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.