A Review of the Preclinical Development of Zaleplon, a Novel Non-Benzodiazepine Hypnotic for the Treatment of Insomnia

GABAA Receptor-Mediated Sleep-Promoting Effect of Saaz-Saphir Hops Mixture Containing Xanthohumol and Humulone

Hops contain flavonoids that have sedative and sleep-promoting activities such as α-acid, β-acid, and xanthohumol. In this study, the sleep-enhancing activity of a Saaz–Saphir hops mixture was measured. In the caffeine-induced insomnia model, the administration of a Saaz–Saphir mixture increased the sleep time compared to Saaz or Saphir administration alone, which was attributed to the increase in NREM sleep time by the δ-wave increase. Oral administration of the Saaz–Saphir mixture for 3 weeks increased the γ-amino butyric acid (GABA) content in the brain and increased the expression of the GABA_A receptor. As the GABA antagonists picrotoxin and bicuculline showed a decrease in sleep activity, it was confirmed that the GABA_A receptor was involved in the Saaz–Saphir mixture activity. In addition, the GABA_A receptor antagonist also reduced the sleep activity induced by xanthohumol and humulone contained in the Saaz–Saphir mixture. Therefore, xanthohumol and humulone contained in the Saaz–Saphir mixture showed sleep-promoting activity mediated by the GABA_A receptors. The mixture of the Saaz and Saphir hop varieties may thus help mitigate sleep disturbances compared to other hop varieties.

The Z-Drugs Zolpidem, Zaleplon, and Eszopiclone Have Varying Actions on Human GABA A Receptors Containing γ1, γ2, and γ3 Subunits

γ-Aminobutyric-acid type A (GABA _A ) receptors expressing the γ1 or γ3 subunit are only found within a few regions of the brain, some of which are involved in sleep. No known compounds have been reported to selectively target γ1- or γ3-containing GABA _A receptors. Pharmacological assessments of this are conflicting, possibly due to differences in experimental models, conditions, and exact protocols when reporting efficacies and potencies. In this study, we evaluated the modulatory properties of five non-benzodiazepine Z-drugs (zaleplon, indiplon, eszopiclone, zolpidem, and alpidem) used in sleep management and the benzodiazepine, diazepam on human α1β2γ receptors using all three γ subtypes. This was accomplished using concatenated GABA _A pentamers expressed in Xenopus laevis oocytes and measured via two-electrode voltage clamp. This approach removes the potential for single subunits to form erroneous receptors that could contribute to the pharmacological assessment of these compounds. No compound tested had significant effects on γ1-containing receptors below 10 μM. Interestingly, zaleplon and indiplon were found to modulate γ3-containing receptors equally as efficacious as γ2-containing receptors. Furthermore, zaleplon had a higher potency for γ3- than for γ2-containing receptors, indicating certain therapeutic effects could occur via these γ3-containing receptors. Eszopiclone modulated γ3-containing receptors with reduced efficacy but no reduction in potency. These data demonstrate that the imidazopyridines zaleplon and indiplon are well suited to further investigate potential γ3 effects on sleep in vivo.

Understanding and Managing Sleep Difficulties in the Elderly

Insomnia is a common complaint in the geriatric population with studies indicating that 23-34% of elderly report symptoms of insomnia. Age-related changes in sleep physiology, diseases common in the elderly, and drug therapies common in the treatment of these diseases may result in difficulties with sleep. Managing these complaints requires a thorough evaluation to determine the etiology of insomnia since it is a symptom and not a disease. Additionally, when treating insomnia, non-pharmacologic issues need consideration before initiating drug therapy. A variety of pharmacologic agents are available to treat insomnia short term. Recently, two new novel agents have been added to the armamentarium of drugs that have some advantages over older, traditional agents.

