A rapid fluorimetric screening method for the 1,4-benzodiazepines: Determination of their metabolite oxazepam in urine

Oxazepam is the major metabolite screened in urine samples for the evidence of the use of benzodiazepine drugs. The methods currently used, however, are laborious and time consuming. This paper proposes an oxazepam detection method based on its hydrolysis and cyclization--a reaction catalysed by cerium (IV) in an ortho-phosphoric acid-containing medium--to form 2-chloro-9(10H)-acridinone, a strongly fluorescent molecule. The variables involved in the hydrolysis and cyclization stages were optimised. Oxazepam was detectable in the 5-900 ng mL(-1) range, with a detection limit of 4.15 ng mL(-1) for k=3. The method was successfully used for the determination of oxazepam in urine samples collected at different times after the oral administration of Valium and Tranxilium.

Very long half-life of paroxetine following intoxication in an extensive cytochrome P4502D6 metabolizer

A very long half-life of paroxetine (195 h instead of the usual value of around 16 h) was measured after an overdose with 2 g paroxetine and 1 g clorazepate in a patient who was an extensive cytochrome P4502D6 metabolizer. The patient recovered well without any clinically significant complications. A consequence of the close monitoring of paroxetine levels in this patient was that it was decided not to reintroduce any other antidepressant despite her suicide attempt, until normal levels of paroxetine had been reached, which took over 1 month.

Stedim 6 and Clearflex, two new multilayer materials for infusion containers. Comparative study of their compatibility with five drugs versus glass flasks and polyvinyl chloride bags

Stedim 6 and Clearflex, two new polyethylene-lined materials for infusion bags, were studied for their compatibility with disodium clodronate, chlorpromazine and maprotiline hydrochlorides, diazepam, and clorazepate dipotassium salt, comparatively with borosilicate glass flasks and polyvinyl chloride bags. Diazepam, the only drug to exhibit a marked sorption in PVC bags (the loss reached 25% of the initial concentration after a contact duration of 72 h), showed lower sorption in Stedim 6 bags (loss about 11% under the same conditions) and none in Clearflex bags. No significant difference was observed between the infusion solutions used as vehicles of the drugs (5% dextrose and 0.9% sodium chloride isotonic solutions). The results are discussed in terms of lipophilicity of the drugs and crystallinity of the polymers.

Effects of a 44-day administration of phenobarbital on disposition of clorazepate in dogs

The disposition of clorazepate, a benzodiazepine anticonvulsant, was determined in dogs after administration of a single oral dose of clorazepate (2 mg/kg of body weight) and after oral administration of clorazepate (2 mg/kg, q 12 h) concurrently with phenobarbital (5 mg/kg, q 12 h) for 44 consecutive days. Serum concentrations of nordiazepam, the active metabolite of clorazepate, were measured. After a single oral dose of clorazepate, maximal nordiazepam concentrations ranged from 569.6 to 1,387.9 ng/ml (mean, 880.2 +/- 248.9 ng/ml) and were detected 16.8 to 131.4 minutes (mean, 85.2 +/- 36 minutes) after dosing. After administration of phenobarbital for 44 consecutive days, maximal nordiazepam concentrations were significantly (P < 0.01) lower, ranging from 209.6 to 698.5 ng/ml (mean, 399.3 +/- 155.6 ng/ml) at 68.4 to 145.8 minutes (mean, 93 +/- 25.8 minutes) after dosing. Mean area under the curve (AUC) on day 1 (mean, 3.37 +/- 0.598 ng.min/ml) was significantly (P < 0.001) greater than AUC on day 44 (1.66 +/- 0.308 ng.min/ml). Oral clearance was significantly (P < 0.01) greater on day 44 (12.44 +/- 2.55 ml/min/kg), compared with that on day 1 (6.16 +/- 1.35 ml/min/kg). Values for area under the first moment curve, oral volume of distribution, mean residence time, and elimination half-life were not significantly altered by concurrent administration of phenobarbital. Administration of phenobarbital altered the disposition of clorazepate such that the amount of nordiazepam in circulation during each dose interval was significantly reduced. Adequate control of seizures in epileptic dogs, therefore, may require higher dosages of clorazepate when it is coadministered with phenobarbital.

