Physostigmine Salicylate Injection

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

Physostigmine Salicylate Injection is a sterile solution of Physostigmine Salicylate in Water for Injection. It contains NLT 90.0% and NMT 110.0% of the labeled amount of physostigmine salicylate (C₁₅H₂₁N₃O₂ · C₇H₆O₃). It may contain an antimicrobial agent and an antioxidant.

[Note—Do not use the Injection if it is more than slightly discolored.]

2 IDENTIFICATION

A. Identification—Organic Nitrogenous Bases 〈181〉

Analysis: Use 1 g of sodium bicarbonate instead of 2 mL of 1 N sodium hydroxide.

Acceptance criteria: Meets the requirements

B. Identification Tests—General, Salicylate〈191〉: Meets the requirements

3 ASSAY

Procedure

Buffer: 3.85 g/L of ammonium acetate in water. Adjust, if necessary, with glacial acetic acid or ammonium hydroxide to a pH of 6 ± 0.1.

Mobile phase: Acetonitrile and Buffer (50:50)

Solution A: 100 µL of USP Benzyl Alcohol RS and 1 µL of benzaldehyde in 400 mL of acetonitrile

Standard solution: 0.03 mg/mL of USP Physostigmine Salicylate RS in Solution A

Sample solution: Nominally 0.03 mg/mL from a suitable volume of Injection containing NLT 3 mg of physostigmine salicylate diluted with acetonitrile

3.1 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 254 nm

Column: 3.9-mm × 30-cm; packing L1

Flow rate: 2 mL/min

Injection volume: 10 µL

3.2 System suitability

Samples: Solution A and Standard solution

[Note—If the peaks due to benzyl alcohol and benzaldehyde co-elute when Solution A is injected, the Standard solution will exhibit only two peaks instead of three. In a suitable system, benzyl alcohol and benzaldehyde elute before physostigmine.] Suitability requirements

Resolution: NLT 2.0 between the physostigmine peak and the adjacent peak (benzyl alcohol or benzaldehyde, or the combination of these), Standard solution

Column efficiency: NLT 1200 theoretical plates from the analyte peak, Standard solution

Relative standard deviation: NMT 2.0%, Standard solution

3.3 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of physostigmine salicylate (C₁₅H₂₁N₃O₂ · C₇H₆O₃) in the portion of Injection taken: 

Result = (r_U /r_S ) × (C_S /C_U) × 100

r_U = peak response from the Sample solution

r_S = peak response from the Standard solution

C_S = concentration of USP Physostigmine Salicylate RS in the Standard solution (mg/mL)

C_U = nominal concentration of physostigmine salicylate in the Sample solution (mg/mL)

Acceptance criteria: 90.0%–110.0%

4 SPECIFIC TESTS

Bacterial Endotoxins Test 〈85〉: NMT 83.4 USP Endotoxin Units/mg of physostigmine salicylate

pH 〈791〉: 3.5–5.0

Other Requirements: It meets the requirements in Injections and Implanted Drug Products 〈1〉.

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in single-dose containers, preferably of Type I glass, protected from light.

USP Reference Standards 〈11〉

USP Benzyl Alcohol RS

USP Physostigmine Salicylate RS