Contributions of GABAA receptor subtype selectivity to abuse liability and dependence potential of pharmacological treatments for anxiety and sleep disorders

When benzodiazepines (BZs) supplanted barbiturates as a favored, safer treatment for anxiety and sleep disorders in the 1960s, the abuse liability and dependence potential of these drugs were little understood. Widespread recognition of the difficulty of stopping use of chronically taken BZs emerged through the popular press in the late 1970s, which resulted in reluctance to prescribe these otherwise clinically useful compounds. Evolution of the understanding of the biochemical basis for BZ effects in the 1980s and 1990s, coupled with regulatory emphasis on collection of data used in legal scheduling decisions, made possible a targeted search for drugs that would provide effective treatment for anxiety disorders in the absence of abuse liability or dependence potential. Compounds that have selective efficacy at subtypes of the gamma-aminobutyric acid type A receptor, are active in preclinical anxiolytic screens, but negative in preclinical studies of behavior relevant to evaluation of abuse liability appear to be one promising means for achieving this end.

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.

Effect of zaleplon, a non-benzodiazepine hypnotic, on melatonin secretion in rabbits

Melatonin, a major hormone secreted by the pineal gland, is known to play an important role in regulation of the circadian rhythm. (N-[3-(3-cyanopyrazolo[1,5-a]pyrimidin-7-yl)phenyl]-N-ethylacetamide (zaleplon) is a non-benzodiazepine hypnotic that acts via the benzodiazepine site of the GABA(A) receptor. In the present study, we investigated the effect of zaleplon on melatonin secretion in rabbits using RIA and compared the effect to triazolam and zopiclone. Zaleplon increased a dose-dependent concentration of melatonin in rabbit plasma collected at 30 min after intravenous administration at doses of 1 and 2 mg/kg. The zaleplon-induced increase in plasma melatonin level was not blocked by flumazenil, a benzodiazepine-receptor antagonist. In contrast, triazolam and zopiclone failed to affect the plasma melatonin level. We also investigated the effect of zaleplon on intracellular cAMP in rat pinealocytes. Consequently, zaleplon had no effect on the intracellular cAMP levels in rat pinealocytes. These results of the present studies suggest that zaleplon may promote melatonin secretion and the elevation of plasma levels of melatonin may suggest an influence of zaleplon on chronobiology.

Is there a rationale for prescription of benzodiazepines in the elderly? Review of the literature

Benzodiazepines (BZDs) constitute the most widely used symptomatic treatment of insomnia and anxiety. Many of these drugs are associated with adverse effects, such as daytime sedation and dependence with continued use. There is a concern about the rationale for and extent of benzodiazepine (BZD) use in the elderly. The sedation due to BZD use is a main risk factor for falls and other accidents. Impaired cognitive function with continuous use appears to be a major side effect. There is a general awareness that BZD use is inappropriate in many patients, and therefore discontinuation should be recommended whenever possible. Moreover, long-term use of these drugs should be actively discouraged. Although no unanimous recommendations concerning the optimal duration of the withdrawal process exist, BZDs may easily be withdrawn during a short period in most patients who are habituated to a low dose, if an initial phase with dose reduction and psychological support are provided. Alternative approaches involve sleep hygiene guidelines, behavioural treatment and psychotherapy tailored to the needs of the individual patient.

Comparison of the effects of zaleplon, zolpidem, and triazolam at various GABA(A) receptor subtypes

The pyrazolopyrimidine zaleplon is a hypnotic agent that acts at the benzodiazepine recognition site of GABA(A) receptors. Zaleplon, like the hypnotic agent zolpidem but unlike classical benzodiazepines, exhibits preferential affinity for type I benzodiazepine (BZ(1)/omega(1)) receptors in binding assays. The modulatory action of zaleplon at GABA(A) receptors has now been compared with those of zolpidem and the triazolobenzodiazepine triazolam. Zaleplon potentiated GABA-evoked Cl(-) currents in Xenopus oocytes expressing human GABA(A) receptor subunits with a potency that was higher at alpha1beta2gamma2 receptors than at alpha2- or alpha3-containing receptors. Zolpidem, but not triazolam, also exhibited selectivity for alpha1-containing receptors. However, the potency of zaleplon at these various receptors was one-third to one-half that of zolpidem. Zaleplon and zolpidem also differed in their actions at receptors containing the alpha5 or gamma3 subunit. Zaleplon, zolpidem, and triazolam exhibited similar patterns of efficacy among the different receptor subtypes. The affinities of zaleplon for [(3)H]flunitrazepam or t-[(35)S]butylbicyclophosphorothionate ([(35)S]TBPS) binding sites in rat brain membranes were lower than those of zolpidem or triazolam. Furthermore, zaleplon, unlike zolpidem, exhibited virtually no affinity for the peripheral type of benzodiazepine receptor.

