Differences of Atomic-Level Interactions between Midazolam and Two CYP Isoforms 3A4 and 3A5

CYP 3A4 and CYP 3A5 are two important members of the human cytochrome P450 family. Although their overall structures are similar, the local structures of the active site are different, which directly leads to obvious individual differences in drug metabolic efficacy and toxicity. In this work, midazolam (MDZ) was selected as the probe substrate, and its interaction with two proteins, CYP 3A4 and CYP 3A5, was studied by molecular dynamics simulation (MD) along with the calculation of the binding free energy. The results show that two protein-substrate complexes have some similarities in enzyme-substrate binding; that is, in both complexes, Ser119 forms a high occupancy hydrogen bond with MDZ, which plays a key role in the stability of the interaction between MDZ and the enzymes. However, the complex formed by CYP 3A4 and MDZ is more stable, which may be attributed to the sandwich structure formed by the fluorophenyl group of the substrate with Leu216 and Leu482. Our study interprets the binding differences between two isoform-substrate complexes and reveals a structure-function relationship from the atomic perspective, which is expected to provide a theoretical basis for accurately measuring the effectiveness and toxicity of drugs for individuals in the era of precision medicine.

Midazolam as a Probe for Heterotropic Drug-Drug Interactions Mediated by CYP3A4

Human cytochrome P450 CYP3A4 is involved in the processing of more than 35% of current pharmaceuticals and therefore is responsible for multiple drug-drug interactions (DDI). In order to develop a method for the detection and prediction of the possible involvement of new drug candidates in CYP3A4-mediated DDI, we evaluated the application of midazolam (MDZ) as a probe substrate. MDZ is hydroxylated by CYP3A4 in two positions: 1-hydroxy MDZ formed at lower substrate concentrations, and up to 35% of 4-hydroxy MDZ at high concentrations. The ratio of the formation rates of these two products (the site of metabolism ratio, SOM) was used as a measure of allosteric heterotropic interactions caused by effector molecules using CYP3A4 incorporated in lipid nanodiscs. The extent of the changes in the SOM in the presence of effectors is determined by chemical structure and is concentration-dependent. MD simulations of CYP3A4 in the lipid bilayer suggest that experimental results can be explained by the movement of the F-F' loop and concomitant changes in the shape and volume of the substrate-binding pocket. As a result of PGS binding at the allosteric site, several residues directly contacting MDZ move away from the substrate molecule, enabling the repositioning of the latter for minor product formation.

Fragmentation studies of selected drugs utilized in palliative care

The results of research on selected drugs used in palliative care are presented, including fentanyl, tramadol, metoclopramide, hyoscine butylbromide, midazolam, haloperidol, levomepromazine and clonazepam. Interpretation of their ESI mass spectra obtained by the use of a triple quadrupole linear ion trap mass spectrometer is given. As a result, fragmentation pathways described in the literature are complemented and presented with more details. On their basis, transitions for quantitative analysis are selected and chromatographic conditions for the determination of the palliative care drugs are proposed as well. These results enable future studies on palliative care drugs in elderly patients including both their quantitation in body fluids and easier identification of their metabolites.

Ionization states, cellular toxicity and molecular modeling studies of midazolam complexed with trimethyl-β-cyclodextrin

We investigated the ionization profiles for open-ring (OR) and closed-ring (CR) forms of midazolam and drug-binding modes with heptakis-(2,3,6-tri-O-methyl)-β-cyclodextrin (trimethyl-β-cyclodextrin; TRIMEB) using molecular modeling techniques and quantum mechanics methods. The results indicated that the total net charges for different molecular forms of midazolam tend to be cationic for OR and neutral for CR at physiological pH levels. The thermodynamic calculations demonstrated that CR is less water-soluble than OR, mainly due to the maximal solvation energy ( = −9.98 kcal·mol⁻¹), which has a minimal of −67.01 kcal·mol⁻¹. A cell viability assay did not detect any signs of TRIMEB and OR/CR-TRIMEB complex toxicity on the cEND cells after 24 h of incubation in either Dulbecco’s Modified Eagles Medium or in heat-inactivated human serum. The molecular docking studies identified the more flexible OR form of midazolam as being a better binder to TRIMEB with the fluorophenyl ring introduced inside the amphiphilic cavity of the host molecule. The OR binding affinity was confirmed by a minimal Gibbs free energy of binding (ΔG_bind) value of −5.57 ± 0.02 kcal·mol⁻¹, an equilibrium binding constant (K_b) of 79.89 ± 2.706 μM, and a ligand efficiency index (LE_lig) of −0.21 ± 0.001. Our current data suggest that in order to improve the clinical applications of midazolam via its complexation with trimethyl-β-cyclodextrin to increase drug’s overall aqueous solubility, it is important to concern the different forms and ionization states of this anesthetic. All mean values are indicated with their standard deviations.

The application of a new microfluidic device for the simultaneous identification and quantitation of midazolam metabolites obtained from a single micro-litre of chimeric mice blood

RATIONALE

Improvements in the design of low-flow highly sensitive chromatographic ion source interfaces allow the detection and characterisation of drugs and metabolites from smaller sample volumes. This in turn improves the ethical treatment of animals by reducing both the number of animals needed and the blood sampling volumes required.

