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Xanomeline
Component: xanomeline
Pronounced: zuh-NOM-uh-leen
Mnemonic phrase: “The gnome line”
Cost: unavailable as a standalone
Mechanism: M1 & M4 muscarinic acetylcholine receptor agonist
FDA-approved for: Schizophrenia (in combination with trospium)
Xanomeline is an agonist at M1 and M4 cholinergic receptors without affecting dopamine receptors. While not available as a standalone medication, it was approved in 2024 in combination with trospium under the brand name Cobenfy for the treatment of schizophrenia. This approval marks a significant advancement in schizophrenia treatment, offering a novel mechanism rather than the traditional dopaminergic approach.
Xanomeline readily enters the central nervous system (CNS) with a high brain-to-plasma ratio of > 10:1. It directly activates muscarinic acetylcholine receptors, affecting downstream dopamine and glutamate circuits.
Xanomeline shares structural and pharmacological traits with arecoline, the primary psychoactive component in betel nut.
Development of xanomeline as an Alzheimer's medication was abandoned in the 1990s due to cholinergic side effects.
Xanomeline Mechanism
Refer to the acetylcholine ballicule below to understand xanomeline in context. Think of xanomeline as a piece of acetylcholine.
Xanomeline Interactions
Trospium (Sanctura)
FDA-approved for:
❖ Overactive bladder (OAB)
❖ Countering muscarinic side effects of xanomeline (Cobenfy combo)
Pronunciation: TROSE-pee-um (SANK-tur-uh)
Mnemonic: “Trusty pee-in’ Sanctuary”
Mechanism: Antimuscarinic
Special feature: Does not readily cross the blood-brain barrier
Year of FDA approval: 2004 for OAB
Available strengths: 20 mg IR tabs and 60 mg SR capsules
Cost: IR tab $30–$100, ER cap $50–$150
"The brain is a Sanctuary"—Trospium is an anticholinergic medication for overactive bladder (OAB) that does not readily cross the blood-brain barrier (BBB) owing to its large size, hydrophilicity, and positive charge. Therefore, it does not have the ability to impair cognition like most other anticholinergics. Trospium is a P-gp substrate, so any molecules that do cross the BBB are promptly expelled from the CNS by P-gp transporters—"pumpers gonna pump."
Central anticholinergic effects have been rarely reported with trospium including dizziness, confusion, hallucinations, and somnolence. CNS effects should not occur unless trospium is combined with a P-gp inHibitor.
Trospium has low oral bioavailability (<10%). Excretion is primarily renal of unchanged drug (60% within 24 hours). Half-life is approximately 20 hours.
Trospium Mechanism
Refer to the "anticholine" ballicule below to understand trospium in context.
Trospium Interactions
Trospium Contraindications
❖ Urinary retention (anticholinergic)
❖ Gastric retention (anticholinergic)
❖ Untreated narrow-angle glaucoma (anticholinergic)
❖ Moderate or severe hepatic impairment
➤ due to potential for drug accumulation
➤ hepatic toxicity is not a concern
Angioedema has occurred as an IgE-mediated hypersensitivity reaction.
Trospium Dosing:
❖ IR tablets: 20 mg BID (20 mg HS if age > 75)
❖ ER capsules: 60 mg QD
❖ With either formulation, give on an empty stomach > 1 hour before meal
Cobenfy (Xanomeline + Trospium)
FDA-approved for: Schizophrenia
Pronunciation: koh-BEN-fee (zuh-NOM-uh-leen + TROS-pee-um)
Mnemonic: “Cob with benefits”
Class: Next-generation antipsychotic
Mechanism: Muscarinic agonist + muscarinic antagonist
FDA approval: September 2024
Anticipated cost: $1,500–$3,000 monthly
Strengths: Capsules 50/20 mg, 100/20 mg, and 125/30 mg
Cobenfy, approved in 2024, is the first antipsychotic for schizophrenia that works exclusively through muscarinic receptors. It consists of a fixed-dose combination of two components in capsule form: xanomeline, the active antipsychotic agent, and trospium, an anticholinergic medication included to manage peripheral side effects.
It is worth noting that the two most effective antipsychotics available in the US—clozapine and olanzapine—have M4 agonist effects, while other available (generally less effective) antipsychotics do not possess this property. This observation provides a rationale for excitement about Cobenfy, which also demonstrated superior efficacy in clinical trials. Notably, Cobenfy stands in stark contrast to clozapine and olanzapine in that it does not cause significant weight gain, a common and problematic side effect of those medications. This favorable side effect profile, combined with its efficacy, makes Cobenfy a promising new option in the treatment of schizophrenia.
The name Cobenfy reflects the dual benefits of xanomeline as both an antipsychotic and cognitive enhancer, as well as the co-administration of xanomeline and trospium.
Developed by Karuna as KarXT, the company was acquired by Bristol Myers Squibb for ~$14 billion. Analysts project Cobenfy as a 2025 blockbuster, with estimated annual sales over $1 billion.
