Midazolam Plasma Research Articles

No clinically relevant CYP3A induction after St. John’s wort with low hyperforin content in healthy volunteers

Induction of CYP3A by St. John's wort (SJW) products with high hyperforin content is well described. Since CYP3A induction is mediated by hyperforin in a concentration-dependent manner, and SJW preparations differ significantly in hyperforin content, the aim of the study was to evaluate the effect of an SJW powder with low hyperforin content on CYP3A function. Twenty healthy male volunteers received an SJW powder with low hyperforin content for 2 weeks. Midazolam plasma concentration time profiles were characterized after a single oral dose of 7.5 mg midazolam on the day before and on the 14th day of SJW medication. Midazolam AUC(0-infinity) slightly decreased from 124.0 +/- 62.5 ng/ml.h at baseline to 105.6 +/- 53.2 ng/ml.h after SJW (P < 0.05), representing a mean 11.3% decrease (95% CI: -22.8 to 0.21). No significant change in midazolam C(max), t(1/2) and t(max) was observed. For all pharmacokinetic parameters, the 90% CI for the geometric mean ratio of treatment over baseline were within the no-effect boundaries of 0.70-1.43. Administration of an SJW product with low hyperforin content resulted in a mild induction of CYP3A not considered clinically relevant.

Pharmacokinetics and clinical efficacy of midazolam in children with severe malaria and convulsions

AIMTo investigate the pharmacokinetics and clinical efficacy of intravenous (IV), intramuscular (IM) and buccal midazolam (MDZ) in children with severe falciparum malaria and convulsions.METHODSThirty-three children with severe malaria and convulsions lasting ≥5 min were given a single dose of MDZ (0.3 mg kg−1) IV (n = 13), IM (n = 12) or via the buccal route (n = 8). Blood samples were collected over 6 h post-dose for determination of plasma MDZ and 1′-hydroxymidazolam concentrations. Plasma concentration–time data were fitted using pharmacokinetic models.RESULTSMedian (range) MDZ Cmax of 481 (258–616), 253 (96–696) and 186 (64–394) ng ml−1 were attained within a median (range) tmax of 10 (5–15), 15 (5–60) and 10 (5–40) min, following IV, IM and buccal administration, respectively. Mean (95% confidence interval) of the pharmacokinetic parameters were: AUC(0,∞) 596 (327, 865), 608 (353, 864) and 518 (294, 741) ng ml−1 h; Vd 0.85 l kg−1; clearance 14.4 ml min−1 kg−1, elimination half-life 1.22 (0.65, 1.8) h, respectively. A single dose of MDZ terminated convulsions in all (100%), 9/12 (75%) and 5/8 (63%) children following IV, IM and buccal administration. Four children (one in the IV, one in the IM and two in the buccal groups) had respiratory depression.CONCLUSIONSAdministration of MDZ at the currently recommended dose resulted in rapid achievement of therapeutic MDZ concentrations. Although IM and buccal administration of MDZ may be more practical in peripheral healthcare facilities, the efficacy appears to be poorer at the dose used, and a different dosage regimen might improve the efficacy. WHAT IS ALREADY KNOWN ABOUT THIS SUBJECTMidazolam (MDZ), a water-soluble benzodiazepine, can be administered via several routes, including intravenously (IV), intramuscularly (IM) and buccal routes to terminate convulsions. It may be a suitable alternative to diazepam to stop convulsions in children with severe malaria, especially at peripheral healthcare facilities. The pharmacokinetics of MDZ have not been described in African children, in whom factors such as the aetiology and nutritional status may influence the pharmacokinetics.WHAT THIS STUDY ADDS Administration of MDZ (IV, IM, or buccal) at the currently recommended dose (0.3 mg kg−1) resulted in rapid achievement of median maximum plasma concentrations of MDZ within the range 64–616 ng ml−1, with few clinically significant cardio-respiratory effects. A single dose of MDZ rapidly terminated (within 10 min) seizures in all (100%), 9/12 (75%) and 5/8 (63%) children following IV, IM and buccal administration, respectively. Although IM and buccal MDZ may be the preferred treatment for children in the pre-hospital settings the efficacy appears to be poorer.

