Pharmacokinetics and anticonvulsant effect of a new hypnotic, CL 284,846, in rats

Electroencephalographic properties of zaleplon, a non-benzodiazepine sedative/hypnotic, in rats

The encephalographic (EEG) properties of zaleplon were investigated in comparison with those of other sedative hypnotics in conscious rats with chronically implanted electrodes. The oral administration of zaleplon (0.25-1.0 mg/kg), triazolam (0.0625-0.25 mg/kg), zopiclone (1.0-4.0 mg/kg), brotizolam (0.0625-0.25 mg/kg), and nitrazepam (0.125-0.5 mg/kg) lengthened the total sleep in a dose-dependent manner. On distribution of sleep-wakefulness stages, zaleplon, in particular, increased the slow wave deep sleep (SWDS), whereas triazolam, brotizolam, and nitrazepam increased the slow wave light sleep (SWLS) in a dose-dependent manner. Zopiclone significantly increased the SWDS at a dose of 2 mg/kg and both the SWLS and the SWDS at a dose of 4 mg/kg. All tested hypnotics caused no influence on fast wave sleep (FWS) at doses tested. The appearance of the sleep-inducing activity of zaleplon was more rapid than those of any compounds tested, and zaleplon significantly increased the relative EEG power density in the delta frequency band over that of triazolam at 20 and 30 min after the administration in the spectral analysis. Therefore, the present findings suggest that the non-benzodiazepine zaleplon can be expected to exhibit high practical potential as a hypnotic and is characterized by an increase in SWDS with rapid onset of hypnotic action.

In Vivo Pharmacological Characterization of Indiplon, a Novel Pyrazolopyrimidine Sedative-Hypnotic

Indiplon (NBI 34060; N-methyl-N-[3-[3-(2-thienylcarbonyl)-pyrazolo[1,5-alpha]pyrimidin-7-yl]phenyl]acetamide), a novel pyrazolopyrimidine and high-affinity allosteric potentiator of GABA(A) receptor function, was profiled for its effects in rodents after oral administration. In mice, indiplon inhibited locomotor activity (ED(50) = 2.7 mg/kg p.o.) at doses lower than the nonbenzodiazepine hypnotics zolpidem (ED(50) = 6.1 mg/kg p.o.) and zaleplon (ED(50) = 24.6 mg/kg p.o.), a sedative effect that was reversed by the benzodiazepine site antagonist flumazenil. Indiplon inhibited retention in the mouse passive avoidance paradigm over a dose range and with a temporal profile that coincided with its sedative activity. Indiplon, zolpidem, and zaleplon were equally effective in inhibiting locomotor activity in the rat and produced dose-related deficits on the rotarod. In a rat vigilance paradigm, indiplon, zolpidem, and zaleplon produced performance deficits over a dose range consistent with their sedative effects, although indiplon alone showed no significant increase in response latency. Indiplon produced a small deficit in the delayed nonmatch to sample paradigm at a dose where sedative effects became apparent. Indiplon was active in the rat Vogel test of anxiety, but it showed only a sedative profile in the mouse open field test. The pharmacokinetic profile of indiplon in both rat and mouse was consistent with its pharmacodynamic properties and indicated a rapid T(max), short t(1/2), and excellent blood-brain barrier penetration. Therefore, indiplon has the in vivo profile of an efficacious sedative-hypnotic, in agreement with its in vitro receptor pharmacology as a high-affinity allosteric potentiator of GABA(A) receptor function, with selectivity for alpha1 subunit-containing GABA(A) receptors.

Comparative pharmacokinetics and pharmacodynamics of short-acting hypnosedatives: zaleplon, zolpidem and zopiclone

Benzodiazepines have historically been the mainstay of treatment for sleeping disorders, yet they have many shortcomings. A new group of sedative hypnotic agents has been developed for this purpose. Similar to the benzodiazepines, zaleplon, zolpidem and zopiclone have activity at the GABA receptor complex, yet they appear to have more selectivity for certain subunits of the GABA receptor. This produces a clinical profile that is more efficacious with fewer side effects. Zaleplon, zolpidem and zopiclone are structurally distinct. Due to variation in binding to the GABA receptor subunits, these three compounds show subtle differences in their effect on sleep stages, and as antiepileptics, anxiolytics and amnestics. The duration of action of zaleplon, zolpidem and zopiclone can be related to their individual pharmacokinetic profile, which subsequently determines the time course of drug effect. Each of these compounds has a unique pharmacokinetic profile with different bioavailability, volume of distribution and elimination half-lives. Zaleplon has a rapid elimination so there are fewer residual side effects after taking a single dose at bedtime. By comparison, zolpidem and zopiclone have a more delayed elimination so there may be a prolonged drug effect. This can result in residual sedation and side effects but may be useful for sustained treatment of insomnia with less waking during the night. There are also differences in potency based on plasma concentrations suggesting that there are differences in binding to the GABA receptor complex. Although zaleplon has a much lower bioavailability (30%), the treatment dose is similar to zolpidem and zopiclone (bioavilaibility of 70%) because of the increased potency of zaleplon. The pharmacokinetics and pharmacodynamics of zaleplon, zolpidem and zopiclone are significantly different from benzodiazepines. The new drugs are sufficiently unique from each other to allow customisation of treatment for various types of insomnia. While zaleplon may be best indicated for the delayed onset of sleep, zolpidem and zopiclone may be better indicated for maintaining a complete night's sleep. Only the patient's symptoms and response to treatment will dictate the best course of treatment.

