Although atypical antipsychotics have lowered the prevalence and severity of extrapyramidal symptoms (EPS), they still contribute to the overall side-effect burden of approved antipsychotics. Drugs with novel mechanisms without D2 dopamine receptor blocking activity have shown promise in treating schizophrenia without the side effects of currently available treatments. KarXT (xanomeline–trospium chloride) represents a possible alternative that targets muscarinic receptors. KarXT demonstrated efficacy compared with placebo in 3 out of 3 short-term acute studies and has not been associated with many of the side effects of D2 dopamine receptor antagonists. Here, we further characterize EPS rates with KarXT in these trials.

EMERGENT-1 (NCT03697252), EMERGENT-2 (NCT04659161), and EMERGENT-3 (NCT04738123) were 5-week, randomized, double-blind, placebo-controlled, inpatient trials in people with schizophrenia experiencing acute psychosis. Data from the safety populations, defined as all participants who received ³1 dose of trial medication, were pooled. For this analysis, we used a broader definition of EPS-related adverse events (AEs) to encompass any new onset of dystonia, dyskinesia, akathisia, or extrapyramidal disorder reported any time after the first dose of medication. Additionally, EPS were assessed by examining change from baseline to week 5 on the Simpson-Angus Scale (SAS), Barnes Akathisia Rating Scale (BARS), and Abnormal Involuntary Movement Scale (AIMS).

A total of 683 participants (KarXT, n=340; placebo, n=343) were included in the analyses. The rate of treatment-emergent AEs (TEAEs) associated with EPS was 3.2% in the KarXT group vs 0.9% in the placebo group. The most commonly reported TEAE was akathisia (KarXT, 2.4%; placebo 0.9%); half of possible akathisia cases in the KarXT group (4/8 TEAEs) were from a single US site, considered by the investigator to be unrelated to trial drug, and resolved without treatment. Overall rates of akathisia TEAEs deemed related to trial drug were low (KarXT, 0.6%; placebo 0.3%). Dystonia, dyskinesia, and extrapyramidal disorder TEAEs were reported by only a single subject each (0.3%) in the KarXT arm. All reported TEAEs were mild to moderate in severity. KarXT was associated with no clinically meaningful mean±SD changes from baseline to week 5 on the SAS (-0.1±0.6), BARS (-0.1±0.9), or AIMS (0.0±0.7).

The incidence of EPS-related TEAEs with KarXT was low in comparison to those observed in similar trials of antipsychotics (D2 dopamine receptor antagonists), although head-to-head studies have not been completed. Moreover, KarXT was not associated with increased scores on EPS scales (SAS, BARS, AIMS) across 5 weeks of treatment. These results, combined with the robust efficacy of KarXT in trials to date, suggest that KarXT’s novel mechanism of action may provide therapeutic benefit in the absence of EPS frequently associated with currently available antipsychotics.

Karuna Therapeutics