Rifabutin Compounded Oral Suspension

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

1 DEFINITION

Rifabutin Compounded Oral Suspension contains NLT 90.0% and NMT 110.0% of the labeled amount of rifabutin (C₄₆H₆₂N₄O₁₁).

Prepare Rifabutin Compounded Oral Suspension 20 mg/mL as follows (see Pharmaceutical Compounding—Nonsterile Preparations 〈795〉).

ᵃ Mycobutin 150-mg capsules, Pfizer Inc., New York, NY.

ᵇ Paddock Laboratories, Minneapolis, MN.

Calculate the required quantity of each ingredient for the total amount to be prepared. Empty the required number of Rifabutin capsules in a suitable mortar, and comminute to a fine powder. Add the Vehicle in small portions, and triturate to make a smooth paste. Add increasing volumes of the Vehicle to make a rifabutin liquid that is pourable. Transfer the contents of the mortar, stepwise and quantitatively, to a calibrated bottle. Add enough of the Vehicle to bring to final volume, and mix well.

2 ASSAY

Procedure

Solution A: 100 mM monobasic potassium phosphate buffer, adjusted with 2 N sodium hydroxide to a pH of 6.5

Mobile phase: Acetonitrile and Solution A (50:50). Filter and degas.

Standard stock solution: 2.0 mg/mL of USP Rifabutin RS in Mobile phase

Standard solution: Transfer 10 mL of Standard stock solution to a 100-mL volumetric flask. Immediately rinse the volumetric apparatus with 10 mL of acetonitrile and 10 mL of Mobile phase. Dilute with Mobile phase to volume to obtain a solution with a nominal concentration of 0.2 mg/mL of rifabutin. Pass through a filter of 0.45-µm pore size.

Sample solution: Shake thoroughly by hand each bottle of Oral Suspension. Pipet 1.0 mL of Oral Suspension into a 100-mL volumetric flask. Immediately rinse the pipette with 10 mL of acetonitrile and 10 mL of Mobile phase. Dilute with Mobile phase to volume to obtain a solution with a nominal concentration of 0.2 mg/mL of rifabutin. Pass through a filter of 0.45-µm pore size.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 254 nm

Column: 4.6-mm × 15-cm; 5-µm packing L7

Flow rate: 1.0 mL/min

Injection volume: 10 µL

System suitability

Sample: Standard solution

[Note—The retention time for the rifabutin is about 14.0 min.]

Suitability requirements:

Column efficiency: NLT 4500 theoretical plates

Tailing factor: NMT 3.0

Relative standard deviation: NMT 2.0% for replicate injections

Analysis

Samples: Standard solution and Sample solution

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

Result = (rᵤ / rₛ) × (Cₛ / Cᵤ) × 100

rᵤ = peak response from the Sample solution

rₛ = peak response 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%

3 SPECIFIC TESTS

pH 〈791〉: 4.5–5.5

4 ADDITIONAL REQUIREMENTS

Packaging and Storage: Package in tight, light-resistant containers. Store in a refrigerator or at controlled room temperature.

Beyond-Use Date: NMT 84 days after the date on which it was compounded, when stored in a refrigerator or at controlled room temperature

Labeling: Label it to indicate that it is to be well shaken before use, and to state the Beyond-Use Date.

USP Reference Standards 〈11〉

USP Rifabutin RS