Xanomeline is unlikely to cause tardive dyskinesia (TD), though long-term data is unavailable. While not a D2 receptor blocker, it indirectly affects dopamine circuits. Normal motor function requires dopamine-acetylcholine balance. Extrapyramidal symptoms (EPS) result from relative dopamine deficiency and acetylcholine excess in the nigrostriatal pathway. EPS can be relieved by antimuscarinics like benztropine, but these do not improve or prevent TD. Animal studies showed no TD-like symptoms with longer-term xanomeline use.
Cobenfy Mechanism of Action
Cobenfy Interactions
Cobenfy Efficacy
Although not directly compared, Cobenfy's effect size (0.6 on PANSS) appears larger than many antipsychotics (0.3-0.5) but smaller than clozapine. Cobenfy's NNT is around 4, compared to 3-10 for older antipsychotics.
Cobenfy showed remarkable efficacy for negative symptoms, with a large effect size of 1.18 and NNT of 2 in this subgroup. It improved negative symptoms beyond secondary effects from positive symptom improvement, unlike most traditional antipsychotics.
Statistically significant benefit seen by week 3; maximal by week 5. Clozapine remains the gold standard for efficacy in schizophrenia (effect size 0.76–1.0, NNT as low as 3 for treatment-resistant cases). Xanomeline's efficacy for treatment-resistant schizophrenia is unknown.
Cobenfy Side Effects
Cobenfy Monitoring
❖ Liver enzymes and bilirubin
❖ Heart rate
❖ Urinary retention symptoms
➤ Hesitancy, weak stream, incomplete emptying, dysuria
Conbenfy FDA warning
❖ Risk of urinary retention, higher in geriatric patients
Conbenfy Contraindications
❖ Urinary retention
❖ Gastric retention
➤ Caution: ulcerative colitis, intestinal atony, myasthenia gravis
❖ Untreated narrow-angle glaucoma
❖ Moderate/severe hepatic impairment
➤ Trospium accumulation risk
➤ Not hepatotoxic; biliary obstruction risk
➤ Discontinue if signs of substantial liver injury
Cobenfy Cautions
❖ See dosing for renal/hepatic details
❖ Active biliary disease (e.g., symptomatic gallstones): not
recommended
➤ Assess for gallbladder/biliary disorders, pancreatitis if vomiting
or upper abdominal pain occurs
Cobenfy in Pregnancy
❖ No detrimental effects in animal studies (rats and rabbits)
Cobenfy Dosing
❖ Take 1h before or 2h after meals
❖ Start 50/20 mg BID for 2+ days
❖ Increase to 100/20 mg BID for 5+ days
❖ Max 125/30 mg BID based on tolerability/response
➤ In trials, Cobenfy was increased to max dose on day 8
❖ Geriatric: Same start, slower titration, max 100/20 mg BID
❖ Hepatic:
➤ Contraindicated in mod/severe hepatic impairment
➤ Not recommended in mild hepatic impairment (↑ xanomeline
exposure)
❖ Renal:
➤ Not recommended if eGFR <60 mL/min
➤ Increased exposure to both drugs with eGFR 60 to <90 mL/min
but safety profile unaffected
Medications Related to Cobenfy:
❖ Cevimeline (Evoxac) shares the -meline suffix
➤ Muscarinic agonist for treating dry mouth in Sjögren's syndrome
➤ Does not cross BBB, limiting central effects
❖ Clozapine (Clozaril): Gold standard for antipsychotic efficacy
➤ Primarily works through non-D2 blocking mechanisms
➤ Clozapine (parent drug):
● M1, M2, M3, and M5 antagonist
● M4 agonist – possible shared mechanism with xanomeline
➤ Norclozapine (metabolite): M1 and M4 agonist
● M1 agonism enhances cognition in schizophrenia
● M4 agonism may contribute to antipsychotic efficacy
● However, norclozapine is more associated with side effects than
therapeutic benefit
➤ Unlike with xanomeline/trospium, the muscarinic/antimuscarinic effects
of clozapine/norclozapine are unbalanced, resulting in:
● Severe constipation (clozapine/antimuscarinic)
● Hypersalivation (norclozapine/muscarinic)
➤ In addition to M4 receptor agonism, mechanisms that may contribute to
clozapine's unique efficacy include indirect NMDA receptor agonism
(glycine binding site) and GABA-A receptor antagonism.
