Abuse liability and clinical pharmacokinetics of alprazolam in alcoholic men

The abuse liability of alprazolam was studied in 17 abstinent alcoholic and 12 control subjects. A single 1-mg oral dose of alprazolam was administered, and subjective effects were measured by scales modified from the Addiction Research Center Inventory (ARCI). Multiple blood samples for alprazolam measurement were drawn over 48 hours. No statistically significant differences in pharmacokinetic parameters were found between groups. Alcoholics had lower baseline scores on the ARCI-Morphine/Benzedrine Group Scale (euphoria) and had greater drug-induced changes than nonalcoholics. The findings suggest that alcoholics may be at high risk to abuse alprazolam because it has a positive mood effect not seen in nonalcoholics.

Desmethyldiazepam pharmacokinetics: studies following intravenous and oral desmethyldiazepam, oral clorazepate, and intravenous diazepam

After single 10-mg intravenous (IV) doses of desmethyldiazepam (DMDZ) to 12 healthy human volunteers, (mean age, 62 years) blood samples were obtained over the next 14 or more days. Mean kinetic variables were volume of distribution (Vd), 90 liters; elimination half-life (t1/2), 93 hours; and clearance, 12.3 mL/min. Vd was significantly correlated with body weight (r = .73, P less than .01) and with percent ideal body weight (r = .91, P less than .001). Eleven of the same subjects also received 5- to 15-mg doses of IV diazepam (DZ). Mean kinetic variables were Vd, 180 liters; t1/2, 83 hours; and clearance, 28 mL/min. Clearances of DZ and DMDZ were significantly correlated (r = .73, P less than .02). Based on area analysis, the extent of conversion of DZ to systemic DMDZ averaged 53%. After oral administration of DMDZ in tablet form (10 mg), or of clorazepate dipotassium in capsule form (15 mg), systemic availability of DMDZ from each of the oral dosage forms was not significantly different from 100%.

Comparative single-dose kinetics and dynamics of lorazepam, alprazolam, prazepam, and placebo

Thirty-nine healthy volunteers received single oral doses of either alprazolam (1 mg), lorazepam (2 mg), prazepam (20 mg), or placebo in a randomized, double-blind, parallel group study. Plasma drug concentrations, subjective self-ratings, and the digit symbol substitution test (DSST) were evaluated during 24 hours after dosage. Alprazolam was absorbed rapidly and produced correspondingly rapid sedation and impaired DSST performance. These effects also resolved rapidly, being similar to placebo by 4 to 6 hours after dosage. Sedative and DSST-impairing effects of lorazepam were of slower onset but longer duration than those of alprazolam. After oral prazepam, appearance of desmethyldiazepam in plasma was slow, with minimal sedative and DSST-impairing effects. Twenty-four hours after dosage, both alprazolam and lorazepam significantly impaired recall of a list of 16 words learned previously 3 hours after dosage. Thus benzodiazepines with approximately equivalent clinical anxiolytic properties may have different sedative, performance-impairing, and amnesic profiles after single doses in healthy volunteers; these differences are explained at least in part by pharmacokinetic variations.

Chronic benzodiazepine administration. II. Discontinuation syndrome is associated with upregulation of gamma-aminobutyric acidA receptor complex binding and function

A "withdrawal" or "rebound" syndrome may follow the abrupt discontinuation of chronic treatment with benzodiazepines. To assess the neurochemical basis of this syndrome, mice were treated with lorazepam, 2 mg/kg/day for 7 days, a course which produces tolerance and downregulation of receptor binding and function. Behavioral studies indicated that open-field activity in lorazepam-treated mice was similar to controls at 1 day postlorazepam. Activity was increased at 4 days postlorazepam, and had returned to control levels by day 7. Benzodiazepine receptor binding as measured by specific uptake of [3H]Ro15-1788 in several brain regions returned to control levels by day 2 postbrazepam but had increased above controls at day 4 postlorazepam. Binding returned to control levels by day 7. Similar results were observed using [3H]flunitrazepam in membrane preparations. A similar time course was also observed for the maximum binding of the chloride channel ligand t-[35S]butylbicyclophosphorothionate during this period. The IC50 value for muscimol inhibition of t-butylbicyclophosphorothionate binding was decreased at day 4, suggesting increased coupling between gamma-aminobutyric acid and the chloride channel. Muscimol-stimulated [36Cl-] up-take in cortical synaptoneurosomes was increased at day 4 postlorazepam. These results indicate that the benzodiazepine discontinuation syndrome is associated with upregulation of receptor binding and function at the gamma-aminobutyric acidA receptor complex.

Chronic benzodiazepine administration. I. Tolerance is associated with benzodiazepine receptor downregulation and decreased gamma-aminobutyric acidA receptor function

