A novel, sensitive and selective stability-representing RP-UPLC method was developed and validated for the quantitative determination of Erythromycin estolate in Erythromycin 250mg capsules. The chromatographic separation was achieved on BEH C18; 50 x 2.1mm; 1.7µm column by using mobile phase containing a mixture of 0.002M di-potassium hydrogen phosphate and acetonitrile 53:47 v/v at a flow rate of 0.6 ml/min. The column temperature was maintained at 40°C and detection were carried out at 210nm. To ascertain the stability-signifying ability of the method, drug product was subjected to strain conditions of acid, base, oxidative, hydrolytic, thermal, and photolytic degradation. The drug undergoes degradation at oxidative and thermal/humidity stress conditions. The resultant degrading peaks were well resolved from the drug peak. The drug was found to be stable in thermal and photolytic conditions. The urbanized method was validated as per ICH guidelines with respect to specificity, linearity, accuracy, precision, and robustness and the method show excellent linearity and a correlation coefficient of more than 0.99. Therefore, the projected method can be employed for the determination of Erythromycin estolate in various pharmaceutical formulations during regular and quality-control analysis.
Key words: Erythromycin estolate, Stability studies, Capsules, RP-UPLC
Erythromycin is a classic representative of the macrolide group of antibiotics and is produced by Streptomyces erythreus. It is extensively used in the treatment and prevention of diseases. Current indications for the drug include respiratory infections, whooping cough, Legionnaires disease and Campylobacter enteritis. The side-effects are comparatively low 1. Erythromycin is effective against penicillin-challenging staphylococcus, Chlamydia, and Mycoplasma bacteria. Chemically Erythromycin estolate is (3R,4S,5S,6R,7R,9R,11R,12R,13S,14R) -4-(2,6-Dideoxy-3-C-methyl-3-O-methyl-?-L-ribo-hexopyranosyl) Oxy -14-ethyl-7,12,13-trihydroxy-3,5,7,9,11,13- hexamethyl-6-3,4,6-trideoxy-3-(dimethylamino) -2-O-propionyl-?-D-Xylo- hexopyranosyl Oxy oxacyclotetradecane-2,10-Dione dodecyl sulfate (erythromycin A 2”-propionate dodecyl sulfate). Having a molecular formula of C40H71NO14, C12H26O4S and molecular weight is 1056 g/Mol and melting point is 135-140°C. Practically insoluble in water and dilute hydrochloric acid, freely soluble in ethanol (96 percent), soluble in acetone. The PKA value is 6.9 and stable at normal temperature and pressure 2,3. Erythromycin Estolate is specified especially for those patients who are allergic or sensitive to sulfa drugs or penicillin.
However, erythromycin is degraded to inactive anhydrous form in acidic fluids. Hence, ester type prodrugs are preferred such as stearate salts, which are poorly soluble in water and suitable for oral administration. Thus the Erythromycin estolate (Fig. 1) Has been formulated both in liquids eg; suspension and solid dosage forms like tablets and capsules. LC represents a tremendous growth that makes it the most popular method used in the pharmaceutical analysis. Literature review reveals numerous analytical methods for the determination of erythromycin either alone, or in combination with other antibacterial agent and its related substances in pharmaceutical formulations and biological fluids, these include HPLC and FTIR 4-10. The stability indicating method is a process that identifies the degradation products of analytes. A very little stability indicating LC methods was reported for erythromycin in dosage forms 11,12So, the need was felt to develop an analytical technique for the estimation of Erythromycin estolate in a capsule formulation. In the present research, a very simple and rapid isocratic RP-UPLC method for the routine analysis of Erythromycin estolate in capsules was developed. The anticipated method was validated with respect to specificity, linearity, precision, accuracy, and robustness. In addition, strain testing of the drug was also conducted, as required by the International Conference on Harmonization (ICH, 2003) to support the suitability of the method