METHODS

A new microfluidic device combining an ultra-high pressure liquid chromatography (UHPLC) analytical column with a nano-flow electrospray source is described. All microfluidic, gas and electrical connections are automatically engaged when the ceramic microfluidic device is inserted into the source enclosure. The system was used in conjunction with a hybrid quadrupole-time-of-flight mass spectrometer.

RESULTS

The improved sensitivity of the system is highlighted in its application in the quantification and qualification of midazolam and its metabolites detected in whole blood from chimeric and wild-type mice. Metabolite identification and full pharmacokinetic profiles were obtained from a single micro-litre of whole blood at each sampling time and significant pharmacokinetic differences were observed between the two types of mice.

CONCLUSIONS

Improvements in the enhanced ionisation efficiency from the microfluidic device in conjunction with nanoUHPLC/MS was sufficiently sensitive for the identification and quantification of midazolam metabolites from a single micro-litre of whole blood. Detection of metabolites not previously recorded from the chimeric mouse in vivo model was made.

Degradation of benzodiazepines after 120 days of EMS deployment

INTRODUCTION

EMS treatment of status epilepticus improves outcomes, but the benzodiazepine best suited for EMS use is unclear, given potential high environmental temperature exposures.

OBJECTIVE

To describe the degradation of diazepam, lorazepam, and midazolam as a function of temperature exposure and time over 120 days of storage on active EMS units.

METHODS

Study boxes containing vials of diazepam, lorazepam, and midazolam were distributed to 4 active EMS units in each of 2 EMS systems in the southwestern United States during May-August 2011. The boxes logged temperature every minute and were stored in EMS units per local agency policy. Two vials of each drug were removed from each box at 30-day intervals and underwent high-performance liquid chromatography to determine drug concentration. Concentration was analyzed as mean (and 95%CI) percent of initial labeled concentration as a function of time and mean kinetic temperature (MKT).

RESULTS

192 samples were collected (2 samples of each drug from each of 4 units per city at 4 time-points). After 120 days, the mean relative concentration (95%CI) of diazepam was 97.0% (95.7-98.2%) and of midazolam was 99.0% (97.7-100.2%). Lorazepam experienced modest degradation by 60 days (95.6% [91.6-99.5%]) and substantial degradation at 90 days (90.3% [85.2-95.4%]) and 120 days (86.5% [80.7-92.3%]). Mean MKT was 31.6°C (95%CI 27.1-36.1). Increasing MKT was associated with greater degradation of lorazepam, but not midazolam or diazepam.

CONCLUSIONS

Midazolam and diazepam experienced minimal degradation throughout 120 days of EMS deployment in high-heat environments. Lorazepam experienced significant degradation over 120 days and appeared especially sensitive to higher MKT exposure.

Stability of midazolam in syrspend SF and syrspend SF cherry

Midazolam is a short-acting benzodiazepine central nervous system depressant available as an injection, tablet, or oral syrup. The need for alternative dosage form options for patients unable to take tablets and shortages of other forms of the drug have led compounding pharmacies to seek alternatives, mainly solutions and suspensions. Additionally, some patients are unable to use suspending agents containing alcohol or sorbitol. The objective of this study was to determine the stability of midazolam in sorbitol-free, alcohol-free SyrSpend SF and SyrSpend SF Cherry suspending agents. The studied samples were compounded into a 1-mg/mL suspension and stored in low-actinic plastic bottles at temperatures between 2 degrees C to 8 degrees C and at room temperature conditions. Six samples were assayed at each time point out to 58 days by a stability-indicating high-performance liquid chromatography method. The method was validated for its specificity through forced-degradation studies. The samples remained within 90% to 110% of the initial concentration throughout the course of the study. Based on the data collected, the beyond-use date of these preparations is at least 58 days when protected from light at both refrigerated and room temperature storage conditions.

Complexation study of midazolam hydrochloride with beta-cyclodextrin: NMR spectroscopic study in solution

(1)H NMR spectroscopic study of midazolam hydrochloride (MDL), beta-cyclodextrin (beta-CD) and their mixtures confirmed the formation of beta-CD-MDL inclusion complex in aqueous solution. The stoichiometry of the complexes was determined by Scott's method to be 1:1, and the association constant (K(a)) was calculated to be 108 M(-1). It was confirmed on the basis of 2D ROESY spectral data that only a fluorine-substituted aromatic ring acted as guest in complexation. Most of the aromatic signals of MDL exhibited induced shift changes as well as splitting, in the presence of beta-CD, indicating chiral differentiation of MDL by beta-CD.

Chemical stability of midazolam injection by high performance liquid chromatography

The chemical stability of midazolam hydrochloride injection, undiluted or diluted with dextrose sterile solution, was studied at different storage conditions by LC. The study was performed at room temperature (23 +/- 2 degrees C) under light exposure and light protection, +8 +/- 1 degrees C and -20 +/- 0.5 degrees C, in glass and plastic containers over 14 days with midazolam hydrochloride injection, undiluted or diluted with 5% dextrose sterile solution. Chromatographic separation was carried out on a RP-18(e) column, using a mobile phase consisting of ACN-phosphate buffer (pH 3.3; 0.1 M) (30:70 v/v) at a flow rate of 1.0 mL/min and UV detection at 220 nm. The concentrations of all samples remained greater than 90% of the original concentration. The chromatographic assay exhibited an adequate linearity (r(2) >0.999), selectivity, precision (RSD <3.1), and accuracy (recoveries from 100.46 to 101.40%). Injectable midazolam hydrochloride was chemically stable in all conditions that were studied.