Active drug metabolites. An overview of their relevance in clinical pharmacokinetics

This review underlines the importance of considering in the overall evaluation of drug effect and efficacy not only the kinetics and activities of the administered drug, but also those of the chemical species (metabolites) which are formed in the body. The circumstances in which a role for active drug metabolites may be suspected are described, and a number of specific examples are given. Four different categories are described: drugs which are inactive precursors of active metabolites (e.g. DOPA and cyclophosphamide); active metabolites which contribute to the duration of action of the parent compound (e.g. hexamethylmelamine and clobazam); active metabolites showing a mechanism of action different from that of the parent compound (e.g. buspirone and 1-pyrimidinyl piperazine; fenfluramine and norfenfluramine); and active metabolites showing an antagonistic effect on the activity of the parent drug (e.g. trazodone and m-chlorophenyl-piperazine; aspirin and salicylate).

Intramuscular bioavailability of chlorazepate as compared to diazepam

Dipotassium chlorazepate (DPC) and diazepam (DZM) were given i.m. and i.v. to 6 healthy volunteers in doses of 20 mg (48.9 mumol) DPC and 15 mg (52.0 mumol) DZM. The interval between the injections was at least 1 week. Plasma samples were analyzed for DPC and DZM by HPLC. The bioavailability of DPC and DZM after i.m. administration, determined from computer calculated AUCs, was 1.04 and 0.85, respectively.

Comparative single-dose kinetics of oxazolam, prazepam, and clorazepate: three precursors of desmethyldiazepam

Twelve healthy volunteers received a single 40-mg oral dose of the benzodiazepine derivative oxazolam, which serves primarily as a precursor of the active substance desmethyldiazepam (DMDZ). Concentrations of DMDZ were measured in multiple serum samples drawn for up to two weeks after the dose. Peak serum DMDZ concentrations averaged 115 ng/ml, measured at 8.6 hours after dosage. Mean DMDZ elimination half-life averaged 61 hours. Three of the subjects also received 40 mg each of prazepam and clorazepate, two other DMDZ precursors, on separate occasions. Although DMDZ elimination half-life was similar, total area under the curve (AUC) for DMDZ was larger for clorazepate, known to be completely transformed into DMDZ, than for oxazolam or prazepam the extent of whose conversion to DMDZ has not been previously established. After correcting for the different molar equivalent of DMDZ available from each preparation, the DMDZ ratio averaged 0.22 for oxazolam vs. clorazepate and 0.51 for prazepam vs. clorazepate. Thus, both oxazolam and prazepam lead to slow appearance of DMDZ in the systemic circulation. Furthermore the extent of DMDZ formation from oxazolam and prazepam is either incomplete or the drugs are incompletely absorbed. Equivalent doses of oxazolam, prazepam, and clorazepate should not be interchanged in clinical practice.

Cimetidine interaction with dipotassium clorazepate disposition in the anesthetized dog

Cimetidine (CIM) was used as an interacting agent on the disposition in dogs of dipotassium clorazepate ( CZP ) and its main metabolite nordiazepam (ND) in order to study some of the factors contributing to pharmacokinetic interspecies variation of benzodiazepines in dogs and man. A 0.5 mg/kg of body weight intravenous (i.v.) bolus dose of CZP was administered to 12 anesthetized mongrel dogs, 6 of them receiving also, 30 min before, a 1 mg/kg i.v. bolus dose of CIM followed by a constant i.v. infusion (1 mg/kg/hr) of CIM. Plasma ND and CZP concentrations were measured as a function of time with an high-performance liquid chromatography method. Plasma levels of CZP declined mono- and biexponentially in 1 and 5 dogs, respectively, for each group of animals. No statistically significant difference was found between CZP pharmacokinetic parameters when the 2 groups of dogs were compared. However, a 37% decrease in ND beta half-life, t1/2 beta, when CZP was associated with CIM, was found to be statistically significant. The i.v. administration of pure ND in two dogs, has shown that ND declines biexponentially with a t1/2 beta similar to the one estimated after CZP dosing in control animals. The hepatic metabolism of ND was found to be flow-independent and restrictive. The data, along with previously reported CIM interactions, suggest that several factors, which would be species-dependent, must be responsible of CIM effect on other drugs.

