Comparative study of the antibacterial activity of amikacin and tobramycin during Pseudomonas pulmonary infection in patients with cystic fibrosis

Tobramycin and amikacin resulted in comparable antimicrobial activity in serum and sputum of patients with cystic fibrosis and Pseudomonas aeruginosa bronchial infection. The medians of the peak bactericidal titres of the sera containing azlocillin and tobramycin or amikacin were 1/32; inactivation of azlocillin reduced these titres to 1/8 in the sera containing amikacin and 1/4 in the sera containing tobramycin. Bactericidal titres in the sputum were ≥1/2 in only 21 of 107 samples tested (median < 1/2; range < 1/2–1/4). Peak sputum concentration represented 5 to 40·2% (mean 14·5%) of the serum peak for tobramycin and 3·3 to 37% (mean 9·3%) for amikacin; the mean ratio of the peak sputum concentration/minimal bactericidal concentration was 0·99 for tobramycin and 0·65 for amikacin. The present results suggest that tobramycin and amikacin might have a comparable efficacy in the treatment of pulmonary infection due to sensitive strains of Ps. aeruginosa in cystic fibrosis patients.