Time-dependent inactivation of P450 3A4 by raloxifene: identification of Cys239 as the site of apoprotein alkylation

Time-dependent inactivation of cytochrome P450s is typically a result of substrate bioactivation to form reactive species that subsequently alkylate the heme group, apoprotein, or both. The chemical identity of many reactive intermediates is generally proposed based on the products of trapping reactions with nucleophilic agents as only a few P450-drug adducts have been directly characterized. We describe the use of mass spectrometry to show that a single equivalent of raloxifene is bound to the intact P450 apoprotein. Furthermore, mass analysis of peptides following digestion with proteinase K revealed that the covalently bound drug is localized to residue Cys239. A mass shift of 471 Da to the intact protein and peptide, relative to control samples, indicated that time-dependent inactivation of P450 3A4 occurred through the raloxifene diquinone methide intermediately prior to nucleophilic attack of the sulfur of Cys239. Association between raloxifene adduction to P450 3A4 apoprotein and the observed time-dependent inactivation was further investigated with the use of cysteine-specific modifying reagents. When P450 3A4 was treated with iodoacetamide or N-(1-pyrene)iodoacetamide, which alkylated residue Cys239 exclusively, time-dependent inactivation of P450 3A4 by raloxifene was prevented. The change in protein mass of 471 Da combined with the protection from inactivation that occurred through pre-alkylation of Cys239 provided conclusive evidence that raloxifene-mediated P450 3A4 inactivation occurred through the bioactivation of raloxifene to the diquinone methide and subsequent alkylation of Cys239.

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.

Enzymatic characteristics of CYP3A5 and CYP3A4: a comparison of in vitro kinetic and drug-drug interaction patterns

CYP3A4 and CYP3A5 exhibit significant overlap in substrate specificity, but can differ in catalytic activity and regioselectivity. To investigate their characteristics further, the enzymatic reactions of the two CYP3A enzymes were compared using midazolam, nifedipine, testosterone and terfenadine as substrates. Both CYP3A5 and CYP3A4 showed sigmoid and substrate inhibition patterns for testosterone 6beta-hydroxylation and terfenadine t-butylhydroxylation (TFDOH), respectively. In the other reactions, the kinetic model for CYP3A5 was not similar to that for CYP3A4. An inhibition study demonstrated that the interactions between alpha-naphthoflavone (alphaNF) and CYP3A substrates were different for the two CYP3A enzymes. alphaNF stimulated nifedipine oxidation catalysed by CYP3A5, but did not stimulate that catalysed by CYP3A4. alphaNF at less than 32 microM inhibited TFDOH catalysed by CYP3A5, but did not inhibit that catalysed by CYP3A4. These results indicate that CYP3A5 has different enzymatic characteristics from CYP3A4 in some CYP3A catalysed reactions.

Analysis of small molecules by ultra thin-layer chromatography-atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry

The feasibility of ultra thin-layer chromatography atmospheric pressure matrix-assisted laser desorption ionization mass spectrometry (UTLC-AP-MALDI-MS) has been studied in the analysis of small molecules. Because of a thinner adsorbent layer, the monolithic UTLC plates provide 10-100 times better sensitivity in MALDI analysis than conventional high performance thin-layer chromatography (HPTLC) plates. The limits of detection down to a low picomole range are demonstrated by UTLC-AP-MALDI-MS. Other advantages of UTLC over HPTLC include faster separations and lower solvent consumption. The performances of AP-MALDI-MS and vacuum MALDI-MS have been compared in the analysis of small drug molecules directly from the UTLC plates. The desorption from the irregular surface of UTLC plates with an external AP-MALDI ion source combined with an ion trap instrument provides clearly less variation in measurements of m/z values when compared with a vacuum MALDI-time-of-flight (TOF) instrument. The performance of the UTLC-AP-MALDI-MS method has been applied successfully to the purity analysis of synthesis products produced by solid-phase parallel synthesis method.

There Are No Useful CYP3A Probes that Quantitatively Predict the In Vivo Kinetics of Other CYP3A Substrates and No Expectation that One Will Be Found

The search for a substrate that may serve as a probe to quantitatively predict the in vivo kinetics of cytochrome P450 3A (CYP3A) drugs has been of particular interest because more than half of all human drugs appear to be substrates for this enzyme. Even three closely related 1,4-benzodiazepines-alprazolam, midazolam, and triazolam-are inadequate probes to predict the pharmacokinetics of each other in an individual. If these drugs--all metabolized through the same CYP3A pathways in humans, all FDA Biopharmaceutical Classification System Class 1 compounds exhibiting high solubility and high permeability and thus unaffected by transporter differences--cannot quantitatively predict the pharmacokinetics of their closely related congeners, there is little hope that any quantitative CYP3A probe will ever be found.

Metamemory without the memory: are people aware of midazolam-induced amnesia?

RATIONALE

Midazolam is a benzodiazepine which produces a dense anterograde amnesia, while permitting relatively well-preserved short-term memory, semantic retrieval, and other higher cognitive functions. Given these preserved abilities, we were interested in whether or not participants given midazolam would be aware of this anterograde amnesia.

METHOD

In the present experiment, participants were given midazolam in one testing session and a saline placebo in another. Participants provided judgments-of-learning (JOLs) immediately following study of cue-target pairs. During the test phase of the experiment, confidence levels and feeling-of-knowing (FOK) judgments were collected.