Clorazepate dipotassium and diazepam in renal insufficiency: serum concentrations and protein binding of diazepam and desmethyldiazepam

5 patients with chronic renal failure on maintenance hemodialysis and 5 healthy matched controls received single 20-mg intravenous doses of clorazepate dipotassium. Clearance of pharmacologically active unbound desmethyldiazepam was reduced in renal failure patients as opposed to controls, and free fraction in serum was greater. Since desmethyldiazepam distribution was reduced in renal patients, elimination half-life was actually shorter than in controls (36 vs. 57 h). In 10 dialysis patients receiving chronic diazepam treatment (5-15 mg/day), steady-state concentrations of diazepam (56 ng/ml) and desmethyldiazepam (77 ng/ml) were significantly lower than in age- and weight-matched controls receiving similar doses (189 and 216 ng/ml, respectively). However after correction for the higher free fractions of both compounds in renal patients as opposed to controls, steady-state concentrations of unbound drug were found to be similar between groups. Interpretation of kinetic variables and steady-state serum concentrations of extensively protein-bound drugs requires consideration of alterations in protein binding that may occur in disease states.

Pharmacokinetic model for diazepam and its major metabolite desmethyldiazepam following diazepam administration

A five-compartment open model was used to simulate the blood concentration profiles of diazepam and its metabolite, desmethyldiazepam, following single- and multiple-dose administrations of diazepam. The parameter estimates for diazepam were previously reported literature values. The parameters estimates for the metabolite were calculated from literature values of blood concentrations of desmethyldiazepam following the administration of clorazepate. The five-compartment open model suggests that approximately 50% of the administered diazepam is biotransformed to desmethyldiazepam, and that the elimination profile of the metabolite is not altered by the presence of the drug. The model may also be readily adapted to predict the concentrations of diazepam and desmethyldiazepam in cerebrospinal fluid following the administration of diazepam by simply correcting the blood or plasma concentrations of the drug and metabolite for the degree of plasma protein binding.

High-performance liquid chromatography determination of dipotassium clorazepate and its major metabolite nordiazepam in plasma

A rapid and sensitive high-performance liquid chromatographic method is described for the quantitative analysis of dipotassium clorazepate (CZP) and its major metabolite nordiazepam (ND) in fresh human and dog plasma. The method consists of two separate selective ND extractions from a plasma sample without and with conversion of all the CZP to ND. For quantitation, diazepam (DZP) is used as the internal standard. The chromatographic phase utilized in a reversed-phase Hibar EC-RT analytical column prepacked with LiChrosolv RP-18 with a solvent system consisting of acetonitrile-0.05 M sodium acetate buffer, pH 5.0 (45:55). The UV absorbance is monitored at 225 nm using a variable-wavelength detector. The mean assay coefficient of variation over a concentration range of 20-400 ng per ml of plasma is less than 3% for the within-day precision. Recoveries of ND, DZP and CZP (as ND) are essentially quantitative at all levels investigated. The calibration curves of ND are rectilinear (r2 = 0.99) from the lower limit of sensitivity (2 ng/ml) to at least 2000 ng/ml in plasma. Applicability of the method to CZP and ND disposition studies in the anaesthetized mongrel dog is illustrated. When the two separate selective nordiazepam extractions from plasma cannot be performed immediately after blood sampling, an extrapolation kinetic method is suggested for the estimation of CZP concentration. In all previous in vivo studies, CZP has been determined only with gas-liquid chromatographic methods.

Cimetidine impairs clearance of antipyrine and desmethyldiazepam in the elderly

Sixteen young (21-40 years) and nine elderly (65-78 years) volunteers received single intravenous doses of antipyrine on two occasions: once in the control state, and again while receiving therapeutic doses of cimetidine (300 mg every six hours). In the control state, antipyrine half-life was longer in elderly than in young subjects (16.4 vs 11.0 hours), and metabolic clearance lower (0.48 vs 0.72 ml/min/kg). However, coadministration of cimetidine prolonged antipyrine half-life to a similar extent in elderly and in young groups (150 and 153 per cent of control) and reduced metabolic clearance to a similar extent in both (79 vs 69 per cent of control) groups. Three young and six elderly volunteers received a single 15 mg oral dose of clorazepate, a precursor of desmethyldiazepam, with and without cimetidine. As in the case of antipyrine, cimetidine prolonged desmethyldiazepam half-life similarly in young and elderly groups (175 vs 164 per cent of control) and similarly reduced metabolic clearance (51 vs 65 per cent of control). The elderly population may already have an impaired capacity to oxidize drugs. This capacity is further impaired by coadministration of cimetidine.

