Cephalexin for Oral Suspension - Definition, Identification, Assay - USP 2025

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 for Oral Suspension is a dry mixture of Cephalexin and one or more suitable buffers, colors, diluents, and flavors. It contains the equivalent of NLT 90.0% and NMT 120.0% of the labeled amount of C₁₆H₁₇N₃O₄S per mL when constituted as directed in the labeling.

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: Mix 10.0 mL of Standard stock solution with 15.0 mL of Mobile phase. 

Sample stock solution: Nominally equivalent to 1 mg/mL of cephalexin from Oral Suspension, constituted as directed in the labeling, freshly mixed and free from air bubbles. Sonicate, if necessary, to assure complete dissolution of the cephalexin. Filter, if necessary, to obtain a clear solution. 

Sample solution: Mix 10.0 mL of Sample stock solution and 15.0 mL of Mobile phase. 

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 each mL of the constituted Suspension 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 stock solution (mg/mL) 

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

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

F = conversion factor, 0.001 mg/µg 

Acceptance criteria: 90.0%–120.0% 

4 PERFORMANCE TESTS 

Uniformity of Dosage Units 〈905〉 For solid packaged in single-unit containers: meets the requirements 

Deliverable Volume 〈698〉: Meets the requirements 

5 SPECIFIC TESTS 

pH 〈791〉: 3.0–6.0, constituted as directed in the labeling 

6 ADDITIONAL REQUIREMENTS 

Packaging and Storage: Preserve in tight containers. 

USP Reference Standards 〈11〉 

USP Cephalexin RS