RESULTS

Although cued recall performance was substantially impaired in the midazolam condition, mean JOLs were unaffected, indicating participants had little insight into their impairment during the study phase. Participants were relatively accurate in confidence levels and FOK judgments in the midazolam condition.

CONCLUSION

When studying items under the influence of midazolam, participants are unaware that their memory will be impaired. Implications for clinical practice and pharmacological studies of amnesia are discussed.

The compatibility and stability of midazolam and dexamethasone in infusion solutions

The delivery of subcutaneous medication by continuous infusion is common in palliative medicine. Many centers combine multiple medications, but the analytical confirmation of the compatibility and stability of these combinations has rarely been performed. This study examined the compatibility and stability of midazolam and dexamethasone using high performance liquid chromatography. Nine different solutions were prepared in polypropylene syringes by combining these two drugs with 0.9% sodium chloride. When these two drugs were combined in a syringe, there was significant loss of midazolam over 48 hours, with only 60-80% of the initial concentration remaining in syringes stored at 35-39 degrees C. This study demonstrates that cloudiness of a solution is not the only predictor of drug loss and that drug loss may occur even in solutions that remain clear at time of preparation. The clinical implications of these results are that dexamethasone and midazolam should not be combined in syringe driver solutions.

Albumin dialysis: a new therapeutic strategy for intoxication from protein-bound drugs

OBJECTIVE

Although water-soluble drugs can be removed by haemofiltration/haemodialysis, morbidity and mortality from intoxication with protein-bound drugs remains high. The present study investigates whether albumin dialysis in the form of the Molecular Adsorbents Recirculating System (MARS) is effective in removal of protein-bound drugs.

DESIGN

Prospective animal study.

SETTING

Surgical research laboratory in a university hospital.

SUBJECTS

Seven female Norwegian Landrace pigs.

INTERVENTION

We studied whether midazolam (97% albumin-bound) and fentanyl (85% alpha-1-acid glycoprotein-bound), administered as anaesthetics to pigs with induced acute liver failure, could be removed by MARS dialysis lasting for 4 h.

MEASUREMENTS

After 4 h of dialysis, total and free anaesthetic concentrations were measured in the blood and dialysate from different segments of the MARS circuit.

MAIN RESULTS

Midazolam: total plasma concentrations fell by 47.1+/-2.1% (in 4 h) across the MARS filter ( p<0.01). The charcoal component of the system reduced the total dialysate drug concentration by 16.4+/-2.2% ( p<0.05). Free midazolam removal followed a similar pattern. Fentanyl: total plasma concentrations fell by 56.1+/-2.4% (in 4 h) across the MARS filter ( p<0.01). Clearance of fentanyl from the dialysate by the charcoal was 70+/-0.7% at 4 h ( p<0.001).

CONCLUSIONS

The results of the study show that MARS can remove both albumin and other protein-bound drugs efficiently from the plasma, and it may have a place for the treatment of patients suffering from intoxication with this class of compounds.

In vitro investigation on the impact of the surface-active excipients Cremophor EL, Tween 80 and Solutol HS 15 on the metabolism of midazolam

The impact of the surface-active formulation ingredients Cremophor EL, Tween 80 and Solutol HS 15 on the intrinsic clearance (Clint) of midazolam (MDZ) was investigated in rat hepatocytes and microsomes. In rat hepatocytes with 0.003%, 0.03% and 0.3% (w/v) Solutol HS 15 already present in the incubation medium, the Clint was significantly reduced in a dose-dependent manner by about 25%, 30% and 50%, respectively. In the presence of Cremophor EL and Tween 80 a significant reduction in Clint by about 30% and 25%, respectively, was observed at 0.03% surfactant concentration. At 0.3% of Cremophor EL and Tween 80, Clint was reduced by about 50% and 20%, respectively. A reduction in Clint was also observed in experiments with rat liver microsomes. At surfactant concentrations up to 0.03%, cytotoxicity assays (lactate dehydrogenase release, adenosine triphosphate content) as well as light microscope investigations did not reveal any cytotoxic impact of the surfactants on the hepatocyte monolayer. A potential interaction of the surfactants with biological membranes was determined using phosphatidylcholine-cholesterol liposomes loaded with self-quenching concentrations of carboxyfluorescein. No marked release of carboxyfluorescein from the liposomes (that would be an indication for a surfactant-dependent disruption of membrane integrity) was observed up to concentrations of 0.03% of the different surfactants. It is concluded that cytochrome P450 3A mediated metabolism of MDZ seems to be prevented by all surfactants at concentrations above 0.03%. In our experiments the surfactants did not show toxic effects at concentrations that resulted in a decreased Clint of MDZ. Thus, a direct inhibition of the metabolizing enzymes, a molecular interaction with the microsomes as well as an alteration of membrane properties that did not yet result in a release of LDH have to be taken into consideration as reasons for the observed changes in the metabolism of MDZ.

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.