Investigation of the in vivo activity of CYP3A in Brazilian volunteers: comparison of midazolam and omeprazole as drug markers

This study compares midazolam with omeprazole as marker drugs for the evaluation of CYP3A activity in nine healthy self-reported white Brazilian volunteers. Omeprazole was also used to evaluate the CYP2C19 phenotype. The volunteers received p.o. 20 mg omeprazole, and blood samples were collected 3.5 h after drug administration. After a washout period of 10 days, the volunteers received p.o. 15 mg midazolam maleate, and serial blood samples were collected up to 6 h after administration of the drug. CYP2C19 was genotyped for the allelic variants CYP2C19*1, CYP2C19*2, CYP2C19*3, and CYP2C19*17. Analysis of omeprazole, hydroxyomeprazole, omeprazole sulfone, and midazolam in plasma was carried out by LC-MS/MS. The volunteers genotyped as CYP2C19*1*17, CYP2C19*17*17, CYP2C19*1*1 (n = 8), or CYP2C19*17*2 (n = 1) presented a median hydroxylation index (omeprazole/hydroxyomeprazole) of 1.35, indicating that all of them were extensive metabolizers of CYP2C19. The volunteers (n = 9) presented a 0.12 log of the omeprazole/sulfone ratio and a median oral clearance of midazolam of 17.89 ml min(-1) kg(-1), suggesting normal CYP3A activity. Orthogonal regression analysis between midazolam clearance and log of the plasma concentrations of the omeprazole/omeprazole sulfone ratio (R = -0.7544, P < 0.05) suggests that both midazolam and omeprazole can be used as markers of CYP3A activity in the population investigated.

Influence of CYP3A5 Genotype on the Pharmacokinetics and Pharmacodynamics of the Cytochrome P4503A Probes Alfentanil and Midazolam

The hepatic and first-pass cytochrome P4503A (CYP3A) probe alfentanil (ALF) is also metabolized in vitro by CYP3A5. Human hepatic microsomal ALF metabolism is higher in livers with at least one CYP3A5*1 allele and higher CYP3A5 protein content, compared with CYP3A5*3 homozygotes with little CYP3A5. The influence of CYP3A5 genotype on ALF pharmacokinetics and pharmacodynamics was studied, and compared to midazolam (MDZ), another CYP3A probe. Healthy volunteers (58 men, 41 women) were genotyped for CYP3A5 *1, *3, *6, and *7 alleles. They received intravenous MDZ then ALF, and oral MDZ and ALF the next day. Plasma MDZ and ALF concentrations were determined by mass spectrometry. Dark-adapted pupil diameters were determined coincident with blood sampling. In CYP3A5(*)3/(*)3 (n=62), (*)1/(*)3 (n=28), and (*)1/(*)1 (n=8) genotypes, systemic clearances of ALF were 4.6+/-1.8, 4.8+/-1.7, and 3.9+/-1.7 ml/kg/min and those of MDZ were 7.8+/-2.3, 7.7+/-2.3, and 6.0+/-1.4 ml/kg/min, respectively (not significant), and apparent oral clearances were 11.8+/-7.2, 13.3+/-6.1, and 12.6+/-8.2 ml/kg/min for ALF and 35.2+/-19.0, 36.4+/-15.7, and 29.4+/-9.3 ml/kg/min for MDZ (not significant). Clearances were not different between African Americans (n=25) and Whites (n=68), or between CYP3A5 genotypes within African Americans. ALF pharmacodynamics was not different between CYP3A5 genotypes. There was consistent concordance between ALF and MDZ, in clearances and extraction ratios. Thus, in a relatively large cohort of healthy subjects with constitutive CYP3A activity, CYP3A5 genotype had no effect on the systemic or apparent oral clearances, or pharmacodynamics, of the CYP3A probes ALF and MDZ, despite affecting their hepatic microsomal metabolism.

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.

