Pharmacokinetic determinants of dynamic differences among three benzodiazepine hypnotics. Flurazepam, temazepam, and triazolam.

Healthy adult volunteers (n = 52) received single oral doses of flurazepam hydrochloride (15 mg), temazepam (15 mg), triazolam (0.25 mg), or placebo in a parallel, double-blind study. Sedative effects were greatest with triazolam, followed next by temazepam; peak effects closely coincided with peak plasma concentrations. Differential recovery from sedation corresponded in part to differences in mean elimination halflife, although sedative effects returned to baseline before plasma drug concentrations became undetectable. Sedation following flurazepam administration was less intense than with triazolam and temazepam. When tested at three hours after dosing, none of the active treatments impaired learning of a 16-item word list. However, at 24 hours, triazolam recipients could not recall a significant fraction of what was learned. Thus, dynamic differences among three benzodiazepine hypnotics may be partly explained by kinetic differences, as well as, we should caution, by possible "clinical inequivalence" in dosage.

Effects of patient age and physician training on choice and dose of benzodiazepine hypnotic drugs.

We conducted a cross-sectional review of all prescriptions (N = 554) for triazolam and flurazepam hydrochloride written by nonpsychiatrists to outpatients at a university affiliated Veterans Administration hospital. We sought to determine whether triazolam, an agent with a short half-life, was used preferentially in older patients (age greater than or equal to 70 years). We also wanted to determine whether dosages of triazolam or flurazepam were lowered in elderly patients. Our findings showed that prescriber level of training was a much stronger determinant of drug choice than patient age. Attending physicians prescribed flurazepam twice as often as interns. Lower dosages of both agents were prescribed more frequently to older patients. Our data suggest that some physicians choose a benzodiazepine hypnotic out of habit rather than application of pharmacologic principles, but reduce doses appropriately when prescribing to elderly patients.

Pharmacology of benzodiazepine hypnotics.

The "revolution" in pharmacologic treatment of insomnia began in 1970 with the availability of flurazepam, the first of the benzodiazepine hypnotics. Flurazepam largely replaced all other hypnotics during the decade of the 1970s. The second revolution began in the early 1980s as shorter half-life hypnotics, triazolam and temazepam, became available and began to replace flurazepam. The decade of the 1990s will probably see a more balanced pattern of benzodiazepine hypnotic use, as well as use of newer nonbenzodiazepine hypnotics. Among available benzodiazepines, all have the capacity to produce dose- and concentration-dependent sedation, drowsiness, performance impairment, and amnesia. Benzodiazepine-induced amnestic effects are characterized by either impairment of information acquisition, impairment of consolidation and storage, or both. In general, apparent clinical differences among benzodiazepine hypnotics are explained by differences in pharmacokinetic properties of absorption, distribution, elimination, and clearance.

Quazepam and flurazepam: differential pharmacokinetic and pharmacodynamic characteristics.

Quazepam and flurazepam share pharmacokinetic properties that result in prevention of early-morning insomnia, daytime rebound anxiety, and withdrawal rebound insomnia. Yet sleep laboratory and performance studies demonstrated that during a 1- to 4-week administration period quazepam had a low potential for causing daytime drowsiness or impairment. This profile may be related to several factors, such as differences in quazepam's metabolic pathways; plasma pharmacokinetics; rate of brain uptake, redistribution, and clearance; as well as differences in receptor binding and kinetics.

Kinetics, brain uptake, and receptor binding characteristics of flurazepam and its metabolites.