Determination of hypnotic benzodiazepines (alprazolam, estazolam, and midazolam) and their metabolites in rat hair and plasma by reversed-phase liquid-chromatography with electrospray ionization mass spectrometry

Sensitive determination of benzodiazepines i.e., alprazolam (ALP), estazolam (EST), and midazolam (MDZ), and their metabolites, was carried out by reversed-phase liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS). The chromatography separations were achieved using a semi-micro HPLC column (3 microm particle size; 100 x 2.0 mm, i.d.) with acetonitrile-water containing 1% acetic acid as eluent. The mass spectrometer was operated in selected-ion monitoring mode at protonated-molecular ions [M+H](+) of parent drugs and the metabolites. The proposed procedure was applied to the determination in hair shaft of Dark Agouti rats after intraperitoneal (i.p.) administration of benzodiazepines twice a day for 5 days. Various metabolites together with parent drugs were identified in the hair shaft, 1-hydroxyalprazolam (1-HA) and 4-hydroxyalprazolam (4-HA) from ALP administration; 8-chloro-6-phenyl-4H-[1,2,4]triazolo[4,3-a][1,4]benzodiazepine-4-one (K-EST) from EST administration; 1-hydroxymidazolam (1-HM) and 4-hydroxymidazolam (4-HM) from MDZ administration. A few unknown metabolites were also detected in the hair samples. These structures were elucidated with acetylation using acetic anhydride and pyridine. The time course studies of parent drugs and the metabolites in both hair root and plasma were also carried out after single i.p. administration of benzodiazepines. The results suggested that the concentrations of parent drugs and the metabolites in the hair samples were mainly dependent upon those in the plasma.

Feasibility of atmospheric pressure desorption/ionization on silicon mass spectrometry in analysis of drugs

The feasibility of atmospheric pressure desorption/ionization on silicon mass spectrometry (AP-DIOS-MS) for drug analysis was investigated. It was observed that only compounds with relative high proton affinity are efficiently ionized under AP-DIOS conditions. The limits of detection (LODs) achieved in MS mode with midazolam, propranolol, and angiotensin II were 80 fmol, 20 pmol, and 1 pmol, respectively. In MS/MS mode the LODs for midazolam and propranolol were 10 fmol and 5 pmol, respectively. The good linearity (r(2) > 0.991), linear dynamic range of 3 orders of magnitude, and reasonable repeatability showed that the method is suitable for quantitative analysis.

Reoxygenation after cold hypoxic storage of cultured precision-cut rat liver slices: effects on cellular metabolism and drug biotransformation

Cultured rat precision-cut liver slices (PCLS) were used to study the influence of hypothermic preservation and reoxygenation at 37 degrees C on cellular metabolism and drug biotransformation. Cold hypoxic storage caused a depressed metabolism in rat liver slices, but reoxygenation for 8 h at 37 degrees C partially restored the levels of both ATP and GSH and totally restored the capacity to synthesize proteins. Metabolism of midazolam (CYP3A-dependent oxidation) by cold preserved liver slices was decreased by 30% but no further affected by reoxygenation, showing the same profile as freshly cut slices. Such a reoxygenation at 37 degrees C is accompanied by a dramatic loss of CYP3A2 protein while CYP3A1 protein was unaffected. These results suggest that CYP3A2 did not play a major role in midazolam oxidation. Such results are not consistent with a putative reoxygenation injury but rather with cold hypoxic damage. Since cold preserved liver slices did not respond to bacterial endotoxin stimulation (lipopolysaccharides), a minor role of non-parenchymal cells is suggested as mediators for deleterious effects developed during the cold storage.

Propofol increases agonist efficacy at the GABA(A) receptor

Using the whole-cell patch-clamp technique, we have determined that propofol, but not midazolam, increases the efficacy of piperidine-4-sulphonic acid (P4S), a partial agonist at alpha1beta1gamma2s, GABA(A) receptors expressed in HEK 293 cells. These findings are consistent with the idea that propofol facilitates receptor gating, while midazolam increases receptor occupancy by the agonist.

Compatibility and stability of ternary admixtures of morphine with haloperidol or midazolam and dexamethasone or methylprednisolone

The concentration range over which compatible admixtures of morphine hydrochloride with haloperidol lactate (Haldol) or midazolam hydrochloride (Dormicum) and dexamethasone-21-sodium phosphate (Decadron and Decadron Pack) or methylprednisolone-21-sodium succinate (Solu-Medrol) can be prepared was determined by visual evaluation of the solutions at 22 degrees C. The compatibility was evaluated for admixtures prepared in a ratio morphine hydrochloride (D1)/drug 2 (D2)/drug 2 (D3) in a ratio 10/1/1 to 10/1/10 (v/v/v). The solutions of morphine hydrochloride used were 10, 20, 30, 40 and 50 mg/ml prepared in water and isotonized with sodium chloride or dextrose. The drug solutions were used undiluted and diluted 1/5 (v/v) in water. All admixtures were prepared by adding the corticosteroid as D2 and as D3 in order to evaluate the influence of the order of mixing on the compatibility. The stability of the drugs in the compatible admixtures was evaluated during storage for 28 days at 22 degrees C and protected from light. Visual inspection, high performance liquid chromatography (HPLC) analysis, pH and osmolality determinations were performed. For each drug combination incompatibility was observed with increasing ratio and/or concentration of the drug solutions. Within the range of compatibility the concentrations of the three drugs could be increased so to allow adequate symptom control with all drug combinations. For a similar admixture a higher concentrations of corticosteroid could be obtained using dexamethasone-21-sodium phosphate versus methylprednisolone-21-sodium succinate and a higher concentration of dexamethasone-21-sodium phosphate could be obtained without incompatibility using Decadron Pack versus Decadron. The admixtures for which the stability was evaluated were stable for 28 days (> 95% of the initial concentration). None of these admixtures showed any visual changes during storage, except for some of the admixtures prepared using undiluted Decadron, in which small crystals were seen after 1-28 days. The initial pH of the admixture ranged from 3.99 to 6.06 and varied less than 0.10 during storage. The initial osmolality of the admixtures ranged from 170 to 323 mOsm/kg and remained almost constant during storage.

