Risperidone is a benzisoxazole derivative with antipsychotic activity that is chemically unrelated to other currently available antipsychotic agents, Its neuropharmacological properties, characterized by potent central antagonism of both serotonin 5-HT2 and dopamine D-2 receptors, also differ from those of most other antipsychotic drugs, The pharmacokinetics of risperidone are well understood, having been studied in healthy subjects as well as in psychotic patients. The absolute oral bioavailability of risperidone is nearly 70%, and after oral administration, it is rapidly absorbed with the plasma level reaching a peak at about 1 h. 9-Hydroxyrisperidone, one of the metabolites of risperidone, is equally active with the parent compound and so the clinical activity of a dose of risperidone is due to the combined actions of both moieties, The plasma concentrations of risperidone and its active metabolite remain dose proportional even at doses exceeding the therapeutic range. In clinical trials with chronic schizophrenia patients, risperidone has an overall therapeutic activity comparable with that of haloperidol, but at doses that produce similar improvements in the positive symptoms of schizophrenia, risperidone has a greater effect on the negative symptoms and produces less extrapyramidal side effects than does haloperidol, However, additional controlled clinical studies are needed before the claims that risperidone is therapeutically superior to haloperidol cah be considered to be established firmly, Although risperidone is effective in acute schizophrenia and in non-treatment-resistant schizophrenics, studies adequately comparing risperidone with clozapine in treatment-resistant schizophrenic patients remain to be published. In addition, risperidone has been reported to be of value in patients with schizodepressive disorders, The clinical success of risperidone suggests that the development of compounds with selective affinity for 5-HT2 or other serotonin receptors may result in even further improvements in the pharmacotherapy of psychiatric disorders.