Prolongation of drug half-life due to obesity: studies of desmethyldiazepam (clorazepate)

Desmethyldiazepam pharmacokinetics were determined after oral administration of its precursor, clorazepate, to 12 obese subjects (mean weight: 105.4 kg; mean percent ideal body weight: 170%) who were matched for age, sex, and smoking habits with 12 normal controls (66.5 kg; percent ideal body weight: 103.3%). After an overnight fast, a single 15-mg clorazepate capsule, equivalent to 10.3 mg of desmethyldiazepam, was administered. Multiple plasma samples drawn 10-42 days postdose were analyzed for desmethyldiazepam by electron-capture GLC. Obese subjects compared to controls had a prolonged desmethyldiazepam elimination half-life (t1/2) (154.1 hr versus 57.1 hr; p less than 0.005). Assuming quantitative conversion of clorazepate to desmethyldiazepam and 100% systemic availability, volume of distribution (Vd) was greatly increased in the obese (158.8 liters versus 63.3 liters; p less than 0.001). The value of Vd remained greater even after correction for body weight (1.52 liter/kg versus 0.94 liter/kg; p less than 0.005). However, clearance of desmethyldiazepam was not different between groups (13.2 ml/min in obese versus 13.4 ml/min in controls). The percent ideal body weight was highly correlated with Vd (r = 0.82), as was total body weight (r = 0.86). The value of t1/2 was correlated highly with Vd (r = 0.89) but only weakly with clearance (r = -0.38). Therefore, the large increase in the desmethyldiazepam t1/2 value seen in obese subjects is predominantly due to the disproportionate distribution of this lipid-soluble drug into body fat as opposed to lean tissue. The contribution of clearance to desmethyldiazepam t1/2 was of much less importance than was Vd in this obese study population.

Use of benzodiazepines during pregnancy, labour and lactation, with particular reference to pharmacokinetic considerations

Knowledge of the pharmacokinetic properties of the benzodiazepines is playing an increasingly important role in their use during pregnancy, labour and lactation. All of the benzodiazepine derivatives are lipophilic, undissociated agents which readily penetrate membranes. Thus, they exhibit rapid placental transfer with significant fetal uptake of the drug. In the first trimester of pregnancy there is seldom a clear indication for the use of benzodiazepines. In late pregnancy and at parturition there may be more clear indications for their use. During delivery, the lowest effective dose should be used, since after high doses the so-called 'floppy infant syndrome' may occur, and the slow elimination of these agents by the newborn should be considered. Oxazepam, lorazepam, nitrazepam and, especially, flunitrazepam, appear to penetrate the human placenta more slowly than diazepam, but the clinical significance of this phenomenon remains uncertain. All of these derivatives appear in human milk, but only high clinical doses might be expected to exert a possible effect on the nursing newborn.

Steady-state plasma desmethyldiazepam during long-term clorazepate use: effects of antacids

The effect of antacid on steady-state plasma desmethyldiazepam (DMDZ) concentrations during long-term treatment with clorazepate dipotassium (CZP) was evaluated in 10 subjects. Each took 7.5 mg CZP nightly for 30 consecutive nights divided into three 10-day treatments given in random sequence as follows: (1) 7.5 mg CZP nightly with no antacid, (2) CZP nightly for 30 ml Maalox, and (3) CZP nightly with Maalox with an additional 30 ml Maalox three times daily. The overall mean steady-state DMDZ plasma level, measured during the last 3 days of each treatment condition, was 175 ng/ml. Within-day means ranged from 159 to 202 ng/ml and were not influenced by treatment condition, time, or trial sequence. DMDZ washout after termination of the 30-day trial was slow, proceeding with a half-life of 75 hr (range, 63 to 109 hr). Thus, Maalox does not alter steady-state DMDZ levels during long-term CZP therapy.

Effect of age and sex on disposition of desmethyldiazepam formed from its precursor clorazepate

Desmethyldiazepam (DMDZ) disposition was evaluated in 32 healthy male and female volunteers who ingested single 15-mg doses of the precursor compound, clorazepate dipotassium. DMDZ concentrations were measured in multiple plasma samples obtained between 7 and 9 days after dosage. Appearance of DMDZ in blood was rapid, with peak concentrations attained on average 1.5 h after dosage. Absorption half-life (t1/2 a) averaged 24 min. Neither peak time nor t1/2 a were influenced by age or sex. After a rapid phase of distribution, DMDZ elimination was slow, with a mean elimination half-life (t1/2 beta) of 82 h (range 27-219 h). t1/2 beta became prolonged with age in men but not in women. Likewise, clearance of total (free bound) DMDZ declined with age in male subjects (r=- 0.47, P less than 0.1), but was unrelated to age in women. DMDZ was extensively bound to protein in all subjects. The mean free fraction (FF) was 3.1% (range 2.0-4.3%), and increased significantly with declining plasma albumin concentrations (r=-0.57, P less than 0.001). Partly due to a decline in plasma albumin with age (r=-0.47, P less than 0.01), FF tended to increase with age (r=0.23). After correction for individual differences in FF, clearance of pharmacologically active unbound DMDZ declined significantly with age in men (r=-0.65, P less than 0.01), but actually was slightly higher in elderly as opposed to young women. Thus, the age-related decline in the capacity for hepatic hydroxylation of DMDZ is highly sex-specific.

