Isoniazid

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

DOWNLOAD PDF HERE

C₆H₇N₃O 137.14 

4-Pyridinecarboxylic acid, hydrazide; 

Isonicotinic acid hydrazide CAS RN®: 54-85-3; UNII: V83O1VOZ8L. 

1 DEFINITION 

Isoniazid contains NLT 98.0% and NMT 102.0% of isoniazid (C₆H₇N₃O), calculated on the dried basis

2 IDENTIFICATION 

Change to read: 

A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K

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

3 ASSAY 

Procedure 

Buffer: 13.6 g/L of monobasic potassium phosphate adjusted with 10 N sodium hydroxide to a pH of 6.9. Add 30 mg/L of triethanolamine. Mobile phase: Methanol and Buffer (5:95) 

Standard solution: 0.32 mg/mL of USP Isoniazid RS in Mobile phase 

Sample solution: 0.32 mg/mL of Isoniazid in Mobile phase 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 254 nm 

Column: 4.6-mm × 25-cm; 5-µm packing L1 

Flow rate: 1.5 mL/min 

Injection volume: 20 µL 

System suitability 

Sample: Standard solution 

Suitability requirements 

Tailing: NMT 2.0 for the isoniazid peak 

Relative standard deviation: NMT 0.73% 

Analysis 

Samples: Standard solution and Sample solution 

Calculate the percentage of isoniazid (C₆H₇N₃O) in the portion of Isoniazid taken: 

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

r_U = peak response of isoniazid from the Sample solution 

r_S = peak response of isoniazid from the Standard solution 

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

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

Acceptance criteria: 98.0%–102.0% on the dried basis 

4 IMPURITIES 

Residue on Ignition 〈281〉: NMT 0.2%

Organic Impurities 

Buffer and Mobile phase: Proceed as directed in the Assay. 

System suitability solution: 1.0 µg/mL each of USP Isoniazid RS, isoniacin, isonicotinamide, picolinohydrazide, and isonicotinonitrile in Mobile phase 

Standard solution: 1.0 µg/mL of USP Isoniazid RS in Mobile phase 

Sample solution: 1.0 mg/mL of Isoniazid in Mobile phase 

Chromatographic system: Proceed as directed in the Assay, except for the following. 

Detector: UV 266 nm 

System suitability 

Samples: System suitability solution and Standard solution 

Suitability requirements 

Resolution: NLT 2.0 between any adjacent peak pair, System suitability solution 

Relative standard deviation: NMT 5.0%, Standard solution 

Analysis 

Samples: Standard solution and Sample solution 

Calculate the percentage of each impurity in the portion of Isoniazid taken: 

Result = (r_U/r_S) × (C_S /C_U) × (1/F) × 100 

r_U = peak response of each impurity from the Sample solution 

r_S = peak response of isoniazid from the Standard solution 

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

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

F = relative response factor (see Table 1) 

Acceptance criteria: See Table 1. Disregard any peak less than 0.05%. 

Table 1 

^aIsonicotinic acid. 

^b 2-Isoniazid. 

^c 4-Cyanopyridine. 

5 SPECIFIC TESTS 

pH 〈791〉 

Sample solution: In a solution (1 in 10) 

Acceptance criteria: 6.0–7.5 

Loss on Drying 〈731〉 

Analysis: Dry at 105° for 4 h. 

Acceptance criteria: NMT 1.0% 

6 ADDITIONAL REQUIREMENTS 

Packaging and Storage: Preserve in tight, light-resistant containers. Store at 25°, excursions permitted between 15° and 30°.