Relationship between cytochrome 3A activity, inflammatory status and the risk of docetaxel-induced febrile neutropenia: a prospective study

We hypothesized that cancer-related inflammation might increase the risk of febrile neutropenia (FN) induced by docetaxel (DCX, Taxotere), by both affecting the exposure to DCX and the tissue sensitivity. Advanced cancer patients with normal liver function, performance status (PS)<3, were included. Cytochrome P450 3A (CYP 3A) activity was estimated before the first cycle of DCX by a single determination of midazolam plasma concentration, 4 hours after 0.015 mg/kg i.v. bolus. Following the first cycle of 75-100 mg/m2 DCX, clearance and area under the concentration versus time curve (AUC) were estimated using a limited sampling strategy. Among 56 assessable patients, 7 FNs occurred after first cycle (13%). In univariate analysis, high midazolam concentration and free DCX AUC were associated with severe neutropenia and FN. In addition to DCX exposure-related parameters, the risk of FN was also correlated with poor PS, baseline lymphopenia and lung cancer, while high ferritin level, indicator of an inflammatory state, reached borderline significance (P=0.07). By multivariate analysis, total DCX AUC and baseline lymphopenia were associated with FN. High midazolam concentration was correlated with elevated ferritin level (r=0.32; P=0.02). Inflammatory status and lymphocyte count should be included in the evaluation of the benefice/risk ratio before the initiation of DCX.

Atmospheric pressure desorption/ionization on silicon ion trap mass spectrometry applied to the quantitation of midazolam in rat plasma and determination of midazolam 1′‐hydroxylation kinetics in human liver microsomes

The application of atmospheric pressure desorption/ionization on silicon (AP-DIOS) coupled with ion trap mass spectrometry (ITMS) was investigated for the quantification of midazolam in rat plasma, and determination of midazolam 1'-hydroxylation kinetics in pooled human liver microsomes. Results indicate good sensitivity with absolute detection limits for midazolam in rat plasma of approximately 300 femtograms. A linear dynamic range from approximately 10-5000 ng/mL was obtained in rat plasma with analysis times of 1 min per sample. Kinetic constants for midazolam 1'-hydroxylation in human liver microsomes yielded an apparent Km of 10.0 microM and Vmax of 6.4 nmol/min/mg. Studies investigating the inhibition of 1'-hydroxymidazolam formation by the cytochrome P450 3A4 model inhibitor ketoconazole yielded an IC50 of 0.03 microM. Quantitative precision for replicate analysis of rat plasma and human liver microsomal samples was variable with relative standard deviation (RSD) values ranging from a low of approximately 3% to over 50%, with the highest variability observed in data from human liver microsomal incubations. While preliminary studies investigating the application of AP-DIOS-ITMS suggested feasibility of this technique to typical pharmacokinetic applications, further work is required to understand the underlying causes for the high variability observed in these investigations.

Pharmacokinetics and Pharmacodynamics of a New Intranasal Midazolam Formulation in Healthy Volunteers

We evaluated the pharmacokinetics and pharmacodynamics of single 5-mg doses of midazolam after administration of a novel intranasal (IN) formula, IM, and IV midazolam in an open-label, randomized, 3-way cross-over study in 12 healthy volunteers. IN doses were delivered as 0.1-mL unit-dose sprays of a novel formulation into both naris. Blood samples were taken serially from 0 to 12 h after each dose. Plasma midazolam concentrations were determined by liquid chromatography/mass spectrometry/mass spectrometry. Noncompartmental analysis was used to estimate pharmacokinetic parameters. The mean midazolam bioavailabilities and % coefficient of variation were 72.5 (12) and 93.4 (12) after the IN and IM doses, respectively. Median time to maximum concentration was 10 min for IN doses. Adverse events were minimal with all routes of administration, but nasopharyngeal irritation, eyes watering, and a bad taste were reported after IN doses. Our results support further development of this novel midazolam nasal spray.

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

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. 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. 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. 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. 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.

