(dex'' a meth' a sone as' e tate).
Pregna-1,4-diene-3,20-dione, 21-(acetyloxy)-9-fluoro-11,17-dihydroxy-16-methyl-, (11,16)-monohydrate.
9-Fluoro-11,17,21-trihydroxy-16-methylpregna-1,4-diene-3,20-dione 21-acetate monohydrate [55812-90-3].
Anhydrous 434.51 [1177-87-3].
» Dexamethasone Acetate contains one molecule of water of hydration or is anhydrous. It contains not less than 97.0 percent and not more than 102.0 percent of C24H31FO6, calculated on the dried basis.
Packaging and storage Preserve in well-closed containers. Store at 25, excursions permitted between 15 and 30.
Labeling Label it to indicate whether it is hydrous or anhydrous.
USP Reference standards 11
B: Ultraviolet Absorption 197U
Solution: 15 µg per mL.
Absorptivities at 239 nm, calculated on the dried basis, do not differ by more than 3.0%.
Specific rotation 781S: between +82 and +88.
Test solution: 10 mg per mL, in dioxane.
Loss on drying 731 Dry it in vacuum at 105 for 3 hours: the hydrous form loses between 3.5% and 4.5%, and the anhydrous form not more than 0.4%, of its weight.
Residue on ignition 281: not more than 0.1%.
Heavy metals, Method II 231: not more than 0.002%.
Format buffer Dissolve 1.32 g of ammonium formate in 1 L of water, adjust with formic acid to a pH of 3.6, and mix.
Mobile phase Prepare a filtered and degassed mixture of Formate buffer and acetonitrile (3:2). Make adjustments if necessary (see System Suitability under Chromatography 621).
Test solution Transfer about 200 mg of Dexamethasone Acetate, accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with acetonitrile to volume, and mix. Transfer about 40 mL of this solution to a 100-mL volumetric flask, dilute with Formate buffer to volume, and mix.
Chromatographic system (see Chromatography 621) The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 25-cm column that contains packing L11. The flow rate is about 1 mL per minute. Chromatograph the Test solution, and record the peak responses as directed for Procedure: the column efficiency is not less than 5400 theoretical plates.
Procedure Inject a volume (about 10 µL) of the Test solution into the chromatograph, record the chromatogram, and measure the peak responses. Calculate the percentage of each impurity in the portion of Dexamethasone Acetate taken by the formula:
100(ri / rS)in which ri is the peak response for each impurity; and rS is the sum of the responses of all the peaks: not more than 1.0% of any individual impurity is found; and not more than 2.0% of total impurities is found.
Mobile phase Prepare a filtered and degassed mixture of water and acetonitrile (550:450). Make adjustments if necessary (see System Suitability under Chromatography 621).
pH 6.0 Buffer solution Transfer 3 mL of 1 N sodium hydroxide, 138 mL of 0.5 N potassium chloride, and 50 mL of 0.5 M monobasic potassium phosphate to a 1-L volumetric flask, dilute with water to volume, and mix.
Diluent Prepare a mixture of acetonitrile and pH 6.0 Buffer solution (1:1).
Standard preparation Transfer about 25 mg of USP Dexamethasone Acetate RS, accurately weighed, to a 250-mL volumetric flask. Add 100 mL of Diluent, and sonicate until a clear solution is obtained. Dilute with Diluent to volume, and mix.
Assay preparation Transfer about 25 mg of Dexamethasone Acetate, accurately weighed, to a 250-mL volumetric flask. Add 100 mL of Diluent, and sonicate until a clear solution is obtained. Dilute with Diluent to volume, and mix.
Chromatographic system (see Chromatography 621) The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm × 30-cm column containing 10-µm packing L1. The flow rate is about 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the capacity factor, k¢, is not less than 2.0; the column efficiency is not less than 1500 theoretical plates; the tailing factor is not more than 2.0; and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure Separately inject equal volumes (about 20 µL) of the Standard preparation (before and after injections of the Assay 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 C24H31FO6 in the portion of Dexamethasone Acetate taken by the formula:
250C(rU / rS)in which C is the concentration, in mg per mL, of USP Dexamethasone Acetate RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.
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USP35NF30 Page 2841Pharmacopeial Forum: Volume No. 29(5) Page 1457