Swedish Study Group. A randomized multicenter trial to compare the influence of cefaclor and amoxycillin on the colonization resistance of the digestive tract in patients with lower respiratory tract infection.

Eighty-four patients with lower respiratory tract infections participated in a randomised double-blind parallel multicenter trial in order to compare the efficacy of cefaclor and amoxycillin as treatment for lower respiratory tract infections and their ability to influence colonization resistance. Cefaclor was given to 40 patients and amoxycillin to 44 patients perorally in doses of 250 mg t.i.d. for seven days in a double-blind fashion. Sputum, oropharyngeal and intestinal specimens were taken for microbial analysis to isolate the causative pathogen of the lower respiratory tract infection and to follow the microflora changes before, during and after antibiotic treatment. The clinical outcome showed 92.5% cured or improved patients on cefaclor versus 88.4% on amoxycillin. The difference in clinical outcome between the two treatment groups was not statistically significant. Among the pathogenic bacteria isolated, Haemophilus influenzae, Branhamella catarrhalis and Streptococcus pneumoniae dominated. There was no difference between the two treatments with regard to microbiological efficacy. Treatment with cefaclor did not cause any significant impact on the oropharyngeal microflora. Administration of amoxycillin caused a significant reduction of the number of Streptococcus salivarius and Veillonella cocci, while an increase in number of enterobacteria was seen in the oropharyngeal microflora. In the intestinal flora, cefaclor significantly reduced the number of streptococci, staphylococci and anaerobic cocci, while the number of enterococci, enterobacteria, bacteroides and Candida albicans significantly increased. The intestinal microflora was partly influenced by amoxycillin treatment. Thus there was a significant increase in the number of enterobacteria, anaerobic gram-positive rods and bacteroides. In conclusion, none of these agents caused any major disturbances in the colonization resistance in patients with lower respiratory tract infections.