MACROMOLECULAR MECHANISMS OF SPUTUM INHIBITION OF TOBRAMYCIN ACTIVITY

Tobramycin, an aminoglycoside antibiotic, is used in the treatment of Pseudomonas aeruginosa infections in cystic fibrosis patients. Tobramy cin bioactivity however, is antagonized by sputum. Glycoproteins (muci ns) and high-molecular-weight DNA make up 2 to 3% (P. L. Masson and J. F. Heremans, p. 412-475, In M. J. Dulfano, ed., Sputum: Fundamentals and Clinical Pathology, 1973) and 3 to 10% CW. S. Chernick and G. J, B arbero, Pediatrics 21:739-745, 1959, and R. Picot, I. Das, and L. Reid , Thorax 33:235-242, 1978) of the dry weight of sputum, respectively. Tobramycin binds to both mucins and DNA obtained from sputum (R. Ramph al, M. Lhermitte, M. Filliat, and P. Roussel, J. Antimicrob. Chemother . 22:483-490, 1988). In vitro, recombinant human DNase (rhDNase) hydro lyzes high-molecular-weight DNA of >50 kb within sputum to fragments o f 2 to 3 kb. Studying dialyzable tobramycin, we examined drug binding to whole sputum and to ''mock sputum,'' which consisted of porcine gas tric mucin and calf thymus DNA. We also studied the effects of rhDNase treatments of sputum, mock sputum, and calf thymus DNA on tobramycin binding. We found that treatments of sputum, mock sputum, and calf thy mus DNA with rhDNase did not significantly increase the tobramycin bio activity within the dialysates; surprisingly, sputum binding of tobram ycin was increased by rhDNase. We conclude that rhDNase does not incre ase the bioactivity of tobramycin in sputum.