Binding and neuropharmacological profile of zaleplon, a novel nonbenzodiazepine sedative/hypnotic

The binding properties of CL284,846 (zaleplon), a novel nonbenzodiazepine sedative/hypnotic, at benzodiazepine receptor subtypes were evaluated. Zaleplon was 14.3 times more potent at inhibiting [3H]flunitrazepam binding to membrane preparations of the cerebellum than to membrane preparations of the spinal cord. The gamma-aminobutyric acid (GABA) ratio of zaleplon was 2.07. Zaleplon produced significant increases in muscimol binding similar to those of diazepam, and it was antagonized by flumazenil. Furthermore, zaleplon showed little affinity for other receptors. Spectral analysis of the electroencephalogram (EEG) of rabbits showed that zaleplon and 3-methyl-6-[3-(trifluoromethyl) phenyl]-1,2,4,-triazolo [4,3-beta] pyridazine (CL218,872), an omega(1) receptor-selective compound (1 mg/kg, i.v., respectively), produced large increases in energy of the delta frequency band without affecting the energy of the alpha and beta frequency bands. In contrast, intravenous administration of triazolam and zopiclone increased the energy of the beta frequency band at doses of 0.1 and 2 mg/kg, respectively. In addition, the zaleplon-induced increase in the energy of the delta frequency band was antagonized by pretreatment with flumazenil (1 mg/kg, i.v.), which did not affect the spontaneous EEG alone. The present results clearly demonstrate that zaleplon is a selective full agonist of the omega(1) receptor subtype, and thus, zaleplon may induce responses closely resembling the physiological pattern of slow wave sleep.

Zaleplon and triazolam: drug discrimination, plasma levels, and self-administration in baboons

Zaleplon is a chemically novel hypnotic that preferentially binds alpha(1)-subunit containing subtypes of the alphabetagamma configuration of the gamma-aminobutyric acid (GABA)(A) receptor. Zaleplon and the non-subtype-selective hypnotic triazolam occasioned 100% drug-appropriate responding in baboons trained to discriminate lorazepam or pentobarbital from vehicle. Flumazenil shifted the zaleplon generalization gradient at least five-fold to the right. A plasma elimination half-life of 6-8 h for oral 10 mg/kg zaleplon and 0.32 mg/kg triazolam was paralleled by discriminative control for 7 h. Zaleplon maintained self-injection greater than vehicle, as did comparison doses of the similarly selective hypnotic zolpidem and triazolam. Concurrent food-maintained responding increased during self-injection of all three drugs. Preferential binding at this alpha(1)-containing GABA(A) subtype did not diminish the benzodiazepine (Bzs)-like behavioral effects of zaleplon.

Zaleplon - a review of a novel sedative hypnotic used in the treatment of insomnia

Zaleplon (N-[3-(3-cyanopyrazolo[1,5-a] pyrimidin-7-yl) phenyl]-N-ethyl acetamide) is a non-benzodiazepine recently introduced for clinical use. This agent is indicated for the short-term treatment of insomnia. Preclinical studies have shown that the benzodiazepines triazolam and Ro17-1812 can substitute for zaleplon in animals trained to distinguish zaleplon from saline. The benzodiazepine antagonist flumazenil can antagonise the discriminative stimulus effect of zaleplon. These findings suggest that zaleplon is recognised by animals as a benzodiazepine agent. Zaleplon is active after ip. and oral administration in a variety of motor performance tests, including locomotor activity, rotarod and the loaded grid. Zaleplon has been shown to be active in a number of different anticonvulsant models, including the pentylenetetrazole, isoniazid and electroshock models. The compound is also reported to be active against convulsions induced by bicuculline, picrotoxin and strychnine. Studies in anxiolytic models suggest that zaleplon may have weak anxiolytic activity. From preclinical studies, it appears zaleplon possesses a reduced risk of tolerance compared to triazolam, is less likely to potentiate the effects of ethanol and is unlikely to produce amnestic effects. In man, zaleplon is rapidly absorbed and undergoes extensive presystemic metabolism. The compound has a plasma half-life of approximately one hour and is metabolised primarily via the aldehyde oxidase system to form 5-oxo-zaleplon. This metabolite, along with other minor metabolites formed in vivo, do not appear to contribute to the activity of zaleplon. Metabolites of zaleplon are excreted primarily via the urine. Phase I studies suggest that single daytime doses of zaleplon up to 15 mg are well-tolerated. Short-term impairment of performance occurs when zaleplon is administered during the day at doses epsilon 20 mg. However, given the short half-life of the compound, significant impairment of daytime performance is unlikely if zaleplon is administered at bedtime or shortly after retiring for the evening. Results from Phase II/III studies suggest that zaleplon (5 - 20 mg) produces a dose-dependent reduction in sleep latency in patients suffering from primary insomnia. The clinical efficacy of zaleplon persists for at least four weeks at doses of 10 mg and 20 mg. Studies in patients with a history of drug abuse suggest that the abuse potential of zaleplon (at doses above the therapeutic dose range) is similar to that seen with the benzodiazepine triazolam.

