Urinary screening for midazolam and its major metabolites with the Abbott ADx and TDx analyzers and the EMIT d.a.u. benzodiazepine assay with confirmation by GC/MS

Ontogeny of Drug-Metabolizing Enzymes

Almost 50% of prescription drugs lack age-appropriate dosing guidelines and therefore are used "off-label." Only ~10% drugs prescribed to neonates and infants have been studied for safety or efficacy. Immaturity of drug metabolism in children is often associated with drug toxicity. This chapter summarizes data on the ontogeny of major human metabolizing enzymes involved in oxidation, reduction, hydrolysis, and conjugation of drugs. The ontogeny data of individual drug-metabolizing enzymes are important for accurate prediction of drug pharmacokinetics and toxicity in children. This information is critical for designing clinical studies to appropriately test pharmacological hypotheses and develop safer pediatric drugs, and to replace the long-standing practice of body weight- or surface area-normalized drug dosing. The application of ontogeny data in physiologically based pharmacokinetic model and regulatory submission are discussed.

Comparison of sedative effects of oral midazolam/chloral hydrate and midazolam/promethazine in pediatric dentistry

Background. The aim of this investigation was to compare the sedative effects of oral midazolam/chloral hydrate and midazolam/promethazine combinations on fearful children needing dental treatment. Methods. This crossover double-blind clinical trial was conducted on 30 children aged 2‒6 years, who had at least two similar teeth needing pulp treatment. Standard vital signs were recorded before and after premedication. Wilson sedation scale was used to judge the level of sedation. Cases were divided into two groups based on the sequence of medication received. This was to overcome the sequence effect. Group I received oral midazolam (0.4 mg/kg/chloral hydrate (50 mg/kg) at the first visit while they received midazolam (0.4 mg/kg)/promethazine (5 mg/kg) in their second visit. Group II received the premedication in the opposite sequence. The operator and child were blinded to the medication administered. Sedative efficacy of the two combinations were assessed and judged by two independent pediatric dentists based on the Wilson scale. Data were analyzed with ANOVA and paired t-test. Results. Only 10% of children who received chloral hydrate with midazolam exhibited high improvement in their behavior while 53% showed reasonable positive changes and 12% had no change or even deterioration of behavior. The difference between the effect of the two combination drugs was statistically significant (P<0.05) in favor of the chloral hydrate group. Conclusion. The results showed a significant difference in the sedation level induced between the two groups. Midazolam/chloral hydrate combination more effectively improved the co-operation for dental treatment.

Dynamically simulating the interaction of midazolam and the CYP3A4 inhibitor itraconazole using individual coupled whole-body physiologically-based pharmacokinetic (WB-PBPK) models

Background

Drug-drug interactions resulting from the inhibition of an enzymatic process can have serious implications for clinical drug therapy. Quantification of the drugs internal exposure increase upon administration with an inhibitor requires understanding to avoid the drug reaching toxic thresholds. In this study, we aim to predict the effect of the CYP3A4 inhibitors, itraconazole (ITZ) and its primary metabolite, hydroxyitraconazole (OH-ITZ) on the pharmacokinetics of the anesthetic, midazolam (MDZ) and its metabolites, 1' hydroxymidazolam (1OH-MDZ) and 1' hydroxymidazolam glucuronide (1OH-MDZ-Glu) using mechanistic whole body physiologically-based pharmacokinetic simulation models. The model is build on MDZ, 1OH-MDZ and 1OH-MDZ-Glu plasma concentration time data experimentally determined in 19 CYP3A5 genotyped adult male individuals, who received MDZ intravenously in a basal state. The model is then used to predict MDZ, 1OH-MDZ and 1OH-MDZ-Glu concentrations in an CYP3A-inhibited state following ITZ administration.

Results

For the basal state model, three linked WB-PBPK models (MDZ, 1OH-MDZ, 1OH-MDZ-Glu) for each individual were elimination optimized that resulted in MDZ and metabolite plasma concentration time curves that matched individual observed clinical data. In vivo K_m and V_max optimized values for MDZ hydroxylation were similar to literature based in vitro measures. With the addition of the ITZ/OH-ITZ model to each individual coupled MDZ + metabolite model, the plasma concentration time curves were predicted to greatly increase the exposure of MDZ as well as to both increase exposure and significantly alter the plasma concentration time curves of the MDZ metabolites in comparison to the basal state curves. As compared to the observed clinical data, the inhibited state curves were generally well described although the simulated concentrations tended to exceed the experimental data between approximately 6 to 12 hours following MDZ administration. This deviations appeared to be greater in the CYP3A5 *1/*1 and CYP3A5 *1/*3 group than in the CYP3A5 *3/*3 group and was potentially the result of assuming that ITZ/OH-ITZ inhibits both CYP3A4 and CYP3A5, whereas in vitro inhibition is due to CYP3A4.