Tolerance occurs to a number of the pharmacodynamic effects of benzodiazepines. To assess pharmacokinetic and neurochemical aspects of tolerance, lorazepam (LRZ) was administered chronically to mice via implantable osmotic pumps and rotarod ataxia, plasma and brain LRZ concentrations, benzodiazepine receptor binding in vivo and in vitro, chloride channel binding and muscimol-stimulated chloride uptake were examined in various brain regions over a 14-day period. Behavioral tolerance, indicated by diminished rotarod ataxia, developed at all doses examined (1, 2, 4 and 10 mg/kg/day), with little change occurring before day 4. The greatest decrease in rotarod ataxia occurred between days 4 and 7. Plasma and brain LRZ concentrations were proportional to dose and were constant over time at each dose, indicating that tolerance was not pharmacokinetic. Benzodiazepine receptor binding as determined by the specific uptake of [3H]Ro15-1788 decreased in cortex, hypothalamus and hippocampus primarily between days 4 and 7, with an approximately 50% decrement in each region by day 7. Receptor binding and rotarod ataxia in cortex were highly correlated at each dose. Apparent affinity in vivo at the receptor was unchanged in cortex, indicating that altered ligand uptake was due to decreased receptor number. Similar results were observed in membrane preparations. There was a small, nonsignificant decrease in chloride channel binding at day 7 compared to day 1. Muscimol-stimulated chloride uptake into cortical synaptoneurosomes was decreased at day 7 compared to day 1. Thus, downregulation of benzodiazepine receptor binding and of gamma-aminobutyric acidA receptor function is closely associated with behavioral tolerance to benzodiazepines.

Low-dose alprazolam augments motor activity in mice

The triazolobenzodiazepine alprazolam appears to have a unique clinical spectrum, and recent studies indicate unusual binding properties at the benzodiazepine receptor when assessed in vivo at low doses (0.02-0.05 mg/kg). To assess the behavioral activity of alprazolam at low doses, we examined open-field activity after one hour in mice treated with alprazolam, triazolam, and clonazepam. Following triazolam and clonazepam administration, open-field activity decreased in a dose-dependent fashion. In contrast, low doses of alprazolam resulted in an increase in open-field activity, whereas higher doses decreased activity. For all three drugs, activity was linearly related to receptor binding. Pretreatment with a dose of the benzodiazepine antagonist Ro15-1788 sufficient to fully occupy receptors had no effect on open-field activity, but when administered concurrently with alprazolam (0.05 mg/kg) prevented the increase in activity seen with alprazolam alone. Increased open-field motor activity represents a behavioral correlate to the increases in receptor binding seen with low-doses of alprazolam. Changes in activity appear to be mediated at the benzodiazepine receptor, since an antagonist prevents increased activity. These data suggest that the unique clinical effects of alprazolam may be due in part to unusual interactions with the benzodiazepine receptor.

The dexamethasone suppression index: enhancement of DST diagnostic utility for depression by expressing serum cortisol as a function of serum dexamethasone

The authors sought to determine whether the performance of the dexamethasone suppression test (DST) could be enhanced by expressing cortisol as a function of dexamethasone. Because cortisol concentration is a function of the reciprocal of dexamethasone concentration, this relationship was approximated by calculating the product of cortisol and dexamethasone as a dexamethasone suppression index. Preliminary assessment of test performance measures (sensitivity, specificity, and predictive power) showed that use of the dexamethasone suppression index was an improvement over the use of cortisol levels alone. Factoring dexamethasone levels into post-dexamethasone cortisol level measures may enhance the utility of neuroendocrine assessment in psychiatry.

Alprazolam pharmacokinetics in women on low-dose oral contraceptives

Sixteen women chronically using low-dose estrogen-containing oral contraceptive steroids (OCs) and 23 drug-free control women received a single 1-mg oral dose of alprazolam. Multiple plasma samples drawn during 48 hours after the dose were analyzed by electron-capture gas-liquid chromatography. There were no significant differences between controls and oral contraceptive users in alprazolam volume of distribution (1.27 versus 1.39 L/kg), elimination half-life (11.9 versus 12.3 hours), total clearance (1.36 versus 1.39 mL/min/kg), or total area under the plasma concentration versus time curve (227 versus 243 ng/mL X hr). Alprazolam free fraction in plasma was slightly but significantly greater in the oral contraceptive group as opposed to the control group (28.4 versus 27.0% unbound), respectively. However, comparison of free clearance between groups revealed no significant difference (4.61 versus 4.89 mL/min/kg, respectively). Thus, low-dose estrogen-containing oral contraceptives do not significantly influence the metabolic clearance of alprazolam.

'GABA shift' in vivo: enhancement of benzodiazepine binding in vivo by modulation of endogenous GABA

The enhancement of benzodiazepine binding by gamma-aminobutyric acid (GABA) and its analogues has been described in detail in brain membrane preparations, but results in in vivo preparations such as tissue slices or animals treated with GABA modulators are conflicting. This 'GABA shift' in vitro has been reported for compounds with agonist effects at the benzodiazepine receptor but not for antagonists. We examined the effects of modulators of endogenous GABA on benzodiazepine receptor binding in vivo as determined by specific uptake of the benzodiazepine antagonist [3H]Ro 15-1788. Enhancement of radioligand uptake was observed in cortex, hypothalamus, hippocampus and pons-medulla 4 h after treatment with aminooxyacetic acid (AOAA), in cortex, cerebellum, hypothalamus, hippocampus and pons-medulla 0.5 h after treatment with valproic acid, and in cortex, cerebellum, hypothalamus and hippocampus 6 h after treatment with gamma-vinyl-GABA. GABA concentrations were increased at each of these points, as were synaptosomal GABA concentrations in prior studies. In contrast, no changes in radioligand uptake or GABA concentrations were observed 12 and 24 h after gamma-vinyl-GABA treatment. Increases in binding appeared to be due to increased apparent affinity at the receptor rather than a change in receptor number. These data indicate that binding of a benzodiazepine antagonist undergoes a GABA shift in vivo analogous to that observed with agonists in vitro.