Safety of zaleplon in the treatment of insomnia

OBJECTIVE

To evaluate the safety of zaleplon, a quick-acting, rapidly eliminated nonbenzodiazepine (non-BZD) hypnotic, as described in clinical investigations of adult and/or elderly subjects.

DATA SOURCES

Published and presented studies evaluating zaleplon, a novel non-BZD, were identified via MEDLINE (1995-July 2001), Current Contents (ISI database), bibliographic reviews, and consultation with sleep specialists who also identified published abstracts containing data not yet published in peer-reviewed journals.

DATA SYNTHESIS

Transient and chronic insomnia are common problems that should be clinically evaluated and appropriately treated. BZDs have been a primary pharmacotherapy for treating insomnia, despite their disadvantages. Newer hypnotics, characterized by increased receptor-binding specificity and favorable pharmacokinetics, provide potentially better alternatives to BZDs. Assessments included residual sedation, psychomotor impairment, or cognitive dysfunction during treatment, as well as the occurrence of rebound insomnia and withdrawal effects after discontinuation of therapy.

CONCLUSIONS

Zolpidem, the first non-BZD hypnotic, appears to have short- and long-term safety profiles similar to those of the BZD triazolam. Zaleplon, a newer non-BZD sleep medication, has a quick onset of action and undergoes rapid elimination, which results in a better safety profile than previously available agents. Additionally, rebound insomnia and other withdrawal effects have not been demonstrated with zaleplon, and the drug is well tolerated in both young and elderly patients. These characteristics may be clinically advantageous for patients who should not receive BZDs.

Noise-induced sleep maintenance insomnia: hypnotic and residual effects of zaleplon

AIMS

The primary objective of the study was to assess the residual effects of zaleplon in the morning, 4 h after a middle-of-the-night administration. The secondary objective was to investigate the effectiveness of zaleplon in promoting sleep in healthy volunteers with noise-induced sleep maintenance insomnia.

METHODS

Thirteen healthy male and female volunteers (aged 20-30 years) with normal hearing, who were sensitive to the sleep-disrupting effects of noise, participated in a double-blind, placebo- and active-drug controlled, four-period cross-over study. The subjects were permitted to sleep for 5 h (22.45-03.45 h) in a quiet environment before they were awoken. At 04.00 h they ingested 10 mg zaleplon, 20 mg zaleplon, 7.5 mg zopiclone (active control), or placebo before a second period of sleep (04.00-08.00 h), during which they were exposed to an 80 dB(A) 1 kHz pure tone pulse with an inter-tone interval of 1 s and a duration of 50 ms. The sound stimulus was stopped after 10 min of persistent sleep or after 2 h if the subject had not fallen asleep. Residual effects were assessed at 08.00 h (4 h after drug administration) using the digit symbol substitution test (DSST), choice reaction time (CRT), critical flicker fusion (CFF), and immediate and delayed free recall of a 20 word list. The data were analysed by analysis of variance. A Bonferroni adjustment was made for the three active treatments compared with placebo.

RESULTS

There were no residual effects of zaleplon (10 and 20 mg) compared with placebo. Zopiclone impaired memory by delaying the free recall of words (P = 0.001) and attenuated performance on DSST (P = 0.004) and CRT (P = 0.001), compared with placebo. Zaleplon reduced the latency to persistent sleep (10 mg, P = 0.001; 20 mg, P = 0.014) and the 20 mg dose reduced stage 1 sleep (P = 0.012) compared with placebo. Zopiclone reduced stage 1 sleep (P = 0.001), increased stage 3 sleep (P = 0.0001) and increased total sleep time (P = 0.003), compared with placebo.

CONCLUSIONS

Zaleplon (10 mg and 20 mg), administered in the middle of the night 4 h before arising, shortens sleep onset without impairing next-day performance.

