Cephalexin Capsules

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 

Cephalexin Capsules contain the equivalent of NLT 90.0% and NMT 120.0% of the labeled amount of cephalexin (C₁₆H₁₇N₃O₄S).  

2 IDENTIFICATION 

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

3 ASSAY 

Procedure 

Mobile phase: 0.985 g/L of sodium 1-pentanesulfonate in a mixture of acetonitrile, methanol, triethylamine, and water (20:10:3:170), adjusted with phosphoric acid to a pH of 3.0 ± 0.1 

Standard stock solution: 1 mg/mL of USP Cephalexin RS in water 

Standard solution: 0.4 mg/mL of cephalexin in Mobile phase from Standard stock solution 

Sample stock solution: Equivalent to 1 mg/mL of cephalexin from combined contents of NLT 20 Capsules in water. Sonicate, if necessary, to dissolve the cephalexin. Filter, if necessary, to obtain a clear solution. 

Sample solution: 0.4 mg/mL of cephalexin in Mobile phase from Sample stock solution 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 254 nm 

Column: 4.6-mm × 25-cm; packing L1 of low acidity 

Flow rate: 1.5 mL/min 

Injection size: 20 µL 

System suitability 

Sample: Standard solution 

Suitability requirements 

Relative standard deviation: NMT 2.0% 

Analysis 

Samples: Standard solution and Sample solution 

Calculate the percentage of cephalexin (C₁₆H₁₇N₃O₄S) in the portion of Capsules taken: 

Result = (r_U/r_S) × (C_S/C_U) × P × F × 100  

r_U = peak response from the Sample solution 

r_S = peak response from the Standard solution 

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

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

P = potency of cephalexin in USP Cephalexin RS (µg/mg) 

F = conversion factor, 0.001 mg/µg 

Acceptance criteria: 90.0%–120.0% 

4 PERFORMANCE TESTS 

Dissolution 〈711〉 

Medium: Water; 900 mL 

Apparatus 1: 100 rpm 

Time: 30 min 

Standard solution: 20 µg/mL of USP Cephalexin RS in Medium 

Sample solution: Pass a portion of the solution under test through a suitable filter. Dilute with Medium, if necessary, to a concentration of about 20 µg/mL. 

Spectrometric conditions 

(See Ultraviolet-Visible Spectroscopy 〈857〉.) 

Mode: UV 

Analytical wavelength: 262 nm 

Analysis 

Samples: Standard solution and Sample solution 

Tolerances: NLT 80% (Q) of the labeled amount of cephalexin (C₁₆H₁₇N₃O₄S) is dissolved. 

Uniformity of Dosage Units 〈905〉: Meet the requirements 

5 ADDITIONAL REQUIREMENTS 

Packaging and Storage: Preserve in tight containers. 

USP Reference Standards 〈11〉 

USP Cephalexin RS