Differential modulation of benzodiazepine receptor binding by ethanol in LS and SS mice

The LS and SS lines of mice were initially selected based on sedative responses to ethanol, but have been found to differ in response to a variety of hypnotics and anesthetics. These differences do not appear to be due to pharmacokinetic factors and several lines of evidence suggest involvement of the GABAergic system. To examine an important component of this system, the benzodiazepine receptor, we analyzed benzodiazepine receptor binding in vivo in LS and SS mice, and modulation of receptor binding by three interventions known to increase binding in other strains: pentobarbital, defeat stress, and ethanol. Receptor binding was determined by specific uptake of [3H]-Ro15-1788. Receptor binding was increased in cortex and hippocampus of LS mice compared to SS mice, with the increase in cortex most likely due to increased receptor number rather than a change in apparent affinity. Pentobarbital (30 mg/kg IP) induced similar increases in binding in both lines in several brain regions. Defeat stress caused increased binding in several brain regions of both SS and LS mice, with greater binding in cortex of LS mice. In contrast, ethanol at 3 doses (0.5, 1, and 2 g/kg) led to greater increases in binding in SS mice compared to LS mice in most brain regions. None of the interventions altered nonspecific binding. Ethanol concentrations were slightly greater in plasma and brain of LS mice. These results indicate differences in benzodiazepine receptor binding in LS and SS mice, with differential modulation of binding by ethanol but not by pentobarbital or stress. These differences may contribute to differential pharmacodynamic responses in the two lines of mice.

Triazolam kinetics: interaction with cimetidine, propranolol, and the combination

Nineteen healthy volunteers received a single 0.5-mg oral dose of triazolam on four occasions under the following conditions: (1) triazolam alone; (2) triazolam with cimetidine, 300 mg four times daily; (3) triazolam with propranolol, 40 mg four times daily; (4) triazolam with both cimetidine and propranolol. Triazolam kinetics were determined from multiple plasma concentrations measured during 24 hours after each dose. Compared with control, peak plasma triazolam concentration (Cmax) was significantly increased by cimetidine (5.4 versus 3.9 ng/mL), total area under the plasma concentration curve (AUC) increased (21.3 versus 16.1 ng/mL X hr), and oral clearance decreased (485 versus 668 mL/min). However triazolam half-life was not increased. During propranolol alone, triazolam Cmax (4.1 ng/mL), AUC (14.3 ng/mL X hr), and clearance (759 mL/min) did not differ significantly from control, whereas kinetic variables for triazolam with cimetidine plus propranolol were similar to those with cimetidine alone. Plasma free fraction for triazolam (17 to 18% unbound) did not differ significantly among the four treatment conditions. Mean steady-state plasma cimetidine concentrations during trials 2 and 4 were similar (1.04 versus .98 micrograms/mL), whereas plasma propranolol was significantly higher during cimetidine plus propranolol than with propranolol alone (47 versus 29 ng/ml, P less than .001). Thus cimetidine coadministration significantly inhibits triazolam clearance, causing increased triazolam AUC and Cmax, but without a prolongation in half-life. Propranolol itself does not impair triazolam clearance, nor does propranolol potentiate the inhibitory effect of cimetidine alone.

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)

Suppression of norepinephrine appearance rate in plasma by diazepam in humans

Studies demonstrating benzodiazepine-induced reductions in plasma norepinephrine (NE) have assumed that changes in circulating plasma NE closely parallel changes in sympathetic nervous system (SNS) activity and that benzodiazepines suppress SNS outflow. However, decreases in plasma NE could also result from increased removal of NE from plasma via neuronal uptake or tissue metabolism. This study used a tritiated norepinephrine ([3H] NE) isotope dilution technique for measurement of plasma NE kinetics to determine if the fall in plasma NE induced by a single dose of diazepam orally administered to eight psychiatrically-healthy volunteers was due to a fall in plasma NE appearance rate or an increase in plasma NE removal. Diazepam decreased plasma NE appearance, but not clearance, and also decreased plasma epinephrine and mean arterial pressure, memory performance and alertness. Plasma levels of diazepam were correlated with drug effects on memory and alertness but not cardiovascular or SNS effects.

Acute barbiturate administration increases benzodiazepine receptor binding in vivo

Barbiturates have been reported to augment benzodiazepine receptor affinity in vitro, but their effects in vivo are uncertain. We determined benzodiazepine receptor binding in vivo by specific uptake of [3H]Ro15-1788 after barbiturate administration. Pentobarbital (30 mg/kg) increased receptor binding in cerebral cortex and cerebellum at 30 min after injection, with a peak effect occurring at 1 h after dosage, and a return to control levels at 2 h. Specific binding was increased at 1 h after pentobarbital administration in a dose-dependent fashion (7.5-90 mg/kg). Pentobarbital at doses up to 30 mg/kg failed to alter nonspecific binding, but at doses of 60 mg/kg increases in nonspecific binding were observed. The increases in specific binding observed after barbiturate administration were most likely due to a change in apparent receptor affinity, as determined by administration of varying doses of clonazepam to pentobarbital-treated (30 mg/kg) animals. The order of potency of a series of barbiturates in augmenting benzodiazepine receptor binding in cerebral cortex and cerebellum in vivo was: secobarbital greater than pentobarbital greater than amobarbital greater than phenobarbital greater than barbital. The same relative rank order of potency exists for the anesthetic/hypnotic activity of these barbiturates. These data suggest that barbiturates increase the apparent affinity of benzodiazepine receptors in vivo; unlike their in vitro actions, these alterations can be detected with a receptor antagonist.