Pharmacokinetics of N-desmethyldiazepam after a single oral dose of clorazepate: the effect of smoking

The pharmacokinetics of N-desmethyldiazepam was evaluated after oral administration of clorazepate 20 mg to 12 healthy male volunteers (6 smokers; 6 non-smokers), aged 23-29 years. Plasma levels of desmethyldiazepam were measured by gas liquid chromatography. The half life of elimination (t1/2 beta) was significantly longer in the non-smoking volunteers than in the smokers: 54.7 +17.7 versus 29.8 +9.9 h (p less than 0.05). Peak plasma concentrations (Cmax) were higher in non-smokers than in smokers, 413 +106 micrograms/l and 245 +50 micrograms/l, respectively (p less than 0.05). The sedative effect of clorazepate was less severe in smokers than in non-smokers.

The use of benzodiazepines in clinical practice

1 The pharmacokinetic characteristics of the six benzodiazepine anxiolytic drugs available in the United States are reviewed.

2 Concern over the abuse potential of the benzodiazepine class of drugs is discussed.

Pharmacokinetics of dipotassium chlorazepate in patients after repeated 50 mg oral doses

Dipotassium chlorazepate (DPC) was administered to ten patients (five males and five females), ages 18-37 years (mean 27.4), as a once daily dose of 50 mg until a steady state was reached. Plasma concentrations of the main metabolite N-desmethyldiazepam (DMD) were monitored by a high pressure liquid chromatographic (HPLC) method during the medication period and for 5 days after withdrawal of the drug. The plasma half life (t1/2), the elimination coefficient (K beta), the steady state concentration (Css), and the apparent volume of distribution (V beta), were calculated at steady state and the mean values +/- SEM were 44 +/- 5 h. 0.0184 +/- 0.0026 h(-1), 1590 +/- 163 ng/ml and 1.41 +/- 0.17 l/kg, respectively. A moderate inter-individual variability was observed. There was no tendency towards dose dependent elimination.

Pharmacokinetics of the placental transfer and distribution of clorazepate and its metabolite nordiazepam in the feto-placental unit and in the neonate

Clorazepate 20 mg was given i.m. to 49 mothers during the first stage of labour. The elimination of the drug was studied in 27 newborns produced by these mothers. The same dose was given to 13 women who underwent amniocentesis and to 7 women who were breast-feeding. "Total nordiazepam", i.e. the sum of clorazepate and its metabolite nordiazepam, was determined by gas-liquid chromatography in maternal blood, umbilical cord blood (both arterial and venous), amniotic fluid and in milk. Clorazepate was found to cross the placental barrier slowly, but nordiazepam was transferred more rapidly. Nordiazepam was found in the milk and in the blood of neonates after breast-feeding had started.

Pharmacokinetics of clorazepate in pregnant and non-pregnant women

A single dose of clorazepate 20 mg was injected i.m. in 7 pregnant and 7 non-pregnant women. Blood samples were collected for one week, and urine was collected for 24 h after the dose. The concentrations of clorazepate and its metabolite nordiazepam were determined by electron capture gas liquid chromatography. There was no difference between the two groups on physical examinations. Clorazepate was rapidly absorbed and the peak concentration was reached within 2 h. Mean pharmacokinetic parameters for clorazepate were absorption half life 0.77 h in pregnant women and 0.56 h in non-pregnant women; elimination half life 1.3 h in pregnant women and 2.0 h in non-pregnant women; volume of distribution: 0.43 1 . kg-1 in the pregnant women and 0.33 1 . kg-1 in non-pregnant women. Nordiazepam reached its peak concentration within 12 h after dosing; its mean half life of elimination was 180 h in pregnant women and 60 h in non-pregnant women. Within 24 h, 1.3% of the clorazepate was recovered in urine from pregnant women and 7% in urine from the non-pregnant women.