DURATION OF PLECONARIL EFFECT ON CYTOCHROME P450 3A ACTIVITY IN HEALTHY ADULTS USING THE ORAL BIOMARKER MIDAZOLAM

The objective of this study was to evaluate the duration of oral pleconaril (a picornavirus inhibitor) effect on intestinal and hepatic cytochrome P450 (P450) 3A activity as assessed by oral midazolam. Healthy adults received oral midazolam (0.075 mg/kg) on days 1 (baseline), 7, 9, 13, 20, 27, and 34. Oral pleconaril (400 mg) three times daily for 15 doses was administered on days 2 through 7. Blood samples were collected during each day of midazolam dosing to determine plasma midazolam concentrations. On days 5, 6, and 7, blood samples were collected to determine plasma pleconaril concentrations. Midazolam pharmacokinetics were determined by noncompartmental analyses, with bioequivalence assessed by least-squares geometric mean ratios (LS-GMR) and 90% confidence intervals (90% CI). Eighteen subjects completed the study. Midazolam C(max) (LS-GMR; 90% CI) decreased 24% on day 7 (0.76; 0.66-0.87). Midazolam oral clearance increased 53% on day 7 (1.53; 1.38-1.69). Midazolam oral clearance remained different on days 9 (1.38; 1.25-1.52) and 13 (1.19; 1.07-1.31) versus day 1. Midazolam volume of distribution (1.82; 1.57-2.11) and elimination half-life (1.19; 1.03-1.38) were also different on day 7 in comparison with day 1. Oral pleconaril increased intestinal and hepatic CYP3A activity. The duration of increased CYP3A activity by pleconaril was at least 6 days (but no longer than 13 days) after pleconaril discontinuation.

OII-C-4Midazolam elimination in human breast milk

BACKGROUND Lactating women undergoing operations under general anesthesia are advised to pump and discard their milk for 24h after the procedure. We determined the kinetics of midazolam elimination in breast milk to ascertain its safety after midazolam administration. METHODS Five lactating women were studied after providing institutionally-approved written informed consent. Patients were premedicated with midazolam, 2 mg IV, 5 min before anesthetic induction with fentanyl, 100 μg IV, and propofol, 2.5 mg/kg IV. Anesthesia was maintained with potent volatile anesthetics. Milk was collected using an electric breast pump before and at 5, 7, 9, 11, and 24h after drug administration. Blood samples were collected before and at regular intervals up to 7h after drug administration. Plasma and milk midazolam concentrations were measured by LC-MS. Midazolam elimination in milk was modelled simultaneously with the plasma kinetics as the cumulative amount of drug in milk just as urinary elimination is modelled, albeit with a delay. RESULTS Plasma midazolam pharmacokinetics were consistent with those reported by ourselves and others. In 24h of milk collection, only 0.005 (± 0.005)% of the midazolam dose was eliminated in milk, representing 0.009 (± 0.005)% of the midazolam elimination clearance with a pharmacokinetic delay of approximately 9h. CONCLUSION The amount of midazolam appearing in breast milk over 24h after administering a single dose is very small and unlikely to affect a healthy term infant. Clinical Pharmacology & Therapeutics (2005) 79, P7–P7; doi: 10.1016/j.clpt.2005.12.021

OV-A-4Induction of cytochrome P450 3A4 (CYP3A4) by vinblastine: Role of the nuclear receptor NR1I2

BACKGROUND Metabolism of the anticancer agent vinblastine is mediated by CYP3A4. It has been demonstrated that other microtubule stabilizing agents such as paclitaxel are capable of inducing this enzyme via activation of NR1I2 (hPXR). Therefore, we evaluated the CYP3A4 induction potential of vinblastine both clinically and in vitro. METHODS The pharmacokinetics of the CYP3A4 phenotyping probe midazolam (i.v. bolus, 0.0145 mg/kg) were determined in 6 patients with renal cell cancer undergoing treatment with vinblastine (72-h i.v. q4w) at baseline and in cycle 3. Midazolam plasma concentrations were measured by LC/MS and clearance (CL) was derived using non-compartmental analysis. Protein expression of CYP3A4 and activation of hPXR by vinblastine were measured by Western blotting and a transactivation assay using transiently transfected HepG2 cells, respectively (Mani et al, Clin Cancer Res 11:6359, 2005). RESULTS Vinblastine increased midazolam CL on average by 60% (range, 2–317%; P=0.0156, Wilcoxon test). In vitro, vinblastine at clinically-relevant concentrations induced CYP3A4 and the hPXR-ligand binding domain, but had only weak to no effect on full length hPXR, suggesting it is only a weak activator of hPXR. CONCLUSIONS Vinblastine is able to induce CYP3A4 in vivo and thus has the potential to facilitate its own elimination and cause interactions with other CYP3A4 substrates. The mechanism of protein induction is likely to be at the level of RNA stabilization or decreased protein turnover. Clinical Pharmacology & Therapeutics (2005) 79, P35–P35; doi: 10.1016/j.clpt.2005.12.125

