Flucytosine Oral Suspension
» Flucytosine Oral Suspension contains not less than 90.0 percent and not more than 110.0 percent of the labeled amount of flucytosine (C4H4FN3O). Prepare Flucytosine Oral Suspension 10 mg per mL as follows (see Pharmaceutical Compounding—Nonsterile Preparations 795):
Flucytosine 1.0 g
Vehicle: a mixture of Vehicle for Oral Solution (regular or sugar-free), NF, and Vehicle for Oral Suspension, NF (1:1),  
a sufficient quantity to make 100 mL
If using Flucytosine Capsules, empty the contents of the capsules providing the appropriate amount of drug into a suitable mortar, or add Flucytosine powder to the mortar. Add about 10 mL of the Vehicle, and mix to a uniform paste. Add the Vehicle in small portions almost to volume, and mix thoroughly after each addition. Transfer the contents of the mortar, stepwise and quantitatively, to a calibrated bottle. Add enough Vehicle to bring to final volume, and mix well.
Packaging and storage— Preserve in tight, light-resistant containers. Store in a cold place.
Labeling— Label it to state that it is to be well shaken, and to state the beyond-use date.
USP Reference standards 11—
USP Flucytosine RS Click to View Structure
pH 791: between 4.0 and 5.0.
Beyond-use date: 60 days after the day on which it was compounded.
Assay—
Buffer— Dissolve 1g of ammonium acetate and 1 mL of diisopropylamine in 1 L of water, and adjust with glacial acetic acid to a pH of 7.5.
Mobile phase— Prepare a filtered and degassed solution of methanol and Buffer (1:1). Make adjustments if necessary (see System Suitability under Chromatography 621).
Standard preparation— Dissolve an accurately weighed quantity of USP Flucytosine RS in Mobile phase, and dilute quantitatively with Mobile phase to obtain a solution having a known concentration of about 50 µg per mL.
Assay preparation— Agitate the container of Oral Suspension for 30 minutes on a rotating mixer, remove a 5-mL sample, and store in a clear glass vial at –70 until analyzed. At the time of analysis, remove the sample from the freezer, allow it to reach room temperature, and mix with a vortex mixer for 30 seconds. Pipet 0.5 mL of the sample into a 100-mL volumetric flask, and dilute with Mobile phase to volume.
Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 280-nm detector and a 4.6- × 200-mm analytical column that contains 5-µm packing L3. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the retention time is about 3 minutes, and the relative standard deviation for replicate injections is not more than 1.0%.
Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of flucytosine (C4H4FN3O) in the volume of Oral Suspension taken by the formula:
200(C/V)(rU / rS)
in which C is the concentration, in µg per mL, of USP Flucytosine RS in the Standard preparation; V is the volume, in mL, of Oral Suspension taken; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Jeanne H. Sun
Assistant Scientific Liaison
1-301-816-3361		 (CMP2010) Compounding
Reference Standards RS Technical Services
1-301-816-8129
rstech@usp.org
USP35–NF30 Page 3211
Pharmacopeial Forum: Volume No. 32(1) Page 92