The effects of single doses of alpidem and lorazepam on memory and psychomotor performance in normal humans

Individual Differences in Working Memory Capacity Predict Topiramate-Related Cognitive Deficits

PURPOSE/BACKGROUND

Topiramate (TPM) and lorazepam (LZP) are two examples of frequently prescribed medications that are associated with a high incidence of cognitive impairment; however, the factors that underlie interindividual differences in side effect profiles have not been fully characterized. Our objective was to determine whether working memory capacity (WMC), the amount of information that can be stored and manipulated in memory over short time intervals, is one such factor.

METHODS/PROCEDURES

Twenty-nine healthy volunteers completed a double-blind, randomized, placebo-controlled crossover study during which they received placebo (PBO), TPM, and LZP in random order. Four hours after drug administration, a blood draw was taken to establish drug concentrations, and subjects performed a verbal working memory task while the accuracy and reaction time of their responses were recorded. Working memory capacity was calculated based on accuracy rates during the PBO session, and the role of WMC in moderating the severity of drug-related cognitive impairment was assessed by examining drug-related performance changes from PBO as a function of WMC.

FINDINGS/RESULTS

Both TPM and LZP had a negative impact on task performance, although only TPM-related deficits were modulated by WMC; high WMC was associated with more severe impairments and heightened sensitivity to increasing TPM concentrations.

IMPLICATIONS/CONCLUSIONS

We have identified a potential clinical risk factor, high WMC, which is associated with drug-related adverse cognitive events. These data provide objective evidence in support of clinical observations that high-functioning patients are more likely to experience severe cognitive impairments.

Characterizing the subjective, psychomotor, and physiological effects of oral oxycodone in non-drug-abusing volunteers

RATIONALE

The subjective, psychomotor, and physiological effects of a widely prescribed and abused prescription opioid, oxycodone, have not been studied in a population of non-drug-abusing people.

OBJECTIVES

To characterize the effects of oxycodone in non-drug-abusing volunteers.

METHODS

Eighteen volunteers participated in a crossover, randomized, double-blind study in which they received, all p.o., placebo, 10 mg oxycodone, 20 mg oxycodone, 30 mg oxycodone, 40 mg morphine, and 2 mg lorazepam. Measures were assessed before and for 300 min after drug administration. End-of-session and 24-h post-session measures were taken to assess residual drug effects and overall subjects' assessments of the drug effects.

RESULTS

Subjective effects of oxycodone were dose related, with the majority of statistically significant effects limited to the two higher doses tested. Oxycodone produced a profile of subjective effects that included both pleasant and unpleasant effects. Morphine in general produced effects similar in magnitude to those of 10 mg and 20 mg oxycodone. Peak liking and drug-wanting ratings were increased by all doses of oxycodone and by morphine, and trough ratings of liking (dislike) were lower in the 20-mg and 30-mg oxycodone conditions, relative to the placebo condition. Post-session ratings of overall liking and drug wanting were not statistically significant, either at the end of the session or 24 h later. Cognitive and psychomotor impairment were obtained with the higher doses of oxycodone, but to a much lesser degree than that of lorazepam. Miosis and exophoria were increased in a dose-related manner by oxycodone.

CONCLUSIONS

Oxycodone produced effects similar to those of other mu opioid agonists. Although oxycodone produced abuse liability-related subjective effects, it also produced unpleasant effects, a phenomenon we have observed in other opioid studies in non-drug-abusing volunteers.

Assessment of the interaction between a partial agonist and a full agonist of benzodiazepine receptors, based on psychomotor performance and memory, in healthy volunteers

Potential interactions between the imidazopyridine anxiolytic alpidem and the full benzodiazepine agonist lorazepam were assessed in a randomized, double-blind, four-way cross-over, placebo-controlled study in 16 healthy young male volunteers. Each volunteer received alpidem, 50 mg, or a placebo twice daily for 8 days with a 1- week wash-out interval. The interaction between alpidem, at the steady state, and a single oral dose of lorazepam 2 mg or a placebo was assessed after concomitant administration on days 7 or 9 of each treatment period. Psycho motor performance and cognitive function were evaluated before and 2, 4, 6 and 8 h post-dose, using objective tests [critical flicker fusion threshold (CFF), choice reaction time (CRT), digit-symbol substitution (DSST), body sway and short-term memory (Sternberg memory scanning)] and self-ratings [line analogue rating scales: (LARS)]. Long-term memory (delayed free recall and recognition of pictures) was assessed before the dose and 2 and 4 h post-dose. Pharmacodynamic interactions were evaluated by applying repeated measures ANOVA to a 2 x 2 factorial interaction model. Alpidem, 50 mg twice daily at the steady state, was free of any clinically relevant detrimental effects on skilled performance, information processing or memory. In contrast, a single 2 mg dose of lorazepam induced marked impairment of psychomotor performance and cognitive function (significant reductions in CFF and DSST and increases in CRT and body sway), as well as subjective sedation from 2 to 8 h post-dose, depending on the test used. In addition, lorazepam induced anterograde amnesia, characterized by a decrease in delayed free recall and recognition, and a deficit in short-term memory. Finally, alpidem 50 mg did not potentiate the detrimental effects of lorazepam 2 mg. On the contrary, alpidem significantly antagonized the lorazepam-induced CRT increase and anterograde amnesia, and produced similar trends on most of the other cognitive parameters; thus, the results obtained with the combination of alpidem and lorazepam consistently indicated less impairment than those measured after lorazepam alone. These results are consistent with the suggested partial agonsist properties of alpidem at the benzodiazepine receptor and indicate that such properties can be assessed in humans based on antagonism of the effects of a full agonist.

