Acetazolamide Extended-Release 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

Acetazolamide Extended-Release Capsules contain NLT 90.0% and NMT 110.0% of the labeled amount of acetazolamide (C₄H₆N₄O₃S₂).

2 IDENTIFICATION

A. The UV spectrum of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained 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

3.1 Procedure

Buffer: 1.38 g/L of sodium phosphate monobasic, prepared as follows. Transfer a suitable quantity of sodium phosphate monobasic to an appropriate volumetric flask. Dissolve in 95% of the flask volume of water. Adjust with 2 M phosphoric acid to a pH of 3.0 and dilute with water to volume.

Mobile phase: Acetonitrile and Buffer (10:90)

Diluent: Methanol and Buffer (90:10)

Standard stock solution: 0.4 mg/mL of USP Acetazolamide RS in Diluent. Sonicate to dissolve.

Standard solution: 0.02 mg/mL of USP Acetazolamide RS in Mobile Phase, from the Standard stock solution

Sample stock solution: Nominally 0.4 mg/mL of acetazolamide, prepared as follows. Transfer a portion of the contents from NLT 10

Capsules to a suitable volumetric flask. Add about 60% of the flask volume of Diluent. Sonicate for NLT 30 min with intermittent shaking and maintain at room temperature. Dilute with Diluent to volume. Pass the solution through a suitable lter.

Sample solution: Nominally 0.02 mg/mL of acetazolamide in Mobile phase, from the Sample stock solution

3.2 Chromatographic system

Mode: LC

Detector: UV 265 nm. For Identi cation A, use a diode array detector in the range of 200–400 nm.

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

Column temperature: 40°

Flow rate: 1.5 mL/min

Injection volume: 25 μL

3.3 System suitability

Sample: Standard solution

3.4 Suitability requirements

Tailing factor: NMT 2.0

Relative standard deviation: NMT 1.0%

3.5 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of acetazolamide (C₄H₆N₄O₃S₂) in the portion of Capsules taken:

Result=(r_u/r_s)×(C_s/C_u)×100

r_u = peak response of acetazolamide from the Sample solution
r_s = peak response of acetazolamide from the Standard solution
C_s = concentration of USP Acetazolamide RS in the Standard solution (mg/mL)
Cu = nominal concentration of acetazolamide in the Sample solution (mg/mL)

Acceptance criteria: 90.0%–110.0%

4 PERFORMANCE TESTS

Change to read

Dissolution 〈711〉

4.1 Test 1

Medium: Acetate buffer, pH 4.5 with 2.2% polysorbate 20,prepared as follows. Dissolve 3.0 g of sodium acetate (RB 1-Jul-2024) in 900mL of water. Add 22 mL of polysorbate 20, and adjust with glacial acetic acid to a pH of 4.5. Dilute with water to 1000 mL; 900 mL.

Apparatus 2: 75 rpm

Times: 0.5, 2, 5, and 12 h

Standard stock solution: 0.28 mg/mL of USP Acetazolamide RS prepared as follows. Transfer USP Acetazolamide RS to a suitable volumetric flask. Add 10% of the flask volume of methanol, and sonicate to dissolve. Dilute with Medium to volume.

Standard solution: 0.017 mg/mL of USP Acetazolamide RS in Medium, from the Standard stock solution

Sample solution: Pass a portion of the solution under test through a suitable lter. Dilute the ltrate with Medium, if necessary. Replace the amount of solution withdrawn at each time point with the same volume of Medium.

Blank: Medium

4.1.1 Instrumental conditions

Mode: UV

Analytical wavelength: 265 nm

Cell: 1.0 cm

4.2 System suitability

Sample: Standard solution

4.2.1 Suitability requirements

Relative standard deviation: NMT 2.0%

4.2.2 Analysis

Samples: Standard solution and Sample solution

Calculate the concentration (C ) of acetazolamide (C₄H₆N₄O₃S₂) in the sample withdrawn from the vessel at each time point (i):

Result = (A_U/A_S) × C_S × D

A_U= absorbance of the Sample solution

A_S = absorbance of the Standard solution

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

D = dilution factor of the Sample solution, if necessary

Calculate the percentage of the labeled amount of acetazolamide (₄H₆N₄O₃S₂) dissolved at each time point (i):

Result₁ = C₁ × V × (1/L) × 100

Result₂ = [(C₂ × V) + (C₁× V_S )] × (1/L) × 100

Result₃ = {[(C₃ × V) + [(C₂ + C₁ ) × V_S ]} × (1/L) × 100

Result₄ = {(C₄ × V) + [(C₃ + C₂ + C₁ ) × V_S ]} × (1/L) × 100

C_i = concentration of acetazolamide in the portion of the sample withdrawn at time point i (mg/mL)

V = volume of Medium, 900 mL

L = label claim (mg/Capsule)

V_S = volume of the Sample solution withdrawn at each time point and replaced with Medium (mL)

Tolerances: See Table 1.