Conclusion

This study represents the first attempt to dynamically simulate metabolic enzymatic drug-drug interactions via coupled WB-PBPK models. The workflow described herein, basal state optimization followed by inhibition prediction, is novel and will provide a basis for the development of other inhibitor models that can be used to guide, interpret, and potentially replace clinical drug-drug interaction trials.

A sensitive and selective method for the detection of diazepam and its main metabolites in urine by gas chromatography–tandem mass spectrometry

A gas chromatography-tandem mass spectrometry method for detection of diazepam, nordazepam and oxazepam is presented. The method associates electron capture ionization and multiple reaction monitoring (MRM). No derivatization is performed; oxazepam undergoes thermal degradation during chromatographic injection and is thus quantified via its decomposition product. The negative molecular ions are so stable that they do not dissociate when collision is performed under "classical" conditions (i.e. with argon as collision gas). With xenon as collision gas, the energy transfer is sufficient to provide two product ions for diazepam and nordazepam and one product ion for the decomposition product of oxazepam. The sample preparation part involves liquid/liquid extraction with TOXI-TUBES A extraction tubes; it provides recovery yields between 68 and 95%, depending of the benzodiazepine considered, with coefficients of variation below 6% for 10 samples. The applicability of the method was demonstrated on urine extracts. From 1 mL of urine, the method provides quantitation limits of 0.15 ng/mL for diazepam, 1.0 ng/mL for nordazepam and 1.5 ng/mL for oxazepam. Mechanisms of dissociation of M*(-) ions of benzodiazepines are suggested.

Sensitive method for the detection of 22 benzodiazepines by gas chromatography-ion trap tandem mass spectrometry

A gas chromatography-ion trap tandem mass spectrometry method for simultaneous detection of 22 benzodiazepines is presented. Four operating modes were first optimized: the electron impact ionization and chemical ionization modes were compared on both underivatized and trimethylsilylated drugs. Results were compared in terms of sensitivity in MS-MS experiments. The trimethylsilylation of benzodiazepines including a protic functional group allows decreasing their detection threshold by a factor of 10-100. In terms of sensitivity, the comparison between both ionization modes shows that the most efficient one depends on the benzodiazepine considered. The use of an ion trap analyzer allows switching from an ionization mode to another one during the chromatographic process. It also provides a great selectivity owing to the MS-MS and multiple reaction monitoring acquisition modes. The detection thresholds are in the range 10-500 pg/microl for all the studied benzodiazepines but the three "triazolo" ones: estazolam, alprazolam and triazolam, have a detection threshold of 1 ng/microl. The applicability of the method on whole blood and urine extracts was demonstrated on an example implying five benzodiazepines among the most frequently encountered in forensic toxicology: nordazepam, oxazepam, bromazepam, flunitrazepam and prazepam.

First experience with the REMEDi HS urine benzodiazepine assay

Ninety eight urine samples were analysed with an immunoassay benzodiazepine kit. A total of 68 urine specimens that were presumptively positive for benzodiazepines were evaluated by the REMEDi HS urine benzodiazepine assay (BIO-RAD, Munich, Germany). Of this number, 53 (78%) specimens were found by REMEDi to contain one or more benzodiazepines or their metabolites, and 15 (22%) were found to be negative. From the discordant group of 15 samples, eight were found to be negative using conventional chromatographic procedures (HPLC or GC/MS), while seven contained one or more benzodiazepines or metabolites, each of which were below the individual cut-off level specified by the manufacturer. Additionally 30 urine specimens that were negative for benzodiazepines using immunoassay were also tested by REMEDi. Two samples were found to be positive. These results could not be confirmed by other chromatographic techniques. The REMEDi HS benzodiazepine assay can be a very useful complementary technique in the clinical/forensic toxicology laboratory, especially for the identification of the parent benzodiazepines administered. The assay provides a rapid result in emergency situations and is useful in confirmation of preliminary positive immunoassay results.