Antipyrine absorption and disposition in the elderly

Twelve young (24-41 years) and 11 elderly (62-77 years) volunteer subjects received a single 1.0-gram dose of antipyrine on three occasions: intravenously, orally in the fasting state and orally following a standard breakfast. Plasma antipyrine concentrations were determined for 24 h after each dose. Compared to young males, elderly men had significantly prolonged elimination half-life (17 vs. 11 h, p less than 0.025) and reduced clearance (32 vs. 54 ml/min, p less than 0.06). However, elderly and young women did not differ in half-life (12 vs. 11 h) or clearance (37 vs. 44 ml/min). After oral dosage in the fasting state, young and elderly groups (regardless of gender) did not differ in peak plasma antipyrine concentration (Cmax) or time of peak concentration (Tmax). Absolute bioavailability was not significantly less than 100% and was not related to age. Postprandial oral dosage of antipyrine caused reduced Cmax and prolonged Tmax in all groups, but absolute bioavailability was not significantly less than 100%. Again, there were no age-related differences. Although aging may lead to reduced clearance of antipyrine among men, there is no evidence that old age is associated with impairment of the rate or extent of antipyrine absorption from the gastrointestinal tract.

Benzodiazepine receptor binding of triazolobenzodiazepines in vivo: increased receptor number with low-dose alprazolam

Triazolobenzodiazepines are in clinical use as hypnotics and anxiolytics. We analyzed in vivo receptor binding and brain concentrations of alprazolam, triazolam, and estazolam. Drug concentrations measured in the cerebral cortex 1 h after administration were directly proportional to dose for all three compounds. In vivo receptor binding, as defined by the specific uptake of [3H]Ro15-1788, decreased with increasing doses of estazolam and triazolam, a finding indicating dose-related increases in receptor occupancy due to these compounds. Triazolam was substantially more potent, with an IC50 value of 16 ng/g, compared with 117 ng/g for estazolam. At higher doses of alprazolam (greater than 0.2 mg/kg), receptor binding by [3H]Ro15-1788, likewise decreased with increasing dose of the former drug. However, at lower doses of alprazolam (0.02-0.05 mg/kg), which resulted in cortex concentrations of 2-7 ng/g, receptor binding was increased above control values in cortex, hypothalamus, and hippocampus but not in several other brain regions. Binding returned to control values at doses of greater than or equal to 0.01 mg/kg. Similar results were obtained in time course studies. At 8 and 10 h after a dose of 1 mg/kg i.p., corresponding to cortex concentrations of 2.7-7 ng/g, receptor binding was increased compared with controls. Similarly, at 1, 2, and 3 h after a single dose of 0.05 mg/kg, corresponding to cortex concentrations of 3.7-5.8 ng/g, receptor binding was also increased. The apparent affinity of benzodiazepine receptors for clonazepam in mice receiving alprazolam (0.05 mg/kg) was unchanged from that in untreated control mice, an observation suggesting that low doses of alprazolam increased receptor number.(ABSTRACT TRUNCATED AT 250 WORDS)

Alprazolam kinetics following sublingual and oral administration

Thirteen healthy volunteers received 1 mg of alprazolam, as the commercially available oral tablet, by sublingual and oral routes on two occasions in random sequence. Plasma alprazolam concentrations during 48 hours after each dose were measured by electron-capture gas-liquid chromatography. The peak plasma concentration after sublingual dosage was higher than after oral administration (17.3 vs. 14.9 ng/ml), and the time of peak concentration following sublingual administration was reached (1.17 vs. 1.73 hours after dose). However, these differences did not reach statistical significance. The mean total area under the plasma concentration curve for sublingual administration was slightly but not significantly larger than that following oral dosage (203.7 vs. 194.4 hr.ng/ml) and no significant differences between sublingual and oral dosage were found for elimination half-life (11.7 vs. 11.8 hours) or for clearance (86.4 vs. 92.4 ml/min). Thus, alprazolam absorption following sublingual administration is as rapid as after oral dosage on an empty stomach, and completeness of absorption is comparable. In clinical terms, sublingual and oral dosages of alprazolam are likely to be therapeutically equivalent. The sublingual route may be a useful alternative for panic disorder patients who cannot swallow pills or for those who do not have access to a liquid at the time of dosing.

Clonazepam pharmacokinetics, brain uptake, and receptor interactions

The 7-nitrobenzodiazepine derivative clonazepam is initially biotransformed by nitroreduction, followed by acetylation. Neither the amino- nor the acetamido- metabolites appear to have important pharmacologic activity. Clonazepam elimination half-life falls in the range of 20 to 80 hours, but means within the population and variance are not well defined. Absorption of orally administered clonazepam is 80% or more. In experimental studies, clonazepam appears to diffuse passively from plasma into brain, with a constant brain-plasma concentration ratio. The drug disappears in a parallel fashion from both brain and plasma, with no evidence of sequestration in brain tissue. Clonazepam has a relatively high molar affinity for the benzodiazepine receptor in vitro, and the fractional extent of benzodiazepine receptor occupation by clonazepam in vivo is directly and predictably related to the drug's concentration in brain tissue. Acute behavioral effects are in turn directly related to the extent of receptor occupancy. Compared to other benzodiazepines, the reportedly unique clinical properties of clonazepam are neither associated with unusual/unexpected pharmacokinetic properties or with a qualitatively different in vivo interaction with the presumed benzodiazepine binding site.

