Azathioprine Oral Suspension
Azathioprine Oral Suspension contains NLT 90.0% and NMT 110.0% of the labeled amount of azathioprine (C9H7N7O2S).
Prepare Azathioprine Oral Suspension of 50 mg/mL as follows (see Pharmaceutical Compounding—Nonsterile Preparations 795).
Azathioprine 5 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 tablets, comminute them to a fine powder in a suitable mortar, or add Azathioprine 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 sufficient Vehicle to bring to final volume, and mix well.
[Caution—Avoid skin contact or inhalation of azathioprine by using protective gloves and a fume hood or surgical mask. ]
•  Procedure
Mobile phase:  Dissolve 1.1 g of sodium-1-heptanesulfonate in 700 mL of water, and add 300 mL of methanol. Adjust with 1 N hydrochloric acid to a pH of 3.5.
Standard solution:  25 mg of USP Azathioprine RS, in a 50-mL volumetric flask. Add 15 mL of methanol and 0.5 mL of ammonium hydroxide to the flask, swirl, and sonicate for 2 min. Dilute with methanol to volume. Transfer 10 mL of this solution to a 50-mL volumetric flask, and dilute with water to volume.
Sample solution:  Agitate the container of Oral Suspension for 30 min 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 s. Pipet 1.0 mL of the Sample into a 100-mL volumetric flask, and dilute with Mobile phase to volume.
Chromatographic system 
Mode:  LC
Detector:  UV 254 nm
Column:  4.6-mm × 25-cm; 5-µm packing L1
Flow rate:  2 mL/min
Injection size:  20 µL
System suitability 
Sample:  Standard solution
[Note—The retention time for the azathioprine peak is about 4 min. ]
Suitability requirements 
Relative standard deviation:  NMT 1.3% for replicate injections
Samples:  Standard solution and Sample solution
Calculate the percentage of the labeled amount of azathioprine (C9H7N7O2S) 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 azathioprine in the Standard solution (µg/mL)
CU== nominal concentration of azathioprine in the Sample solution (µg/mL)
Acceptance criteria:  90.0%–110.0%
•  pH 791: 3.8–4.8
•  Packaging and Storage: Package in tight, light-resistant containers. Store at room temperature, or in a cold place.
•  Labeling: Label it to state that it is to be well shaken before use, and to state the Beyond-Use Date.
•  Beyond-Use Date: NMT 60 days after the day on which it was compounded
•  USP Reference Standards 11
USP Azathioprine RS Click to View Structure
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
(CMP2010) Compounding
Reference Standards RS Technical Services
USP35–NF30 Page 2277
Pharmacopeial Forum: Volume No. 32(1) Page 48