Table 1

The percentages of the labeled amount of acetazolamide (C₄H₆N₄O₃S₂) dissolved at the times specied conform to Dissolution 〈711〉, Acceptance Table 2.

4.3 Test 2

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

Medium: Acetate buffer, pH 4.5 with 2.2% polysorbate 20, prepared as follows. Weigh and transfer 2.99 g of sodium acetate into a 1000-mL volumetric flask. Add 14.0 mL of 2 N acetic acid and dilute with water to volume. The measured pH should be 4.5. Transfer the resulted solution to a suitable container and add about 22.0 mL of polysorbate 20. Shake vigorously and further sonicate for about 10–15 min; 900 mL.

Apparatus 2: 75 rpm

Times: 1, 2, and 7 h

Standard stock solution: 0.22 mg/mL of USP Acetazolamide RS prepared as follows. Transfer a suitable amount of USP Acetazolamide RS to a suitable volumetric flask. Add 5% of the flask volume of methanol, and sonicate to dissolve if necessary. Dilute with Medium to volume.

Standard solution: 0.022 mg/mL of USP Acetazolamide RS from the Standard stock solution in Medium. [Note—The Standard solution may be stable for 22 h at room temperature.]

Sample solution: At the speci ed time points, withdraw a suitable volume of the solution under test. Pass through a suitable lter of 0.45-μm pore size, discarding an appropriate volume of ltrate so that a consistent result can be obtained. Dilute 1.0 mL of the ltrate with Medium to 25 mL. Replace the amount of solution withdrawn at each time point with the same volume of Medium. [Note—The Sample solution may be stable for 22 h at room temperature.]

4.3.1 Instrumental conditions

Mode: UV

Analytical wavelength: 265 nm

Cell: 0.5 cm

Blank: Medium

4.3.2 Analysis

Samples: Standard solution and Sample solution

Calculate the concentration (C_i ) of acetazolamide (C₄H₆N₄O₃S₂) in the sample withdrawn from the vessel at each time point (i):

Result = (A_u/A_s ) × C_s × D

A_u = absorbance from the Sample solution

A_s = absorbance from the Standard solution

C_u = concentration of USP Acetazolamide RS in the Standard solution (mg/mL)

D = dilution factor of the Sample solution

Calculate the percentage of the labeled amount of acetazolamide (C₄H₆N₄O₃S₂) dissolved at each time point (i):

Result₁ = C₁ × V × (1/L) × 100

Result₂ = [(C₂ × V) + (C₁ × V_s )] × (1/L) × 100

Result₃ = {(C₃ × V) + [(C₂ + C₁ ) × V_s ]} × (1/L) × 100

C_i = concentration of acetazolamide in the portion of the sample withdrawn at time point i (mg/mL)

V = volume of Medium, 900 mL

L = label claim (mg/Capsule)

V_s = volume of the Sample solution withdrawn at each time point and replaced with Medium (mL)

Tolerances: See Table 2.

Table 2

The percentages of the labeled amount of acetazolamide (C₄H₆N₄O₃S₂) dissolved at the times specied conform to Dissolution 〈711〉, Acceptance Table 2.

4.4 Test 3

 If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 3.

Medium: Acetate buffer, pH 4.5 with 2.2% polysorbate 20, prepared as follows. Dissolve 3 g of sodium acetate in 1000 mL of water. Adjust with acetic acid to a pH of 4.5. Add 22 g of polysorbate 20 and stir to dissolve; 900 mL.

Apparatus 2: 75 rpm

Times: 1, 2, 5, and 12 h

Standard stock solution: 0.55 mg/mL of USP Acetazolamide RS in methanol. Sonicate to dissolve, if necessary.

Standard solution: 0.011 mg/mL of USP Acetazolamide RS from the Standard stock solution in Medium

Sample solution: At the specied time points, withdraw a suitable volume of the solution under test. Pass through a suitable lter of 0.45-μm pore size, discarding an appropriate volume of ltrate so that a consistent result can be obtained. Dilute 2.0 mL of the ltrate with Medium to 100 mL. Replace the amount of solution withdrawn at each time point with the same volume of Medium.

