Erythromycin Estolate
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C40H71NO14·C12H26O4S 1056.39

Erythromycin, 2¢-propanoate, dodecyl sulfate (salt).
Erythromycin 2¢-propionate dodecyl sulfate (salt) [3521-62-8].
» Erythromycin Estolate has a potency equivalent to not less than 600 µg of erythromycin (C37H67NO13) per mg, calculated on the anhydrous basis.
Packaging and storage— Preserve in tight containers.
Identification, Infrared Absorption 197K.
Crystallinity 695: meets the requirements.
Water, Method I 921: not more than 4.0%, 20 mL of methanol containing 10% of imidazole being used in place of methanol in the titration vessel.
Free erythromycin— Prepare a test solution of it in methanol containing 10.0 mg per mL. Prepare a Standard solution of USP Erythromycin RS in methanol containing 0.3 mg per mL. [note—Prepare these solutions immediately before use.] Prepare a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Before using, place the plate in an unlined developing chamber containing about 100 mL of methanol, and allow the solvent front to move to the top of the plate, marking the direction of travel. Remove the plate, and allow to dry. Apply separate 1-µL volumes of the test solution and the Standard solution on the plate, allow the spots to dry, and develop the chromatograms in a freshly prepared solvent system consisting of a mixture of methanol and chloroform (85:15) until the solvent front has moved about one-half of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the plate to dry. Place the plate under a hood, and spray uniformly with a solution consisting of 150 mg of xanthydrol dissolved in a mixture of hydrochloric acid and glacial acetic acid (92.5:7.5). Heat the sprayed plate in an oven at 100 for 5 minutes. [Caution—Avoid exposure to acid fumes when removing the plate from the oven. ] Examine the plate for reddish violet spots: free erythromycin has an RF value of about 0.3, and erythromycin estolate has an RF value of about 0.7. Any spot corresponding to free erythromycin obtained from the test solution does not exceed in size or intensity that of the principal spot obtained from the Standard solution (3.0%).
Assay— Proceed with Erythromycin Estolate as directed for erythromycin under Antibiotics—Microbial Assays 81, using an accurately weighed quantity of Erythromycin Estolate dissolved in methanol to obtain a solution containing the equivalent of 1.0 mg of erythromycin per mL. Immediately dilute quantitatively with 9 volumes of Buffer No. 3, and allow to stand at room temperature for 18 hours. Dilute a portion of this solution quantitatively with Buffer No. 3 to obtain a Test Dilution having a concentration assumed to be equal to the median dose level of the Standard.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Ahalya Wise, M.S.
(MDANT05) Monograph Development-Antibiotics
Reference Standards Lili Wang, Technical Services Scientist
USP32–NF27 Page 2288