Transfer in vitro of three benzodiazepines across the human placenta

A comparative study of the placental transfer to the foetus of three benzodiazepines was performed using a dual perfusion system of the human placental lobule. A transport fraction was calculated for each benzodiazepine and was compared with reference substances. Relative to antipyrine, the transport fraction of diazepam was 85%, and that of nordiazepam was 84%. The transport fraction of clorazepate represented only 20% of that of tritiated water. The relatively high transfer of diazepam and nordiazepam can be attributed to their high lipid solubility, and the lower transfer of clorazepate is due to its polar nature. It is suggested that in certain instances this benzodiazepine may be of especial value to obstetricians.

Self-rated sedation and plasma concentrations of desmethyldiazepam following single doses of clorazepate

Plasma concentrations of desmethyldiazepam (DMDZ) and intensity of self-rated sedation (SRS) were measured at multiple points in time during 6 h after a single 15 mg oral dose of clorazepate dipotassium. Mean plasma DMDZ levels and mean SRS scores both became maximal at 1.0--2.5 h after drug dosage. By 6 h, however, mean SRS had returned to the predrug baseline score while mean DMDZ concentration fell only slighty from the maximum value. Disappearance of SRS despite persistence of high DMDZ levels might be due to adaptation or tolerance. If this is the case, subjective effects of benzodiazepines may depend upon duration of drug exposure as well as dose and concentration.

Impaired absorption of desmethyldiazepam from clorazepate by magnesium aluminum hydroxide

Ten healthy volunteers ingested single 15-mg doses of clorazepate dipotassium (CZP) with 60 ml of water, or with 60 ml of magnesium aluminum hydroxide (Maalox), on two occasions in a randomized, two-way crossover study. Plasma concentrations of desmethyldiazepam (DMDZ) were determined in multiple samples drawn during 48 hr after each dose. Mean kinetic variables for DMDZ in CZP-water and CZP-magnesium aluminum hydroxide treatment conditions, respectively, were: peak measured concentration, 273 and 188 ng/ml (p 0.001); time of peak concentration, 1.8 and 2.8 hr after dose (p less than 0.01); apparent absorption half-life, 14.8 and 30.7 min (p less than 0.02); area under the 48-hr plasma concentration curve, 6,028 and 5,433 ng/ml X hr (p less than 0.02). Self-rated sensations of feedling "spacey," "thinking slowed down," and of generalized sedation, were reported with both treatment conditions, but these subjective effects occurred earlier and were more profound when CZP was taken with water as opposed to magnesium aluminum hydroxide. Thus administration of single doses of CZP with usual doses of a commonly prescribed antacid reduces the rate and extent of appearance in blood of DMDZ (the compound responsible for clinical activity) and attenuates self-rated clinical effects.

Effect of abdominal radiation therapy on drug absorption in humans

The absorption of oral digoxin and of desmethyldiazepam, from its precursor clorazepate, was studied in seven patients who had received abdominal and/or pelvic radiation therapy for neoplastic disease. All patients were in remission and had normal renal function and no evidence of malabsorption. Single 0.5-mg doses of digoxin tablets and 15-mg doses of clorazepate were administered in the fasting state. Concentrations of digoxin (by radioimmunoassay) and desmethyldiazepam (by gas chromatography) were determined in multiple plasma samples and all urine collected during 24 hours after dosage. The mean (+/- S.E.) weight-normalized area under the 24-hour plasma digoxin concentration curve (WtN-AUC-24) in the patients (722 +/- 40 ng/ml-hr-kg) was similar to that in five normal controls (713 +/- 57 ng/ml-hr-kg), but 24-hour urinary excretion of digoxin in patients (54.5 +/- 4.4 microgram) was significantly less (P less than 0.025) than in controls (83.4 +/- 11.4 microgram). Neither age, sex, nor renal function explained the difference. In the clorazepate study, WtN-AUC-24 for desmethyldiazepam in the patients (187 +/- 19 microgram/ml-hr-kg) was significantly less (P less than 0.01) than in 15 normal control subjects (230 +/- 5 microgram/ml-hr-kg). Age and sex did not explain the difference. Thus, radiation therapy, or the underlying disease, is associated with malabsorption of these two drugs, possibly because of damage to gastric acid-secreting cells.

