Background Many patients with schizophrenia require high doses of medication for their ongoing psychotic symptoms. Glutamate theories and findings from studies showing efficacy of sarcosine, an endogenous, non-selective glycine-reuptake inhibitor mediated by GlyT1, offer an alternative approach. We undertook the SearchLyte trial programme to examine the efficacy of bitopertin, a selective GlyT1-mediated glycine-reuptake inhibitor, as an adjunctive treatment to ongoing antipsychotic treatment. Methods SearchLyte consisted of three phase 3, randomised, double-blind, parallel-group, placebo-controlled, multicentre studies done in outpatient clinics in Asia, Europe, and North and South America (TwiLyte done at 109 sites, NightLyte at 84, and MoonLyte at 87). Participants were male and female outpatients, aged at least 18 years, meeting DSM-IV criteria for schizophrenia with suboptimally controlled positive symptoms despite treatment with antipsychotics. Inclusion criteria included a Positive and Negative Syndrome Scale (PANSS) total score of at least 70 and antipsychotic treatment stability for the past 12 weeks before randomisation. Key exclusion criteria included meeting criteria for symptomatic remission or previous treatment with a GlyT1 inhibitor or any other investigational drug. After a screening or 4-week prospective stabilisation period, we randomly assigned participants (1:1:1) to a 12-week, double-blind treatment of either placebo or one of two fixed doses of oral, once-daily bitopertin (10 or 20 mg in TwiLyte and NightLyte; 5 or 10 mg in MoonLyte) added to their current antipsychotic medicine. After completion of 12 weeks’ treatment, the study design allowed for additional double-blind treatment for 40 weeks to assess maintenance of the effect, followed by a randomised 4-week washout period to assess withdrawal effects. Subsequently, all patients were offered the opportunity to receive bitopertin treatment in a 3-year follow-up. The primary efficacy endpoint was the mean change from baseline in the PANSS Positive Symptom Factor Score (PSFS) at week 12, analysed in the modified intention-to-treat population. The trials were registered at ClinicalTrials.gov (numbers NCT01235520 [TwiLyte], NCT01235585 [MoonLyte], and NCT01235559 [NightLyte]). Findings Between Nov 19, 2010, and Dec 12, 2014, we randomly assigned 1794 patients to treatment, of whom 1772 were treated and analysed. MoonLyte was discontinued in September, 2014, on the basis of results from futility analyses. Across studies and treatment arms, most patients completed 12 weeks of treatment (505 in TwiLyte, 517 in NightLyte, and 506 in MoonLyte). Only one study, NightLyte, met the primary endpoint where the PANSS PSFS significantly differed from placebo at week 12, and only in the 10-mg arm: mean difference in score −1·37, 95% CI −2·27 to −0·47; p=0·0028. Improvements from baseline for the bitopertin 20-mg arm in Nightlyte were not significant compared with placebo: −3·77, 95% CI −4·40 to −3·14; p=0·3142. Results from the other two studies also did not differ from placebo (TwiLyte 0·58, 95% CI −0·34 to 1·50, p=0·22 for 10 mg and 0·43, −0·49 to 1·36, p=0·36 for 20 mg; MoonLyte 0·06, 95% CI −0·79 to 0·92, p=0·88 for 5 mg and 0·44, −0·41 to 1·28, p=0·31 for 10 mg). Placebo responses varied across studies and might have contributed to the differences in efficacy between studies. Four deaths occurred during the 12-week treatment period, three in NightLyte (upper gastrointestinal haemorrhage, alcohol poisoning and related head injury, and a completed suicide) and one in MoonLyte (myocardial infarction in a patient with pre-existing risk factors). Only the death by suicide was deemed related to the study drug. The incidence of serious adverse events was low across treatment groups in all three studies; psychiatric disorders were the most frequently reported serious adverse events and the most frequent cause of adverse events leading to discontinuation. Interpretation Only one of six active treatment arms across the three studies offered an advantage of adjunctive bitopertin over placebo for the treatment of suboptimally controlled symptoms of schizophrenia. The small improvement associated with bitopertin together with the varying placebo response suggests that adjunctive bitopertin treatment might offer only modest benefit to suboptimal responders to antipsychotics, if any. Funding F Hoffmann-La Roche.
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