Amisulpride is an antipsychotic medication used to treat schizophrenia. In Italy, it is also used as a treatment for dysthymia. It is usually classed with the newer generation of antipsychotics, the so called atypical antipsychotics. Chemically it is a benzamide and like other benzamide antipsychotics, such as sulpiride, it is associated with a high risk of elevating blood levels of the lactation hormone, prolactin (thereby potentially causing the absence of the menstrual cycle, breast enlargement, even in males, breast milk secretion not related to breastfeeding, impaired fertility, impotence, breast pain, etc.), and a low risk, relative to the typical antipsychotics, of causing movement disorders. It has also been found to be slightly more effective in treating schizophrenia than the typical antipsychotics.
Amisulpride, like all other approved antipsychotics, is believed to work by reducing signalling via the dopamine D2 receptor. In amisulpride's case this is by blocking, or antagonizing, the receptor. Amisulpride's effectiveness in treating dysthymia and the negative symptoms of schizophrenia is believed to stem from its blockade of the presynaptic dopamine D2 receptors. These presynaptic receptors regulate the release of dopamine into the synapse, so by blocking them amisulpride increases dopamine concentrations in the synapse. This increased dopamine concentration is theorized to act on dopamine D1 receptors to relieve depressive symptoms (in dysthymia) and the negative symptoms of schizophrenia.
It was introduced by Sanofi-Aventis in the 1990s. Its patent had expired by 2008 and hence generic formulations are now available. It is not marketed in the Canada or the United States, although in all other English-speaking countries it is marketed.
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Medical uses
Schizophrenia
In a 2013 study in a comparison of 15 antipsychotic drugs in effectiveness in treating schizophrenic symptoms, amisulpride was ranked second, demonstrating high effectiveness. 11% more effective than olanzapine (3rd), 32-35% more effective than haloperidol, quetiapine, and aripiprazole, and 25% less effective than clozapine (1st). Although according to other studies it appears to have comparable efficacy to olanzapine in the treatment of schizophrenia. Amisulpride augmentation, similarly to sulpiride augmentation, has been considered a viable treatment option (although this is based on low-quality evidence) in clozapine-resistant cases of schizophrenia. Another recent study concluded that amisulpride is an appropriate first-line treatment for the management of acute psychosis.
Adverse effects
- Extrapyramidal side effects (EPS; including dystonia, tremor, akathisia, parkinsonism). Produces a moderate degree of EPS; more than aripiprazole (not significantly, however), clozapine, iloperidone (not significantly), olanzapine (not significantly), quetiapine (not significantly) and sertindole; less than chlorpromazine (not significantly), haloperidol, lurasidone (not significantly), paliperidone (not significantly), risperidone (not significantly), ziprasidone (not significantly) and zotepine (not significantly).
- Hyperprolactinaemia (which can lead to galactorrhoea, breast enlargement and tenderness, sexual dysfunction, etc.)
- Weight gain (produces less weight gain than chlorpromazine, clozapine, iloperidone, olanzapine, paliperidone, quetiapine, risperidone, sertindole, zotepine and more (although not statistically significantly) weight gain than haloperidol, lurasidone, ziprasidone and approximately as much weight gain as aripiprazole and asenapine)
- Anticholinergic side effects (although it does not bind to the muscarinic acetylcholine receptors and hence these side effects are usually quite mild) such as
- Blood dyscrasias such as leucopenia, neutropenia and agranulocytosis
- QT interval prolongation (in a recent meta-analysis of the safety and efficacy of 15 antipsychotic drugs amisulpride was found to have the 2nd highest effect size for causing QT interval prolongation)
Hyperprolactinaemia results from antagonism of the D2 receptors located on the lactotrophic cells found in the anterior pituitary gland. Amisulpride has a high propensity for elevating plasma prolactin levels as a result of its poor blood-brain barrier penetrability and hence the resulting greater ratio of peripheral D2 occupancy to central D2 occupancy. This means that to achieve the sufficient occupancy (~60-80%) of the central D2 receptors in order to elicit its therapeutic effects a dose must be given that is enough to saturate peripheral D2 receptors including those in the anterior pituitary.
- Somnolence. It produces minimal sedation due to its absence of cholinergic, histaminergic and alpha adrenergic receptor antagonism. It is one of the least sedating antipsychotics.
Contraindications
Amisulpride's use is contraindicated in the following disease states
- Pheochromocytoma
- Concomitant prolactin-dependent tumours e.g. prolactinoma, breast cancer
- Movement disorders (e.g. Parkinson's disease and dementia with Lewy bodies)
- Lactation
- Children before the onset of puberty
Neither is it recommended to use amisulpride in patients with hypersensitivities to amisulpride or the excipients found in its dosage form.
Interactions
Amisulpride should not be used in conjunction with drugs that prolong the QT interval (such as citalopram, venlafaxine, bupropion, clozapine, tricyclic antidepressants, sertindole, ziprasidone, etc.), reduce heart rate and those that can induce hypokalaemia. Likewise it is imprudent to combine antipsychotics due to the additive risk for tardive dyskinesia and neuroleptic malignant syndrome.
Overdose
Torsades de pointes is common in overdose. Amisulpride is moderately dangerous in overdose (with the TCAs being very dangerous and the SSRIs being modestly dangerous).
Pharmacology
Amisulpride function primarily as a D2 and D3 receptor antagonist. It has high affinity for these receptors with dissociation constants of 2.2 nM and 2.4 nM, respectively. Although standard doses used to treat psychosis inhibit dopaminergic neurotransmission, low doses preferentially block inhibitory pre-synaptic autoreceptors. This results in a facilitation of dopamine activity, and for this reason, low dose amisulpride has also been used to treat dysthymia.
Amisulpride and its relative sulpiride have been shown to bind to and activate the GHB receptor at doses that are used for therapeutic purposes.
Though it has long been widely assumed that dopaminergic modulation is solely responsible for the respective antidepressant and antipsychotic properties of amisulpride, it has recently been shown that it also acts as a potent antagonist at the 5-HT7 receptor. Several of the other atypical antipsychotics such as risperidone and ziprasidone are potent antagonists at the 5-HT7 receptor as well, and selective antagonists of the receptor show antidepressant properties themselves. To characterize the role of the 5-HT7 receptor in the antidepressant effects of amisulpride, a study prepared 5-HT7 receptor knockout mice. The study found that in two widely used rodent models of depression, the tail suspension test, and the forced swim test, those mice did not exhibit an antidepressant response upon treatment with amisulpride. These results suggest that 5-HT7 receptor antagonism mediates the antidepressant effects of amisulpride.
Amisulpride also appears to bind with high affinity to the 5-HT2B receptor (see below table), though the clinical implications of this, if any, are unclear.
Availability
Amisulpride is not approved by the Food and Drug Administration for use in the United States, but it is used in Europe (France, Germany, Italy, Switzerland, Russia, United Kingdom, etc.), Israel, India, New Zealand and Australia (TGA approved in February 2002) to treat psychosis and schizophrenia.
Brand names include: Amazeo, Amipride (AU), Amival, Solian (AU, IE, RU, UK, ZA), Soltus, Sulpitac (IN), Sulprix (AU) and Socian (BR).
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