Clorazepate kinetics in treated epileptics

Clorazepate is decarboxylated to form desmethyldiazepam and is a convenient way of administering it. Its kinetics were investigated in epileptic patients after single oral and multiple oral doses. Peak serum concentrations of demethyldiazepam occurred in 0.5 to 1 hr. There appeared to be a brief lag before rapid absorption. Because of the rapid absorption with resulting high serum levels, daily doses should be divided. Serum concentration/time curves were best fitted by the two-compartment open model. The apparent t1/2 of the distribution phase was 1.28 +/- 0.44 hr and the t1/2 of the disposition phase was 40.8 +/- 9.96 hr. Serum concentrations rose after meals. Whole body apparent volume of distribution (VB/F) was 1.63 +/- 0.24 L/kg. Total plasma clearance was 34.4 +/- 7.2 ml/min, which is greater than clearance levels for desmethyldiazepam in normals and reflects the greater hepatic metabolism which occurs in treated epileptics. The discrepancy illustrates the hazards of extrapolating data collected in normals to patients with multiple drug exposures.

Determination of desmethyldiazepam in plasma by electron-capture GLC: application to pharmacokinetic studies of clorazepate

Plasma desmethyldiazepam concentrations were quantitated by a rapid and sensitive technique using electron-capture GLC. Following addition of diazepam as the internal standard, plasma is extracted at physiological pH into benzene-isoamyl alcohol. The extract is evaporated to dryness and reconstituted with toluene-isoamyl alcohol prior to chromatography. Both diazepam and desmethyldiazepam are quantitatively extracted. The variation of identical samples is 5%, and the sensitivity is 5 ng of desmethyldiazepam/ml of original sample. The method is applicable to pharmacokinetic studies of clorazepate, a benzodiazepine derivative transformed to desmethyldiazepam prior to absorption.

Microcalorimetric method to determine competitive binding. Action of a psychotropic drug (dipotassium chlorazepate) on L-tryptophan . human serum albumin complex

A mathematical treatment and an original microcalorimetric method are developed to verify an eventual competitive binding between any two substances for the same macromolecule. To apply this method, a competitive binding of L-tryptophan and one benzodiazepin (dipotassium chlorazepate) for human serum albumin is perfectly demonstrated. The association constants and the enthalpy variations are equal to 14 000 +/- 2000 M-1 and --6.6 +/- 0.2 kcal/mol for human serum albumin . tryptophan complex and 13 000 +/- 1000 M-1 and --10.0 +/- 0.2 kcal/mol for human serum albumin . chlorazepate complex. In all cases the stoichiometry is equal to one. The binding of tryptophan to human serum albumin is partially stereospecific; the association constant and the enthalpy variation for D-tryptophan complex are equal, respectively, to 1000 +/- 200 M-1 and --2.6 +/- 0.3 kcal/mol.

Behavioural and pharmacokinetic studies in the monkey (Macaca mulatta) with diazepam, nordiazepam and related 1,4-benzodiazepines

1. Behavioural activity (delayed differentiation and spatial delayed alternation) and pharmacokinetics of diazepam and its metabolites, N-desmethyldiazepam (nordiazepam), 3-hydroxydiazepam (temazepam) and 3-hydroxy-N-desmethyldiazepam (oxazepam), and of dipotassium clorazepate (clorazepate), were studied in the monkey (Macaca mulatta). Diazepam and its metabolites (1.8 and 3.0 mg/kg) and clorazepate (2.6 and 4.3 mg/kg) were given by intraperitoneal injection. 2. Hydroxylation of diazepam (temazepam and oxazepam) led to a loss of, or a considerable reduction in, behavioural activity, whereas activity was preserved, though modified, by demethylation (nordiazepam). It was not possible to establish change in behaviour at specific time intervals after clorazepate, but combined performance data revealed an effect. 3. The maximum mean plasma concentrations of diazepam, temazepam, oxazepam and clorazepate were observed at 0.5 h, and the maximum mean plasma concentration of nordiazepam was observed at 1 hour. Plasma concentrations of nordiazepam were the highest and decreased monoexponentially. Plasma concenqrations of the other drugs declined rapidly at first but more slowly later, and these data were analysed as biexponential models. In the analysis for metabolites, nordiazepam reached measurable levels after the injection of diazepam and clorazepate. 4. It is suggested that differences in the effects of closely related benzodiazepines may not be due solely to their plasma pharmacokinetic properties, but may arise from differences in their intrinsic activity.

Effect of antacids on absorption of clorazepate

The effect of a magnesia and alumina antacid suspension on the absorption of clorazepate dipotassium was studied in 15 normal healthy adult subjects who ingested a 15-mg dose of clorazepate alone or with single or multiple doses of antacid. The results of this three-period randomized complete crossover study showed a trend of initially slower absorption and lower peak nordiazepam plasma levels when administered with the antacid suspension. However, there were no significant differences among treatments in the extent of absorption as measured by the area under the plasma level-time curves. Clorazepate plasma levels were of relatively short duration and similar for all treatments. The urinary excretion pattern was likewise comparable with conjugated oxazepam, the major species measured. Plasma elimination half-lives of nordiazepam and clorazepate were not affected by the antacid treatments.

