risperidone

INTRODUCTION

Schizophrenia is a chronic psychiatric disorder that often necessitates lifelong medical treatment. Patients with this condition may exhibit poor compliance with oral antipsychotic therapy. It has been reported that only one-third of such patients are fully adherent, taking their antipsychotics as prescribed, one-third are partially adherent, and the remaining third are completely nonadherent. Factors potentially con­tributing to noncompliance include the patient’s lack of insight about the disease itself, drug-related adverse effects, lack of therapeutic rapport with medical professionals, misunderstandings about pharmacotherapy, and complex dosing schedules.

Long-acting risperidone for injection was the first atypical antipsychotic available for depot injection in Canada. Its main advantage is improvement in compliance with therapy for patients who do not take their oral medications consistently. Also, as an atypical antipsychotic, risperidone has a lower risk of dose-dependent extrapyramidal movement disorders than conventional agents such as haloperidol.

Long-acting risperidone for injection has a specially formulated drug delivery system, whereby particles of the drug are encapsulated into organic polymer matrixes called micro- spheres. These microspheres do not degrade appreciably, to release the risperidone, until 3 weeks after the first intramuscular injection. Accordingly, the manufacturer recommends that all patients receiving the drug for the first time should also receive overlapping therapy with another oral antipsychotic to maintain therapeutic plasma concentrations during the initial period. After the first dose, long-acting risperidone for injection is administered every 2 weeks to maintain oscillations between peak and trough levels within the therapeutic range. Peak levels of the drug are expected when most of the drug has been released from the microspheres, at 4 to 6 weeks after each injection. Steady-state concentrations in the plasma are reached after 4 injections. Given the unique pharmacokinetic profile of this drug, the manufacturer recommends that dose escalations be made no more frequently than every 4 weeks. Some experts have even suggested that the timeframe for assess­ing any specific dose of the drug be extended to 6 to 8 weeks after the initial dose to ensure that the patient’s response is being observed at steady-state plasma concentrations. viagra jelly

The unique pharmacokinetic characteristics of long-acting risperidone for injection may pose challenges to clinicians who are more familiar with conventional antipsychotics for depot injection, such as decanoate formulations of haloperidol, fluphenazine, flupenthixol, and zuclopenthixol. An under­standing of and adherence to guidelines for appropriate prescribing may improve patient response, minimize dose- related side effects, and decrease unnecessary costs. An evaluation of prescribing and usage patterns for long-acting risperidone for injection within the Fraser Health Authority was undertaken to determine if patients were receiving this medication appropriately and if there was a need to provide education or create usage protocols to promote safe and effective drug therapy.