❖ Olanzapine (Zyprexa): Superior antipsychotic efficacy
● M1 and M3 antagonist
● M4 agonist (less potent that clozapine)
❖ Pimavanserin (Nuplazid) has antipsychotic effects in Parkinson's disease
without blocking D2 receptors
➤ 5-HT2A inverse agonist without M1/M4 agonist effects
➤ Highlights alternative approaches to antipsychotic action
❖ Emraclidine (Phase 2 trial developmental status)
➤ Potential best-in-class next-generation antipsychotic
➤ M4 receptor positive allosteric modulator (PAM)
➤ Provisional mascot: "M(4) Raccoon"
Zorn, S. H., Jones, S. B., Ward, K. M., & Liston, D. R. (1994). Clozapine is a potent and selective muscarinic M4 receptor agonist. European Journal of Pharmacology: Molecular Pharmacology, 269(3), R1-R2.
Zeng, X. P., Le, F., & Richelson, E. (1997). Muscarinic M4 receptor activation by some atypical antipsychotic drugs. European journal of pharmacology, 321(3), 349-354.
Clozapine + Metabolite is also an M1 & M4 agonist
Clozapine is the gold standard for treatment-resistant schizophrenia. Several potential explanations have been proposed for clozapine's unique efficacy.
Clozapine has a complex pharmacological profile, interacting with multiple neurotransmitter systems including dopamine, serotonin, norepinephrine, and acetylcholine receptors. Its relatively weak D2 receptor antagonism combined with strong affinity for other receptors may contribute to its superior efficacy and reduced extrapyramidal side effects.
Clozapine has anti-inflammatory properties and may promote neuroplasticity and neurogenesis.
Clozapine influences glutamate signaling via modulation of NMDA receptors at the glycine binding site.
Increasing glycinergic activity through agonists or glycine reuptake inhibitors improves efficacy of non-clozapine antipsychotics, but not clozapine. Glycine at doses of 30–60 g/day has been shown to worsen the positive symptoms of schizophrenia when coadministered with clozapine.
Norclozapine (N-desmethylclozapine) is the primary active metabolite of clozapine. Although trials of norclozapine itself as an antipsychotic were unsuccessful, its contribution to clozapine's antipsychotic efficacy remains unclear.
As an M1 agonist, norclozapine likely benefits cognition; indeed, higher clozapine-to-norclozapine ratios have been associated with poorer cognitive function. Norclozapine is associated with more metabolic dysfunction than clozapine, which is not fully explained by known receptor binding affinities.
Acetylcholine (ACh)
❖ First neurotransmitter discovered (1914); crucial in proving neurotransmission concept (1921)
❖ Endogenous ligand for both muscarinic and nicotinic receptors
➤ Muscarinic: named after muscarine (mushroom compound)
➤ Nicotinic: named after nicotine
❖ "Cholinergic" and "anticholinergic" often refer specifically to "muscarinic" and "antimuscarinic" effects, excluding nicotinic.
❖ Muscarinic receptor activation associated with parasympathetic "rest and digest" response.
➤ Muscarinic agonists: cholinomimetics or parasympathomimetics
❖ Adrenoceptor activation (NE and EPI) involved in sympathetic"fight or flight" response, generally opposing muscarinic effects.
❖ Nicotinic receptors found on:
➤ Postsynaptic membrane of skeletal muscle cells at neuromuscular junctions
➤ Some neurons
Acetylcholine Ballicule
Acetylcholine Mnemonics
M1 Muscarinic Acetylcholine Receptor Agonist
M2 Muscarinic Acetylcholine Receptor Agonist
M3 Muscarinic Acetylcholine Receptor Agonist
M4 Muscarinic Acetylcholine Receptor Agonist
M5 Muscarinic Acetylcholine Receptor Agonist
Neuromuscular Nicotinic Receptor Agonist
Neuronal Nicotinic Receptor (NNR) Agonist
Neuronal nicotinic receptor partial agonist
Other medications related to acetylcholine
Botulinum toxin (Botox)
❖ Causes flaccid paralysis
❖ Blocks presynaptic ACh release at neuromuscular junction
Donepezil (Aricept)
❖ Inhibits acetylcholinesterase
❖ ↑ ACh levels by preventing breakdown
❖ Also rivastigmine (Exelon), galantamine (Razadyne), and benzgalantamine (Zunveyl)
Anticholinergic / Antimuscarinic Mnemonics
"Anticholine" Ballicule Concept for Understanding Anticholinergic Medications
M1 Muscarinic Acetylcholine Receptor Antagonist
M2 Muscarinic Acetylcholine Receptor Antagonist
M3 Muscarinic Acetylcholine Receptor Antagonist
M4 Muscarinic Acetylcholine Receptor Antagonist
M5 Muscarinic Acetylcholine Receptor Antagonist
Nonselective Antimuscarinics
CNS Anticholinergic Burden Scale
Antinicotinic Mechanisms
Neuromuscular Nicotinic Receptor Antagonist
Neuronal Nicotinic Receptor (NNR) Antagonist
Depolarizing Neuromuscular Blocker
Also:
Pralidoxime (2-PAM)
❖ Reactivates inhibited cholinesterases (which break down acetylcholine)
❖ Antidote for organophosphate poisoning from pesticides and nerve agents (e.g., sarin)
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