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Category  Antibacterial. 

      Erythromycin Ethylsuccinate consists primarily of the 2’- ethylsuccinate ester of erythromycin A.  The sum of the percentages of erythromycin A, erythromycin B, and erythromycin C is not less than 76.5 per cent, calculated on the anhydrous basis. 

Description  White, crystalline powder; hygroscopic.

Solubility  Practically insoluble in water; freely soluble in acetone, in ethanol and in methanol.

Stability  It is hygroscopic. 

Contra-indication; Warning; Precaution  See under Erythromycin, p. 99. 

Additional information

       1. Erythromycin ethylsuccinate is better absorbed when taken with meals.

      2. In pediatric patients, equivalent doses of erythromycin ethylsuccinate and erythromycin base produce comparable blood levels.

Packaging and storage Erythromycin Ethylsuccinate shall be kept in tightly closed containers, protected from light.

Labelling The label on the container states (1) number of μg per mg; (2) storage condition.

Identification

      A. The infrared absorption spectrum is concordant with the spectrum obtained from Erythromycin Ethylsuccinate RS (Appendix) or with the reference spectrum of Erythromycin Ethylsuccinate.

      B. To 5 mg add 2 ml of sulfuric acid and shake gently: a reddish brown colour is produced.

      C. Dissolve 3 mg in 2 ml of acetone and add 2 ml of hydrochloric acid: an orange colour is produced, which changes to red and then to deep purplish red. Add 2 ml of chloroform and shake: the chloroform layer becomes purple.

Crystallinity It is crystalline (Appendix 4.14); except that when it is labelled as being in the amorphous state it does not meet the requirements.

Specific rotation –70º to –82º, calculated on the anhydrous basis, determined in a 1.0 per cent w/v solution in acetone (Appendix 4.8). The specific rotation is determined at least 30 minutes after preparing the solution.

 

Water Not more than 3.0 per cent w/w (Karl Fischer Method, Appendix 4.12). Use 20 ml of methanol containing 10 per cent of imidazole in place of methanol in the titration vessel.

Sulfated ash Not more than 1.0 per cent after ignition at 600º, the charred residue being moistened with 2 ml of nitric acid and 5 drops of sulfuric acid (Method II, Appendix 5.3).

Related substances Complies with the test described under Assay, begin peak integration after the two peaks for succinates that elute just after the solvent front. Measure the areas of the peak responses.

      Calculation Calculate the percentage of each related substance having the greatest response, other than erythromycin A, erythromycin B, erythromycin C, erythromycin A enol ether, and erythromycin Nethylsuccinate (retention time relative to erythromycin A peak is about 1.3), in the portion of Erythromycin Ethylsuccinate taken by the expression:

50(C_S2P/W)(r_i /r_S2),

in which C_S2 is the concentration, in mg per ml, of Erythromycin RS in Standard preparation 2, P is the designated percentage of erythromycin A in Erythromycin RS, W is the quantity, in mg, of Erythromycin Ethylsuccinate taken to prepare the Assay substance, ri is the peak response of each related substance, other than erythromycin A, erythromycin B, erythromycin C, erythromycin A enol ether, and erythromycin Nethylsuccinate, in the chromatogram obtained from Assay preparation, and r_S2 is the erythromycin A peak response in the chromatogram obtained from Standard preparation 2: not more than 3.0 per cent of any individual related substance is found.

      Calculate the percentage of erythromycin A enol ether in the portion of Erythromycin Ethylsuccinate taken by the expression:

(50/11)(C_S2P/W)(r_E/r_S2),

in which 11 is the response factor for erythromycin A enol ether in relation to that of erythromycin A; r_E is the peak response of the erythromycin A enol ether observed in the chromatogram obtained from Assay preparation; and the other terms are as defined above: not more than 3.0 per cent of erythromycin A enol ether is found.

      Calculate the percentage of erythromycin N ethylsuccinate in the portion of Erythromycin Ethylsuccinate taken by the expression:

(50/7.4)(C_S2P/W)(r_N/r_S2),

in which 7.4 is the response factor for erythromycin N-ethylsuccinate in relation to that of erythromycin A, r_N is the peak response of the erythromycin Nethylsuccinate (retention time relative to the erythromycin A peak is about 1.3) observed in the chromatogram obtained from Assay preparation; andthe other terms are as defined above: not more than 3.0 per cent of erythromycin N-ethylsuccinate is found.

Assay Carry out the determination as described in the “High-pressure Liquid Chromatography” (Appendix 3.5).