Methods for the measurement of benzodiazepines in biological samples

A review of methods for the measurement of benzodiazepines in biological specimens published over the last five years is presented. A range of immunoassay procedures using EIA, ELISA, FPIA, agglutination or kinetic interaction of microparticles, or RIA methods are now available. Cross reactivities to benzodiazepines are variable such that no one kit will recognise all benzodiazepines and their relevant metabolites at concentrations likely to be encountered during therapeutic use. Prior hydrolysis of urine to convert glucuronide metabolites to immunoreactive substances improves detection limits for many benzodiazepines. Several radioreceptor assays have now been published and show good sensitivity and specificity to benzodiazepines and offer the advantage (over immunoassay) of being able to detect these drugs with equal sensitivity. Solvent extraction techniques using a variety of solvents were still popular and offer acceptable recoveries and lack of significant interference from other substances. A number of papers describing solid phase extraction procedures were also published. Direct injection of specimens into a HPLC column with back flushing were also successfully described. Seventy two chromatographic methods using HPLC, LC-MS, GC and GC-MS methods were reviewed. HPLC was able to achieve detection limits for many benzodiazepines using UV or DAD detection down to 1-2 ng/ml using 1-2 ml of urine or serum (blood). ECD detectors gave detection limits better than 1 ng/ml from 1 ml of specimen, which was an order of magnitude lower than for NPD. EI-MS offered similar sensitivity, whilst NCI-MS was capable of detection down to 0.1 ng/ml. Methods suitable for the separation of enantiomers of benzodiazepines have been described using HPLC. Electrokinetic micellar chromatography has also been shown to be capable of the analysis of benzodiazepines in urine.

Gas chromatographic determination of midazolam in low-volume plasma samples

A gas chromatographic method for the sensitive determination of midazolam in plasma volumes as low as 40 microliters was developed, utilizing clinazolam as the internal standard. After liquid-liquid extraction at basic pH into 1-chlorobutane-dichloromethane (96:4) a 2- to 4-microliters portion of the reconstituted extract was injected under electronic pressure control onto a 12 m x 0.2 mm I.D. methyl silicone capillary column, and was exposed to a three-step temperature program from 120 to 310 degrees C, to separate the analytes from the plasma constituents. The compound of interest was identified and quantified by means of a mass-selective detector. The assay was linear from 10 to 500 ng/ml using 40 microliters of plasma (limit of quantification: 10 ng/ml) and was linear from 0.25 to 100 ng/ml using 500 microliters of plasma (limit of quantification: 0.25 ng/ml). The intra-day precision for the 40-microliters aliquots varied from 2.2 to 6.6%, the corresponding accuracy from -7.4 to -4.4%; the inter-day precision ranged from 5 to 7.2% and the corresponding accuracy from -7.2 to -5.1%.

Systematic toxicological analysis of drugs and their metabolites by gas chromatography-mass spectrometry

Gas chromatographic-mass spectrometric (GC-MS) procedures for the systematic toxicological analysis of several categories of drugs relevant to clinical toxicology, forensic toxicology and doping control are reviewed. Papers from 1981 to 1991 are taken into consideration. They describe the detection of acute or chronic intoxication and the detection of drug abuse. Screening procedures are included for the following categories: barbiturates and other sedative-hypnotics, anticonvulsants, benzodiazepines, antidepressants, phenothiazine and butyrophenone neuroleptics, central stimulants (amphetamines, cocaine), hallucinogens (LSD, phencyclidine, tetrahydrocannabinol), opioid (narcotic) and other potent analgesics, non-opioid analgesics, antihistamines (histamine H1-receptor blockers), antiparkinsonian drugs, beta-blockers (beta-adrenoceptor blockers), antiarrhythmics (class I and IV), diuretics, laxatives and their metabolites. Methods for confirmation of results obtained by screening procedures using immunoassay or chromatographic techniques are also included. GC-MS procedures for the simultaneous detection of several categories of drugs, the so-called "general unknown analysis", are reviewed. The toxicological question to be answered and the consequence for the choice of an adequate method, the sample preparation and the chromatography itself are discussed. The basic information about the biosample assayed, work-up, GC column, mass spectral detection mode, reference data and sensitivity of each procedure are summarized in tables, arranged according to the category of drug. Examples of typical GC-MS applications are presented. Fragment ions that are suitable for mass spectral screening for particular categories of drugs and for general unknown are tabulated.

A rapid solid-phase extraction and HPLC/DAD procedure for the simultaneous determination and quantification of different benzodiazepines in serum, blood and post-mortem blood

A rapid and quantitative method for the determination of benzodiazepines using high-performance liquid chromatography (HPLC) with diode-array detection (DAD) is reported. The drugs were extracted from serum, blood or post-mortem blood using C18 extraction columns. Brotizolam was used as internal standard. Experiments with spiked serum/blood samples resulted in recoveries between 75% and 94% for all investigated benzodiazepines. Excellent linearity was obtained over the concentration range 5-1500 ng benzodiazepine/ml. The limit of detection was approximately 2 ng/ml. The detection of low therapeutic serum levels of highly potent benzodiazepines is also possible.