Xanomeline-Trospium

Xanomeline-trospium (KarXT; marketed as Cobenfy) is a fixed-dose oral combination of xanomeline tartrate, a functionally selective muscarinic acetylcholine receptor agonist with preferential activity at the M1 and M4 receptor subtypes, and trospium chloride, a quaternary ammonium muscarinic antagonist that does not appreciably cross the blood-brain barrier. The combination was designed to preserve the central antipsychotic and procognitive effects of muscarinic M1/M4 agonism while mitigating the dose-limiting peripheral cholinergic adverse events (nausea, vomiting, diarrhea, hypersalivation, diaphoresis) that had previously terminated the clinical development of xanomeline as a monotherapy agent. The United States Food and Drug Administration approved xanomeline-trospium on 26 September 2024 for the treatment of schizophrenia in adults, making it the first antipsychotic mechanism approved since the introduction of the dopamine D2 receptor antagonist and partial agonist classes and the first muscarinic-based treatment registered for any psychotic disorder.

Xanomeline was originally synthesized in a collaboration between Eli Lilly and Novo Nordisk in the early 1990s under the development code LY-246708. Initial clinical development targeted Alzheimer's disease, where a 343-patient Phase 2 trial (Bodick et al. 1997) demonstrated stabilization of cognitive decline and significant dose-dependent reductions in behavioral and psychological symptoms including hallucinations, delusions, agitation, and vocal outbursts. However, peripheral cholinergic adverse events led to unacceptable dropout rates and the Alzheimer's program was discontinued. A subsequent proof-of-concept trial in schizophrenia (Shekhar et al. 2008) confirmed antipsychotic-like activity through a non-dopaminergic mechanism but was similarly limited by tolerability. The critical innovation was the combination with trospium chloride, a muscarinic antagonist previously approved for overactive bladder (Sanctura, Allergan) that is restricted to the peripheral compartment by its quaternary ammonium structure and does not undergo cytochrome P450 metabolism. This combination strategy was advanced by Karuna Therapeutics, which was subsequently acquired by Bristol Myers Squibb for approximately 14 billion United States dollars in 2024.

The registration of xanomeline-trospium was supported by three randomized, double-blind, placebo-controlled, 5-week Phase 3 trials (EMERGENT-1, EMERGENT-2, EMERGENT-3) in adults with schizophrenia experiencing acute psychosis. In pooled analyses across all three trials, xanomeline-trospium produced a statistically significant reduction in Positive and Negative Syndrome Scale (PANSS) total score compared to placebo (least squares mean difference, minus 9.9 points; 95 percent confidence interval, minus 12.4 to minus 7.3; p less than 0.0001; Cohen's d effect size, 0.65). Effects were observed across positive symptom, negative symptom, and general psychopathology PANSS subscales and on the Clinical Global Impression-Severity scale. Long-term safety and efficacy were characterized in the 52-week open-label extension trials EMERGENT-4 and EMERGENT-5, which demonstrated sustained symptom improvement, a mean change in body weight of minus 1.9 kilograms from acute trial baseline, no clinically meaningful changes in prolactin levels, and no treatment-emergent akathisia or tardive dyskinesia. The most common adverse events were gastrointestinal (nausea, dyspepsia, constipation, vomiting) and were generally mild to moderate, transient, and manageable without treatment discontinuation in most patients.

The compound is currently in Phase 3 development for additional indications including psychosis associated with Alzheimer's disease (ADEPT program), agitation associated with Alzheimer's disease (ADAGIO program), and cognitive impairment in Alzheimer's disease. An enteric-coated xanomeline formulation (KarX-EC) is in development with the aim of further reducing gastrointestinal adverse events. This monograph reviews the chemistry, synthesis, and pharmacology of both components; the composite mechanism of action through central muscarinic M1/M4 agonism with peripheral muscarinic blockade; the pharmacokinetics including CYP2D6 polymorphism effects; the complete clinical evidence base across schizophrenia and Alzheimer's disease indications; sourcing and quality considerations; reconstitution and handling; stack-interaction implications; adverse-event and safety signal; and a comparative assessment of five alternative antipsychotic or muscarinic-targeted agents against xanomeline-trospium on five competency standards.