The entrance of a long-acting injectable form of an atypical antipsychotic into U.S. clinical practice may improve patient compliance and decrease variability in blood levels. The new formulation of risperidone, which introduces the drug within auto-degrading polymer-based microspheres, is designed to deliver and maintain therapeutic drug levels with 1 injection every 2 weeks.

Previous studies have shown that as many as 75 percent of patients with schizophrenia find it difficult to take their oral medication on a regular basis, and intermittent use of medication can lead to relapse or worsening of existing symptoms. John Kane, MD, commented on the possibilities of a long-acting formulation: “By providing consistent levels of medication during a 2-week period, [the long-acting risperidone formulation] eliminates many of the peaks and valleys that you get with medication that you have to take daily. Patients also don’t have to remember to take a pill every single day, which is difficult for anyone with a chronic disease. It gives patients a new choice and helps them change their lives.”

Atypical antipsychotic medications have become the most commonly prescribed treatment in the U.S. for schizophrenia, but the new formulation is the first drug product to have long-lasting activity. Its efficacy was established in a 12-week, placebo-controlled trial involving 400 adults in inpatient and outpatient settings.

The researchers found that 47 percent of patients given 25-mg dose injections of active drug showed clinical improvement compared with 17 percent of patients given placebo, with clinical improvement defined as a reduction of 20 percent or more in total score on the Positive and Negative Syndrome Scale.

The most common side effects among patients in the active drug group were headache, agitation, psychosis, insomnia, dizziness, rhinitis, and pain. Overall, the percentage of patients reporting an adverse effect was similar in the drug and placebo groups (83 percent and 80 percent, respectively); reporting of serious adverse effects was actually more common in placebo patients (23.5 percent compared with 13 percent for 25-mg dose risperidone and 14 percent for the 50-mg dose risperidone). The rate for extrapyramidal symptoms was similar for 25-mg dose risperidone and placebo (10 percent and 13 percent, respectively), whereas the rate was higher (24 percent) for the 50-mg dose risperidone group.

Discontinuation of treatment due to side effects was the same, 12 percent, for patients receiving risperidone (37 of 302 patients) and patients receiving placebo (12 of 98).