Proguanil Hydrochloride

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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C₁₁H₁₆ClN₅ .HCl 290.19 

Biguanide, 1-(4-chlorophenyl)-5-isopropyl, hydrochloride; 

1-(p-Chlorophenyl)-5-isopropylbiguanide hydrochloride CAS RN®: 637-32-1; UNII: R71Y86M0WT. 

1 DEFINITION 

Proguanil Hydrochloride contains NLT 98.5% and NMT 101.0% of proguanil hydrochloride (C₁₁H₁₆ClN₅. HCl), calculated on the dried basis. 

2 IDENTIFICATION

Change to read: 

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

B. Identification Tests—General, Chloride〈191〉: Meets the requirements 

3 ASSAY 

Procedure 

Solution A: 0.65 g/L of 1-pentanesulfonic acid sodium salt and 7.0 g/L of sodium perchlorate in water. Adjust with 1% trifluoroacetic acid to a pH of 3.0. 

Solution B: 0.65 g/L of 1-pentanesulfonic acid sodium salt and 7.0 g/L of sodium perchlorate in a mixture of methanol, acetonitrile, and water (400:400:200). Add 4 mL of 1% trifluoroacetic acid to 1 L of this solution. 

Mobile phase: See Table 1. 

Table 1 

Diluent: Acetonitrile, methanol, and water (200:200:600) 

Standard solution: 0.2 mg/mL of USP Proguanil Hydrochloride RS in Diluent 

Sample solution: 0.2 mg/mL of Proguanil Hydrochloride in Diluent 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 235 nm 

Column: 4.6-mm × 7.5-cm; 3.5-µm packing L7 

Column temperature: 40° 

Flow rate: 1.5 mL/min 

System suitability 

Sample: Standard solution 

Suitability requirements 

Tailing factor: NMT 2.0 

Relative standard deviation: NMT 0.73% 

Analysis 

Samples: Standard solution and Sample solution 

Calculate the percentage of proguanil hydrochloride (C₁₁H₁₆ClN₅.HCl) in the portion of Proguanil Hydrochloride taken:

Result = (r_U/r_S) × (C_S/C_U) × 100 

r_U = peak response of proguanil from the Sample solution 

r_S = peak response of proguanil from the Standard solution 

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

C_U = concentration of Proguanil Hydrochloride in the Sample solution (mg/mL) 

Acceptance criteria: 98.5%–101.0% on the dried basis 

4 IMPURITIES 

Residue on Ignition 〈281〉: NMT 0.1% 

Limit of Chloroaniline 

Solution A: 3.45 g/L solution of sodium nitrite 

Solution B: 50 g/L solution of ammonium sulfamate 

Solution C: 1 mg/mL of naphthylethylenediamine dihydrochloride in water. Prepare immediately before use. Standard solution: 1.25 mg/L solution of chloroaniline 

Sample solution: Dissolve 100 mg in 1 mL of 2 N hydrochloric acid, and dilute with water to 20 mL. 

Analysis: Cool the Sample solution to 5°. Add 1 mL of Solution A, and allow to stand at 5° for 5 min. Add 2 mL of Solution B, and allow to stand for 10 min. Add 2 mL of Solution C, dilute with water to 50 mL, and allow to stand for 30 min. 

Acceptance criteria: Any red color produced is not more intense than that of a standard prepared at the same time and in the same manner, using 20 mL of Standard solution (250 ppm). 

Organic Impurities, Procedure 1 

[Note—On the basis of the synthetic route, perform either Procedure 1 or Procedure 2. Procedure 2 is recommended when proguanil related compound A, proguanil related compound E, proguanil related compound F, and proguanil related compound G (see Table 3) may be present.] Mobile phase: Dissolve 3.78 g of sodium hexanesulfonate in a mixture of 1200 mL of methanol, 800 mL of water, and 10 mL of glacial acetic acid. 

Identification solution: 0.5 µg/mL of USP Proguanil Related Compound C RS in Mobile phase 

System suitability stock solution: 0.5 µg/mL of USP Proguanil Related Compound D RS in Mobile phase 

System suitability solution: Dilute 1 mL of the Standard stock solution with Mobile phase to 200 mL. To 1 mL of the resulting solution, add 1 mL of System suitability stock solution. 

