Source: Health Products Regulatory Authority (ZA) Publisher: Abex Pharmaceutica (Pty) Ltd, Suite C, Rubenstein Ridge, 617 Rubenstein Drive, Moreleta Park, 0181
Category and class: A.2.6.5 Central nervous system depressants. Miscellaneous structures.
Pharmacotherapeutic group: Other antipsychotics
ATC code: N05AX08
Risperidone is an antipsychotic of the benzoxazole derivatives. It is a selective monoaminergic antagonist. Risperidone has affinity for serotonin-5-HT2, dopamine-D2, H1histamine, α1 and α2-adrenergic receptors. Risperidone has no affinity for cholinergic receptors. It is a dopamine D2-antagonist.
Risperidone is completely absorbed after oral administration. Peak plasma concentrations are attained within 1 to 2 hours. Food does not affect the absorption of risperidone. Steady state is reached within 1 day for risperidone in most patients and 4 to 5 days for 9-hydroxy-risperidone.
Risperidone is bound to albumin and alpha1-acid glycoprotein. Plasma protein binding of risperidone is 88% and 77% for 9-hydroxy-risperidone.
Risperidone is metabolised by cytochrome CYP2D6 to 9-hydroxy-risperidone, which has a similar pharmacological activity to risperidone. Risperidone and 9-hydroxy-risperidone form the active antipsychotic fraction.
One week after administration, 70% of the dose is excreted in the urine and 14% in the faeces. In urine, risperidone and 9-hydroxy-risperidone represent 35 to 45% of the dose. After oral administration to psychotic patients, risperidone's half-life is about 3 hours. The elimination half-life of 9-hydroxy-risperidone and the active antipsychotic fraction is 24 hours.
Risperidone plasma concentration is dose-proportional within the therapeutic dose-range.
A single dose study showed higher active plasma concentrations and a reduced clearance of the active antipsychotic fraction by 30% in the elderly and 50% in patients with moderate renal insufficiency. In patients with severe renal insufficiency the clearance was one third that of normal. The plasma concentrations of risperidone were normal in patients with liver insufficiency, but the mean free fraction of risperidone in plasma was increased by about 35%.
The pharmacokinetics of risperidone, 9-hydroxy-risperidone and the active moiety in children are similar to those in adults.
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