Stability of midazolam and fentanyl in infusion solutions

The administration of drugs by subcutaneous infusion is routinely practiced in palliative medicine for the management of patients who are no longer able to take oral medication. It is not uncommon for two or more drugs to be combined in subcutaneous infusion solutions. The combination of an opioid and a short-acting benzodiazepine is frequently required. Unfortunately, the stability of benzodiazepines and newer opioids, such as fentanyl, has not been determined. This study examined the stability of solutions containing either fentanyl alone or fentanyl and midazolam in combination. Eight different solutions were assessed for up to 7 days following preparation. The solutions were prepared in polypropylene syringes using 0.9% saline as a diluent. Duplicate syringes were stored at approximately 5 degrees C, 22 degrees C, and 38 degrees C. High performance liquid chromatography was the analytical technique used to measure fentanyl and midazolam. Initial concentrations ranges were 13.2-38.9 micrograms/mL for fentanyl and 282-959 micrograms/mL for midazolam. It was found that fentanyl (+/- midazolam) was very stable (> 95%) when stored at temperatures ranging from 5 degrees C to 38 degrees C for at least 1 week. Midazolam (+ fentanyl) was not as stable as fentanyl under the same storage conditions and underwent time-dependent decomposition of up to 12.1% (observed at 7 days when stored at 38 degrees C). When stored at 22 degrees C and 38 degrees C, more than 90% of initial midazolam concentrations were retained for 4 days following preparation and for 7 days when stored at 5 degrees C. The clinical implications of these results are that, on the basis of physicochemical stability, subcutaneous infusion solutions containing fentanyl and midazolam may be prepared at intervals of 4 days (or 7 days if stored under refrigerated conditions).

Development of midazolam sublingual tablets: in vitro study

Midazolam is a benzodiazepine with short elimination half-life, used as induction or continuous agent for general anesthesia. At present, only injectable solution is available from French hospital pharmacies. The aim of the study is the development of 5 mg midazolam sublingual tablets to realize a short general anesthesia without intravenous or intramuscular injection. Incorporation of citric acid in the tablet formulation leads to an increase of dissolution rates of active drug, but a decrease of diffusion through lipid membranes is observed with 10 mg of citric acid when using the Dibbern's Resomat three phases apparatus. One explanation of this result is that midazolam (pKa = 6.1) in presence of 10 mg of citric acid is ionised. The ionised form, more hydrophilic, cannot cross the artificial lipid membrane and therefore the diffusion decreases. On the other hand, the decrease of diffusion's rate, when pH increases, is explained by the precipitation of midazolam at pH higher than 6. A compromise between dissolution and diffusion results leads us to choose the sublingual formulation containing 5 mg of citric acid per tablet.

Antiprogestin-mediated inactivation of cytochrome P450 3A4

Based on previous observations of very short periods of linearity for antiprogestin metabolite formation and the presence of a common tertiary amine moiety in each compound as the principal site of their metabolism, we hypothesized that mifepristone, lilopristone and onapristone are oxidized by cytochrome P450 (CYP) 3A4 to reactive nitroso species that complex the heme of the enzyme, thereby inactivating it. Upon preincubation with human liver microsomes in the presence (but not the absence) of NADPH, mifepristone inhibited midazolam 1'-hydroxylation, a marker of CYP3A4 catalytic activity, very potently (IC50 approximately 3.5 mumol/l) and extensively (by approximately 87%). Lilopristone and onapristone also displayed NADPH and time-dependent inactivation of CYP3A4 with characteristics very similar to mifepristone. These data support antiprogestin-mediated inactivation of CYP3A4 and suggest the potential for drug-drug interactions and time-dependent nonlinearities in pharmacokinetics upon their long-term administration.

Compatibility and stability of fentanyl admixtures in polypropylene syringes

OBJECTIVE

To determine the physicochemical stability of fentanyl in combination with midazolam and either hyoscine butylbromide or metoclopramide, and stored in 30 ml polypropylene syringes.

METHODS

Solutions containing approximately 40 microg/ ml of fentanyl in combination with midazolam (approximately 600 microg/ml) and either metoclopramide (approximately 700 microg/l) or hyoscine (approximately 850 microg/ml) were prepared from commercial ampoules of the drugs. The solutions were stored, in triplicate, in the dark at 32 degrees C (to simulate usage conditions) for 10 days, and the concentration of each constituent drug was periodically determined using a stability-indicating high-performance liquid chromatography assay.

RESULTS

The combinations were relatively stable, with all drugs maintaining over 90% of their initial chemical potency for at least 1 week. There were no evident changes in either the physical appearance or pH values of the solutions over the course of the study.

CONCLUSIONS

On the basis of physicochemical stability, polypropylene syringes containing fentanyl with midazolam and either hyoscine butylbromide or metoclopramide can be safely prepared and stored at or below 32 degrees C for periods of up to 1 week prior to use by palliative care patients receiving the drugs via a portable subcutaneous infusion device.

