Nitroglycerin Ointment

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

Nitroglycerin Ointment is Diluted Nitroglycerin in a suitable ointment base. It contains NLT 90.0% and NMT 115.0% of the labeled amount of nitroglycerin (C₃H₅N₃O₉).

2 IDENTIFICATION

A. The retention time of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

3 ASSAY

3.1 Procedure

Mobile phase: Methanol and water (500:500)

Standard solution: 0.075 mg/mL of nitroglycerin from USP Diluted Nitroglycerin RS in Mobile phase

Sample solution: Transfer a quantity of Ointment equivalent to 2.0 mg of nitroglycerin to a glass-stoppered, 50-mL conical flask, and add 25.0 mL of Mobile phase. Immerse the flask containing the sample in a water bath maintained at a temperature of 50° for 10 min. Shake intermittently until the sample is dispersed. Remove the flask from the bath, and shake vigorously for 1 min to obtain a coagulated solid. Repeat the heating and shaking steps one more time, and filter.

Chromatographic system

• (See Chromatography 〈621〉, System Suitability.)
• Mode: LC
• Detector: UV 220 nm
• Column: 4.6-mm × 25-cm; packing L1
• [Note-If necessary, a short precolumn that contains packing L1 may be used.]
• Flow rate: 1 mL/min
• Injection volume: 20 µL

System suitability

• Sample: Standard solution
• Suitability requirements
• Column efficiency: NLT 3000 theoretical plates
• Tailing factor: NMT 2.5
• Relative standard deviation: NMT 3.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of nitroglycerin (C₃H₅N₃O₉) in the portion of Ointment taken:

Result = (rᵤ/rₛ) × (Cₛ/Cᵤ) × 100

rᵤ = peak response from the Sample solution

rₛ = peak response from the Standard solution

Cₛ = concentration of nitroglycerin in the Standard solution (mg/mL)

Cᵤ = nominal concentration of nitroglycerin in the Sample solution (mg/mL)

Acceptance criteria: 90.0%–115.0%

4 PERFORMANCE TESTS

4.1 Minimum Fill 〈755〉

Meets the requirements

4.2 Homogeneity

Analysis: In the case of single-dose containers, perform the Assay on specimens from each of 10 containers. In the case of multiple-dose containers, perform the Assay on one sample from the top and one from the bottom of each of five containers.

Acceptance criteria: Each sample contains NLT 90.0% and NMT 110.0% of the mean value.

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers.

Labeling: Label multiple-dose containers with a direction to close tightly immediately after each use.

USP Reference Standards 〈11〉

USP Diluted Nitroglycerin RS