Asenapine
Asenapine, sold under the brand name Saphris among others, is an atypical antipsychotic medication used to treat schizophrenia and acute mania associated with bipolar disorder.It was chemically derived via altering the chemical structure of the tetracyclic (atypical) antidepressant, mianserin.It was initially approved in the United States in 2009 and approved as a generic medication in 2020.

Medical uses
Asenapine has been approved by the FDA for the acute treatment of adults with schizophrenia and acute treatment of manic or mixed episodes associated with bipolar I disorder with or without psychotic features in adults. In Australia asenapines approved (and also listed on the PBS) indications include the following:
Schizophrenia
Treatment, for up to 6 months, of an episode of acute mania or mixed episodes associated with bipolar I disorder
Maintenance treatment, as monotherapy, of bipolar I disorderIn the European Union and the United Kingdom, asenapine is only licensed for use as a treatment for acute mania in bipolar I disorder.Asenapine is absorbed readily if administered sublingually, asenapine is poorly absorbed when swallowed. A transdermal formulation of asenapine was approved in the United States in October 2019 under the brand name Secuado.

Schizophrenia
A Cochrane systematic review found that while Asenapine has some preliminary evidence that it improves positive, negative, and depressive symptoms, it does not have enough research to merit a certain recommendation of Asenapine for the treatment of schizophrenia.

Acute mania
As for its efficacy in the treatment of acute mania, a recent meta-analysis showed that it produces comparatively small improvements in manic symptoms in patients with acute mania and mixed episodes than most other antipsychotic drugs (with the exception of ziprasidone) such as risperidone and olanzapine. Drop-out rates (in clinical trials) were also unusually high with asenapine. According to a post-hoc analysis of two 3-week clinical trials it may possess some antidepressant effects in patients with acute mania or mixed episodes.

Adverse effects
Adverse effect incidenceVery common (>10% incidence) adverse effects include:

SomnolenceCommon (1-10% incidence) adverse effects include:

Weight gain
Increased appetite
Extrapyramidal side effects (EPS; such as dystonia, akathisia, dyskinesia, muscle rigidity, parkinsonism)
Sedation
Dizziness
Dysgeusia
Oral hypoaesthesia
Increased alanine aminotransferase
FatigueUncommon (0.1-1% incidence) adverse effects include:

Hyperglycaemia — elevated blood glucose (sugar)
Syncope
Seizure
Dysarthria
sinus bradycardia
Bundle branch block
QTc interval prolongation (has a relatively low risk for causing QTc interval prolongation.)
sinus tachycardia
Orthostatic hypotension
Hypotension
Swollen tongue
Dysphagia (difficulty swallowing)
Glossodynia
Oral paraesthesiaRare (0.01-0.1% incidence) adverse effects include:

Neuroleptic malignant syndrome (Combination of fever, muscle stiffness, faster breathing, sweating, reduced consciousness, and sudden change in blood pressure and heart rate)
Tardive dyskinesia
Speech disturbance
Rhabdomyolysis
Angioedema
Blood dyscrasias such as agranulocytosis, leukopenia and neutropenia
Accommodation disorder
Pulmonary embolism
Gynaecomastia
GalactorrhoeaUnknown incidence adverse effects

Allergic reaction
Restless legs syndrome
Nausea
Oral mucosal lesions (ulcerations, blistering and inflammation)
Salivary hypersecretion
HyperprolactinaemiaAsenapine seems to have a relatively low weight gain liability for an atypical antipsychotic (which are notorious for their metabolic side effects) and a 2013 meta-analysis found significantly less weight gain (SMD [standard mean difference in weight gained in those on placebo vs. active drug]: 0.23; 95% CI: 0.07-0.39) than, paliperidone (SMD: 0.38; 95% CI: 0.27-0.48), risperidone (SMD: 0.42; 95% CI: 0.33-0.50), quetiapine (SMD: 0.43; 95% CI: 0.34-0.53), sertindole (SMD: 0.53; 95% CI: 0.38-0.68), chlorpromazine (SMD: 0.55; 95% CI: 0.34-0.76), iloperidone (SMD: 0.62; 95% CI: 0.49-0.74), clozapine (SMD: 0.65; 95% CI: 0.31-0.99), zotepine (SMD: 0.71; 95% CI: 0.47-0.96) and olanzapine (SMD: 0.74; 95% CI: 0.67-0.81) and approximately (that is, no statistically significant difference at the p=0.05 level) as much as weight gain as aripiprazole (SMD: 0.17; 95% CI: 0.05-0.28), lurasidone (SMD: 0.10; 95% CI: –0.02-0.21), amisulpride (SMD: 0.20; 95% CI: 0.05-0.35), haloperidol (SMD: 0.09; 95% CI: 0.00-0.17) and ziprasidone (SMD: 0.10; 95% CI: –0.02-0.22). Its potential for elevating plasma prolactin levels seems relatively limited too according to this meta-analysis. This meta-analysis also found that asenapine has approximately the same odds ratio (3.28; 95% CI: 1.37-6.69) for causing sedation [compared to placebo-treated patients] as olanzapine (3.34; 95% CI: 2.46-4.50]) and haloperidol (2.76; 95% CI: 2.04-3.66) and a higher odds ratio (although not significantly) for sedation than aripiprazole (1.84; 95% CI: 1.05-3.05), paliperidone (1.40; 95% CI: 0.85-2.19) and amisulpride (1.42; 95% CI: 0.72 to 2.51) to name a few and is hence a mild-moderately sedating antipsychotic. The same meta-analysis suggested that asenapine had a relatively high risk of extrapyramidal symptoms compared to other atypical antipsychotics but a lower risk than first-generation or typical antipsychotics.

Discontinuation
For all antipsychotics, the British National Formulary recommends a gradual dose reduction when discontinuing to avoid acute withdrawal syndrome or rapid relapse. Symptoms of withdrawal commonly include nausea, vomiting, and loss of appetite. Other symptoms may include restlessness, increased sweating, and trouble sleeping. Less commonly there may be a feeling of the world spinning, numbness, or muscle pains. Symptoms generally resolve after a short period of time.There is tentative evidence that discontinuation of antipsychotics can result in psychosis. It may also result in recurrence of the condition that is being treated. Rarely tardive dyskinesia can occur when the medication is stopped.

Pharmacology
Pharmacodynamics
Asenapine shows high affinity (pKi) for numerous receptors, including the serotonin 5-HT1A (8.6), 5-HT1B (8.4), 5-HT2A (10.2), 5-HT2B (9.8), 5-HT2C (10.5), 5-HT5A (8.8), 5-HT6 (9.5), and 5-HT7 (9.9) receptors, the adrenergic α1 (8.9), α2A (8.9), α2B (9.5), and α2C (8.9) receptors, the dopamine D1 (8.9), D2 (8.9), D3 (9.4), and D4 (9.0) receptors, and the histamine H1 (9.0) and H2 (8.2) receptors. It has much lower affinity (pKi < 5) for the muscarinic acetylcholine receptors. Asenapine behaves as a partial agonist at the 5-HT1A receptors. At all other targets asenapine is an antagonist. As of November 2010 asenapine is also in clinical trials at UC Irvine to treat stuttering.
Even relative to other atypical antipsychotics, asenapine has unusually high affinity for the 5-HT2A, 5-HT2C, 5-HT6, and 5-HT7 receptors, and very high affinity for the α2 and H1 receptors.

References
External links
"Asenapine". Drug Information Portal. U.S. National Library of Medicine.
"Asenapine maleate". Drug Information Portal. U.S. National Library of Medicine.