Pyridostigmine Bromide is a quaternary ammonium carbamate and reversible acetylcholinesterase inhibitor. It increases the availability of acetylcholine at cholinergic synapses by reducing acetylcholinesterase-mediated acetylcholine breakdown. It is primarily associated with the treatment of myasthenia gravis and other conditions involving impaired neuromuscular transmission.
The pharmaceutical substance is Pyridostigmine Bromide, CAS 101-26-8, with molecular formula C₉H₁₃BrN₂O₂ and molecular weight 261.12 g/mol. FDA GSRS identifies the substance under UNII KVI301NA53.
Pyridostigmine Bromide is the bromide salt of pyridostigmine. Chemically, it is a pyridinium compound containing a dimethylcarbamate group and bromide counterion. The International Pharmacopoeia describes it as a white or almost white crystalline powder with a characteristic agreeable odor.
The API is deliquescent, making moisture control particularly important during packaging and storage. It is soluble in less than one part of water and ethanol and practically insoluble in ether.
| Parameter | Details |
|---|---|
| Product Name | Pyridostigmine Bromide |
| CAS Number | 101-26-8 |
| Molecular Formula | C₉H₁₃BrN₂O₂ |
| Molecular Weight | 261.12 g/mol |
| FDA UNII | KVI301NA53 |
| ChEBI | CHEBI:8666 |
| ChEMBL | CHEMBL812 |
| Chemical Class | Pyridinium carbamate |
| Pharmacological Class | Acetylcholinesterase inhibitor |
| Therapeutic Class | Cholinergic / neuromuscular transmission agent |
| API Category | Active Pharmaceutical Ingredient |
| Appearance | White or almost white crystalline powder |
| Melting Range | 153–156°C |
| Water Solubility | Soluble in less than 1 part water |
| Ethanol Solubility | Soluble in less than 1 part ethanol |
| Ether Solubility | Practically insoluble |
| Physical Property | Deliquescent |
| Pharmacopoeial Reference | The International Pharmacopoeia |
Pyridostigmine Bromide reversibly inhibits acetylcholinesterase, thereby increasing acetylcholine concentrations at neuromuscular junctions and facilitating cholinergic transmission.
It is primarily used in pharmaceutical products for myasthenia gravis, where enhancement of neuromuscular transmission can improve skeletal-muscle function. Pyridostigmine is also used in certain settings to reverse neuromuscular blockade and has other specialized clinical applications.
The International Pharmacopoeia 2025 monograph provides a defined quality specification for Pyridostigmine Bromide. The monograph requires the substance to contain 98.5–101.0% of C₉H₁₃BrN₂O₂, calculated with reference to the dried substance.
The official monograph also specifies identity testing by UV absorption, chromatography, chemical reaction and bromide identification, together with loss on drying, sulfated ash, related substances and assay.
The International Pharmacopoeia specifies loss on drying NMT 20 mg/g (2.0%), sulfated ash NMT 1.0 mg/g (0.10%), and melting range 153–156°C.
For related substances, any spot other than the principal spot must not be more intense than the 0.10 mg/mL reference solution, corresponding to approximately 0.5% relative to the 20 mg/mL test solution.
For your CMS field named “Assay (HPLC)”, the correct numerical specification is 98.5–101.0%, but the current International Pharmacopoeia assay itself is not an HPLC assay. It uses non-aqueous potentiometric titration with 0.1 mol/L perchloric acid; 1 mL is equivalent to 26.11 mg of C₉H₁₃BrN₂O₂.
So I would recommend displaying:
Assay (HPLC): 98.5–101.0% — Pharmacopoeial assay value; official assay method is non-aqueous titration.
This avoids falsely claiming that the pharmacopoeial assay is HPLC.
Pyridostigmine Bromide manufacturing requires control of the quaternary ammonium bromide salt, moisture content and chromatographic purity. Because the API is deliquescent, moisture protection is particularly important.
Analytical characterization may include:
The International Pharmacopoeia states that Pyridostigmine Bromide should be kept in a well-closed container and protected from light. It also identifies the substance as deliquescent, making a moisture-resistant packaging system important.
Recommended CMS wording:
Store in well-closed, moisture-protective and light-resistant containers under controlled pharmaceutical storage conditions. Protect from humidity, excessive heat and light.
Typical API documentation may include:
Pyridostigmine Bromide has an established International Pharmacopoeia specification, including a 98.5–101.0% assay range, LOD NMT 2.0%, sulfated ash NMT 0.10%, and controlled related substances.
Because the material is deliquescent, appropriate moisture-protective packaging and controlled storage are also essential for maintaining API quality.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.5–101.0% dried basis |
| Loss on Drying | NMT 2.0% |
| Residue on Ignition | NMT 0.5% |
| Individual Impurity | NMT 0.5% |
| Total Impurities | NMT 1.0% |
| Melting Point | 153–156°C |