The benzodiazepine derivative flurazepam (FLZ) is widely used as a hypnotic, but the relative contributions of FLZ and its metabolites desalkylflurazepam (DA-FLZ), hydroxyethylflurazepam (ETOH-FLZ), and flurazepam aldehyde (CHO-FLZ) to overall clinical activity remain uncertain. A single 20 mg/kg dose of FLZ.HCl was administered to mice, with plasma and brain concentrations of FLZ and metabolites determined during 5 h after dosage. Brain and plasma concentrations of FLZ were maximal at 0.5 h after dosage, then declined rapidly in parallel, whereas those of DAFLZ were maximal at 2 h, then declined slowly. Concentrations of ETOH-FLZ, the most polar metabolite, were maximal at 0.5 h, and were undetectable after 3 h. Little CHO-FLZ was detected in either brain or plasma. A single 30-mg oral dose of FLZ.HCl was given to 18 human volunteers, with plasma levels determined over 9 days. FLZ was detected in plasma at low concentrations for no more than 3 h after dosage. ETOH-FLZ concentrations were higher and persisted for 8 h after dosage. CHO-FLZ reached intermediate peak levels and was present longer than FLZ or ETOH-FLZ. In contrast, DA-FLZ achieved the greatest peak concentrations, occurring at 10 h after dosage. Levels declined very slowly, with a mean half-life of 71.4 h, and were still detectable 9 days after FLZ dosage. Plasma free fractions (percent unbound) in mice were 40.3, 51.4, and 25.0% for FLZ, ETOH-FLZ and DA-FLZ, respectively; in humans, values were 17.2, 35.2, and 3.5%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic flurazepam treatment on firing rate of rat substantia nigra pars reticulata neurons.

The effect of a benzodiazepine, flurazepam, on the spontaneous activity of neurons in the pars reticulata of the substantia nigra was studied in chloral hydrate anesthetized rats. Flurazepam produced a dose-related suppression of neuronal activity. In rats that were chronically treated with flurazepam, tolerance to flurazepam was present after 7 and 28 days, but not after only 3 days of treatment. Tolerance persisted at least 2, but not 7 days after 4 weeks of chronic treatment.

Intranasal absorption of flurazepam, midazolam, and triazolam in dogs.

Intranasal delivery of flurazepam, midazolam, and triazolam was studied in a dog model as a possible alternate route of drug administration for treatment of insomnia. Four beagles received each hypnotic by both intranasal and oral routes on two separate occasions. Plasma concentrations for each hypnotic after dosing were measured by electron-capture gas-liquid chromatography. The mean intranasal absorption rates (tmax) of flurazepam, midazolam, and triazolam were 1.7, 2.0, and 2.6 times faster, respectively, compared with oral dosing. The mean dose-normalized peak concentrations (Cmax) after intranasal delivery were 16.4, 2.9, and 3.4 times higher, respectively, versus oral administration. The mean dose-normalized AUCs estimated for these compounds after nasal administration were 2.4-, 2.5-, and at least 2-fold larger than after oral administration for midazolam, triazolam, and flurazepam, respectively. If these observations can be extrapolated to humans, the faster absorption achieved by the intranasal route would appear to benefit insomniacs characterized by difficulty in falling asleep because of an anticipated faster sedative effect onset. The higher peak concentrations and larger amounts absorbed in the case of intranasal midazolam and triazolam delivery may lead to dose reduction.

Post-mortem drug redistribution--a toxicological nightmare.

Detailed human case data is presented to illustrate the dramatic extent of the phenomenon of post-mortem drug redistribution. The data suggests that there is a post-mortem diffusion of drugs along a concentration gradient, from sites of high concentration in solid organs, into the blood with resultant artefactual elevation of drug levels in blood. Highest drug levels were found in central vessels such as pulmonary artery and vein, and lowest levels were found in peripheral vessels such as subclavian and femoral veins. In individual cases, in multiple blood samples obtained from ligated vessels, concentrations of doxepin and desmethyldoxepin ranged from 3.6 to 12.5 mg/l and 1.2 to 7.5 mg/l, respectively; amobartital, secobarbital and pentobarbital from 4.3 to 25.8 mg/l, 3.9 to 25.3 mg/l and 5.1 to 31.5 mg/l respectively; clomipramine and desmethylclomipramine from 4.0 to 21.5 mg/l and 1.7 to 8.1 mg/l, respectively and flurazepam 0.15 to 0.99 mg/l; imipramine and desipramine from 4.1 to 18.1 mg/l and 1.0 to 3.6 mg/l, respectively. We conclude that this poorly studied phenomenon creates major difficulties in interpretation and undermines the reference value of data bases where the site of origin of post-mortem blood samples is unknown.