Clinical implications of benzodiazepine pharmacokinetics

Pharmacokinetic research has shown that clear differences exist among benzodiazepines in rate and route of elimination and in the presence or absence of pharmacologically active metabolites. These findings and other results of pharmacokinetic research have clinical implications in terms of dosage schedules, drug accumulation during long-term therapy, antianxiety therapy in the elderly, drug interactions, pharmacotherapy in specific disease states, and the influence of route of administration on drug action.

Disposition of three benzodiazepines after single oral administration in man

Three benzodiazepines in equipotent doses: oxazepam 15 mg, dipotassium chlorazepate 10 mg and diazepam 5 mg, were administered in single, oral doses to seven healthy volunteers in a three-way cross-over study. The serum concentrations of oxazepam, N-desmethyldiazepam and diazepam were followed for 72 hours by gas chromatography and electron capture detection. The absorption of diazepam was most rapid and the mean time required to reach peak serum concentration was 45 minutes, followed by N-desmethyldiazepam 80 minutes and oxazepam 114 minutes. The serum concentration decay curves were biphasic with terminal mean half-lives of 48, 62 and 11 hours for diazepam, N-desmethyldiazepam and oxazepam, respectively. The mean and individual serum concentration time data were fitted to a two-compartment open model with first order absorption using a non linear least square program. The mean serum data fitted the model well. The same rank order was obtained with mean absorption half-lives as when comparing mean peak times while slightly shorter terminal half-lives were obtained in the curve fitting of mean serum data. Due to irregularities in the serum concentration time curves only five out of the 21 sets of individual data could satisfy the convergence criterion. The obtained parameters in the curve fitting were also accompanied with very large asymptotic standard deviations.

Steady-state bioavailability of two clorazepate dipotassium dosage forms

A specially designed tablet dosage form of the benzodiazepine clorazepate dipotassium (Tranxene) was developed for once-a-day administration. The drug was administered at a dose of 22.5 mg as (1) the tablet, (2) three 7.5 mg capsules, or (3) one 7.5-mg capsule given every 6 hours. Peak serum levels from the tablet were intermediate between those of the single- and divided-dose capsule regimens. The desired decrease in magnitude of peak levels was obtained without affecting the extent of absorption. Pharmacokinetic analysis of the data according to a two-compartment open model with first-order absorption indicated that the serum half-life (t0.5beta) of nordiazepam, the major biotransformation product present in serum, was about 48 hours and served as a basis for the design of a multiple-dose steady-state study. Multiple-dose administration of the tablet and divided-capsule regimen to two groups of subjects for ten days indicated each dosage form yielded similar minimum steady-state serum levels of about 0.6 micrograms/ml which plateaued following seven days of drug administration. The dosage forms were crossed over between the groups on day 11 and administered for an additional four days. The minimum serum levels obtained with the tablet and capsule were not statistically different. Additionally, the peak serum level and area under the curve (pi=24 hours) at steady state were equivalent between the dosage forms. Good agreement was obtained between model-predicted and observed serum levels during multiple-dose administration for both the tablet and capsule regimens. The serum half-life of nordiazepam following 14 days of clorazepate dipotassium administration was similar to that found after a single dose. These results indicate that a single daily dose of drug as the tablet produced serum levels equivalent to a divided-capsule regimen.

Clinical and biochemical comparison of clorazepate and diazepam

Clorazepate and diazepam were compared with respect to clinical effectiveness and concentrations of benzodiazepine compounds in plasma in 15 severely anxious outpatients. Each patient was studied in a double blind trial incorporating two-week periods of the two drugs and of placebo. The doses were almost equimolar—5 mg diazepam or 7·5 mg clorazepate three times daily. Clinical progress was assessed by visual analogue scales and by the Symptom Rating Test. Psychopathology scores were highest at the end of the placebo periods, and lowest at the end of the clorazepate periods, regardless of the order of treatments. After diazepam, both diazepam and N-desmethyldiazepam (nordiazepam) were detected in blood, and after clorazepate, only N-desmethyldiazepam was detected. N-Desmethyldiazepam concentrations were higher after clorazepate. Clinical progress was apparently related to the concentration of N-desmethyldiazepam in plasma.