Standard stock solution: 0.1 mg/mL of USP Proguanil Hydrochloride RS in Mobile phase 

Standard solution: 0.2 µg/mL of USP Proguanil Hydrochloride RS from the Standard stock solution in Mobile phase Sample solution: 0.1 mg/mL of Proguanil Hydrochloride in Mobile phase 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 230 and 254 nm 

Column: 4.6-mm × 12.5-cm; 5-µm packing L1, or 4.6-mm × 15-cm; 5-µm packing L1 

Flow rate: 1 mL/min 

Injection volume: 20 µL 

Run time: At least 5 times the retention time of the proguanil peak at both wavelengths 

System suitability 

Samples: System suitability solution and Standard solution 

Suitability requirements 

Resolution: NLT 5 between proguanil related compound D and proguanil, System suitability solution at 230 nm 

Relative standard deviation: NMT 10.0%, Standard solution at 230 nm 

Analysis 

Samples: Identification solution, System suitability stock solution, Standard solution, and Sample solution 

[Note—The relative retention times for proguanil related compound D, proguanil, and proguanil related compound C are about 0.46, 1.0, and 2.5, respectively.] 

Identify the components based on their relative retention times, and measure the responses for the major peaks. 

Calculate the percentage of proguanil related compound C and proguanil related compound D, as detected at 230 nm, in the portion of Proguanil Hydrochloride taken: 

Result = (r_U/r_S) × (C_S/C_U) × 100 

r_U = peak response of proguanil related compound C or proguanil related compound D from the Sample solution 

r_S = peak response of proguanil from the Standard solution 

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

C_U = concentration of Proguanil Hydrochloride in the Sample solution (mg/mL) 

Calculate the percentage of any other impurity, as detected at 230 nm, in the portion of Proguanil Hydrochloride taken: 

Result = (r_U/r_S) × (C_S/C_U) × 100 

r_U = peak response of each impurity at 230 nm from the Sample solution 

r_S = peak response of of proguanil at 230 nm from the Standard solution 

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

C_U = concentration of Proguanil Hydrochloride in the Sample solution (mg/mL) 

Calculate the percentage of any other impurity, as detected at 254 nm, in the portion of Proguanil Hydrochloride taken: 

Result = (r_U/r_S) × (C_S/C_U) × 100 

r_U = peak response of each impurity at 254 nm from the Sample solution 

r_S = peak response of of proguanil at 254 nm from the Standard solution 

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

C_U = concentration of Proguanil Hydrochloride in the Sample solution (mg/mL) 

Calculate the percentage of total impurities as the sum of the calculated percentage contents of known and unknown impurities, considering each peak at the wavelength at which the peak shows the higher value. 

Acceptance criteria: See Table 2. 

Table 2 

^a1,5-Diisopropylbiguanide or 1,5-Bis(1-methylethyl)biguanide.

^b 1,5-Bis(4-chlorophenyl)biguanide. 

^c Disregard any peak below 0.05%. 

Organic Impurities, Procedure 2 

Solution A, Solution B, Mobile phase, and Diluent: Proceed as directed in the Assay. 

Standard stock solution: 0.2 mg/mL each of USP Proguanil Related Compound A RS, USP Proguanil Related Compound C RS, USP Proguanil Related Compound D RS, USP Proguanil Related Compound E RS, USP Proguanil Related Compound F RS, and USP Proguanil Related Compound G RS in Diluent 

Standard solution: 0.2 µg/mL of USP Proguanil Hydrochloride RS and 0.2 µg/mL each of USP Proguanil Related Compound A RS, USP Proguanil Related Compound C RS, USP Proguanil Related Compound D RS, USP Proguanil Related Compound E RS, USP Proguanil Related Compound F RS, and USP Proguanil Related Compound G RS in Diluent from the Standard stock solution 