Effect of gradual withdrawal on the rebound sleep disorder after discontinuation of triazolam

Sixty volunteers with insomnia participated in a randomized, double-blind, controlled clinical trial. After an initial six nights of placebo, 30 subjects (the abrupt-withdrawal group) received 0.5 mg of triazolam nightly for 7 to 10 nights, after which they received placebo. The other 30 subjects (the tapered-dosage group) received the same initial placebo treatment, then triazolam at 0.5 mg for seven nights, at 0.25 mg for two nights, and at 0.125 mg for two nights, and then placebo. As compared with the initial placebo period, the triazolam period significantly reduced the interval before the onset of sleep (sleep latency), and it prolonged sleep duration, reduced the number of awakenings, and improved the self-rated soundness of sleep in all cohorts. In the abrupt-withdrawal group, plasma levels of triazolam were undetectable the morning after the first night of placebo substitution, and subjects reported prolongation of sleep latency (57 minutes longer than base line), reduction in sleep duration (1.4 hours less than base line), and increased awakenings (1.2 per night above base line). The symptoms of rebound sleep disorder lasted one or possibly two nights, and there was a reversion toward base line on subsequent placebo nights. In the tapered-dosage group, however, plasma triazolam levels fell gradually to zero, and rebound symptoms were decreased or eliminated. Thus, rebound sleep disorder following abrupt discontinuation of triazolam can be attenuated by a regimen of tapering.

Trazodone kinetics: effect of age, gender, and obesity

Single 25 mg intravenous and 50 mg oral doses of trazodone were given to 43 healthy subjects, divided into young men and women (aged 18 to 40 years) and elderly men and women (aged 60 to 76 years). Among men, trazodone volume of distribution (Varea) was increased in elderly vs. young subjects (1.15 vs. 0.89 L/kg; P less than 0.05), and clearance decreased (1.65 vs. 2.31 ml/min/kg; P less than 0.05), thereby increasing elimination half-life (t1/2) in elderly men (8.2 vs. 4.7 hours; P less than 0.001). Varea in women was also increased in the elderly (1.5 vs. 1.27 L/kg; P less than 0.02), causing increased t1/2 (7.6 vs. 5.9 hours; P less than 0.05), but clearance was unrelated to age. Absolute bioavailability of oral trazodone averaged 70% to 90% and was unrelated to age or sex. In 23 obese subjects (mean weight 112 kg) vs. 23 matched control subjects of normal weight (mean 65 kg), Varea was greatly increased (162 vs. 67 L; 1.43 vs. 1.04 L/kg; P less than 0.001) and was highly correlated with body weight (r = 0.91). Clearance was unchanged between groups (146 vs. 136 ml/min), but the increased Varea caused prolonged t1/2 in obese subjects (13.3 vs. 5.9 hours; P less than 0.001). Reduced clearance of trazodone among elderly men may indicate a need for dosage reduction during chronic therapy. In obese individuals, choice of dosage during chronic treatment should be based on ideal rather than total body weight.

Rapid increase in brain benzodiazepine receptor binding following defeat stress in mice

Defeat stress in mice, a model of social stress, increases benzodiazepine receptor binding as measured by specific [3H]Ro15-1788 binding in vivo, but not by [3H]flunitrazepam binding in vitro. This increase occurs rapidly, by 20 min following exposure to stress, and resolves by 60 min. Increased benzodiazepine receptor binding is observed in the cerebral cortex, cerebellum and hypothalamus, and appears to be due to an increase in receptor number rather than apparent affinity. The stress-induced increase in central benzodiazepine receptors is decreased in a dose-dependent fashion by lorazepam, a benzodiazepine agonist, but not by the receptor antagonist Ro15-1788. The stress-induced increase in benzodiazepine receptors is also blocked by adrenalectomy and is restored by corticosterone replacement.

Bromazepam pharmacokinetics: influence of age, gender, oral contraceptives, cimetidine, and propranolol

Pharmacokinetics of the benzodiazepine bromazepam were evaluated in volunteer subjects who received single 6 mg oral doses followed by blood sampling during the next 48 hours. Age and gender effects were studied in 32 subjects, divided into young (aged 21 to 29 years) and elderly (aged 60 to 81 years) groups. Compared with young subjects, the elderly had significantly higher peak serum bromazepam concentrations (132 vs. 82 ng/ml), smaller volume of distribution (0.88 vs. 1.44 L/kg), lower oral clearance (0.41 vs. 0.76 ml/min/kg), and increased serum free fraction (34.8% vs. 28.8% unbound). However, gender had no significant influence on bromazepam kinetics. In 11 young female users of oral contraceptive steroids, compared with seven age- and weight-matched control women not using oral contraceptives, no differences in bromazepam kinetics were observed. Coadministration of cimetidine (1.2 gm daily) significantly reduced bromazepam clearance (0.41 vs. 0.82 ml/min/kg) and prolonged elimination half-life (29 vs. 23 hours). Propranolol (160 mg daily) significantly prolonged bromazepam half-life (28 vs. 23 hours), but the reduction in clearance associated with propranolol (0.65 vs. 0.82 ml/min/kg) did not reach significance. Bromazepam has the pharmacokinetic characteristics of benzodiazepines with half-life values between 20 and 30 hours. Consistent with its biotransformation pathway by hepatic microsomal oxidation, bromazepam clearance is significantly impaired in elderly individuals, by coadministration of cimetidine and possibly propranolol.

