Rifabutin 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

Rifabutin Capsules contain NLT 90.0% and NMT 110.0% of the labeled amount of rifabutin (C₄₆H₆₂N₄O₁₁).

2 IDENTIFICATION

A. Spectroscopic Identification Tests 〈197〉, Ultraviolet-Visible Spectroscopy: 197U

Standard solution: 20 µg/mL of USP Rifabutin RS in methanol, prepared with the aid of sonication. Pass through a filter of 0.5-µm or finer pore size.

Sample solution: Nominally 20 µg/mL of rifabutin prepared as follows. Suspend a quantity of Capsule contents, equivalent to 200 mg of rifabutin, in 20 mL of methanol. Sonicate for 5 min, and pass through a suitable filter of 0.5-µm or finer pore size. Dilute a portion of the filtrate with methanol to obtain a solution containing 20 µg/mL of rifabutin.

Acceptance criteria: Meet the requirements

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

Change to read:

Procedure

Solution A: 13.6 g/L of monobasic potassium phosphate

Mobile phase: Acetonitrile and Solution A (50:50). Adjust with 2 N sodium hydroxide to a pH of 6.5 ± 0.1. Pass through a suitable filter of 0.5-µm or finer pore size.

System suitability solution:

Dissolve 10 mg of Rifabutin in 2 mL of methanol, add 1 mL of 2 N sodium hydroxide, and allow to stand for 4 min.

Add 1 mL of 2 N hydrochloric acid, and dilute with Mobile phase to 50 mL.

[Note—Portions of this solution may be stored in the frozen state for future use.]

Standard solution:

0.5 mg/mL of USP Rifabutin RS prepared as follows. Transfer an amount of USP Rifabutin RS to a suitable volumetric flask.

Add acetonitrile to fill 10% of the volume of the flask, and dilute with Mobile phase to volume.

Sample solution:

Nominally 0.5 mg/mL of rifabutin prepared as follows.

Remove the contents of NLT 20 Capsules, weigh, and determine the average weight of the Capsule contents.

Transfer a portion of the powder, equivalent to 25 mg of rifabutin, to a 50-mL volumetric flask.

Add 5 mL of acetonitrile, and dilute with Mobile phase to volume.

Pass through a suitable filter of 0.5-µm or finer pore size.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 254 nm

Column: 4.6-mm × 12.5-cm; 5-µm packing L7

Flow rate: 1 mL/min

Injection volume: 10 µL

Run time: NLT 2 times the retention time of the rifabutin peak

System suitability

Samples: System suitability solution and Standard solution

[Note—The chromatogram of the System suitability solution exhibits a major peak for a degradant, two minor peaks for degradants, and a major peak for rifabutin at relative retention times of about 0.5, 0.6, 0.8, and 1.0, respectively.]

Suitability requirements:

Resolution: NLT 1.3 between the rifabutin peak and the degradant peak eluting at a relative retention time of about 0.8, System suitability solution

Relative standard deviation: NMT 2.0%, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of rifabutin (C₄₆H₆₂N₄O₁₁) in the portion of Capsules taken:

Result = (rᵤ / rₛ) × (Cₛ / Cᵤ) × 100

rᵤ = peak response of rifabutin from the Sample solution

rₛ = peak response of rifabutin from the Standard solution

Cₛ = concentration of USP Rifabutin RS in the Standard solution (mg/mL)

Cᵤ = nominal concentration of rifabutin in the Sample solution (mg/mL)

Acceptance criteria: 90.0%–110.0%

4 PERFORMANCE TESTS

Dissolution

Medium: 0.01 N hydrochloric acid; 900 mL

Apparatus 1: 100 rpm

Time: 45 min

Standard solution: A known concentration of USP Rifabutin RS in Medium

Sample solution: A filtered portion of the solution under test, suitably diluted with Medium to a concentration similar to that of the Standard solution, taking into account its designated potency.