System suitability solution: 0.2 mg/mL of USP Proguanil Hydrochloride RS and 2 µg/mL each of USP Proguanil Related Compound A RS, USP Proguanil Related Compound C RS, USP Proguanil Related Compound D RS, USP Proguanil Related Compound E RS, USP Proguanil Related Compound F RS, and USP Proguanil Related Compound G RS in Diluent from the Standard stock solution 

Sample solution: 0.2 mg/mL of Proguanil Hydrochloride in Diluent 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 235 nm 

Column: 4.6-mm × 7.5-cm; 3.5-µm packing L7 

Column temperature: 40° 

Flow rate: 1.5 mL/min 

Injection volume: 20 µL 

System suitability 

Sample: System suitability solution 

Suitability requirements 

Resolution: NLT 2.0 between proguanil and proguanil related compound G 

Tailing factor: NMT 2.0 for proguanil 

Relative standard deviation: NMT 2.0% for the proguanil peak 

Analysis 

Samples: Standard solution and Sample solution 

Calculate the percentage of each proguanil related compound and any other impurity in the portion of Proguanil Hydrochloride taken: 

Result = (r_U/r_S) × (C_S/C_U) × 100 

r_U = peak response of the proguanil related compound or any other impurity from the Sample solution

r_S = peak response of the corresponding proguanil related compound or proguanil (for calculating any other impurity) from the Standard solution 

C_S = concentration of the corresponding proguanil related compound or proguanil hydrochloride (for calculating any other impurity) in the Standard solution (mg/mL) 

C_U = concentration of Proguanil Hydrochloride in the Sample solution (mg/mL) 

Acceptance criteria: See Table 3. 

Table 3 

^a 1-Cyano-3-isopropylguanidine.

^b 1,5-Diisopropylbiguanide or 1,5-Bis(1-methylethyl) biguanide. 

^c 1-(4-Chlorophenyl)-3-cyanoguanidine. 

^d 1-(3-Chlorophenyl)-5-isopropylbiguanide. 

^e 1-(3,4-Dichlorophenyl)-5-isopropylbiguanide. 

^f 1,5-Bis(4-chlorophenyl)biguanide. 

5 SPECIFIC TESTS 

Acidity or Alkalinity 

Sample: 400 mg 

Analysis: Add 0.4 mL of methyl red–methylene blue TS to 35 mL of water maintained at 60°–65°. Neutralize with either 0.01 N sodium hydroxide or 0.01 N hydrochloric acid to a gray color. Add the Sample, and stir until completely dissolved. 

Acceptance criteria: The solution is gray or green. NMT 0.2 mL of 0.01 N hydrochloric acid is required to change the color of the solution to reddish-violet. 

Loss on Drying 〈731〉 

Analysis: Dry a sample at 105° for 2 h. 

Acceptance criteria: NMT 0.5% 

6 ADDITIONAL REQUIREMENTS 

Packaging and Storage: Preserve in well-closed, light-resistant containers, and store at room temperature. 

Labeling: If a test for Organic Impurities other than Procedure 1 is used, then the labeling states with which Organic Impurities test the article complies. 

USP Reference Standards 〈11〉 

USP Proguanil Hydrochloride RS 

USP Proguanil Related Compound A RS 

1-Cyano-3-isopropylguanidine. 

C₅H₁₀N₄ 126.16 

USP Proguanil Related Compound C RS 

1,5-Bis(4-chlorophenyl)biguanide. 

C₁₄H₁₃Cl₂N₅ 322.19 

USP Proguanil Related Compound D RS 

1,5-Bis(1-methylethyl)biguanide or 

1,5-Diisopropylbiguanide. 

C₈H₁₉N₅ 185.27 

USP Proguanil Related Compound E RS 

1-(4-Chlorophenyl)-3-cyanoguanidine. 

C₈H₇ClN₄ 194.62 

USP Proguanil Related Compound F RS 

1-(3,4-Dichlorophenyl)-5-isopropylbiguanide. 

C₁₁H₁₅Cl₂N₅ 288.18 

USP Proguanil Related Compound G RS 

1-(3-Chlorophenyl)-5-isopropylbiguanide. 

C₁₁H₁₆ClN₅ 253.73