      Hydrolysis reagent Prepare a solution of potassium dihydrogenphosphate (2 in 100), and adjust with phosphoric acid  to a pH of 8.0.

      pH 8.0 buffer Prepare a solution of potassium dihydrogenphosphate (3.5 in 100), and adjust with phosphoric acid  to a pH of 8.0.

      pH 3.5 buffer Adjust 20 ml of pH 8.0 buffer with phosphoric acid  to a pH of 3.5.

      Mobile phase Mix 50 ml of pH 8.0 buffer with 400 ml of water, add 175 ml of 2-methyl-2-propanol and 30 ml of acetonitrile, dilute with water to 1000 ml, and mix. Make adjustments if necessary

(Note Use the following solutions promptly, or within 1 day if stored in a refrigerator.)

      Standard preparation 1 Transfer about 50 mg of Erythromycin RS, accurately weighed, to a 25-ml volumetric flask, add 12.5 ml of methanol, and swirl to dissolve. Dilute with Hydrolysis reagent  to volume, and mix.

      Standard preparation 2 Transfer about 5 mg each of Erythromycin B RS and Erythromycin C RS, both accurately weighed, to a 50-ml volumetric flask, add 25.0 ml of methanol, and swirl to dissolve. Add 2.5 ml of Standard preparation 1, dilute with Hydrolysis reagent to volume, and mix.

      System suitability solution Dissolve 2 mg of NDemethylerythromycin A RS in 20 ml of Standard preparation 2, and mix.

      Erythromycin A enol ether solution Dissolve 10 mg of Erythromycin RS in 2 ml of methanol. Add 10 ml of pH 3.5 buffer, mix, and allow to stand for about 30 minutes. Refrigerate this solution until used, and discard 8 hours after preparation.

      Assay preparation Transfer about 115 mg of Erythromycin Ethylsuccinate, accurately weighed, to a 50-ml volumetric flask, add 25.0 ml of methanol, and swirl to dissolve. Add 20 ml of Hydrolysis reagent, mix, and allow to stand at room temperature for about 12 hours to effect hydrolysis. Dilute with Hydrolysis reagent to volume, and mix.

      Chromatographic system The chromatographic procedure may be carried out using (a) a stainless steel column (25 cm × 4.6 mm) packed with a rigid spherical styrene-divinylbenzene copolymer (5 to 10 μm) maintained at a constant temperature of about 70º, (b) Mobile phase at a flow rate of about 2 ml per minute and (c) an ultraviolet photometer set at 215 nm.

      To determine the suitability of the chromatographic system, chromatograph System suitability solution, and record the peak responses as directed under Procedure: the order of elution of the components is N-demethylerythromycin A, erythromycin C, erythromycin A, and erythromycin B; and the resolution, R, between Ndemethylerythromycin A and erythromycin C is not less than 0.8 and between N-demethylerythromycin A and erythromycin A not less than 5.5. Chromatograph Erythromycin A enol ether solution, and record the peak responses as directed under Procedure: adjust the duration of chromatography to include the erythromycin A enol ether peak, which has a retention time of about 4.3 to 4.7 times that of erythromycin A. Chromatograph Standard preparation 1, and record the peak responses as directed under Procedure: the relative standard deviation for replicate injections is not more than 1.0 per cent.

      Procedure Separately inject equal volumes (about 200 μl) of Standard preparation 1, Standard preparation 2, and Assay preparation into the chromatograph; record the chromatograms for a period of time that is adequate to include the erythromycin A enol ether peak, if present. For assay preparation, begin peak integration after the two peaks for succinates that elute just after the solvent front. Measure the areas of the peak responses.

      Calculation Calculate the percentage of erythromycin A in the portion of the Erythromycin Ethylsuccinate taken by the expression: 

50(C_S1P/W)(r_U/r_S1),

in which C_S1 is the concentration, in mg per ml, of Erythromycin RS in Standard preparation 1; P is the designated percentage of erythromycin A in Erythromycin RS; W is the quantity, in mg, of Erythromycin Ethylsuccinate taken to prepare Assay preparation; and r_u and r_s1 are the erythromycin A peak responses in the chromatograms obtained from Assay preparation and Standard preparation 1, respectively.

      Calculate the percentage of erythromycin B and erythromycin C in the portion of the Erythromycin Ethylsuccinate taken by the expression:

50(CS2P/W)(rU/rS2),

in which C_S2 is the concentration, in mg per ml, of Erythromycin RS in Standard preparation 2; P is the designated percentage of erythromycin B or erythromycin C in Erythromycin B RS or Erythromycin C RS, respectively; W is the quantity, in mg, of Erythromycin Ethylsuccinate taken to prepare Assay preparation; and r_U and r_S2 are the erythromycin B or erythromycin C peak responses in the chromatograms obtained from Assay preparation and Standard preparation 2, respectively.