The similarities and differences between meprobamate and barbiturates

The ups and downs of alkyl-carbamates in epilepsy therapy: How does cenobamate differ?

Since 1955, several alkyl-carbamates have been developed for the treatment of anxiety and epilepsy, including meprobamate, flupirtine, felbamate, retigabine, carisbamate, and cenobamate. They have each enjoyed varying levels of success as antiseizure drugs; however, they have all been plagued by the emergence of serious and sometimes life-threatening adverse events. In this review, we compare and contrast their predominant molecular mechanisms of action, their antiseizure profile, and where possible, their clinical efficacy. The preclinical, clinical, and mechanistic profile of the prototypical γ-aminobutyric acidergic (GABAergic) modulator phenobarbital is included for comparison. Like phenobarbital, all of the clinically approved alkyl-carbamates share an ability to enhance inhibitory neurotransmission through modulation of the GABA_A receptor, although the specific mechanism of interaction differs among the different drugs discussed. In addition, several alkyl-carbamates have been shown to interact with voltage-gated ion channels. Flupirtine and retigabine share an ability to activate K⁺ currents mediated by KCNQ (Kv7) K⁺ channels, and felbamate, carisbamate, and cenobamate have been shown to block Na⁺ channels. In contrast to other alkyl-carbamates, cenobamate seems to be unique in its ability to preferentially attenuate the persistent rather than transient Na⁺ current. Results from recent randomized controlled clinical trials with cenobamate suggest that this newest antiseizure alkyl-carbamate possesses a degree of efficacy not witnessed since felbamate was approved in 1993. Given that ceno-bamate's mechanistic profile is unique among the alkyl-carbamates, it is not clear whether this impressive efficacy reflects an as yet undescribed mechanism of action or whether it possesses a unique synergy between its actions at the GABA_A receptor and on persistent Na⁺ currents. The high efficacy of cenobamate is, however, tempered by the risk of serious rash and low tolerability at higher doses, meaning that further safety studies and clinical experience are needed to determine the true clinical value of cenobamate.

Meprobamate use in the elderly. A report from the Dunedin program

Meprobamate use was studied in an ambulatory elderly population in Dunedin, Florida. All participants taking this medication were mailed a questionnaire concerning their pattern of use. From 2,278 subjects, 30 (1.3%) reported the use of this drug. The average age of participants using this drug was 81.3 years. Five participants began using the drug over 27 years ago and over one-half of the respondents reported using the drug on a regular basis for over 10 years. With this type of history of meprobamate use, one might expect to encounter a large number of patients in the future who, in a similar manner, have been using benzodiazepines for many decades.

Evaluation of the safety and side effects of antianxiety agents

Historically, the use of anxiolytic drugs has been associated with a relatively high incidence of side effects, particularly those related to central nervous system depression and sedation. These side effects can impair the patient's ability to function and, thus, interfere with the full achievement of therapeutic goals. In this article, the evolution of anxiolytic drug therapy from the perspective of safety and side effects is reviewed. Moreover, data concerning the safety of buspirone--a novel, non-benzodiazepine anxiolytic that has been shown to provide anxiolytic efficacy comparable to that of the benzodiazepines, but with a significantly lower potential for central nervous system depressant effects, interactions with alcohol, dependence, and abuse--are discussed.

Impact of anxiety therapy on patients' quality of life

The treatment of anxiety is one of the leading problems in medicine today. Although traditional anxiolytic drugs have been effective in reducing the symptoms of anxiety, their efficacy has often been achieved at the expense of the patient's quality of life. The sedative side effects and impaired psychomotor functioning associated with the use of benzodiazepine anxiolytics not only impede the success of therapy, but jeopardize the patient's safety. This article addresses these salient issues and provides evidence suggesting that the antianxiety drug buspirone better achieves the goal of optimal anxiolytic therapy with minimal unwanted effects.

