Comparative effects of cefadroxil and phenoxymethylpenicillin on the normal oropharyngeal and intestinal microflora.

The ecological effects on the commensal microflora in saliva and stool samples were studied during administration of two commonly used antibiotics: cefadroxil 500 mg b.i.d. for 10 days and phenoxymethylpenicillin 1 g b.i.d. for 10 days. Twenty healthy volunteers participated in the study. In the oropharyngeal microflora the aerobic microflora was significantly suppressed during administration of cefadroxil while no significant changes were noticed in the anaerobic microflora. Administration of phenoxymethylpenicillin caused a strong decrease in the number of viridans streptococci and an overgrowth of Neisseria cocci. The total numbers of anaerobic oropharyngeal microorganisms were suppressed during phenoxymethylpenicillin administration. In the intestinal microflora the variation in numbers of aerobic and anaerobic microorganisms was minor in both groups. The microflora became normalised 2 weeks after withdrawal of the drugs. It was concluded that peroral administration of cefadroxil to healthy volunteers resulted in minor ecological disturbances in the oropharyngeal and intestinal microflora, which were in the same range as for phenoxymethylpenicillin.