US-based biopharmaceutical company Acadia Pharmaceuticals has reported that its Phase III ADVANCE-2 clinical trial of pimavanserin for the treatment of negative symptoms of schizophrenia did not meet its primary endpoint.

The 26-week, placebo-controlled ADVANCE-2 trial enrolled 454 adult subjects with negative schizophrenia symptoms and attained control of positive symptoms with ongoing antipsychotic therapy.

Patients in the trial were given a 34mg dose of pimavanserin.

The efficacy of the treatment was measured using the Negative Symptom Assessment-16 (NSA-16) scale, which measures a range of negative symptoms across five subscales.

The scale assesses 16 varying items in these subscales and covers symptoms such as blunted affect, poor socialisation and lack of motivation.​

The top-line results indicated that pimavanserin did not achieve a statistically significant difference compared with placebo in the change from baseline to week 26 on the NSA-16 total score. This was the study's primary endpoint.

Despite the lack of statistically significant improvement over placebo, the safety and tolerability profile of pimavanserin remained consistent with prior trials.

The placebo effect in ADVANCE-2 was observed to be higher than that reported in the ADVANCE-1 trial.

The drug was found to be well-tolerated, with a 30.4% adverse event rate versus 40.3% in the placebo group.

Acadia CEO Steve Davis said: “We are disappointed the trial did not meet its primary endpoint given the significant unmet need in patients with negative symptoms of schizophrenia.

“We will continue to analyse these data with our scientific advisors, but we do not intend to conduct any further clinical trials with pimavanserin.

“We want to thank the patients, their families and the investigators for their contributions to this important study.”

Last November, the company began a Phase II clinical trial assessing the safety and efficacy of ACP-204 to treat hallucinations and delusions linked to Alzheimer’s disease psychosis.