Beyond dopamine: KarXT and emerging mechanism-based therapies in schizophrenia

Abstract

KarXT (marketed as Cobenfy™), a fixed-dose combination of xanomeline and trospium chloride, represents the first new mechanism of action of an antipsychotic used for adult schizophrenia approved by the US Food and Drug Administration (FDA) in over 30 years. While mainstream drugs (e.g. haloperidol, chlorpromazine, risperidone, olanzapine, quetiapine, aripiprazole) mainly antagonize dopamine D2 or serotonin 5-HT2A receptors, KarXT acts through transient activation of muscarinic M1 and M4 receptors. M4 stimulation influences the functioning of mesolimbic dopaminergic pathways, providing an indirect means of regulating dopamine release that bypasses D2 blockade. Trospium, a peripherally acting muscarinic receptor antagonist, was used to reduce anticholinergic adverse effects (AEs). It does not cross the blood–brain barrier and therefore minimizes central adverse events. In a series of randomized placebo-controlled phase 2 and 3 studies, the KarXT significantly and clinically meaningfully reduced Positive and Negative Syndrome Scale (PANSS) total scores. The effect sizes were moderate to large with few extrapyramidal symptoms (EPS), minimal metabolic disturbances and no significant prolactin level increases. In this narrative review, we discuss in detail the pharmacological mechanism, basis of preclinical development, and clinical outcomes of KarXT. We also contextualize this drug within the development of a new wave of non-D2 antipsychotics, highlighting cholinergic dysfunction as one important mechanistic pathway within the broader multidimensional neurobiology of schizophrenia.