[Storage stability of flunitrazepam, flurazepam, diazepam and metabolites in blood and plasma]. / Zur Lagerungsstabilität von Flunitrazepam, Flurazepam, Diazepam und Metaboliten in Blut und Plasma.

The stability of flunitrazepam, flurazepam, diazepam and some of their metabolites in spiked blood and plasma samples was studied bei GC-ECD analysis at defined time intervals up to 240 days. Validation data of the method are given. The blood or plasma samples were stored either at 22 degrees C or at 4 degrees C, and were exposed to global natural light irradiation or protected from light. All substances considerably decreased during the time interval studied. Flunitrazepam soon disappeared completely at room temperature (22 degrees C), while diazepam and flurazepam proved to be more stable, but a clear pattern of breakdown could not be established. The data obtained suggest a result from a long-term stored sample to be cautiously interpreted. Further investigation concerning the stability of drugs and the establishment of optimal storage conditions seem necessary.

Benzodiazepine-mediated structural changes in the multidrug transporter P-glycoprotein: an intrinsic fluorescence quenching analysis.

P-glycoprotein expressed in Pichia pastoris was used to study the drug binding sites of different benzodiazepines. The effect of bromazepam, chlordiazepoxide, diazepam and flurazepam on P-glycoprotein structure was investigated by measuring the intrinsic fluorescence of the transporter tryptophan residues. Purified mouse mdr1a transporter in mixed micelles of 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonic acid and 1,2-dimiristoyl-sn-glycerol-3-phosphocholine emitted fluorescence at 340 nm indicative of the fluorophores in a relatively apolar environment. Acrylamide and iodide ion were used as collisional quenchers toward distinct regions of the transporter, the protein and the interface protein-surface, respectively. Binding of ATP induced conformational changes at the protein surface level in accordance with the location of the nucleotide binding sites. Bromazepam interaction with the transporter was located at the protein-surface interface, diazepam at the membrane region and chlordiazepoxide at the protein surface. Only the flurazepam interaction site was not detected by the quenchers used. All benzodiazepines were able to elicit reorientation of the protein fluorophores on the P-glycoprotein-ATP complex.

A double-blind, placebo- and flurazepam-controlled investigation of the residual psychomotor and cognitive effects of modified release zolpidem in young healthy volunteers.

Short-acting hypnotic drugs, such as zolpidem, have minimal residual effects but may not provide optimal efficacy throughout the night for all insomnia patients. A modified-release formulation of zolpidem, zolpidem-MR, has been developed to overcome this limitation. This was a phase I, double-blind, 3-way crossover, placebo-controlled study to investigate the residual psychomotor and cognitive effects of a single oral dose of zolpidem-MR 12.5 mg in 18 healthy young adults. Flurazepam 30 mg was used as a positive control. No comparison with standard immediate-release zolpidem was made. Five neuropsychological tests and 2 subjective tests were performed 8 hours after dosing. The safety of zolpidem-MR was also investigated. Performance on the Critical Flicker Fusion Frequency test, Choice Reaction Time, Immediate and Delayed Word Recall, and the Compensatory Tracking Task was significantly impaired by flurazepam but not by zolpidem-MR (with the exception of the Compensatory Tracking Task) or placebo. No significant effects were observed on the Digit Symbol Substitution Test. The Leeds Sleep Evaluation Questionnaire showed that both drugs improved the ease of getting to sleep and perceived quality of sleep, whereas only flurazepam significantly impaired the ease of awakening. Neither drug scored significantly better than placebo on the Bond and Lader contentedness scale, but both induced a significant difference in calmness; only flurazepam significantly reduced alertness. The safety profile of zolpidem-MR was comparable to placebo. In conclusion, the study showed the good tolerance of zolpidem-MR in terms of residual neuropsychological effects as well as a beneficial effect on sleep quality in young healthy adults.

