Carbachol Ophthalmic Solution
» Carbachol Ophthalmic Solution is a sterile solution of Carbachol in an isotonic, aqueous medium. It contains not less than 95.0 percent and not more than 105.0 percent of the labeled amount of C6H15ClN2O2. It may contain suitable preservatives and antimicrobial agents.
Packaging and storage Preserve in tight containers.
USP Reference standards 11
Identification Dilute the test article to a concentration of about 1 mg of carbachol per mL. Add 5 mL of ammonium reineckate solution (1 in 30), and shake vigorously for 1 minute: a red precipitate soluble in acetone is formed.
Sterility 71: meets the requirements.
pH 791: between 5.0 and 7.0.
Hypochlorite reagent Dilute 1 volume of sodium hypochlorite TS with water to 15 volumes, allow to stand for 30 minutes, then mix equal volumes of the resulting solution and 1 N sodium hydroxide. Prepare fresh daily.
Standard preparation Dissolve a suitable quantity of USP Carbachol RS, accurately weighed, in water, and dilute quantitatively and stepwise with water to obtain a solution having a known concentration of about 100 µg per mL.
Assay preparation Dilute an accurately measured volume of Ophthalmic Solution quantitatively and stepwise with water to obtain a solution containing about 100 µg of carbachol per mL.
Procedure Transfer 2.0-mL portions each of the Assay preparation and the Standard preparation, and of water to provide a blank, to separate 50-mL conical flasks. To each flask add 1.0 mL of 0.1 N hydrochloric acid, and mix. Treat each as follows. Add 4.0 mL of Hypochlorite reagent, rinsing the inner walls of the flask with small portions of water, mix, and allow to stand for 15 minutes, accurately timed. Add 2.0 mL of phenol solution (1 in 200), rinsing the walls of the flask with the solution and with additional small portions of water. Mix, and allow to stand for 5 minutes. Add 2.0 mL of 3.5 N hydrochloric acid, washing the sides of the flask upon addition. Rinse the flask sparingly with 0.1 N hydrochloric acid to assure complete acidification of all contents, then mix. Add 1.0 mL of potassium iodide solution (3 in 1000), mix, and allow to stand for 5 minutes. Add 3.0 mL of starch TS, mix, transfer the solutions to 50-mL volumetric flasks with the aid of several small portions of water, and dilute each solution with water to volume. Concomitantly determine the absorbances of the solutions from the Assay preparation and the Standard preparation in 1-cm cells at the wavelength of maximum absorbance at about 590 nm, with a suitable spectrophotometer, against the blank. Calculate the quantity, in mg, of C6H15ClN2O2 in each mL of the Ophthalmic Solution taken by the formula:
0.001CD(AU / AS)in which C is the concentration, in µg per mL, of USP Carbachol RS in the Standard preparation, D is the dilution factor used in the Assay preparation, and AU and AS are the absorbances of the solutions from the Assay preparation and the Standard preparation, respectively.
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USP35NF30 Page 2481Pharmacopeial Forum: Volume No. 33(2) Page 214