Pyridostigmine Bromide Oral Solution
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
Pyridostigmine Bromide Oral Solution contains, in each 100 mL, not less than 1.08 g and not more than 1.32 g of pyridostigmine bromide (C9H13BrN2O2).
Packaging and storage—Preserve in tight, light-resistant containers.
USP Reference standards 〈11〉—
USP Pyridostigmine Bromide RS
Identication—To 5 mL of Oral Solution in a separator add 100 mL of 2.5 N hydrochloric acid, and mix. Extract with ve 20-mL portions of chloroform, place 2 mL of the aqueous solution in a 50-mL volumetric flask, and add water to volume: the UV absorption spectrum of this solution exhibits maxima and minima at the same wavelengths as that of a similar solution of USP Pyridostigmine Bromide RS, concomitantly measured.
Assay—
Phosphate solution—Dissolve 38 g of monobasic sodium phosphate and 2 g of anhydrous dibasic sodium phosphate in water to make 1000 mL. Adjust the pH, if necessary, by slight variation of the ratio of the two ingredients, to 5.3 ± 0.1.
Bromocresol green solution—Dissolve 250 mg of bromocresol green sodium salt in 250 mL of Phosphate solution.
Standard preparation—Dissolve a suitable quantity of USP Pyridostigmine Bromide RS, accurately weighed, in water, to obtain a solution having a known concentration of about 1.2 mg per mL.
Assay preparation—Transfer an accurately measured volume of Oral Solution, equivalent to about 120 mg of pyridostigmine bromide, to a 100- mL volumetric flask, add water to volume, and mix.
Procedure—Transfer 10 mL each, accurately measured, of the Assay preparation and the Standard preparation to separate 125-mL separators. Into each separator pipet 10 mL of water, 20 mL of Phosphate solution, and 5 mL of Bromocresol green solution. Extract each solution with six 15-mL portions of chloroform, collecting the chloroform extracts in respective 100-mL volumetric flasks, then add chloroform to volume in each flask, and mix. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 415 nm, with a suitable spectrophotometer, using chloroform as the blank. Calculate the quantity, in mg, of pyridostigmine bromide (C9H13BrN2O2 in the portion of Oral Solution taken by the formula:
100C(AU/AS)
in which C is the concentration, in µg per mL, of USP Pyridostigmine Bromide RS in the Standard solution, V is the volume, in mL, of Injection taken, and AU and AS are the absorbances of the solutions obtained from the Assay preparation and the Standard solution, respectively.