Limited Sampling Models for Oral Midazolam: Midazolam Plasma Concentrations, Not the Ratio of 1‐Hydroxymidazolam to Midazolam Plasma Concentrations, Accurately Predicts AUC as a Biomarker of CYP3A Activity

Oral midazolam is used as a phenotyping probe for cytochrome P450 (CYP) 3A activity and requires multiple plasma samples to measure drug exposure. Limited sampling is a useful strategy for optimizing sampling and reducing costs and labor. We studied limited sampling models using multiple linear regressions to predict the area under the concentration versus time curve (AUC) of midazolam using either midazolam plasma concentrations or the ratio of 1-hydroxymidazolam (1-OH MDZ) to midazolam plasma concentrations. CYP3A baseline activity data for oral midazolam from previous studies were used (45 healthy adults for models using midazolam plasma concentrations and 41 healthy adults for models using the ratios of 1-OH MDZ to midazolam plasma concentrations). Limited sampling models were derived, validated, and evaluated for precision and bias. Two equations using the time points at 0.5 and 6 hours and 0.5, 2, and 6 hours were acceptable and predictive of midazolam AUC using midazolam plasma concentrations. No 1-OH MDZ to midazolam plasma concentration ratios accurately predicted midazolam AUC.

The extent of induction of CYP3A by St. John’s wort varies among products and is linked to hyperforin dose

Induction of CYP3A by St. John's wort (SJW) extracts with high hyperforin (HYF) content is well described. Since SJW products vary in the amount of HYF and other main constituents, the aim of the study was to evaluate the effect on CYP3A function of SJW preparations with a range from very low to high HYF content. Forty-two male, healthy volunteers were randomized into six parallel SJW medication groups with varying composition especially with regard to HYF content. Midazolam plasma concentration profiles were characterized after a single oral dose of 7.5 mg midazolam on the day before and on the 14th day of SJW medication. All SJW preparations tested resulted in a decrease in midazolam AUC, although the extent of the effect differed. The extract LI 160 (HYF 41 mg/day) decreased midazolam AUC0-12h by 79.4% (95% CI -88.6; -70.1), which was significantly greater than the effect by any other medication (p<0.05). SJW powder tablets 2.7 g/day (HYF 12 mg/day) resulted in a midazolam AUC0-12h decrease of 47.9% (95% CI -59.7;-36.2), while 2.7 g/day SJW powder tablets that were almost devoid of HYF (0.13 mg/day) reduced midazolam AUC0-12h by only 21.1% (95% CI -33.9; -8.3). Considering all six SJW medications tested, the extent of midazolam AUC decrease correlated significantly with increasing HYF dose (r=-0.765, p<0.001), but not with hypericin dose (r=-0.067; p=0.673). The extent of induction of CYP3A varies among St. John's wort products and depends on hyperforin dose.

Analysis of omeprazole, midazolam and hydroxy-metabolites in plasma using liquid chromatography coupled to tandem mass spectrometry

A method has been developed and validated for the quantitation of midazolam, alphahydroxy-midazolam, omeprazole, and hydroxyomeprazole from one 250 microL sample of human plasma using high performance liquid chromatography coupled to tandem mass spectrometry. The method was validated for a daily working range of 0.400-100 ng/mL, with limits of detection between 2 and 15 pg/mL. The inter-assay variation was less than 15% for all analytes at four control concentrations and the samples were stable for three freeze-thaw cycles under the analysis conditions and 24 h in the post-preparative analysis matrix. This method was used to analyze samples in support of clinical studies probing the activity of the cytochrome P-450 enzyme system.

Prospective study of predictive factors of docetaxel (DCX)-induced febrile neutropenia (FN): Relevance of in vivo cytochrome 3A (CYP3A) phenotyping