Pharmacodynamic profile of Zaleplon, a new non-benzodiazepine hypnotic agent

The challenge in developing hypnotic agents for the treatment of insomnia is to balance the sedative effect needed at bedtime with the residual sedation on awakening. Zaleplon is a novel pyrazolopyrimidine hypnotic agent that acts as a selective agonist to the brain omega(1) receptor situated on the alpha(1) subunit of the GABA(A) receptor complex. Zaleplon was proven to be an effective hypnotic drug as it consistently and significantly reduced latency to persistent sleep in insomniac patients for doses of 10 mg and above in polysomnography studies. The pharmacodynamic profile of zaleplon on psychomotor performance, actual driving and cognitive function, including memory, was assessed in several randomized, double-blind, placebo-controlled studies in healthy young subjects as well as insomniac patients by using various positive controls (zolpidem, zopiclone, triazolam and flurazepam). The recommended hypnotic dose of zaleplon in young adults (10 mg) produced minimal or no impairment of psychomotor and memory performance even when administered during the night as little as 1 h before waking. No impairment of actual driving was observed when zaleplon 10 mg was administered either at bedtime or in the middle of the night as little as 4 h before waking. Zaleplon 20 mg, twice the recommended dose, generally produced significant impairment of performance and cognitive functions when these functions were measured at the time of peak plasma concentration, i.e. 1 h after dose administration, and no impairment of driving abilities was observed 4 h after a middle-of-the-night administration. In contrast, consistent detrimental residual effects on various aspects of psychomotor and cognitive functions were observed with the therapeutic doses of the various commonly prescribed hypnotic agents used as comparators, e.g. zolpidem 10 mg up to 5 h after dose administration, zopiclone 7.5 mg up to 10 h after, flurazepam 30 mg up to 14 h after and triazolam 0.25 mg up to 6 h after. Also, zolpidem 10 mg and zopiclone 7.5 mg were also shown to significantly impair driving ability the next morning when this was measured 4 h and up to 10 h after dose administration, respectively. The present review shows that zaleplon 10 mg has little or no residual effect when administered in the middle of the night, as late as 1 h before waking, and is devoid of impairment of driving abilities as assessed by actual driving 4 h after dose administration. The lack of clinically significant or minimally statistically significant residual effects of zaleplon even at its peak concentration may be explained by its unique pharmacokinetic (rapid elimination half-life) and pharmacodynamic (low affinity, and specific binding profile to various subunits of the GABA(A)receptor) profiles. These properties allow zaleplon to be used for treatment of symptoms only when they occur, either at bedtime or later in the night, without incurring significant risk of developing next-day impairment of psychomotor and cognitive functioning. Copyright 2001 John Wiley & Sons, Ltd.

Residual effects of zaleplon and zolpidem following middle of the night administration five hours to one hour before awakening

The objective was to assess residual effects of zaleplon and zolpidem after a middle of the night administration. This was a randomized, double-blind, placebo-controlled, crossover study, conducted in 40 healthy young male and female subjects. Subjects were awakened in the middle of the night and administered either placebo or zaleplon 10 or 20 mg or zolpidem 10 mg. A battery of objective tests exploring psychomotor and cognitive functions such as critical flicker fusion (CFF), choice reáction time (CRT), digit symbol substitution test (DSST), and memory tests (Sternberg memory scanning and a word list) were administered immediately after morning waking. Zaleplon 10 mg was devoid of residual effects whatever - the time of dosing - except a minimal but significant decrease in DSST scores when administered 1 h before awakening. Zaleplon 20 mg produced significant residual effects on performance (increase in CRT, and decrease in CFF threshold and in DSST scores) and memory (decrease in immediate and delayed free recall of words) only when administered 1 h before awakening. In contrast, zolpidem 10 mg produced significant detrimental residual effects on CRT and delayed free recall of words, when administered up to 5 h before waking, on DSST and Sternberg when administered up to 3 h before awakening and on CFF when administered 1 h before awakening. The residual effects of zolpidem 10 mg were more marked than those observed after zaleplon 20 mg. The present results demonstrate that zaleplon 10 mg has no or minimal residual effects when administered in the middle of the night as little as 1 h before waking. The lack of clinically significant residual effects with zaleplon may be explained by its unique pharmacokinetic (rapid elimination half-life) and pharmacodynamic (selective binding for GABA(A) receptors with the alpha(1) subunit, dissociation between sleep inducing properties and impairment of cognitive functions) profiles. Copyright 2001 John Wiley & Sons, Ltd.