Recent developments in the behavioral pharmacology of benzodiazepine (omega) receptors: evidence for the functional significance of receptor subtypes

Recent research in molecular biology has demonstrated the complexity of GABAA receptors and shown that benzodiazepine (BZ-omega) receptor subtypes have a structural reality. It is therefore appropriate to ask whether the different pharmacological effects produced by benzodiazepines (anticonvulsant activity, anxiety reduction, motor incoordination, learning deficits, characteristic discriminative stimulus effects, tolerance and dependence) are associated with activity at different receptor subtypes. The present paper reviews the literature dealing with the behavioral effects of novel BZ (omega) receptor ligands relevant to the question of the functional significance of the BZ1 (omega 1) and BZ2 (omega 2) receptor subtypes. The only drugs currently available with a considerable degree of selectivity are alpidem and zolpidem. These compounds have relatively high affinity for GABAA receptors containing the alpha 1 subunit (corresponding to the BZ1 (omega 1) subtype) and very low affinity for receptors with the alpha 5 subunit (corresponding to one type of BZ2 (omega 2) receptor). Pharmacological effects observed with these, and other, less selective compounds allow several tentative conclusions to be drawn: (a) Little is known of the role of subtype selectivity in anxiolytic or amnestic effects but compounds with low intrinsic activity may reduce anxiety without giving rise to sedation or motor incoordination and BZ1 (omega 1) selective drugs appear to disrupt memory only at sedative doses; (b) Selectivity for BZ1 (omega 1) receptors may be associated with sleep-inducing activity but not with motor incoordination, suggesting that BZ2 (omega 2) receptors may be of particular importance in mechanisms of muscle relaxation; (c) The discriminative stimulus effects of different BZ (omega) receptor ligands are not identical and differences may be related to receptor selectivity; (d) Compounds with BZ1 (omega 1) selectivity and compounds with low intrinsic activity produce little or no tolerance and dependence. A wider range of selective compounds will be necessary to investigate these factors in detail and many different pharmacological profiles can be expected from drugs with selectivity and different levels of intrinsic activity.

Computed axial brain tomograms in long-term benzodiazepine users

Computed axial brain tomograms were recorded in four groups of subjects: (a) subjects who had never taken benzodiazepines (n = 25); (b) subjects who had taken them in the past for less than a year (n = 9); (c) patients currently taking benzodiazepines (n = 30); and (d) patients who had taken benzodiazepines in the past for at least a year and who had been withdrawn from medication for at least 6 months (n = 17). Ventricle-to-brain ratios and tissue absorption to X-rays were computed. No overall differences were found between the main groups. However, a few brain regions differed in density between nonusers and heavy users, particularly those taking lorazepam.

Memory and psychomotor effects of oxcarbazepine in healthy human volunteers

Cognitive and psychomotor impairments can be unwanted adverse effects of antiepileptic drugs. The present double-blind, cross-over study with healthy volunteers was designed to assess the effects of two doses of oxcarbazepine (OXCZ) (150 mg b.i.d.; 300 mg b.i.d.) and a placebo, each given over a two week period. Twelve subjects completed a battery of tests before and 4 h after morning doses on days 1, 8 and 15. Results of objective tests indicated that OXCZ improved performance on a focussed attention task and increased manual writing speed. Subjective ratings showed OXCZ increased feelings of altertness, clear-headedness and quickwittedness. OXCZ had no effect on the range of long-term memory processes assessed in this study. It is concluded that at the doses employed, OXCZ has a slightly stimulant effect on some aspects of psychomotor functioning.