Instrumental conditions

Mode: UV

Analytical wavelength: 280 nm

Analysis

Samples: Standard solution and Sample solution

Determine the percentage of the labeled amount of rifabutin (C₄₆H₆₂N₄O₁₁) dissolved:

(Aᵤ / Aₛ) × Cₛ × D × (V / L) × 100

Aᵤ = absorbance of the Sample solution

Aₛ = absorbance of the Standard solution

Cₛ = concentration of the Standard solution (mg/mL)

D = dilution factor of the Sample solution, if needed

V = volume of Medium, 900 mL

L = label claim (mg/Capsule)

Tolerances: NLT 75% (Q) of the labeled amount of rifabutin (C₄₆H₆₂N₄O₁₁) is dissolved.

5 IMPURITIES

Change to read:

Organic Impurities

Solution A: 13.6 g/L of monobasic potassium phosphate in water

Solution B: Acetonitrile and Solution A (40:60). Adjust with 2 N sodium hydroxide to a pH of 6.5.

Solution C: Acetonitrile and Solution A (70:30). Adjust with 2 N sodium hydroxide to a pH of 6.5.

Mobile phase: See Table 1.

Table 1

Diluent: Acetonitrile and Solution A (50:50). Adjust with 2 N sodium hydroxide to a pH of 6.5.

System suitability solution: Prepare as directed in the Assay.

Standard stock solution:

0.75 mg/mL of USP Rifabutin RS prepared as follows.

Transfer an amount of USP Rifabutin RS to a suitable volumetric flask and dissolve it by adding acetonitrile to fill 20% of the final volume. Sonicate, if necessary. Dilute with Diluent to volume.

Standard solution:

0.0075 mg/mL of USP Rifabutin RS in Diluent from the Standard stock solution

Sensitivity solution:

0.75 µg/mL of USP Rifabutin RS in Diluent from the Standard solution

Sample solution:

Nominally 0.75 mg/mL of rifabutin prepared as follows.

Remove the contents of NLT 20 Capsules as completely as possible, weigh, and determine the average weight of the Capsule contents.

Transfer a portion of the crushed powder, equivalent to 75 mg of rifabutin, to a 100-mL volumetric flask and add 20 mL of acetonitrile.

Sonicate for 5 min. Add 50 mL of Diluent and sonicate for 5 more min. Dilute with Diluent to volume.

[Note—The Sample solution is stable up to 25 h at 10°.]

Chromatographic system

Mode: LC

Detector: UV 254 nm

Column: 4.6-mm × 15-cm; 3.5-µm packing L1

Temperatures:

Autosampler: 10°

Column: 40°

Flow rate: 1 mL/min

Injection volume: 20 µL

System suitability

Samples: System suitability solution, Standard solution, Sensitivity solution

Suitability requirements:

Resolution: NLT 4.0 between the rifabutin 21R epimer and rifabutin peaks, System suitability solution

Relative standard deviation: NMT 5.0%, Standard solution

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

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of any individual impurity in the portion of Capsules taken:

Result = (rᵢ / rₛ) × (Cₛ / Cᵤ) × P × (F₁ / F₂) × 100

rᵢ = peak response of each individual impurity from the Sample solution

rₛ = peak response of rifabutin from the Standard solution

Cₛ = concentration of USP Rifabutin RS in the Standard solution (mg/mL)

Cᵤ = nominal concentration of rifabutin in the Sample solution (mg/mL)

P = potency of USP Rifabutin RS (µg/mg)

F₁ = conversion factor (0.001 mg/µg)

F₂ = relative response factor (see Table 2)

Acceptance criteria: See Table 2. The reporting threshold is 0.1%.

Table 2

ᵃ (Long chemical name preserved exactly as in file)

ᵇ (Long chemical name preserved exactly as in file)

ᶜ (Long chemical name preserved exactly as in file)

ᵈ (Long chemical name preserved exactly as in file)

ᵉ This is a process impurity and is not included in total impurities.

ᶠ (Long chemical name preserved exactly as in file)

ᵍ (Long chemical name preserved exactly as in file)

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers, protected from light and from excessive heat. Store at controlled room temperature.

USP Reference Standards 〈11〉 USP Rifabutin RS