Simultaneous determination of flurazepam and five metabolites in serum by high-performance liquid chromatography and its application to pharmacokinetic studies in rats.

A reversed-phase high-performance liquid chromatographic method is described which allows the quantification of flurazepam and five of its metabolites with a single, isocratic determination. In addition, it has the advantage of possessing a low detection limit and high precision. A 2 mm I.D. column was used to minimize sample size (50 microliter), increase sensitivity and reduce solvent consumption. The method was used to demonstrate that N-1-desalkylflurazepam, the major metabolite, has a short half-life in the rat in contrast to its prolonged life in humans.

Determination of flurazepam and its major metabolites N-1-hydroxyethyl- and N-1-desalkylflurazepam in plasma by capillary gas chromatography.

In the present paper we describe a method for the quantitative determination of flurazepam (I) and two of its metabolites, N-1-desalkylflurazepam (II) and N-1-hydroxyethylflurazepam (III), in serum after therapeutic dosings is described. The method is sensitive (lower limit of quantification for I and III: 1 ng/ml, for II: 2 ng/ml), selective and--compared to the analytical approaches already published--simple to handle. Thus this assay is well suitable for determinations during clinical studies (e.g. evaluating the pharmacokinetics, bioavailability/bioequivalence). Following simple extraction- and derivatization steps (the latter being only required for III) the extract is injected directly onto a fused-silica, bonded-phase capillary column of a gas chromatograph and the compounds of interest detected by an electron-capture detector (ECD). The assay has been used successfully during several clinical studies, especially as very low dosages result in also very low blood concentrations.

Pharmacokinetics and CSF entry of flurazepam in dogs.

Anesthetized dogs received a single 1.0-mg/kg intravenous dose of flurazepam hydrochloride, following which multiple blood and cerebrospinal fluid (CSF) samples were taken over the next 8 h. Concentrations of flurazepam and its metabolite, desalkylflurazepam, were determined by gas chromatography with electron-capture detection. Mean kinetic variables for flurazepam were: volume of distribution 7.9 l/kg, elimination half-life 2.3 h, clearance 37 ml/min/kg, serum free fraction 25% unbound. The metabolic product desalkylflurazepam appeared in serum in low concentrations, and was eliminated with a half-life of 4.9 h. Flurazepam rapidly entered CSF, then was eliminated in parallel with flurazepam in serum. However, the extent of entry into CSF was limited, with the mean ratio of area under the curve for CSF versus serum (0.24) nearly identical to the serum free fraction. Thus, intravenous flurazepam in dogs is characterized by extensive distribution, high clearance, and short half-life. Entry into CSF is rapid, and appears governed by passive diffusion. The extent of CSF entry is limited by protein binding in serum.

Simultaneous determination of flurazepam and its metabolites in human plasma by high-performance liquid chromatography.

A sensitive isocratic high-performance liquid chromatographic method is described, which allows the precise and accurate quantification of flurazepam and four metabolites with a single determination. A pharmacokinetic study was performed on nine volunteers and the main pharmacokinetic data are reported. The method was used to demonstrate that monodesethylflurazepam and didesethylflurazepam are major metabolites in men. One more unidentified flurazepam metabolite was detected.

Hepatic vs. gastrointestinal presystemic extraction of oral midazolam and flurazepam.

