Mercaptopurine Tablets

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

Mercaptopurine Tablets contain NLT 93.0% and NMT 110.0% of the labeled amount of mercaptopurine (C₅H₄N₄S · H₂O).

2 IDENTIFICATION

A. The UV absorption spectrum exhibits a maximum at 325 ± 2 nm, and the ratio A /A does not exceed 0.09.

Sample: 5 μg/mL of mercaptopurine in a mixture of methanol and water (1:1), from the Sample solution in the Assay

B. 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

Solution A: 0.77 g/L of ammonium acetate in water

Solution B: Methanol and Solution A (5:95)

Solution C: Methanol and Solution A (30:70)

Mobile phase: Solution B and Solution C (80:20)

Diluent: Methanol and water (1:1)

Standard solution: 0.25 mg/mL of USP Mercaptopurine RS in a mixture of methanol and water (1:1). Transfer USP Mercaptopurine RS into a suitable volumetric flask, and add methanol equivalent to 50% of the final volume. Shake mechanically to dissolve, and dilute with water to volume.

Sample stock solution: 0.5 mg/mL of mercaptopurine in Diluent from NLT 5 Tablets. Place the Tablets into a suitable volumetric flask, add methanol equivalent to 50% of the final volume, and shake mechanically for a minimum of 30 min. Dilute with water to volume. Pass through a PVDF filter of 0.45-μm pore size, and discard the first 3 mL of filtrate.

Sample solution: 0.25 mg/mL of mercaptopurine in Diluent from the Sample stock solution

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 260 nm

Column: 4.6-mm × 10-cm; 3-μm packing L1

Column temperature: 30°

Flow rate: 1.0 mL/min

Injection size: 10 μL

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 2.0

Relative standard deviation: NMT 2.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of mercaptopurine (C₅H₄N₄S · H₂O) in the portion of Tablets taken:

Result = (r_U/r_S) × (C_S/C_U) × (M_r1/Mr2) × 100

r_U = peak response from the Sample solution

r_S = peak response from the Standard solution

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

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

M_r1 = molecular weight of mercaptopurine, 170.19

M_r2 = molecular weight of anhydrous mercaptopurine, 152.18

Acceptance criteria: 93.0%–110.0%

4 PERFORMANCE TESTS

Dissolution 〈711〉

Test 1

Medium: 0.1 N hydrochloric acid; 900 mL

Apparatus 2: 50 rpm

Time: 60 min

Mobile phase: 0.1% acetic acid in water

Standard solution: USP Mercaptopurine RS in Medium

Sample solution: Pass a portion of the solution under test through a suitable filter. Dilute with Medium to a concentration that is similar to the Standard solution, if necessary.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 230 nm

Column: 3.9-mm × 15-cm; packing L1

Flow rate: 2.5 mL/min

Injection size: 10 μL

System suitability

Sample: Standard solution

[Note—The retention time for mercaptopurine is NLT 4 min.]

Suitability requirements

Relative standard deviation: NMT 2.0%

Analysis

Samples: Standard solution and Sample solution

Tolerances: NLT 80% (Q) of the labeled amount of C₅H₄N₄S · H₂O is dissolved.

Test 2: If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 2.

Medium, Apparatus 2, Chromatographic system, and Analysis: Proceed as directed for Test 1.

Time: 120 min

Tolerances NLT 80% (Q) of the labeled amount of C₅H₄N₄S · H₂O is dissolved.

Uniformity of Dosage Units 〈905〉: Meets the requirements

5 IMPURITIES

Organic Impurities

Procedure

Solution A: 0.1% (v/v) formic acid in water

Solution B: Methanol and Solution A (2:98)

Solution C: Methanol and Solution A (1:1)

Mobile phase: See Table 1.

Table 1

Standard stock solution: 0.06 mg/mL of USP Mercaptopurine RS in Solution A. [Note—Use methanol equivalent to 2.5% of the final volume to help dissolve.]

Standard solution: 1.2 μg/mL of USP Mercaptopurine RS in Solution B from the Standard stock solution

Sensitivity solution: 0.06 μg/mL of USP Mercaptopurine RS in Solution B from the Standard solution

Sample stock solution: 0.5 mg/mL of mercaptopurine in a mixture of methanol and Solution A (1:9) from NLT 5 Tablets. Place the Tablets into a suitable volumetric flask, add methanol equivalent to 10% of the final volume, and shake mechanically for a minimum of 30 min.

Dilute with Solution A to volume. Pass through a PVDF filter of 0.45-μm pore size, and discard the first 3 mL of filtrate.

Sample solution: 0.12 mg/mL of mercaptopurine in Solution A. Transfer 6.0 mL of the Sample stock solution into a 25-mL volumetric flask, and dilute with Solution A to volume. Pass through a PVDF filter of 0.45-μm pore size, and discard the first 5 mL of filtrate. [Note—Inject the Sample solution within 1 h of preparation.]

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 260 nm

Column: 4.6-mm × 10-cm; 3-μm packing L1

Temperature

Column: 30°

Sample: 4°

Flow rate: 1.0 mL/min

Injection size: 50 μL

System suitability

Samples: Standard solution and Sensitivity solution

Suitability requirements

Tailing factor: NMT 2.0, Standard solution

Signal-to-noise ratio: NLT 10, Sensitivity solution

Relative standard deviation: NMT 2.0%, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of each impurity in the portion of Tablets 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 mercaptopurine from the Standard solution

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

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

F = relative response factor for each individual impurity (see Table 2)

Acceptance criteria

Individual impurities: See Table 2. [Note—Disregard any impurity peak less than 0.05%.]

Table 2

^a Hypoxanthine.

^b 1,2-Di(9H-purin-6-yl)disulfane.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

Labeling: When more than one Dissolution test is given, the labeling states the Dissolution test used only if Test 1 is not used.

USP Reference Standards 〈11〉

USP Mercaptopurine RS