Clinical pharmacokinetics and tolerability of alpidem in healthy subjects given increasing single doses

In a double-blind, placebo-controlled, cross-over experiment in 21 healthy male volunteers, aged 19 to 27 y, the pharmacokinetics and tolerance of the new anxiolytic drug alpidem (SL80.0342) and its three major metabolites were studied after single doses of 25, 50, 100 and 200 mg. Plasma concentrations of alpidem (in 20 subjects) and metabolites (in 6 subjects) were measured by HPLC over a period of 54 h after dosing. Cmax, tmax and AUC(0-54) and, when possible, t1/2 were determined for alpidem and metabolites and the dose linearity of the parameters was investigated. The time to peak of alpidem was dose independent in most subjects and was short (1-4 h); the mean values at the four dosing levels were 1.9, 1.7, 1.6 and 1.8 h. The peak concentration increased with the dose, the mean values being 17, 34, 88 and 115 ng.ml-1, respectively. In 50% of the subjects Cmax tended to stabilize between the 100 and 200 mg dose. Dose linearity was also present for the AUC, which plateaued between the 100 and 200 mg dose in only 3 out of 20 subjects; the mean AUC was 119, 281, 669 and 1117 ng.ml-1.h, respectively. The apparent half-life of elimination appeared to be dose independent, mean values at the increasing dosing levels being 18.7, 19.9, 18.1, and 17.9 h. A similar relationship between the kinetics parameters and dose of the alpidem was observed for the metabolites SL83.0912, SL80.0522 and SL83.0725. The formation of metabolites was not saturated as their AUCs relative to corresponding alpidem AUCs were not dose related.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzodiazepines, memory and mood: a review

The amnestic effects of benzodiazepines (BZs) have attracted considerable research interest. This reflects not only the clinical implications of memory failure for people prescribed these drugs but also the potential of BZs as tools in modelling organic memory problems. As well as impairing certain aspects of human memory functions, BZs affect mood states by reducing anxiety and inducing sedation. An unresolved issue is the extent to which the amnestic effects of BZs are separable from their sedative and anxiolytic effects. The present review focuses on this issue, first presenting a conceptual framework for evaluating the interrelationship between the various effects of BZs, and then summarising recent volunteer and patient research relevant to dissociating amnestic from other effects. Clinical implications are discussed in terms of the use of BZs alone or as adjuncts to psychotherapy for anxiety disorders, and attention is drawn to the need for more ecological validity in psychopharmacological research. Theoretical implications are explored in terms of BZs as tools in studying both memory failure and the relationship between mood and cognition.

The differential effects of flumazenil on the psychomotor and amnesic actions of midazolam

Forty-four patients given midazolam prior to day-care urological surgery had the benzodiazepine antagonist, flumazenil, or placebo administered postoperatively. Flumazenil reversed the psychomotor impairments induced by midazolam but not its amnesic effects. There was no evidence of resedation for up to 6 h following the use of flumazenil.

Plasma protein binding of alpidem in healthy volunteers, in neonates and in liver or renal insufficiency

The binding of alpidem, a new anxiolytic drug, has been studied in plasma from 6 healthy subjects, 12 patients with renal failure, 12 patients with liver cirrhosis and 12 chronic uraemics maintained on haemodialysis, as well as in 12 serum samples from the placental cord, to represent the situation in the newborn. The unbound fraction was 0.61% (healthy volunteers), 1.31% (newborns), 0.86% (cirrhotic patients), 0.72 (patients with renal failure), 0.70% (before haemodialysis) and 0.79% (after haemodialysis). Binding in the volunteers was significantly different from that in neonates and cirrhotics only. Alpidem became bound to isolated albumin (45 g.l-1) and alpha 1-acid glycoprotein (0.75 g.l-1) to 97.2% and 97.1%, respectively. The bound fraction of the drug in a mixture of two proteins was 99.1%. For alpidem, it appears that alpha 1-acid glycoprotein may balance the effect of any decrease in the albumin concentration.

Clinical pharmacology of non-benzodiazepine anxiolytics

Non-benzodiazepine anxiolytics can be conveniently divided into those which are not primarily used as anxiolytics, those which pharmacologically but not chemically resemble benzodiazepines, and those which are novel both chemically and pharmacologically. The former include antidepressants, antipsychotic drugs, antihistamines and beta-adrenergic antagonists. The second group comprises a variety of compounds which act on the benzodiazepine/GABA complex and include alpidem and zuriclone. The most important of the non-benzodiazepine anxiolytics is buspirone, which seems to act on 5-HT mechanisms. The field of anxiolytic therapy is changing rapidly. New drugs are being introduced and the use of old ones questioned. It is hoped that drugs will be developed which are not only effective and safe with no sedation, but also with little or no propensity to dependence and abuse.