An experimental model was developed to elucidate the site of presystemic extraction of drugs with incomplete bioavailability due to high extraction after p.o. dosage. Domestic pigs received single i.v. or p.o. doses of midazolam (1 mg/kg) or flurazepam (2 mg/kg), two benzodiazepine derivatives with high presystemic extraction after p.o. dosage. Multiple blood samples were simultaneously drawn from the portal vein and from a systemic vein during 8 hr after dosage. After i.v. administration, both drugs had high systemic serum clearance, averaging 24 ml/min/kg. Area under the serum concentration curve (AUC) for systemic vs. portal sites was nearly identical for midazolam (769 vs. 737 ng/ml x hr); for flurazepam, systemic AUC exceeded portal AUC (1035 vs. 778 ng/ml x hr, P less than .01). After p.o. dosage, the systemic/portal AUC ratio averaged 0.15 for midazolam and 0.11 for flurazepam; for both drugs, portal AUC after p.o. dosage did not differ significantly from systemic AUC after i.v. administration. Thus, the extensive presystemic extraction of orally administered midazolam and flurazepam are mainly attributable to hepatic biotransformation rather than metabolism either within the gastrointestinal tract or during absorption into the portal circulation.

[Preliminary report on the blood levels of Flurazepam administered in two different pharmaceutical formulations]. / Studio preliminare sui livelli ematici di Flurazepam somministrato in due formulazioni farmaceutiche.

Flurazepam (15 mg) was administered to 4 beagles in solution and in capsules. Blood levels of unchanged Flurazepam were measured by GLC using an electron capture detector. In the case of solution blood levels were measurable over a 2 hour period with the peak at 30 min in all dogs. In the case of capsules these levels were measurable in only one dog, which also showed the highest blood levels with the solution. Flurazepam is a drug which is rapidly metabolized into a series of metabolites. In the case of capsules the metabolization rate is more rapid than the enteral absorption rate, and consequently the blood levels of the unchanged drug are hardly measurable. The administration of Flurazepam in solution allows a more rapid enteral absorption rate and consequently the levels of the unchanged drug are measurable over a 2 hour period.

Effects of itraconazole on the plasma kinetics of quazepam and its two active metabolites after a single oral dose of the drug.

The effects of itraconazole, a potent inhibitor of cytochrome P450 (CYP) 3A4, on the plasma kinetics of quazepam and its two active metabolites after a single oral dose of the drug were studied. Ten healthy male volunteers received itraconazole 100 mg/d or placebo for 14 days in a double-blind randomized crossover manner, and on the fourth day of the treatment they received a single oral 20-mg dose of quazepam. Blood samplings and evaluation of psychomotor function by the Digit Symbol Substitution Test and Stanford Sleepiness Scale were conducted up to 240 h after quazepam dosing. Itraconazole treatment did not change the plasma kinetics of quazepam but significantly decreased the peak plasma concentration and area under the plasma concentration-time curve of 2-oxoquazepam and N-desalkyl-2-oxoquazepam. Itraconazole treatment did not affect either of the psychomotor function parameters. The present study thus suggests that CYP 3A4 is partly involved in the metabolism of quazepam.

Sleep, performance, and plasma levels in chronic insomniacs during 14-day use of flurazepam and midazolam: methodology.

Methods are described for a five-center study of flurazepam and midazolam, in which 107 patients with histories of benzodiazepine use for chronic insomnia were enrolled. Data were available for 99 of these patients. Staff and patient manuals and a behavior-based computer system were specially designed to measure and delineate clearly the study procedures and parameters. Patients were carefully followed and supported during a 20-day washout period and underwent extensive training on psychomotor performance tasks. They received placebo for 2 nights and were then randomly assigned to one of four study treatments--flurazepam 15 or 30 mg, midazolam 15 mg, or placebo--for 14 consecutive nights. All-night sleep electroencephalographic recordings were obtained on study nights--1 and 0 (placebo) and 1, 2, 7, 13, and 14 (treatment nights). Results of four computer-generated psychomotor performance tasks and three cognitive tasks, plus subjective evaluations of sleep, performance, and mood, were recorded in the morning after each night spent in the sleep laboratory. Blood and urine samples were analyzed for drug concentrations in plasma and for compliance with the protocol. A pilot study, using a high (nonclinical) dose of flurazepam (45 mg), preceded the multi-center study and was designed to evaluate tests in healthy volunteers and to familiarize staff with equipment and tests.