Benzodiazepine receptor occupancy in vivo: correlation with brain concentrations and pharmacodynamic actions

A tracer radioligand technique employing [3H]Ro 15-1788 was used to measure in vivo benzodiazepine receptor occupancy in mice. Animals were administered clonazepam (CNZ) or lorazepam (LRZ) i.p. or i.v., followed by [3H]Ro 15-1788. Plasma and cerebral cortical concentrations of the drug and cortical benzodiazepine receptor occupancy were determined at varying doses and times after administration. For both drugs, plasma and brain concentrations decreased in parallel with decreasing doses and with time, and the brain/plasma ratios remained constant. Receptor occupancy was maximal for CNZ and LRZ at doses above 1 and 4 mg/kg, respectively, and decreased with decreasing doses. Comparison of receptor occupancy with brain concentration yielded IC50 values of 21 ng/g for CNZ and 133 ng/g for LRZ. The apparent dissociation constant (Kd) for CNZ was 56 pmol/g and, for LRZ, 372 pmol/g. Hill plots yielded slopes of 1.30 for CNZ and 1.71 for LRZ. Alterations in the nonspecific uptake or elimination of Ro 15-1788 did not explain occupancy changes, inasmuch as brain concentrations of unlabeled Ro 15-1788 (6 mg/kg) were not changed by LRZ administration. The correlation between receptor occupancy and the pharmacodynamic actions of these drugs in blocking pentylenetetrazol seizures and inducing rotarod ataxia indicated that ED50 for these effects occurred at receptor occupancy of 30 to 60% for both drugs.

Effect of age, body composition, and lipid solubility on benzodiazepine tissue distribution in rats

Changes in body composition with age may alter tissue drug uptake and result in altered pharmacokinetics and pharmacodynamics. Four young, 4 middle-aged and 4 old Fischer-344 male rats were given a single intraperitoneal dose of alprazolam (2.5 mg/kg), diazepam (5 mg/kg) and triazolam (1.25 mg/kg) and sacrificed after 1 h. Diazepam, desmethyldiazepam, oxazepam, temazepam, alprazolam, and triazolam concentrations were determined in brain, kidney, liver, spleen, lung, heart, adrenal, muscle, fat and plasma by gas chromatography. Free fraction in plasma was determined by equilibrium dialysis. Drug uptake varied widely among tissues. Highest uptake ratios relative to free (unbound) drug in plasma were in adrenal (56-135), liver (35-116) and kidney (19-50). Free fraction in plasma varied from 0.13 for desmethyldiazepam to 0.30 for triazolam, and was unrelated to age. Tissue drug uptake relative to muscle, total plasma or free plasma concentration showed no significant variation with age or body habitus. In vivo fat uptake was highly correlated (R = 0.95) with in vitro octanol/buffer partition ratio. Muscle and fat were the largest quantitative drug storage sites, with total uptake explained by lipophilicity. Thus, age-related changes in body habitus and clearance do not alter tissue binding of benzodiazepines at distribution equilibrium.

Actual versus reported benzodiazepine usage by medical outpatients

Benzodiazepines are widely prescribed, and in 1979 almost 10% of the adult population was taking them. Prior studies of outpatient usage of benzodiazepines have relied on survey or prescription data, which may be confounded by noncompliance. To determine the actual use of benzodiazepines, plasma benzodiazepine concentrations were measured in 225 consecutive outpatients from a university cardiology outpatient service. Self reports indicated that the great majority of the patients (191) were taking at least one medicine, and 70 reported being on a psychotropic drug. Seventy-seven patients reported taking benzodiazepines, the majority being on bromazepam (20), diazepam (26) or oxazepam (19). In 25 of those 77 patients, the reported drug could not be detected in plasma. Conversely, in 10 of the 225 patients, benzodiazepines which were not reported were detected (diazepam or flurazepam). Of those taking benzodiazepines, many had a low concentration, suggesting intermittent rather than regular use. Thus, many patients for whom benzodiazepines are prescribed take them irregularly, and a small group uses them without reporting their prescription. These findings have implications for the clinical presentation of illness and for the possibility of drug interactions.

Benzodiazepine hypnotic metabolism: drug interactions and clinical implications

Benzodiazepines are the drugs of choice when initiating hypnotic therapy. Though the mechanism of benzodiazepine action in the central nervous system is similar for all drugs in this class, differences in absorption and pathway of elimination are associated with differences in observed clinical effect. After single-dose administration, onset of hypnotic effect is most closely related to rate of drug absorption and duration of effect is more closely associated with extent of drug distribution. Relative affinity of the individual benzodiazepine for the specific central nervous system binding site may also determine duration of action. During multiple-dose chronic therapy, route of metabolic biotransformation and elimination half-life assume more importance. An increased incidence of adverse drug effects due to high doses of accumulating benzodiazepines may be seen in the elderly and patients with central nervous system deficits or chronic liver disease. Benzodiazepine metabolic biotransformation and clearance is broken into three groups. Group 1--oxidative biotransformation; Group 2--high clearance drugs; Group 3--drug conjugation. Groups 1 and 2 are implicated in a number of drug-disease and drug-drug interactions. Group 3 drugs have little change in patients with liver disease or when administered with inhibitors of drug biotransformation. Clinical implications of these metabolic interactions are variable, but inhibition of Group 1 and 2 benzodiazepine clearance has been associated with increased sedation and psychomotor impairment.