Rational use of anxiolytic/sedative drugs

The benzodiazepines are the most effective, safest, and most widely used antianxiety drugs. As a class of drugs, there are few major differences between the various benzodiazepine derivatives. The main distinguishing features are different plasma half-lives and the presence or absence of pharmacologically active metabolites. Plasma half-lives vary considerably, from 2 to 3 hours to more than 100 hours. All benzodiazepines are equally effective in the short term management of anxiety and insomnia, and their classification into 'anxiolytics' and 'hypnotics' is not justified. There are numerous other indications for benzodiazepine use, such as muscle spasm in osteoarthritic conditions, and acute alcohol withdrawal, but the benzodiazepines have no antidepressive or analgesic effects. While there is no good evidence for their long term efficacy in the treatment of anxiety and insomnia, the benzodiazepines are more effective and safer than their main predecessors, the barbiturates. Some of the benzodiazepines, particularly those with long plasma half-lives which are commonly used as hypnotics, have a prolonged duration of action and cause marked 'hang-over' effects. Alcohol enhances the effects of these drugs, and thus can also increase their side effects. Adversely effects such as oversedation, tremor, ataxia and confusion are much more common in elderly patients. Ever since the benzodiazepines were first marketed 20 years ago their use has increased rapidly, and it is now estimated that between 12 and 16% of the adult population in developed countries use tranquillisers at some time each year. However, their overall use has probably diminished somewhat in the last few years. Although their indications are very common, it is possible that some of this extensive usage may be the result of dependence. Until recently, published reports of such dependence were comparatively few. However, withdrawal symptoms have now been demonstrated in a substantial proportion of patients on long term, normal dose benzodiazepine treatment. The abstinence syndrome usually lasts for 8 to 10 days, and is characterised by insomnia, anxiety, loss of appetite and bodyweight, tremor, perspiration, and a host of perceptual disturbances. More serious developments such as epileptic fits and psychosis are probably infrequent during withdrawal from therapeutic doses. The overall incidence of benzodiazepine dependence remains unknown.

Dopamine and antianxiety activity

Clinical trials have indicated that buspirone (Buspar) is effective in the treatment of anxiety with efficacy and dosage comparable to diazepam. Until recently it has been thought that antianxiety drugs must alter benzodiazepine receptor binding in vitro. However, buspirone lacks any structural similarity to te benzodiazepines and does not interact with the benzodiazepine/gamma-aminobutyric acid (GABA) axis. Specifically, buspirone neither stimulates nor inhibits [3H]benzodiazepine binding, does not affect the influence o GABA or halide anions on benzodiazepine binding, and does not interfere with GABA binding or uptake. Behavioral testing has revealed that buspirone does not produce muscle weakness, does not control seizures, does not potentiate the impairment of psychophysiological function or lethality produced by administration of CNS depressants, does not produce sedation/hypnosis and does not appear to possess any abuse potential or liability for physical dependence. Thus, buspirone has been termed an anxioselective agent. Buspirone appears to only interact with the dopaminergic system with reasonable potency and exhibits properties of both a dopamine agonist and a dopamine antagonist. This suggests that dopamine is implicated in the etiology and expression of anxiety. A discussion of this implication is presented with a review of the clinical efficacy of nonbenzodiazepine drugs, especially dopamine agonists and dopamine antagonists, in the management of anxiety. In addition, neuropharmacological studies which have investigated the role of dopamine in animal models of anxiety are considered. Finally, the multiplicity of dopamine receptors and their regional localization in the brain are considered in the formulation of an hypothesis which features a role for the dopaminergic agents in the pharmacotherapy of anxiety.

Use of antianxiety agents in anxious outpatients

The present paper reviews the role of antianxiety agents in the treatment of nonpsychotic anxious patients. Major emphasis is placed on findings from clinical trials conducted by this research group. Consideration is given to the relative efficacy of available antianxiety agents, to patients response in relation to patterns of symptomatology, and to the degree of symptom relief experienced by drug-treated anxious patients. Also discussed are some of the many nonspecific factors that affect improvement with drug treatment in general and with the benzodiazepines in particular. It is concluded that many anxious patients are not currently receiving adequate drug treatment, and may require longer periods of drug therapy or supplemental nondrug intervention.