Zaleplon

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Comparative kinetics and dynamics of zaleplon, zolpidem, and placebo

PURPOSE

This study evaluated the relationship of dose, plasma concentration, and time to the pharmacodynamics of zaleplon and zolpidem, 2 structurally distinct benzodiazepine receptor agonists.

METHOD

Ten healthy male volunteers received single oral doses of placebo, 10 mg zaleplon, 20 mg zaleplon, 10 mg zolpidem, and 20 mg zolpidem in a double-blind, 5-condition crossover study, with 48 hours elapsing between trials. Plasma drug concentrations and pharmacodynamic effects were measured during the 8 to 24 hours after administration.

RESULTS

Kinetics of zaleplon and zolpidem were not significantly related to dose. However, zaleplon had more rapid elimination (apparent elimination half-life [t1/2] of 1 hour) and higher apparent oral clearance (approximately 4300 mL/min) than zolpidem (t1/2, 2.0 to 2.2 hours; apparent oral clearance, 340 to 380 mL/min). Active treatments produced pharmacodynamic effects consistent with benzodiazepine agonist activity: self- and observer-rated sedation, impairment of digit symbol substitution test (DSST) performance, impaired memory, and increased electroencephalographic activity in the beta frequency range. The overall order of agonist potency was as follows: placebo < 10 mg zaleplon < 20 mg zaleplon < 10 mg zolpidem < 20 mg zolpidem; on a number of measures, 20 mg zaleplon was comparable to 10 mg zolpidem. Quantitative effects of zolpidem 20 mg far exceeded those of other treatments. Dynamic effects of both drugs were significantly related to plasma concentration.

CONCLUSIONS

Benzodiazepine agonist effects of zaleplon and zolpidem were dose and concentration dependent. At the usual clinically effective hypnotic dose (10 mg of either drug), agonist effects of zolpidem exceeded those of zaleplon.

Dose-response cocaine pharmacokinetics and metabolite profile following intravenous administration and arterial sampling in unanesthetized, freely moving male rats

Despite the wealth of experimental data on cocaine abuse, there are no published dose-response pharmacokinetic studies with bolus i.v. cocaine injection in the male rat. The present study examined the pharmacokinetics of arterial plasma concentrations of cocaine and metabolite profile [benzoylecgonine (BE), ecgonine methyl ester (EME), norcocaine (NC)] following a single i.v. injection of 0.5, 1.0, or 3.0 mg/kg cocaine. Male Sprague-Dawley rats (N = 25) were anesthetized and surgically instrumented with both jugular vein (drug administration) and carotid artery (blood withdrawal) catheters and allowed to recover for at least 24 h. Arterial plasma samples (200 microliters) were obtained at eight time points (0.5, 1.5, 2.5, 10, 20, 30 min) following i.v. bolus injection (15-s injection, 15-s flush) and analyzed by single ion monitoring using GC/MS. Nonlinear regression and noncompartmental pharmacokinetic analysis were employed. Mean +/- SEM peak plasma concentrations of cocaine occurred at 30 s in a dose-response manner (370 +/- 14,755 +/- 119,2553 +/- 898 ng/ml for 0.5, 1.0, and 3.0 mg/kg groups, respectively). T1/2 alpha was < 1 min for all groups, but inversely related to dose. T1/2 beta was independent of dose 13.3 +/- 1.6, 13.0 +/- 1.5, and 12.0 +/- 2.0 min for 0.5, 1.0, and 3.0 mg/kg groups, respectively). MRT (16.0, 15.9, 14.5 min), VdSS (3.3, 3.2, and 2.8 l/kg), and ClTOT (204, 201, and 195 ml/min/kg) also provided little evidence of dose-dependent effects. Although the metabolic profile of i.v. cocaine was similarly ordered for all dose groups (BE > EME > NC), a quantitative shift in metabolite profile was evident as a function of increasing dose. This metabolic shift, perhaps attributable to saturation of plasma and liver esterases, suggests that the recently reported pharmacodynamic effects positively correlated with i.v. cocaine dose are unlikely attributable to NC, a minor but pharmacologically active metabolite. In sum, the i.v. pharmacokinetic profile in rats is distinct from that observed via the SC, IP, and PO routes of administration and offers the potential to provide a reasonable clinically relevant rodent model.