Enhancement of the antipseudomonal activity of some beta-lactams by subinhibitory concentration of roxithromycin

ABSTRACT

The antipseudomonal activity of cefoperazone, cefotaxime, ceftazidime, ceftriaxone and unasyn was determined in presence and absence of subinhibitory concentration of roxithromycin [ROX] using a turbidimetric method over 24-hour period against 2 multiresistant Pseudomonas aeruginosa strains isolated from sputum from patients suffering from respiratory tract infections. ROX enhanced variably the antipseudomonal activity of beta-lactams tested, depending on the beta- lactam, the isolate tested and time of incubation. Culturing the bacterial cells for 24 hours in subinhibitory concentration of ROX resulted in more significant inhibition by the beta-lactam tested. Similar observation was noticed even after short time [3 hours] preincubation with subinhibitory concentration of ROX. The data obtained pointed out to the in vitro beneficial effect of ROX beta- lactam regimen against Ps. aeruginosa, particularly by starting with ROX, followed by beta-lactams