The in vitro combined effects of erythromycin and methanol extract of leaves ofEuphorbia hirta against clinical isolates of Staphylococcus aureus were investigated using the Checkerboard technique. The organism was susceptible to the extract with MIC of 25 mg/ml, while erythromycin had MIC of 0.005 mg/ml. The research aims to investigate the possible interaction that may exist when standardize herbal drugs are combined with synthetic antimicrobials. Previously, stock solutions of both the extract and erythromycin were prepared in appropriate volume of dimethylsulphoxide and water respectively to get a final concentration of 50 mg/ml each. Minimum inhibitory concentration was determined by method of serial dilution while interaction study was carried out according to the continuous variation checkerboard method. Upon combination, some ratios showed synergistic (9:1, 8:2, 7:3, 6:4, 3:7, 2,8, 1:9) while others indicated indifference (5:5, 4:6) activities against the isolates. These results indicate that some combinations of the extract with erythromycin could be synergistic in activity for some ratio combinations and indifferent for some others.
Key words: In vitro, erythromycin, Euphorbia hirta, staphylococcus aureus, MICcheckerboard.
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