Stability of parenteral midazolam in an oral formulation

Midazolam is increasingly being used for oral sedation in pediatric dentistry. Unfortunately, it is available only as a parenteral formulation in Canada and the United States. Preparation of the parenteral solution for oral use is not uniform and leads the clinician to question the stability of this drug when used in conjunction with these vehicles. Therefore, the purpose of this study was to investigate the chemical stability of parenteral midazolam as an oral formulation to determine its expiry date. This was evaluated using a validated stability-indicating liquid chromatographic method. Midazolam was diluted in orange-flavored syrup to yield concentrations of 0.35, 0.64, and 1.03 mg/ml and then stored at room temperature. Samples were drawn on each of 9 study days (0, 1, 2, 6, 7, 9, 13, 21, and 102) and chromatographed. On each study day, solutions were inspected visually for changes in color, clarity, and appearance of particulate matter. Midazolam concentrations were considered within acceptable limits if they were not less than 90% of the initial concentration. Over the 102-day study period, there was no significant change in concentration in any of the solutions. On day 102, the remaining midazolam was within 7% of the day zero concentration. Therefore, these formulations of midazolam are stable at room temperature for a period of 102 days and would be suitable for clinical use.

Isomerism and anaesthetic drugs

Isomers are two or more different substances with the same molecular formula (i.e., the same number of different types of atoms). There are two main types of isomerism: 1) structural isomerism, and 2) steroisomerism. Structural isomers (e.g., enflurane and isoflurane) have different molecular structures, and usually behave like different drugs. Occasionally, structural isomers are interconvertible (i.e., they are tautomers or dynamic isomers); this occurs with the barbiturates and midazolam. Steroisomers have identical structures, but a different configuration or spatial arrangement. Stereiosomerism in drugs is often due to chirality or "handedness"; i.e., the presence of right-handed (R)- and left-handed (S)- forms of drugs which are nonsuperimposable mirror images ("enantiomers"). Approximately 60% of anaesthetic agents are chiral drugs; some of these are administered as single enantiomers. However, many synthetic chiral drugs are equal mixtures of (R)- and (S)-isomers, and there are often important differences in their activity and pharmacokinetics. Halothane, enflurane, and isoflurane are chiral drugs with different anaesthetic potencies. Similar differences occur with intravenous anaesthetics; thus, (S) (+)-ketamine causes fewer psychotic emergence reactions, less agitated behaviour, and better intraoperative amnesia and analgesia than its enantiomer. Some local anaesthetics are administered as chiral mixtures; the (S)-isomers have a longer action because of enhanced vasoconstriction. (S)-prilocaine is more slowly metabolized than its enantiomer, while (S)-bupivacaine may produce less cardiotoxicity than (R)-bupivacaine. These differences suggest that some anaesthetic drugs (particularly ketamine and chiral local anaesthetics) should be administered as single enantiomers. In recent years, their synthesis has been greatly simplified, and almost all new drugs may soon be introduced in this form.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative analysis of fentanyl in pharmaceutical preparations by gas chromatography-mass spectrometry

Fentanyl (1-[2-phenethyl]-4-N-[N-propionylanilino]piperidine) is a potent synthetic opiate commonly used for surgical analgesia and sedation. Reports of abuse of this highly addictive drug among health care personnel have prompted the need to verify the concentration in the unused portion of single-dose ampules returned to the pharmacy. We describe a simple quantitative method for the analysis of fentanyl citrate (Sublimaze) in syringes returned to the pharmacy following surgery. Fentanyl citrate (0.1 mL) and 2H5-fentanyl (internal standard, 0.05 mL, 100 mg/L) were extracted with Toxi-A tubes (Toxi-Lab, Irvine, CA) and analyzed by gas chromatography-mass spectrometry. Calibration was linear from 1 to 60 mg/L (correlation coefficient of 0.997, n = 13) and had a limit of detection of 0.4 mg/L. Mean recovery at concentrations from 5 to 50 mg/L was 89% (range, 69-104%). No interferences were found with morphine, ketamine, midazolam, sufentanil, or alfentanil. These drugs were not selected for their potential chromatographic interference but for their availability in surgical syringes. This assay is useful in verifying that any unused fentanyl is discarded according to narcotic regulations, thereby avoiding the possibility of diversion for illicit consumption.

Stability of an oral midazolam solution for premedication in paediatric patients

The objectives of this study were to assess the stability of a 1 mg/ml oral midazolam solution elaborated by our Hospital Pharmacy Service, and to confirm its clinical effect in presurgical paediatric patients. The solution's stability was tested by determining its pH and its UV-visible absorption spectrum at room temperature for up to 60 days. A high performance liquid chromatography method was used to confirm it. There was no significant change in pH value of either the test or a control solution. No loss of midazolam could be detected during the test. The Anaesthesiology Service assessed the sedation quality (very good, good, bad) and the venous puncture response, 20 minutes after the administration of 0.3 mg/kg of an oral midazolam solution. Twenty children were examined (age: 4-7 years). In addition, the haemodynamic and ventilatory functions were evaluated.

