Our aim was to describe the efficacy and tolerability of pimavanserin, a highly selective serotonin 5-HT2A receptor inverse agonist/antagonist indicated for the treatment of hallucinations and delusions associated with Parkinson’s disease psychosis (PDP), using the metrics of number needed to treat (NNT) and number needed to harm (NNH).

Categorical efficacy and tolerability data were extracted from the clinical trial databases of the double-blind placebo-controlled studies of pimavanserin in persons with PDP. NNT and NNH values were calculated with their respective 95% confidence intervals. The likelihood to be helped or harmed (LHH) was then calculated contrasting therapeutic response versus discontinuation because of an adverse event.

NNT values for pimavanserin 34 mg/d versus placebo for several definitions of clinical response are <10, and as robust as 4. NNH values for tolerability outcomes for pimavanserin 34 mg/d (as well as for doses that range from 8.5 to 51 mg/d) are >10, and/or are not statistically significant, and/or show an advantage for pimavanserin over placebo (such as for postural hypotension). In terms of LHH, pimavanserin 34 mg/d is about five times more likely to result in clinical response (as measured by a ≥3 point decrease from baseline on the Scale for the Assessment of Positive Symptoms adapted for Parkinson’s disease) versus discontinuation due to an adverse event.

Using the metrics of NNT, NNH, and LHH, pimavanserin 34 mg/d for the treatment of PDP appears to have a compelling benefit/risk profile.