Zaleplon and triazolam physical dependence assessed across increasing doses under a once-daily dosing regimen in baboons

The ability of the GABA(A)-receptor-subtype-selective hypnotic zaleplon to produce physical dependence was compared to the nonselective benzodiazepine triazolam. Progressively increasing doses of zaleplon and triazolam were given to baboons by intragastric infusion once each day, with doses increasing every 17 days. Next, the highest dose was given for 10-34 additional days by continuous infusion. Both drugs produced increases in food-maintained lever pressing, ataxia, and time to complete a fine motor task. Plasma levels increased dose-dependently; drug was detectable 24 h after higher doses. Flumazenil produced a mild or intermediate precipitated-withdrawal syndrome on day 14 of all dosing conditions. When drug delivery ended after 85-100 days, a benzodiazepine-type withdrawal syndrome occurred. Physical dependence potential of zaleplon and triazolam appear similar.

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 its use in the treatment of insomnia

Zaleplon is a pyrazolopyrimidine hypnotic agent which is indicated for the short term (2 to 4 weeks) management of insomnia. Zaleplon 5 and 10 mg at bedtime (usual recommended doses) significantly reduced sleep latency compared with placebo in clinical trials in nonelderly and elderly patients with insomnia. In general, sleep maintenance (sleep duration and number of awakenings) and sleep quality were not significantly different from placebo with zaleplon 5 and 10 mg/night. Zaleplon 20 mg/night significantly improved sleep latency and duration in nonelderly patients, but effects on number of awakenings were inconsistent and sleep quality generally did not improve. The relative hypnotic efficacy of zaleplon compared with that of triazolam and zolpidem is not yet clearly established. Tolerance to the hypnotic effects of zaleplon generally did not occur during 5 weeks' treatment, or during long term treatment (6 or 12 months) according to a small number of studies presented as abstracts. Zaleplon was well tolerated in clinical trials. The most common event was headache but the incidence was similar to that observed with placebo. Zaleplon 5 and 10 mg did not impair psychomotor function or memory even immediately after the dose in studies in volunteers or patients with insomnia. Zaleplon 20 mg, however, impaired psychomotor function and memory immediately after the dose but next-day effects were not observed. The psychomotor profile of zaleplon appears to be better than that of comparator agents. Rebound insomnia was not observed after sudden discontinuation of up to 12 months' treatment with zaleplon 5 and 10 mg/night and up to 4 weeks' treatment with zaleplon 20 mg/night. In addition, the potential for withdrawal syndrome with zaleplon appears to be low according to limited data. In conclusion, zaleplon 5, 10 and 20 mg administered at bedtime, or later if patients have difficulty sleeping, is an effective and well tolerated hypnotic agent. There was no evidence of next-day residual effects with the 5 and 10 mg dosages, and the incidence of withdrawal effects with zaleplon 5, 10 and 20 mg did not differ significantly to that observed with placebo. In addition, tolerance to the effects of zaleplon is unlikely to develop when administered for the recommended treatment period. The comparative efficacy and tolerability of zaleplon with other short acting nonbenzodiazepine hypnotics is difficult to establish. However, on the basis of current efficacy evidence and the lower incidence of residual effects with zaleplon 5 and 10 mg relative to comparator agents, this drug represents a useful option in the management of patients with insomnia who have difficulties initiating sleep.

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.