4.4.1 Instrumental conditions

Mode: UV

Analytical wavelength: 265 nm

Blank: Medium

4.4.2 Analysis

Samples: Standard solution and Sample solution

Calculate the concentration (C_i ) of acetazolamide (C₄H₆N₄O₃S₂) in the sample withdrawn from the vessel at each time point (i):

Result = (A_u /A_s ) × C_s × D

A_u = absorbance from the Sample solution

A_s = absorbance from the Standard solution

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

D = dilution factor of the Sample solution

Calculate the percentage of the labeled amount of acetazolamide (C₄H₆N₄O₃S₂) dissolved at each time point (i):

Result₁ = C₁ × V × (1/L) × 100

Result₂ = [(C₂ × V) + (C₁ × V_s )] × (1/L) × 100

Result₃ = {(C₃ × V) + [(C2 + C₁ ) × V_s ]} × (1/L) × 100

Result₄ = {(C₄ × V) + [(C₃ + C₂ + C₁ ) × V_s ]} × (1/L) × 100

C_i = concentration of acetazolamide in the portion of the sample withdrawn at time point i (mg/mL)

V = volume of Medium, 900 mL

L = label claim (mg/Capsule)

V_s = volume of the Sample solution withdrawn at each time point and replaced with Medium (mL)

Tolerances: See Table 3.

Table 3

The percentages of the labeled amount of acetazolamide (C₄H₆N₄O₃S₂) dissolved at the times specied conform to Dissolution 〈711〉,Acceptance Table 2.

4.5 Test 4

If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 4.

Medium: Acetate buffer, pH 4.5 with 2.2% (w/v) polysorbate 20 (Dissolve 2.99 g of sodium acetate in 800 mL of water. Adjust with glacial acetic acid to a pH of 4.5. Add 22 g of polysorbate 20 and dilute with water to 1000 mL.); 900 mL

Apparatus 2: 75 rpm with sinker2

Times: 1, 2, 5, and 12 h

Buffer: Dissolve 4.11 g of sodium acetate, anhydrous in 1000 mL of water. Adjust with glacial acetic acid to a pH of 4.0.

Mobile phase: Methanol and Buffer (25:75)

Standard solution: (L/900) mg/mL of USP Acetazolamide RS, where L is the label claim in mg/Caspule, prepared as follows. Transfer a quantity of USP Acetazolamide RS to an appropriate volumetric flask and dissolve in 5% of the flask volume of methanol. Sonicate to dissolve, if necessary. Allow to cool and add 60%–70% of the flask volume of Medium. Sonicate to dissolve, if necessary. Dilute with Medium to volume.

Sample solution: At the speci ed time points, withdraw a suitable volume of the solution under test. Pass through a suitable lter of 0.45-μm pore size, discarding an appropriate volume of ltrate so that a consistent result can be obtained. Replace the amount of solution withdrawn at each time point with the same volume of Medium.

4.5.1 Chromatographic system

Mode: LC

Detector: UV 265 nm

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

Flow rate: 1 mL/min

Injection volume: 5 μL

Run time: NLT 1.5 times the retention time of acetazolamide

4.6 System suitability

Sample: Standard solution

4.7 Suitability requirements

Tailing factor: NMT 2.0

Relative standard deviation: NMT 2.0%

4.7.1 Analysis

Samples: Standard solution and Sample solution

Calculate the concentration (C_i ) of acetazolamide C₄H₆N₄O₃S₂ in the sample withdrawn from the vessel at each time point (i):

Result = (r_u /r_s ) × C

r_u = peak response of acetazolamide from the Sample solution

r _s= peak response of acetazolamide from the Standard solution

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

Calculate the percentage of the labeled amount of acetazolamide (C₄H₆N₄O₃S₂) dissolved at each time point (i):

Result₁ = C₁ × V × (1/L) × 100

Result₂ = [(C₂ × V) + (C₁ × V_s )] × (1/L) × 100

Result₃ = {(C₃ × V) + [(C2 + C₁ ) × V_s ]} × (1/L) × 100

Result₄ = {(C₄ × V) + [(C₃ + C₂ + C₁ ) × V_s ]} × (1/L) × 100

C_i = concentration of acetazolamide in the portion of the sample withdrawn at time point i (mg/mL)

V = volume of Medium, 900 mL

L = label claim (mg/Capsule)

V_s = volume of the Sample solution withdrawn at each time point and replaced with Medium (mL)

The percentages of the labeled amount of acetazolamide (C₄H₆N₄O₃S₂) dissolved at the times specied conform to Dissolution 〈711〉,

Acceptance Table 2.

Tolerances: See Table 4.