2046 Background: FN is a rare but severe side effect of DCX, remaining unpredictable. DCX is metabolised by CYP3A which displays high inter-individual variability. We studied the respective role of baseline characteristics of the patient and CYP3A phenotype on the risk of DCX-induced FN. We hypothesized that inflammation and/or denutrition might affect CYP3A activity and the risk of FN. Methods: Eligibility criteria included cancer for which DCX was indicated, normal liver function, performance status (PS) < 3. CYP3A activity was estimated by a single determination of midazolam plasma concentration (MPC), 4 H after 0.015 mg/kg IV bolus. Ferritine plasma concentration and nutritional and inflammatory status (NIS) ratio, defined as (C-reactive protein x alpha-1 acid glycoprotein)/(albumin x prealbumin) were evaluated at baseline. DCX 75–100 mg/m2 was administered. Occurrence of FN evaluated after the first cycle, was defined as fever ≥ 38.5°C associated to neutropenia <1.0x109/L. Kruskal-Wallis test and exact logistic regression were used for univariate and multivariate analysis, respectively. Results: 58 patients (F/M: 29/29; 31% breast, 29% prostate, 20% lung and 20% other cancers) with median age 61 years (47–75) were included.; FN occurred in 7 patients (12%). In univariate analysis, variables associated to increased risk of FN were: high MPC, poor PS, low lymphocytes count baseline values (p<.05). Statistical association reached border-line significance for high baseline ferritine plasma concentration and NIS ratio (p=0.06 and 0.08, respectively). Age, dose of DCX and site of primary tumor were not associated to increased risk of FN. In multivariate analysis, only MPC remained significantly associated to increased risk of FN. High MPC was correlated with high ferritine level (r=0.32, p=0.02). Conclusion: In vivo CYP3A phenotyping using the dosage of MPC may be a potent and useful predictive factor for DCX-induced FN. This parameter should be further evaluated in larger patient populations. No significant financial relationships to disclose.

Cerebral and plasma kinetics of a high dose of midazolam and correlations with its respiratory effects in rats

Benzodiazepine poisoning causes coma and respiratory depression. Our objective was to determine whether, and to what extent, arterial blood gas disturbances correlated with blood or cerebral kinetics of midazolam. A 160 mg kg −1 single dose of midazolam was infused intravenously over 20 min in catheterized male Sprague–Dawley rats. Midazolam kinetics was simultaneously determined in plasma and brain using striatal microdialysis. Midazolam concentrations were measured using a high-performance liquid chromatographic assay with ultraviolet detection. Midazolam (160 mg kg −1) reproducibly induced deep coma with respiratory acidosis. Plasma midazolam kinetics was well described by a bi-exponential model, with an elimination half-life of 6.4 ± 1.8 h. The striatal dialysate concentration peaked at 50.0 ± 8.9 min after the end of infusion, with a significant delay to peak concentration compared to plasma. Respiratory depression, assessed by the elevation in PaCO 2, was more closely correlated with midazolam striatal dialysate rather than plasma kinetics. These results suggest a central mechanism for midazolam respiratory effects at toxic doses in rats. In conclusion, our study showed a delayed onset in peak PaCO 2 and pH effects after the slow infusion of a toxic dose of midazolam in rats. The effects on arterial blood gases were better correlated with midazolam striatal concentrations than with plasma concentrations. This study may contribute to better understanding of benzodiazepine-induced respiratory depression in poisonings.

The ratio of 1-hydroxymidazolam (1-OH MDZ) to midazolam (MDZ) plasma concentrations is not an accurate measurement for CYP3A activity when using oral (PO) MDZ

Background The ratio of 1-OH MDZ to MDZ plasma concentrations has been proposed as an index to reduce sampling when measuring CYP3A activity. The aims of this study were to 1) assess if this ratio can be used to predict MDZ AUC when used as a CYP3A probe and 2) determine an optimal sampling strategy for the use of this ratio. Methods Data from 3 previous studies in 41 healthy adults were used. Subjects abstained from any drugs known to affect CYP3A. Plasma samples were collected at specified time points (Chr) after PO MDZ (0.075mg/kg) administration. 1-OH MDZ and MDZ concentrations were analyzed by LC/MS/MS. MDZ AUC0-∞ was determined by non-compartmental analysis. 20 subjects were randomly selected for the training set and the remaining 21 subjects for the validation set. The ratios of 1-OH MDZ to MDZ C0.5, 1, 2, 4, and 6 and AUC0-∞ were log-transformed. Stepwise multiple linear regression was used to derive equation models to predict MDZ AUC (AUCpred). Results One equation using C2 was statistically significant but had a low regression coefficient (R2=0.32): Log(AUCpred)=4.43–0.75[log(1-OH MDZ C2/MDZ C2)]. This equation did not meet the acceptable limits of bias and precision (Mean prediction error=−9.8%, Root mean square error=52.3%). Conclusions The ratio of 1-OH MDZ to MDZ plasma concentrations does not correlate with MDZ AUC and cannot be used to accurately predict MDZ exposure when PO MDZ is used as a CYP3A biomarker. Clinical Pharmacology & Therapeutics (2005) 77, P32–P32; doi: 10.1016/j.clpt.2004.12.016

