Benzonatate
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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)
Benzonatate
C₃₀H₅₃NO₁₁ (average) 603.74 (average)
Benzoic acid, 4-(butylamino)-, 2,5,8,11,14,17,20,23,26-nonaoxaoctacos-28-yl ester.
2,5,8,11,14,17,20,23,26-Nonaoxaoctacosan-28-yl p-(butylamino)benzoate
CAS RN®: 104-31-4; UNII: 5P4DHS6ENR.
Benzonatate contains not less than 95.0 percent and not more than 105.0 percent of C₃₀H₅₃NO₁₁.
Packaging and storage—Preserve in tight, light-resistant containers.
USP Reference standards 〈11〉—
USP Benzonatate RS
1 Identification
A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197F.
Sample: The contents of Capsules
Acceptance criteria: Meets the requirements. If a difference is observed, or if excipients are present, use an amount of the contents of Capsules equivalent to about 100 mg of benzonatate. Mix with 25 mL of 0.01 N hydrochloric acid, and proceed as directed in Identification—Organic Nitrogenous Bases 〈181〉, beginning with “Transfer the liquid to a separator”.
B. Spectroscopic Identification Tests 〈197〉, Ultraviolet-Visible Spectroscopy: 197U.
Solution: 15 µg per mL.
Medium: Water.
Refractive index 〈831〉: between 1.509 and 1.511 at 20°.
Water Determination, Method I 〈921〉: not more than 0.3%.
Residue on ignition 〈281〉: not more than 0.1%.
Chloride 〈221〉—Mix 20 mL of a solution (1 in 10) with 20 mL of water and 1 mL of nitric acid, shake for 1 hour, and allow to stand for 1 hour. Pass through a filter having a porosity of 0.2 µm, and to the filtrate add 1 mL of silver nitrate TS. Dilute with water to 50 mL, mix, and allow to stand protected from light for 10 minutes: the turbidity does not exceed that produced by 0.10 mL of 0.020 N hydrochloric acid (0.0035%).
Sulfate 〈221〉—Mix 5 mL of a solution (1 in 20) with 5 mL of water and 1 mL of 3 N hydrochloric acid, shake for 1 hour, and allow to stand for 1 hour. Pass through a filter having a porosity of 0.2 µm, and to the filtrate add 1 mL of barium chloride TS. Mix, and allow to stand for 10 minutes: the turbidity does not exceed that produced by 0.10 mL of 0.020 N sulfuric acid (0.04%).
2 Assay
Weigh accurately about 5 g of Benzonatate, and reflux with 25.0 mL of 0.5 N sodium hydroxide VS for 1 hour. Cool, add 25 mL of water and 10 drops of bromothymol blue TS, and titrate the excess alkali with 0.5 N hydrochloric acid VS. Perform a blank determination (see Residual Titrations under Titrimetry 〈541〉). Each mL of 0.5 N sodium hydroxide is equivalent to 301.5 mg of C₃₀H₅₃NO₁₁.
