Abstract
In a previous pilot study, MK-0777--a γ-aminobutyric acid (GABA)(A) α2/α3 partial agonist--was reported to improve delayed memory and cognitive measures of prefrontal cortical function in people with schizophrenia. The current study was designed to further examine the efficacy and safety of MK-0777 for the treatment of cognitive impairments in schizophrenia. Sixty people with DSM-IV schizophrenia entered a 4-week, multi-center, double-blind, placebo-controlled, randomized clinical trial. Participants were randomized to: MK-0777 3 mg b.i.d. (n = 18); MK-0777 8 mg b.i.d. (n = 21); or placebo (n = 21). Participants were clinically stable. The Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) Consensus Cognitive Battery, AX-Continuous Performance Test, and N-Back were used to assess cognition. The University of California San Diego (UCSD) Performance Based Skills Assessment-2 and the Schizophrenia Cognition Rating Scale assessed functional capacity and served as functional outcome coprimary measures. There were no significant group differences on the primary outcome measure, the MATRICS Consensus Cognitive Battery composite score. Secondary analyses suggested that participants randomized to placebo performed significantly better on visual memory and reasoning/problem-solving tests than participants assigned to either MK-0777 dose. There were no significant group differences on the AX-Continuous Performance Test or N-Back d prime scores or UCSD Performance-Based Skills Assessment-2 and Schizophrenia Cognition Rating Scale total scores. In general, MK-0777 was well-tolerated with minimal side effects. The study results suggest that MK-0777 has little benefit for cognitive impairments in people with schizophrenia. The GABA(A) receptor remains a promising target, but a more potent partial agonist with greater intrinsic activity at the GABA(A) α2 site might be needed for cognitive enhancement in schizophrenia.
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