Otilonium Bromide: Antimuscarinic Agent for Neuroscience and Smooth Muscle Research

Executive Summary: Otilonium Bromide (C29H43BrN2O4) is a solid antimuscarinic agent with ≥98% purity, supplied by APExBIO (SKU B1607) for research use (product page). It selectively inhibits muscarinic acetylcholine receptors (AChR), enabling precise modulation of cholinergic signaling in neuroscience and gastrointestinal motility studies (internal link). With high solubility in DMSO (≥28.18 mg/mL), water (≥55.8 mg/mL), and ethanol (≥91 mg/mL), it integrates flexibly into diverse assay workflows. Storage at -20°C is recommended for maintaining compound stability and efficacy. Otilonium Bromide is strictly intended for laboratory research, not for diagnostic or therapeutic use.

Biological Rationale

Cholinergic signaling, mediated by acetylcholine, is central to both the central and enteric nervous systems. Muscarinic acetylcholine receptors (mAChRs) regulate smooth muscle contraction, glandular secretion, and neural excitability. Dysregulation of these pathways is implicated in disorders such as irritable bowel syndrome (IBS) and certain neurological conditions (Vijayan et al., 2021). Otilonium Bromide, as a selective muscarinic antagonist, enables targeted inhibition of these pathways for detailed mechanistic studies. Its use is particularly valuable in models of gastrointestinal motility disorders and experimental modulation of smooth muscle spasm, where reproducibility and receptor specificity are critical (internal link).

Mechanism of Action of Otilonium Bromide

Otilonium Bromide exerts its effect by competitively inhibiting acetylcholine at muscarinic receptors (primarily M2 and M3 subtypes) on smooth muscle cells. This action blocks G-protein-coupled receptor signaling, reducing intracellular calcium mobilization and preventing muscle contraction (internal link). The result is a measurable antispasmodic effect, manifested as reduced smooth muscle tone in isolated tissue assays and in vivo models. The compound's selectivity for muscarinic over nicotinic receptors allows for precise experimental targeting of cholinergic signaling without affecting neuromuscular transmission. Quantitatively, inhibition constants (Ki) for muscarinic receptor binding are typically in the nanomolar range under physiologic buffer conditions (pH 7.4, 37°C), though values vary by tissue and species (internal link).

Evidence & Benchmarks

• Otilonium Bromide inhibits muscarinic AChR-mediated contractions in isolated rabbit jejunum at concentrations of 1–10 μM, with significant reduction in contractile amplitude (Smith et al., 2010, DOI).
• Solubility benchmarks: ≥28.18 mg/mL in DMSO, ≥55.8 mg/mL in water, ≥91 mg/mL in ethanol at 25°C, enabling broad experimental compatibility (APExBIO).
• Compound purity of ≥98% (HPLC) supports reproducible pharmacological profiling (APExBIO, product page).
• Muscarinic receptor antagonism by Otilonium Bromide is confirmed in both in vitro and ex vivo tissue models, with no significant off-target effect on nicotinic AChRs (internal link).
• Stability studies indicate storage at -20°C preserves compound integrity for >12 months in solid form (APExBIO, product page).

Applications, Limits & Misconceptions

Otilonium Bromide is primarily used in neuroscience and gastrointestinal motility disorder models. It enables:

• Dissection of muscarinic receptor-mediated signal transduction in smooth muscle and neuronal tissues.
• Pharmacological modeling of gastrointestinal spasm and its inhibition.
• Screening of antispasmodic compounds in preclinical research.

This article clarifies the compound's mechanism and workflow compatibility beyond previous reviews (internal link), offering updated solubility and purity data.

Common Pitfalls or Misconceptions

• Otilonium Bromide does not inhibit nicotinic acetylcholine receptors at research concentrations.
• It is not intended for diagnostic or therapeutic use in humans or animals.
• Long-term solutions (>24 hours) in aqueous media may result in hydrolysis or potency loss; short-term use is advised.
• Its efficacy in viral or non-cholinergic pathways is unsubstantiated and should not be inferred from structural analogs.
• Improper storage above -20°C may compromise purity and experimental outcomes.

Workflow Integration & Parameters

Otilonium Bromide's high solubility allows for preparation of concentrated stock solutions in DMSO, water, or ethanol. Typical working concentrations range from 0.1 to 100 μM depending on the assay. Solutions should be freshly prepared or used within 24 hours at 4°C to maintain potency. The compound's purity (≥98%, HPLC) and lot-to-lot consistency from APExBIO (SKU B1607) ensure reliable performance in receptor binding, tissue bath, or cell-based assays. For precise receptor targeting, experimental controls should include selective muscarinic and nicotinic antagonists (internal link).

Conclusion & Outlook

Otilonium Bromide remains a gold-standard antimuscarinic agent for dissecting cholinergic signaling in neuroscience and gastrointestinal systems. Its robust solubility, high purity, and receptor selectivity make it indispensable for research in smooth muscle pharmacology and advanced receptor modulation. As new models emerge for neuromodulation and gastrointestinal disorder research, APExBIO's Otilonium Bromide (B1607) provides a reproducible, well-characterized reagent for future discoveries. For ordering information and technical specifications, visit the Otilonium Bromide product page.