Differentiating benzodiazepine- and barbiturate-like discriminative stimulus effects of lorazepam, diazepam, pentobarbital, imidazenil and zaleplon in two- versus three-lever procedures

Previous studies found that animals trained to discriminate pentobarbital show a relatively inclusive generalization profile. They generalize to sedative-hypnotics and anxiolytics, regardless of differences among such drugs in molecular mechanism of action. In contrast, animals trained to discriminate lorazepam have shown a generalization profile that appears selective for compounds with in-vitro profiles as full agonists at the benzodiazepine modulatory site. The present study investigated whether benzodiazepine receptor ligands, to which pentobarbital-trained rats had generalized under a two-lever procedure, would occasion pentobarbital- or lorazepam-appropriate responding when the rats were retrained to discriminate among pentobarbital, lorazepam and the no-drug condition under a three-lever procedure. A second group of rats was trained first to discriminate lorazepam and then retrained under the same three-lever procedure. Under the two-lever procedure, all pentobarbital-trained rats showed dose-dependent generalization to lorazepam, but not all lorazepam-trained rats showed full generalization to pentobarbital. Both groups showed full generalization to diazepam and zaleplon, a novel hypnotic that is selective for alpha, 1-subunit-containing subtypes of the gamma-aminobutyric acid (GABA)A receptor. Pentobarbital-trained rats, but not all lorazepam-trained rats, generalized to imidazenil. Under the three-lever procedure, dose-dependent generalization to lorazepam and pentobarbital was demonstrated on the appropriate levers. Diazepam shared discriminative effects with pentobarbital, zaleplon shared discriminative effects with lorazepam, and imidazenil shared discriminative effects with lorazepam and pentobarbital. These results show that when the opportunity for finer differentiation of discriminative effects of GABAergic drugs is provided, a generalization profile more in line with differential in-vitro profiles can be revealed.

A five week, polysomnographic assessment of zaleplon 10 mg for the treatment of primary insomnia

Objective: To examine the hypnotic efficacy of zaleplon 10 mg, a selective benzodiazepine receptor agonist, over a period of 35 nights in primary insomniacs.Methods: A double-blind, parallel-group, placebo-controlled design was employed. Subjects were 113 men and women, ages 18 to 65 years. Polysomnographic and subjective sleep data were collected during baseline, on two nights during each of five treatment weeks, and on the first two nights after discontinuation of active medication.Results: Sleep latency was significantly shortened with zaleplon 10 mg for all 5 weeks of treatment as assessed by polysomnography and by subjective sleep measures. Total sleep time, whether evaluated with polysomnography or with subjective estimates, was inconsistently affected. Sleep architecture was similar with zaleplon and placebo. There was no evidence of tolerance to the sleep promoting effects of zaleplon during the five weeks of administration, and there was no rebound insomnia upon discontinuation. Adverse events occurred with equal frequency in the zaleplon and placebo groups.Conclusions: Zaleplon 10 mg is effective in the treatment of sleep onset insomnia over a period of 35 nights, with minimal evidence of undesired effects.

A comparison of the residual effects of zaleplon and zolpidem following administration 5 to 2 h before awakening

AIMS

To compare the duration of the residual hypnotic and sedative effects of zaleplon with those of zolpidem and placebo following nocturnal administration at various times before morning awakening.

METHODS

Zaleplon 10 mg, zolpidem 10 mg, or placebo was administered double-blind to 36 healthy subjects under standardized conditions in a six-period, incomplete-block, crossover study. Subjects were gently awakened and given medication at predetermined times 5, 4, 3, or 2 h before morning awakening, which occurred 8 h after bedtime. When the subjects awoke in the morning, a battery of subjective and objective assessments of residual effects of hypnotics was administered.

RESULTS

No residual effects were demonstrated after zaleplon 10 mg, when administered as little as 2 h before waking, on either subjective or objective assessments, whereas zolpidem 10 mg showed significant residual effects on DSST and memory (immediate and delayed free recall) after administration up to 5 h before waking and choice reaction time, critical flicker fusion threshold and Sternberg memory scanning after administration up to 4 h before waking. Residual effects of zolpidem were apparent in all objective and subjective measurements when the drug was administered later in the night.

CONCLUSIONS

The present results demonstrate that zaleplon at the dose of 10 mg is free of residual hypnotic or sedative effects when administered nocturnally as little as 2 h before waking in normal subjects. In contrast, residual effects of zolpidem are still apparent on objective assessments up to 5 h after nocturnal administration, longer than has been reported from studies involving daytime administration.