Identification—
Transfer an amount of Cream, equivalent to about 2 mg of betamethasone, to a separator, add 20 mL of water and 2 mL of dilute hydrochloric acid (1 in 120), and mix. Extract with four 50-mL portions of chloroform, and combine the extracts. Filter through a cotton pledget, previously layered over with anhydrous sodium sulfate. Evaporate the filtrates on a steam bath under a stream of dry nitrogen to dryness. Dissolve the residue in alcohol to obtain a solution containing about 1 mg per mL. Proceed as directed in
Identification test
B under
Betamethasone Valerate, beginning with “Apply 10 µL of this solution.”
Assay—
Mobile phase
,
Internal standard solution,
Standard preparation, and
Chromatographic system—Proceed as directed in the
Assay under
Betamethasone Valerate.
Assay preparation—
Transfer an accurately weighed portion of Cream, equivalent to about 2.5 mg of betamethasone, to a 50-mL centrifuge tube. Add 10.0 mL of the
Internal standard solution and 5.0 mL of a 1 in 1000 solution of glacial acetic acid in methanol. Insert the stopper into the tube, and place in a water bath held at 60
until the specimen melts. Remove from the bath, and shake vigorously until the specimen resolidifies. Repeat the heating and shaking two more times. Place the tube in an ice-methanol bath for 20 minutes, then centrifuge to separate the phases. Decant the clear supernatant into a suitable stoppered flask, and allow to warm to room temperature.
Procedure—
Proceed as directed for
Procedure in the
Assay under
Betamethasone Valerate. Calculate the quantity, in mg, of C
22H
29FO
5 in the portion of Cream taken by the formula:
(392.46 / 476.59)(15C)(RU / RS),
in which 392.46 and 476.59 are the molecular weights of betamethasone and betamethasone valerate, respectively;
C is the concentration, in mg per mL, of
USP Betamethasone Valerate RS in the
Standard preparation; and
RU and
RS are the peak response ratios obtained from the
Assay preparation and the
Standard preparation, respectively.
61
—
It meets the requirements of the tests for absence of Staphylococcus aureus and Pseudomonas aeruginosa.