Population study of triazolam pharmacokinetics

The kinetics of a single 0.5 mg oral dose of the triazolobenzodiazepine hypnotic triazolam, were studied in 54 healthy young men aged 20-44 years, with a mean body weight of 77 kg. Triazolam kinetics were determined from multiple plasma concentrations measured during 14 h post-dose. The overall mean +/- s.e. mean (with range) kinetic variables were: peak plasma concentration, 4.4 +/- 0.3 (1.7-9.4) ng ml-1; time of peak, 1.3 +/- 0.1 (0.5-4.0) h after dose; elimination half-life, 2.6 +/- 0.1 (1.1-4.4) h; total AUC: 19.1 +/- 1.1 (4.4-47.7) ng ml-1 h; oral clearance, 526 +/- 38 (175-1892) ml min-1. All kinetic variables were consistent with Poisson distributions, based on the Kolmogorov-Smirnov Goodness of Fit test. None of the variables fit normal distributions. Four of five were consistent with a log normal distribution. Peak plasma level was highly correlated with clearance (r = -0.85, P less than 0.0001), and AUC (r = 0.85, P less than 0.0001) but not with body weight (r = 0.21, NS). Clearance and body weight were not correlated (r = -0.01). Triazolam clearance may vary widely even within a homogeneous group of healthy young men.

Obesity effects on nitrazepam disposition

Nitrazepam pharmacokinetics were studied in 14 obese (mean +/- s.e. mean body weight 107 +/- 9 kg; percent ideal body weight [IBW] 166 +/- 12%) and 14 normal body weight (63 +/- 3 kg; percent IBW 98 +/- 2%) subjects. After an overnight fast, each subject ingested 10 mg nitrazepam orally. Nitrazepam concentrations were determined in plasma samples obtained over the following 72 h. Comparison of peak nitrazepam plasma concentration (94.2 +/- 10.3-obese vs 119 +/- 14.6 ng ml-1; NS) and time required after drug administration to reach peak concentration (1.52 +/- 0.24-obese vs 1.59 +/- 0.36 h; NS) indicated no differences between obese and control subjects. Elimination half-life was markedly increased in obese subjects (33.5 +/- 2.2 vs 23.9 +/- 1.2 h; P less than 0.001) due to increased apparent volume of distribution (Vd) (290 +/- 45 vs 137 +/- 12 l; P less than 0.005). Oral clearance was also increased in the obese subjects (101 +/- 12.4 vs 66.8 +/- 12.4 ml min-1; P less than 0.02). Extent of nitrazepam binding to plasma proteins was slightly decreased in obese subjects (% unbound--19.7 +/- 0.4-obese vs 17.9 +/- 0.3%; P less than 0.005). Correction of both Vd (2.62 +/- 0.17-obese vs 2.22 +/- 0.19 l kg-1; NS) and clearance (0.93 +/- 0.06-obese +/- 1.07 +/- 0.07 ml min-1 kg-1; NS) for total body weight (TBW) suggested that increases in obese subjects of both of these parameters were a function of body weight.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics and dynamics of single doses of oxazepam in the elderly: implications of absorption rate

Five healthy elderly volunteers aged 64 to 67 years and 12 healthy young subjects aged 23 to 44 years received single 30 mg oral doses of oxazepam in two different dosage forms (two 15 mg tablets or one 30 mg capsule) on two occasions in a random crossover sequence, with at least 1 week elapsing between trials. In both age groups, rate of oxazepam absorption of the capsule form of the drug was significantly slower than that of the tablets. Peak plasma concentrations were lower and were delayed longer with the capsule form; however, the relative extent of oxazepam absorption did not differ between preparations in either age group. Clinical self-ratings in the elderly group, based on visual analog scales, were consistent with the delayed onset of sedative effects that is associated with the capsule form of administration. Kinetic comparisons in the two groups indicated a significantly prolonged oxazepam elimination half-life with the tablet (p less than .001) and with the capsule (p less than .06) and a trend (p less than .08) toward reduced oxazepam clearance in the elderly. The delayed absorption of oxazepam from the capsule was found in both the young and elderly groups.

Pharmacokinetics of diphenhydramine and a demethylated metabolite following intravenous and oral administration

Ten healthy volunteers received a single 50-mg dose of diphenhydramine (DP) hydrochloride intravenously and orally on two separate occasions. Kinetics of DP and a major demethylated metabolite (DMDP) were determined from multiple plasma samples drawn during a 24- to 48-hour period after dosage. Modification of a gas chromatographic (GC) technique allowed simultaneous quantitation of DP and DMDP. Mean kinetic variables for DP after intravenous (IV) dosage were: volume of distribution, 4.5 L/kg; elimination half-life, 8.4 hours; clearance, 6.2 mL/min/kg. After oral DP administration, a peak plasma level of 66 ng/mL was reached 2.3 hours after dosage. Systemic availability was 72%, nearly identical to the predicted estimate (71%) based on clearance of IV DP relative to hepatic blood flow. Appearance of the metabolite, DMDP, mirrored disappearance of DP; the area under the plasma concentration-time curve (AUC) for DMDP was highly correlated (r = .79, P less than .05) with a clearance of IV DP. However, metabolite AUC was significantly higher after oral as opposed to IV DP (218 vs 145 hr-ng/mL, P less than .05). Because DP and DMDP elute nearly identically on standard GC systems, methodologic modifications are needed to resolve them. Coelution of the two compounds could bias kinetic data based on plasma concentration presumed to be specific for intact DP.