New anticonvulsant drugs. Focus on flunarizine, fosphenytoin, midazolam and stiripentol

In the past decade, several new antiepileptic drugs have been tested. Most recently, 5 new antiepileptic drugs have been launched onto European and US markets. These include vigabatrin, oxcarbazepine and lamotrigine in Europe, and felbamate and gabapentin in the US. In addition to these, 3 additional drugs are in the clinical investigational stage: flunarizine, fosphenytoin and stiripentol. A fourth agent is midazolam, which was originally introduced in 1986, but recently has shown effectiveness in the treatment of status epilepticus. Flunarizine is a selective calcium channel blocker that has shown anticonvulsant properties in both animal and human studies. It is a long-acting anticonvulsant that clinical studies have shown to have effects similar to those of phenytoin and carbamazepine in the treatment of partial, complex partial and generalised seizures. Fosphenytoin was developed to eliminate the poor aqueous solubility and irritant properties of intravenous phenytoin. It is rapidly converted to phenytoin after intravenous or intramuscular administration. In clinical studies, this prodrug showed minimal evidence of adverse events and no serious cardiovascular or respiratory adverse reactions. It may have a clear advantage over the present parenteral formulation of phenytoin. Midazolam is a benzodiazepine that is more potent than diazepam as a sedative, muscle relaxant and in its influence on electroencephalographic measures. It has been shown to be an effective treatment for refractory seizures in status epilepticus. Stiripentol has anticonvulsant properties as well as the ability to inhibit the cytochrome P450 system. There are significant metabolic drug interactions between stiripentol and phenytoin, carbamazepine and phenobarbital (phenobarbitone). Stiripentol has been studied in patients with partial seizures, refractory epilepsy and refractory absence seizures with some efficacious results.

Photochemical decomposition of midazolam. III--Isolation and identification of products in aqueous solutions

Midazolam, 8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5- a][1,4]benzodiazepine, decomposes photochemically in aqueous solution both under irradiation from a high-pressure mercury lamp and in normal daylight. The main decomposition product under the artificial radiation was 6-(8-chloro-1-methyl-4,5-dihydro-2,5,10b-triaza-benzo[e]-azulen -6-ylidene)- cyclohexa-2,4-dienone, which was not present in the solution exposed to daylight. 6-Chloro-2-methyl-4-(2-fluorophenyl)quinazoline was formed in both irradiation experiments and was the main decomposition product in normal daylight. Several minor products were formed in both solutions, the amounts depending on the pH of the solution. Only one decomposition product was formed in acidic solutions (pH < 2) irradiated with the high-pressure mercury lamp but numerous products were formed at higher pH.

Stability of midazolam prepared for oral administration

Midazolam is used frequently as an oral premedication in children. To make it more palatable, it is often mixed in various syrups and solutions. No previous studies have documented the stability of midazolam when mixed in these solutions. Using high-pressure liquid chromatography, we assayed midazolam concentrations over time when mixed at two different concentrations (2.5 mg/mL and 3.0 mg/mL) in a sucrose-based syrup (Simple Syrup, NF). Each assay was done in triplicate on three different days (days 1, 14, and 38). Solution A concentrations (2.5 mg/mL) were 2.28 mg/mL on day 1, mg/mL) were 2.82 mg/mL on day 1, 2.91 mg/mL on day 14, and 2.24 mg/mL on day 38. Our results confirm the stability of midazolam for up to 14 days when mixed for oral administration.

Stability of midazolam hydrochloride in extemporaneously prepared flavored gelatin

The stability of midazolam hydrochloride in flavored gelatin was evaluated after storage at 4 degrees C for 14 days and at -20 degrees C for 28 days. A flavored liquid gelatin mixture was prepared and mixed with midazolam hydrochloride injection in final concentrations of midazolam 1 and 2 mg/mL. Gelatin cups containing 5 and 15 mg of midazolam were prepared by measuring appropriate volumes of the gelatin stock solutions and were stored in a refrigerator at 4 degrees C or in a freezer at -20 degrees C. Immediately after preparation and at 7 and 14 days, three refrigerated and three frozen gelatin samples of each midazolam concentration were visually inspected, tested for pH, and assayed for midazolam concentration by high-performance liquid chromatography. The frozen gelatin samples were also evaluated at 21 and 28 days; three whole and three partial gelatin samples were assayed for midazolam content to determine the uniformity of drug distribution within each sample. All samples maintained greater than 96% of the initial midazolam concentration throughout the study. There was no appreciable change in color, odor, or pH. The midazolam content of the gelatin in the cups was uniform. An extemporaneously compounded preparation of midazolam hydrochloride in flavored gelatin was stable when stored for 14 days at 4 degrees C and for 28 days at -20 degrees C. Distribution of midazolam hydrochloride in the gelatin was uniform.

Stability of midazolam hydrochloride in parenteral nutrient solutions

The compatibility and stability of midazolam hydrochloride in three parenteral nutrient (PN) solutions and the stability of 15 amino acids in the presence of midazolam hydrochloride were studied. Six combinations of three PN solutions with amino acid concentrations of 1.5%, 2.5%, and 5% and two midazolam concentrations (0.1 and 0.5 mg/mL) were prepared in triplicate and stored at room temperature under normal fluorescent lighting. Duplicate samples were visually inspected for color change, precipitation, or gas formation and tested for pH. The samples were evaluated for midazolam and amino acid content by high-performance liquid chromatography at zero, one, three, and five hours. Midazolam and amino acid concentrations did not change significantly during the study. There was no evidence of color change, precipitation, or gas formation with any midazolam-PN solution combination when the combinations were examined visually and under a microscope, and no substantial changes in pH occurred. Midazolam 0.1 and 0.5 mg/mL (as the hydrochloride salt) was stable in the three PN solutions studied; in addition, the amino acids present in the 1.5%, 2.5%, and 5% amino acid PN solutions were stable when combined with midazolam at concentrations of 0.1 and 0.5 mg/mL.