Pimavanserin tartrate: a 5-HT2A inverse agonist with potential for treating various neuropsychiatric disorders

Role of 5-HT2A receptor antagonists in the treatment of insomnia

Insomnia encompasses a difficulty in falling asleep (sleep-onset insomnia) and/or a difficulty in staying asleep (SMI). Several selective serotonin-2A (5-HT2A) receptor antagonists have been in development as potential treatments for SMI. However, none have shown a sufficiently robust benefit-to-risk ratio, and none have reached market approval. We review the role of the 5-HT2A mechanism in sleep, the preclinical and clinical data supporting a role for 5-HT2A receptor antagonism in improving sleep maintenance, and the status of 5-HT2A receptor antagonists in clinical development. Overall, the polysomnography data strongly support an increase in slow-wave sleep and a decrease in waking after sleep onset following treatment with 5-HT2A receptor antagonists, although it has been more difficult to show subjective improvements in sleep with these agents. The incidence and prevalence of SMI, whether primary or secondary to psychiatric, neurologic, or other medical conditions, will increase as our population ages. There will be an increased need for safe and efficacious treatments of insomnia characterized by difficulty maintaining sleep, and there remains much promise for 5-HT2A receptor antagonism to play a role in these future treatments.

Insomnia pharmacology

Insomnia is not only the most common sleep disorder in the population, it is a frequent complaint heard overall by primary care physicians and specialists alike. Given the high prevalence of this disorder, its tendency to persist, and the frequency with which patients complain of symptoms in practice, it is imperative to have an understanding of basic sleep-wake mechanisms and the evolving field of pharmacologic approaches to enhance sleep. Currently, pharmacologic approaches are among the most widely used therapies for insomnia. This article reviews sleep-wake mechanisms, the neuroanatomic targets for sleep and wake-promoting agents, and discusses currently used agents to promote sleep and investigational hypnotics.

Acute antipsychotic-induced akathisia revisited

Akathisia remains one of the most prevalent and distressful antipsychotic-induced adverse events. Effective and well-tolerated treatment is a major unmet need in akathisia that merits a search for new remedies. Accumulating evidence indicates that agents with marked serotonin-2A receptor antagonism may represent a new class of potential anti-akathisia treatment.

Emerging drugs for insomnia: new frontiers for old and novel targets

BACKGROUND

Insomnia is the most prevalent sleep disorder, with up to 50% of the US adult population reporting symptoms of insomnia on a weekly basis and approximately 12% with insomnia disorder. Comorbid conditions such as depression and anxiety are frequent. Insomnia is more common with older age, female gender and socioeconomic status. Traditionally, therapy has focused on GABA(A) receptor agonists, and off-label antidepressant and antihistamine use.

OBJECTIVE

With increased understanding of complex neural networks involved in sleep and wake, hypnotics are being developed to target a broader variety of receptors with increasing selectivity. This review summarizes promising compounds in Phase II and III trials with evidence supporting efficacy for treatment of insomnia.

METHODS

5-HT(2A) and 5-HT(2C) antagonists, melatonergic (MT1/MT2) agonists, orexin receptor (OX1/OX2) antagonists, as well as GABA(A) receptor agonists are reviewed and summarized. Data are collected from PubMed and Pharmaprojects database searches, company websites, recent scientific meeting presentations and abstracts.

RESULTS/CONCLUSIONS

A variety of drugs targeting several pathways, including GABA(A) agonism, MT1/MT2 agonism, 5-HT(2A) antagonism, OX1/OX2 antagonism and others, are in Phase II and III trials. More work should be done to understand the impact of these drugs in certain populations and in the context of comorbid conditions.

Hallucinations in Parkinson disease

Patients with Parkinson disease (PD) can experience hallucinations (spontaneous aberrant perceptions) and illusions (misinterpretations of real perceptual stimuli). Of such phenomena, visual hallucinations (VHs) and illusions are the most frequently encountered, although auditory, olfactory and tactile hallucinations can also occur. In cross-sectional studies, VHs occur in approximately one-third of patients, but up to three-quarters of patients might develop VHs during a 20-year period. Hallucinations can have substantial psychosocial effects and, historically, were the main reason for placing patients in nursing homes. Concomitant or overlapping mechanisms are probably active during VHs, and these include the following: central dopaminergic overactivity and an imbalance with cholinergic neurotransmission; dysfunction of the visual pathways, including specific PD-associated retinopathy and functional alterations of the extrastriate visual pathways; alterations of brainstem sleep-wake and dream regulation; and impaired attentional focus. Possible treatments include patient-initiated coping strategies, a reduction of antiparkinson medications, atypical neuroleptics and, potentially, cholinesterase inhibitors. Evidence-based studies, however, only support the use of one atypical neuroleptic, clozapine, and only in patients without dementia. Better phenomenological discrimination, combined with neuroimaging tools, should refine therapeutic options and improve prognosis. The aim of this Review is to present epidemiological, phenomenological, pathophysiological and therapeutic aspects of hallucinations in PD.

Antipsychotics in the early stage of development

PURPOSE OF REVIEW

In this article, we will summarize some of the most recent pharmacological approaches by briefly reviewing the latest research results related to different neurotransmitter receptor systems but also alternative approaches that do not affect central nervous system receptors directly.

RECENT FINDINGS

Although the field still struggles with the lack of major breakthroughs, some novel pharmacological leads have provided encouraging findings in proof of concept or early phase II clinical trials. Although some of these approaches are based on the modified dopamine/glutamate hypothesis of schizophrenia, others appear to have been driven by more serendipitous observations. Apart from this, more traditional routes such as compounds targeting D2/HT2 receptors are also still being pursued. Attempts to advance treatment response of negative symptoms and cognitive impairment, two areas of considerable unmet need have been an overriding theme in many studies.

SUMMARY

Clinical psychopharmacologists increasingly realize that it is highly unlikely that we have a magic bullet to treat adequately all aspects of this complex disorder in the foreseeable future. Rational polypharmacy may be the trend for the next decade.