Influence of age, gender, and obesity on salicylate kinetics following single doses of aspirin

Salicylate kinetics following single, 650-mg intravenous and oral doses of aspirin were evaluated in humans in 2 studies. Complete conversion of aspirin to salicylate was assumed. The first study involved 25 young (25-40 years) and 21 elderly (66-89 years) healthy male and female volunteers. Mean salicylate clearance was lower in elderly females compared with that in young females; however, the difference between young men and elderly men was not significant. Salicylate free fraction in plasma increased significantly with age in men and women. After correction for free fraction, unbound mean clearance was reduced in elderly men compared with young men, and in elderly women compared with young women. Peak plasma salicylate concentrations after taking oral aspirin were not significantly influenced by age, and systemic availability of salicylate in all groups was complete. The second study compared 20 obese subjects (mean weight 113 kg) with 20 normal weight controls (mean weight 67 kg) matched for age, sex, height, and smoking habits. Small differences between obese and control groups were observed in total salicylate volume of distribution (Vd), unbound Vd, and mean clearance of total or unbound salicylate. Following normalization for total weight, however, values of total Vd and mean clearance were significantly smaller in obese subjects than in normal weight subjects. Rate and completeness of salicylate absorption were not influenced by obesity when aspirin was ingested, although peak levels were lower in obese subjects. If applied to multiple doses, the reduced unbound clearance of salicylate in the elderly would imply increased accumulation unless doses are appropriately adjusted downward. During long-term therapy, salicylate dosage for obese individuals should not be adjusted upward in proportion to total weight.

Sedative effects and impaired learning and recall after single oral doses of lorazepam

Seven healthy subjects received oral placebo, 1.5 mg lorazepam, or 3.0 mg lorazepam in a single-dose, three-way crossover study. Plasma lorazepam concentrations and subjects' self-rated sedative effects were evaluated at multiple points during 24 hours after each dose. Information acquisition and recall was studied by use of a 16-item word list at 3 and 24 hours after dosing. Lorazepam plasma concentrations were proportional to dose. Self-rated sedation was maximal 2 to 3 hours after lorazepam dosing, persisted for 8 hours, and was dose dependent in intensity; no significant sedation occurred with placebo. At 3 hours after placebo dosing, subjects learned a mean 96% of words presented during six trials; this was reduced to 79% and 62% after lorazepam, 1.5 and 3.0 mg, respectively (F = 6.2; P less than 0.02). Twenty-four hours after placebo, subjects recalled 92% of words presented the previous day, then improved to 99% after six relearning trials. After 1.5 and 3.0 mg lorazepam, however, only 52% and 44% of words were initially recalled from the previous day. Thus single oral doses of lorazepam within the therapeutic range produce dose-dependent sedation and impairment of information acquisition and recall.

Does carbamazepine-induced reduction of plasma haloperidol levels worsen psychotic symptoms?

Seven psychotic patients' plasma haloperidol levels, determined with gas-liquid chromatography, fell a mean of 60% when carbamazepine treatment was instituted. Two patients' levels became undetectable, and their symptoms worsened. Haloperidol level monitoring may be required for patients given both haloperidol and carbamazepine.

Interaction of diazepam with famotidine and cimetidine, two H2-receptor antagonists

Famotidine is currently under investigation as an H2-receptor antagonist. Eleven healthy male volunteers received a single 10 mg intravenous dose of diazepam on three occasions: once during coadministration of famotidine 40 mg bid, once during coadministration of cimetidine 300 mg qid, and once without other drug treatment (control). Multiple blood samples were drawn during the seven days after each diazepam dose. Diazepam and desmethyldiazepam plasma concentrations were measured by electron capture gas chromatography. There were no significant differences among the three treatment conditions in diazepam central compartment volume or total volume of distribution. During the cimetidine as compared with the control treatment, diazepam elimination half-life was significantly increased (72 vs 55 hr, P less than .05), total area under the curve (AUC) increased (11.8 vs 9.8 hr-micrograms/mL, P less than .05), and total clearance reduced (0.20 vs 0.28 mL/min/kg, P less than .05). Seven-day AUC for desmethyldiazepam also increased (4.6 vs 3.8 hr-micrograms/mL, P less than .05). However, there were no significant differences between famotidine and control treatment conditions in diazepam elimination half-life (53 vs 55 hr), total AUC (9.5 vs 9.8 hr-micrograms/mL), or total clearance (0.28 vs 0.28 mL/min/kg) or in seven-day AUC for desmethyldiazepam (3.9 vs 3.8 hr-micrograms/mL). Thus, therapeutic doses of cimetidine significantly impair the clearance of diazepam and desmethyldiazepam. Therapeutic doses of famotidine do not impair diazepam and desmethyldiazepam kinetics, suggesting that there is no significant kinetic interaction when diazepam and famotidine are administered concurrently in clinical practice.

Enhanced bioavailability of triazolam following sublingual versus oral administration

The rate and extent of the absorption of triazolam following sublingual and oral administration were evaluated in this study. Eight healthy volunteers received triazolam 0.5 mg in a commercially available tablet, by sublingual and oral routes on two occasions in random sequence. Plasma triazolam concentrations during 24 hours after each dose were measured by electron-capture gas-liquid chromatography. The mean total area under the curve for sublingual administration was significantly larger than that following oral dosage (28.9 vs 22.6 ng-hr/mL, P less than .025). The peak plasma concentration after sublingual dosage was also higher than after oral administration (4.7 vs 3.9 ng/mL, P less than .1). No significant differences between sublingual and oral administration were found for the elimination half-life of triazolam (4.1 vs 3.7 hr) and the time of peak concentration (1.22 vs 1.25 hr) after dose. Thus, the bioavailability of triazolam after sublingual administration is increased by an average of 28% compared with oral administration of the same dose, possibly because first-pass extraction is bypassed. Clinical effects of triazolam may likewise be enhanced by sublingual dosage.