Simethicone Emulsion

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

Simethicone Emulsion is a water-dispersible form of Simethicone composed of Simethicone, suitable emulsifiers, preservatives, and water. It may contain suitable viscosity-increasing agents. It contains an amount of polydimethylsiloxane ([–(CH₃)₂SiO–]_n) that is NLT 85.0% and NMT 110.0% of the labeled amount of simethicone.

2 IDENTIFICATION

Change to read:

SPECTROSCOPIC IDENTIFICATION TESTS 〈197〉 , Infrared Spectroscopy (CN 1-MAY-2020)

Standard solution and Sample solution: Prepare as directed in the Assay.

Analysis: Place a suitable amount of the Sample solution in a suitable container, and dry it with a stream of nitrogen or other appropriate means to evaporate the solvent. Similarly proceed with the Standard solution. Record the spectra of the residues using 〈 197A〉 or  〈197F〉, and examine the spectra in the range between 1400 cm−1 and 700 cm−1.

Acceptance criteria

For spectra obtained using 〈 197A〉: The spectrum from the Sample solution shows strong bands at 1260 ± 10 cm−1, 1015 ± 15 cm−1, and 795 ± 15 cm−1, and a broad shoulder at 1085 ± 15 cm−1, similar to the spectrum from the Standard solution. [NOTE—The exact maxima of the broad shoulder near 1085 cm−1 may differ by up to 15 cm−1 for the spectra from the Sample solution and the Standard solution.]

For spectra obtained using 〈 197F〉: The spectrum from the Sample solution shows a strong band at 1260 ± 10 cm−1 and partially resolved bands near 1095 ± 15 cm−1, 1020 ± 15 cm−1, and 800 ± 15 cm−1, similar to the spectrum from the Standard solution.

3 ASSAY

PROCEDURE

Use glass apparatus only; avoid use of plasticware. Proper mixing of the Emulsion before sampling and testing is crucial.

Standard solution: 2 mg/mL of USP Polydimethylsiloxane RS in toluene. Treat a 25.0-mL aliquot of this solution in the same manner as the Blank, beginning with “add 50 mL of dilute hydrochloric acid (2 in 5)…”.

Sample: Equivalent to 50 mg of simethicone from the Emulsion

Sample solution: To the Sample add 25.0 mL of toluene. Treat in the same manner as the Blank, beginning with “add 50 mL of dilute hydrochloric acid (2 in 5)…”.

Instrumental conditions

(See Mid-Infrared Spectroscopy 〈854〉.)

Mode: Infrared

Cell: 0.5 mm

Analytical wavelength: Maximum absorbance at about 7.9 µm (1259 cm−1)

Blank: To 25.0 mL of toluene add 50 mL of dilute hydrochloric acid (2 in 5), close the bottle securely with a cap having an inert liner, vigorously shake by hand for 5 s, then shake for 5–20 min on a suitable shaker. [NOTE—The following shakers were found suitable: (1) a reciprocating shaker at a rate of about 200 oscillations/min and a stroke of 38 ± 2 mm or (2) a wrist-action shaker with a radius of 13.3 ±

0.4 cm (measured from center of shaft to center of bottle) that uses an arc of 10° at a frequency of 300 ± 30 strokes/min. The recommended shaking time is about 20 min, which can be adjusted as needed.] Centrifuge the mixture. [NOTE—The following centrifuging condition was found suitable: 1500 × g for 30–40 min.] Remove from the centrifuge, and immediately transfer about 5 mL of the upper organic (toluene) layer to a 15-mL screw-capped test tube containing about 1 g of anhydrous sodium sulfate. Close the tube with a screw- cap having an inert liner, agitate vigorously, and centrifuge the mixture until a clear supernatant is obtained. [NOTE—The following centrifuging condition was found suitable: 1500 × g for about 10 min.]

Analysis

[NOTE—Wash the cell with copious amounts of toluene to ensure that there is no carryover or residue.]

Samples: Standard solution, Sample solution, and Blank

Calculate the percentage of polydimethylsiloxane ([–(CH₃)₂SiO–]_n) in the labeled amount of simethicone in the Emulsion:

Result = (A_U/A_S) × (C_S/C_U) × 100

A_U = absorbance of the Sample solution

A_S = absorbance of the Standard solution

C_S = concentration of USP Poly dimethylsiloxane RS in the Standard solution (mg/mL)

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

Acceptance criteria: 85.0%–110.0%

4 SPECIFIC TESTS

MICROBIAL ENUMERATION TESTS 〈61〉: The total aerobic microbial count does not exceed 102 cfu/g.

DEFOAMING ACTIVITY

Foaming solution: 10 mg/mL of octoxynol 9 in water

Sample solution: Transfer a quantity of Emulsion, equivalent to 300 mg of simethicone, to a 60-mL bottle. Dilute with water to 30 g, cap the bottle, and shake vigorously.

Analysis

[NOTE—For each test, use a clean, unused, 250-mL glass jar.]

Add, dropwise, 500 µL of the Sample solution to a clean, unused, cylindrical 250-mL glass jar, fitted with a 50-mm cap and containing 100 mL of the Foaming solution. Cap the jar, and clamp it in an upright position on a wrist-action shaker. Using a radius of 13.3 ± 0.4 cm (measured from the center of the shaft to the center of the bottle), shake for 10 s through an arc of 10° at a frequency of 300 ± 30 strokes/min. Record the time, in s, required for the foam to collapse. The time for foam collapse is determined at the instant the first portion of foam-free liquid surface appears, measured from the end of the shaking period.

Acceptance criteria: The defoaming activity time does not exceed 15 s.

5 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight containers.

USP REFERENCE STANDARDS 〈11〉

USP Polydimethylsiloxane RS