Risperidone receptor blockades

Travis, M. J., Busatto, G. F., Pilowsky, L. S. et al. 5-HT2A receptor blockade in patients with schizophrenia treated with risperidone or clozapine. A SPET study using the novel 5-HT2A ligand 123I-5-I-R-91150. Br. J.Psychiatr. 173 236-241, 1998. 

There are two classes of a-adrenergic receptors, aj and a2. Agents with the greatest affinity for aj blockade are chlorpromazine, thioridazine, and risperidone. There are no known beneficial effects associated with a -adrenergic receptor antagonism. However, aj-adrenergic receptor blockade can lead to hypotension, dizziness, and reflex tachycardia (Table 26.2). a2 Blockade is modest for most agents except for risperidone and clozapine. As with aj receptors, there are no benefits that have yet to be associated with a2 receptor... 

Aripiprazole Blockade of 5HT2A receptors > blockade of D2 receptors Some a blockade (clozapine, risperidone, ziprasidone) and M-receptor blockade (clozapine, olanzapine) variable receptor blockade (all) Schizophrenia—improve both positive and negative symptoms bipolar disorder (olanzapine or risperidone adjunctive with lithium) agitation in Alzheimer s and Parkinson s (low doses) major depression (aripiprazole) Toxicity Agranulocytosis (clozapine), diabetes (clozapine, olanzapine), hypercholesterolemia (clozapine, olanzapine), hyperprolactinemia (risperidone), QT prolongation (ziprasidone), weight gain (clozapine, olanzapine)... 

Hypothermia associated with hypothalamic and thermoregulatory dysfunction has been reported in a patient with Prader-Willi syndrome taking risperidone and olanzapine (222). Hypothermia in response to these drugs is said to result from 5-HT2 receptor blockade, and it is recommended that patients with hypothalamic dysfunction should be carefully monitored if risperidone or olanzapine are used. 

Lauterbach EC, Abdelhamid A, Annandale JB. Posthallucinogen-hke visual illusions (palinopsia) with risperidone in a patient without previous hallucinogen exposure possible relation to serotonin 5HT2a receptor blockade. Pharmacopsychiatry 20(K) 33(1 ) 38—41. 

Atypical antpipsychotics provoke fewer extra-pyramidal effects (less blockade of dopamine D -receptors in the nigrostriatal pathway). Nevertheless, extrapyramidal effects are seen, notably with high dose of risperidone (8-12 mg per day) and olanzapine (> 20 mg/day). 

Hypothalamus and Endocrine Systems Endocrine changes occur because of effects of antipsychotic drugs on the hypothalamus or pituitary, including their antidopaminergic actions. Most older antipsychotics and risperidone increase prolactin secretion, probably due to a blockade of the pituitary actions of the tuberoinfundibular dopaminergic neurons. These neurons project from the arcuate nucleus of the hypothalamus to the median eminence, where they deliver DA to the anterior pituitary via the hypophyseoportal blood vessels. Dj receptors on lactotropes in the anterior pituitary mediate the tonic prolactin-inhibiting action of DA (see Chapter 55). 

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