Induction of CYP3A by St. Johns Wort (SJW) depends on hyperforin (HYF) dose

Background Induction of CYP3A by SJW with high HYF content is known. SJW products vary in the amount of main constituents. The aim of the study was to evaluate the influence of SJW preparations with low and high HYF content on CYP3A function. Methods A one-sequence crossover study was performed in 42 male, healthy volunteers, who were randomized into 6 SJW groups. Midazolam (MDZ) plasma concentration profiles were characterized after a single oral dose of 7.5 mg MDZ on the day before and on the 14th day of SJW medication. Results Effect of SJW on % change in MDZ AUC 0–12h compared to baseline, mean and 95% confidence interval (CI): (see Table) Decrease in MDZ AUC was correlated with HYF content (r= −0.78, p<0.01). Conclusion Induction of CYP3A varies between SJW products. SJW products with low HYF content induce CYP3A significantly less than high HYF SJW products. The degree of induction depends on HYF dose. Clinical Pharmacology & Therapeutics (2005) 77, P36–P36; doi: 10.1016/j.clpt.2004.12.031 SJW dose/d (HYF content mg/d) Mean % change 95 %-CI 900mg extract LI 160 (41.25) −79.4 −88.6; −70.1 2.7g plant (0.13) −21.1 −33.9; −8.3 2.7g plant (12.06) −47.9 −59.7; −36.2 1.8g plant (8.04) −37.0 −58.2; −15.8 1.2g plant (5.36) −31.3 −45.3; −17.3 0.6g plant (2.68) −20.4 −40.0; −0.8

Effects of posture (P) induced changes in hepatic blood flow (HBF) and plasma protein binding (PB) on the clearance (CL) of the intravenous (IV) cytochrome P450 3A (CYP3A) biomarker midazolam (MDZ)

Background Use of IV MDZ as a CYP3A probe assumes MDZ CL accurately reflects hepatic CYP3A activity. Because MDZ is a moderate hepatic extraction drug, P induced changes in HBF and/or MDZ plasma PB may affect MDZ CL. Methods 15 healthy, nonsmoking subjects were randomized to a crossover study of supine or ambulant (sitting, standing, walking) P. Fasting subjects received MDZ 0.025 mg/kg IV push and indocyanine green (ICG) 0.5 mg/kg IV to quantify HBF. 18 plasma samples were collected over 6 hr and analyzed by LC/MS/MS (MDZ), HPLC/UV (ICG), and ultra filtration (free MDZ; protein binding). Least squares geometric mean ratios (LS-GMR) and 90% CIs were compared by P. A paired t-test compared free MDZ concentrations and MDZ free fraction by P. Results 13 subjects (7 women) completed the study. (see Table) Correlation of MDZ CL and ICG CL in supine P was r=0.6 (p≤0.05) and ambulant P was r=0.11 (p=0.72). MDZ free fraction 30 min post MDZ and 3 min post ICG were not related to posture (p>0.05). Total MDZ CL did not correlate to MDZ free fraction (r=0.17; p=0.41). Conclusions P induced changes in HBF were minimal and thus the effect of HBF on MDZ CL was not seen. No relationship was observed between MDZ free fraction and MDZ CL. Clinical Pharmacology & Therapeutics (2005) 77, P33–P33; doi: 10.1016/j.clpt.2004.12.017 GM Supine GM Ambulant LS-GMR 90% CI ICG CL (mL/min) 617.8 605.9 0.98 0.86–1.1 MDZ CL (mL/min) 595.6 565.1 0.95 0.88–1.02 GM (SD) GM (SD) p-value Free MDZ (ng/mL)30 min post MPZ 0.25 (0.2, 0.3) 0.28 (0.21, 0.36) p = 0.07 Free MDZ (ng/mL)3 min post ICG 0.16 (0.13, 0.2) 0.16 (0.12, 0.23) p = 0.81