Table 4

The percentages of the labeled amount of acetazolamide (C₄H₆N₄O₃S₂) dissolved at the times speci ed conform to Dissolution 〈711〉, Acceptance Table 2. (RB 1-Jul-2024)

Uniformity of Dosage Units 〈905〉: Meet the requirements

5 IMPURITIES

Change to read:

5.1 Organic Impurities

Buffer: 6.8 g/L of potassium phosphate, monobasic in water

Mobile phase: Acetonitrile and Buffer (8:92)

System suitability stock solution: 0.1 mg/mL each of USP Acetazolamide Related Compound D RS and USP Acetazolamide Related Compound E RS in methanol

System suitability solution: 0.002 mg/mL each of USP Acetazolamide Related Compound D RS and USP Acetazolamide Related Compound E RS in Mobile phase, from the System suitability stock solution

Sensitivity solution: 0.5 μg/mL of USP Acetazolamide RS in Mobile phase

Standard stock solution: 0.1 mg/mL each of USP Acetazolamide RS and USP Acetazolamide Related Compound D RS in methanol

Standard solution: 0.002 mg/mL each of USP Acetazolamide RS and USP Acetazolamide Related Compound D RS in Mobile phase, from the Standard stock solution

Sample solution: Nominally 1.0 mg/mL of acetazolamide, prepared as follows. Transfer a portion of the contents from NLT 10 Capsules to a suitable volumetric flask. Add 10% of the flask volume of methanol, and sonicate to disperse. Add about 70% of the flask volume of Mobile phase, and sonicate for NLT 30 min with intermittent shaking while using cold water to maintain the temperature of the ultrasonic bath between 20° and 25°. Dilute with Mobile phase to volume. Pass a portion of the solution through a suitable lter.

5.2 Chromatographic system

Mode: LC

Detector: UV 265 nm

Column: 4.6-mm × 25-cm; 5-μm packing L11

Column temperature: 30°

Flow rate: 1.2 mL/min

Injection volume: 10 μL

Run time: NLT 4 times the retention time of acetazolamide

5.3 System suitability

Samples: System suitability solution, Sensitivity solution, and Standard solution

[Note—The relative retention times in Table 5 (RB 1-Jul-2024) are provided as information that could aid in peak assignment.]

▲Table 5▲ (RB 1-Jul-2024)

^a 5-Amino-1,3,4,-thiadiazole-2-thiol.

^b N-(1,3,4-Thiadiazol-2-yl)acetamide.

^c N-(5-Mercapto-1,3,4-thiadiazol-2-yl)acetamide.

^d N-(5-Chloro-1,3,4-thiadiazol-2-yl)acetamide.

^e N,N′-{5,5′-[(Hydrosulfonylamino)sulfonyl]bis(1,3,4-thiadiazole-5,2-diyl)}diacetamide.

5.4 Suitability requirements

Resolution: NLT 2.0 between acetazolamide related compound D and acetazolamide related compound E, System suitability solution

Relative standard deviation: NMT 5.0% for acetazolamide and acetazolamide related compound D, Standard solution Signal-to-noise ratio: NLT 10, Sensitivity solution

5.5 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of acetazolamide related compound D in the portion of Capsules taken:

Result = (r_u /rs ) × (C_s /C_u ) × 100

r_u = peak area of acetazolamide related compound D from the Sample solution

r_s = peak area of acetazolamide related compound D from the Standard solution

C_s = concentration of USP Acetazolamide Related Compound D RS in the Standard solution (mg/mL)

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

Calculate the percentage of acetazolamide related compound E (free acid), acetamidothiadiazole, and any unspeci ed degradation

product in the portion of Capsules taken:

Result = (r_u /r_s ) × (C_s /C_u ) × (1/F) × 100

r_u = peak area of acetazolamide related compound E (free acid), acetamidothiadiazole, and any unspecied degradation product from the Sample solution

r_s = peak area of acetazolamide from the Standard solution

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

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

F = relative response factor (see able 6 (RB 1-Jul-2024) )

Acceptance criteria: See Table 6. (RB 1-Jul-2024) The reporting threshold is 0.05%.

Table 6 (RB 1-Jul-2024)

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers, and store at controlled room temperature.

Labeling: The labeling states the Dissolution test used only if Test 1 is not used.

USP Reference Standards 〈11〉

USP Acetazolamide RS

5-Amino-1,3,4,-thiadiazole-2-sulfonamide.

C₂H₄N₄O₂S₂ 180.20

Potassium 5-acetamido-1,3,4-thiadiazole-2-sulfonate.

C₄H₄KN₃O₄S₂ 261.31