Physostigmine, also known as Eserine, is a naturally occurring indole alkaloid and reversible cholinesterase inhibitor used as a specialized pharmaceutical active ingredient. Physostigmine has the CAS Number 57-47-6, molecular formula C15H21N3O2, and molecular weight 275.35 g/mol. It is chemically distinct from Physostigmine Salicylate, which is a separate salt form with CAS Number 57-64-7.
Physostigmine works primarily by reversibly inhibiting acetylcholinesterase, an enzyme responsible for breaking down acetylcholine. By slowing acetylcholine degradation, Physostigmine increases cholinergic activity. Its ability to cross the blood-brain barrier distinguishes it from some other cholinesterase inhibitors and contributes to its pharmacological applications.
Physostigmine has historically been used in ophthalmic preparations because of its miotic and cholinergic properties. It has also been used in clinical management of severe anticholinergic toxicity. Because of its potent pharmacological activity, Physostigmine API requires controlled handling, analytical testing and appropriate pharmaceutical quality procedures.
The chemical structure of Physostigmine contains an indole ring system and a carbamate group. Its molecular structure includes defined stereochemistry, making control of identity and stereochemical characteristics important during pharmaceutical development. PubChem and NIST identify Physostigmine with CAS 57-47-6 and molecular weight approximately 275.35 g/mol.
Physostigmine Base should not be confused with Physostigmine Salicylate. Physostigmine Salicylate is the salicylate salt of Physostigmine and has a significantly higher molecular weight of approximately 413.47 g/mol. The USP-NF monograph for Physostigmine Salicylate specifies an assay range of 97.0% to 102.0% on the dried basis. This numerical assay specification applies to Physostigmine Salicylate and should not be transferred to Physostigmine Base.
For Physostigmine Base, quality assessment can include identity, assay, related substances, moisture or loss on drying, residual solvents and other analytical parameters established under the applicable pharmaceutical specification. A current universally applicable numerical pharmacopoeial specification for the free-base form was not verified from the authoritative sources reviewed. Therefore, numerical values from the Physostigmine Salicylate monograph or research-grade commercial materials should not be represented as universal specifications for Physostigmine Base.
Analytical characterization of Physostigmine may involve chromatographic techniques, infrared spectroscopy and other validated methods appropriate to the intended pharmaceutical grade. These tests help establish identity, purity and consistency of the active ingredient.
Proper storage and handling are also important because Physostigmine is a pharmacologically active cholinesterase inhibitor. Pharmaceutical manufacturers should use suitable packaging, controlled environmental conditions and validated stability requirements based on the intended grade and regulatory market.
Physostigmine API is therefore a specialized pharmaceutical ingredient with established pharmacological significance. Accurate control of its chemical identity, stereochemical characteristics and purity profile is essential for pharmaceutical research, formulation development and regulated manufacturing.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |
| Loss on Drying | NMT 1.0% |
| Residue on Ignition | NMT 0.1% |
| Individual Impurity | NMT 0.5% |
| Total Impurities | NMT 1.0% |
| Water Content | NMT 0.5% |