazolam binds significantly to brain benzodiazepine receptors. Pretreatment with UDCA significantly enhanced the binding. This correlated well with significant enhancement by UDCA of the plasma midazolam concentration. The brain benzodiazepine receptor binding of oral midazolam was significantly enhanced by pretreatment with ketoconazole, a potent inhibitor of CYP3A, whereas it was significantly reduced by treatment with dexamethasone, an inducer of this enzyme. These effects paralleled changes in the plasma concentration of midazolam. The results indicate that pharmacokinetic changes such as altered CYP3A activity significantly influence the pharmacodynamic effect of midazolam by affecting occupancy of benzodiazepine receptors in the brain. They also suggest in-vivo or ex-vivo time-dependent measurements of receptor occupancy by radioligand binding assay to be a tool for elucidating the pharmacokinetic interaction of benzodiazepines with other agents in pre-clinical and clinical evaluations.

Liposome-encapsulated midazolam for oral administration

The oral administration of midazolam has often been used for sedation in pediatric patients. However, oral administration of an intravenous formulation of midazolam is difficult for younger pediatric patients because of its bitter taste. Liposomes have been developed as vesicles encapsulating various kinds of drugs to serve as a medical drug-delivery system. Thus, the aim of the present study was to produce pH-sensitive liposomes encapsulating midazolam and to evaluate its pharmacokinetics on rabbits. Liposome-encapsulated midazolam was produced from hydrogenated L-α-phosphatidylcholine, cholesterol, dipalmitoylphosphatidic acid, and midazolam. The capacity of liposomes to encapsulate midazolam (encapsulation efficiency), stability of encapsulation, and release efficiency were evaluated in vitro. Further, the produced liposome-encapsulated midazolam solution was orally administered to rabbits in vivo. As a result, midazolam was encapsulated by liposomes with a high encapsulation efficiency and was stably encapsulated in a physiological medium. Further, the produced liposomes rapidly and effectively released midazolam in an acidic medium in vitro. When the liposome-encapsulated midazolam solution was orally administered to rabbits, the time to achieve the maximum plasma concentration of midazolam after administration was slightly longer, but both the maximum plasma concentration and area under the concentration-time curve were higher than those receiving midazolam solution. In conclusion, we produced pH-sensitive liposome-encapsulated midazolam, which remained stable in a physiological medium and showed efficient release in an acidic environment. The results suggest that it is possible to clinically use liposome-encapsulated midazolam for oral administration as a useful drug-delivery vehicle.

Propofol Reduces the Distribution and Clearance of Midazolam

Midazolam, at sedative levels, increases blood propofol concentrations by 25%. We evaluated the reverse interaction and determined the influence of propofol on the pharmacokinetics of midazolam. Eight healthy male volunteers were studied on 2 occasions in a random crossover manner. During session A, volunteers received midazolam 0.035 to 0.05 mg x kg(-1) IV for 1 minute followed by an infusion of 0.035 to 0.05 mg x kg(-1) x h(-1) for 59 minutes. During session B, in addition to this midazolam infusion scheme, a target-controlled infusion of propofol (constant C(T): 0.6 or 1.0 microg x mL(-1)) was given from 15 minutes before the start until 6 hours after termination of the midazolam infusion. Arterial blood samples for propofol and midazolam concentration analysis were taken until 6 hours after termination of the midazolam infusion. Nonlinear mixed-effect models examining the influence of propofol and hemodynamic variables on midazolam pharmacokinetics were constructed using Akaike's information-theoretic criterion for model selection. In the presence of a mean blood propofol concentration of 1.2 microg x mL(-1), the plasma midazolam concentration was increased by 26.9% + or - 9.4% compared with midazolam given as a single drug. Propofol (C(blood): 1.2 microg x mL(-1)) reduced midazolam central volume of distribution from 5.37 to 2.98 L, elimination clearance from 0.39 to 0.31 L x min(-1), and rapid distribution clearance from 2.77 to 2.11 L x min(-1). Inclusion of heart rate further improved the pharmacokinetic model of midazolam. Propofol reduces the distribution and clearance of midazolam in a concentration-dependent manner. In addition, inclusion of heart rate as a covariate improved the pharmacokinetic model of midazolam predominantly through a reduction in the intraindividual variability.

The effect of midazolam on neutrophil mitogen-activated protein kinase

Neutrophil p38 mitogen-activated protein kinase (MAPK) is a key enzyme in the intracellular signalling pathway that is responsible for many neutrophil functions, which are important in neutrophil-endothelial interaction. The imidazole compounds are inhibitors of this enzyme system. The objectives of this in-vitro investigation were to examine the effect of midazolam on neutrophil p38 MAPK activation (phosphorylation) following in-vitro ischaemia-reperfusion injury, and the expression of adhesion molecule CD11b/CD18. In-vitro injury was produced by incubating the neutrophils with N-formyl-methionyl-leucyl-phenylalanine. Neutrophils were treated with either 10 or 50 times the therapeutic plasma concentrations of midazolam and SB203580 (known inhibitor of p38 MAPK). The concentrations of phosphorylated p38 MAPK and expression of neutrophil adhesion molecules CD11b/CD18 were measured. Flow cytometry was used to estimate adhesion molecule expression. The concentration of phosphorylated p38 MAPK was less in neutrophils subjected to ischaemia-reperfusion and treated with midazolam either 10 microg ml [13.6 (3.2) ng ml] or 50 microg ml [12.4 (3.6) ng ml], or SB203580 [13 (2.6) ng ml] than those subjected to ischaemia-reperfusion alone [18 (3.18) ng ml] at a P value of less than 0.05.Following ischaemia-reperfusion injury, CD11b/CD18 expression (expression mean channel fluorescence) on neutrophils was greater when compared with controls. The magnitudes of CD11b and CD18 expression on ischaemia-reperfusion-injured neutrophils were decreased by midazolam (10 microg ml) as compared with control of 10.3 (2.6) vs. 14 (3.1) microg ml and 28.3 (12.9) vs. 44 (12.1) microg ml, respectively, at a P value of less than 0.05. Similarly, the expression of CD11b and CD18 was less in ischaemia-reperfusion-injured neutrophils treated with inhibitor of 10.3 (2.8) vs. 14 (3.18) microg ml and 29.5 (12.5) vs. 44.3 (12.3) microg ml when compared with controls at a P value of less than 0.05. Midazolam diminishes in-vitro ischaemia-reperfusion-induced phosphorylation of p38 MAPK in neutrophils. This decrease in p38 MAPK activation results in decreased neutrophil CD11b/CD18 molecule expression.