In a test of possible antipsychotic-antidepressant interaction, blood levels of extended-release paliperidone were not increased in healthy volunteers when the drug was given in combination with paroxetine, according to a presentation at the annual meeting of the American Psychiatric Association.

Paroxetine is a potent inhibitor of the CYP2D6 enzyme in the liver and can inhibit the metabolism of some atypical antipsychotic drugs. Approximately 50 percent of patients with schizophrenia have at least one other psychiatric or medical condition requiring medication, most commonly depression.

"Drug interactions frequently occur in patients with schizophrenia because this population is often treated for multiple medical and psychiatric conditions," said Dr. Joseph Palumbo, Franchise Medical Leader for Psychiatry, Johnson & Johnson Pharmaceutical Research & Development, L.L.C. "Drug interactions are an under-appreciated factor that can reduce optimal treatment outcomes in our patients. This study shows that paliperidone extended release can be an important new option for patients with schizophrenia who also require treatment with an antidepressant metabolized through the CYP2D6 system."

In the current study, 60 healthy male volunteers were randomized to one of two treatment arms: (A) one day’s treatment with 3 mg paliperidone extended release or (B) treatment for 13 days with paroxetine 20 mg daily and 3 mg paliperidone on day 10.After completing their first treatment cycle, patients took no medication for 14 days. Then, patients who had received treatment A received treatment B and vice versa.

Four days after paliperidone administration, investigators measured the maximum concentration of the drug in the body and total exposure over time to paliperidone extended release. No clinically significant increase in paliperidone exposure was seen when the medication was administered together with paroxetine compared with when it was given alone.

There were no serious adverse events or clinically important changes in laboratory values, vital signs or cardiac parameters.

"These results demonstrate that prescribers can administer a CYP2D6- inhibiting antidepressant, paroxetine, with paliperidone extended release without having to adjust the dose of paliperidone extended release (ER)," Palumbo said. "This, when combined with once-daily oral dosing and well demonstrated efficacy, safety, and tolerability, adds to paliperidone ER's usefulness as a new option for the treatment of schizophrenia."