Cloxacillin Sodium 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

Cloxacillin Sodium Capsules contain the equivalent of NLT 90.0% and NMT 120.0% of the labeled amount of cloxacillin (C₁₉H₁₈CIN₃O₅S).

2 ASSAY

2.1 PROCEDURE

Buffer: 0.02 M monobasic potassium phosphate in water, adjusted with 2 N sodium hydroxide to a pH of 6.8

Mobile phase: Acetonitrile and Buffer (20:80)

Standard solution: 0.55 mg/mL of USP Cloxacillin Sodium RS in Buffer

Sample solution: Nominally 0.5 mg/mL of cloxacillin in Buffer, prepared as follows. Mix the contents of NLT 10 Capsules. Transfer a suitable portion of the powder to a volumetric flask, dilute with Buffer to volume, and stir for 10 min. Pass a portion of the solution through a suitable filter, discarding the first 5 mL of the filtrate. Use the clear filtrate.

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 225 nm

Column: 4.6-mm x 25-cm; packing L1

Flow rate: 1 mL/min

Injection volume: 20 µL

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 1.8

Relative standard deviation: NMT 2.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of cloxacillin (C19H18CINOS) in the portion of Capsules taken:

Result = (r_u/r_s) × (C_s/C_u) x P x F x 100

r_u = peak response from the Sample solution

r_s = peak response from the Standard solution 

C_s = concentration of USP Cloxacillin Sodium RS in the Standard solution (mg/mL)

C_u = nominal concentration of cloxacillin in the Sample solution (mg/mL)

P = potency of cloxacillin in USP Cloxacillin Sodium RS (µg/mg)

F = conversion factor, 0.001 mg/µg

Acceptance criteria: 90.0%-120.0%

3 PERFORMANCE TESTS

3.1 DISSOLUTION (711)

Medium: 0.05 M pH 6.8 potassium phosphate buffer; 900 mL

Apparatus 1: 100 rpm

Time: 30 min

Buffer, Mobile phase, Chromatographic system, and System suitability: Proceed as directed in the Assay.

Standard solution: USP Cloxacillin Sodium RS in Medium

Sample solution: Sample per the chapter.

Tolerances: NLT 80% (Q) of the labeled amount of cloxacillin (C19H18CINOS) is dissolved.

3.2 UNIFORMITY OF DOSAGE UNITS (905): Meet the requirements

4 SPECIFIC TESTS

4.1 WATER DETERMINATION (921), Method /: NMT 5.0%

5 ADDITIONAL REQUIREMENTS

5.1 PACKAGING AND STORAGE: Preserve in tight containers.

5.2 USP REFERENCE STANDARDS (11)

USP Cloxacillin Sodium RS