Interactions of clindamycin with antibacterial defenses of the lung.

Clindamycin is speculated to have select advantages in the treatment of certain infections because biologically active antibiotic is internalized by macrophages and PMNs in vitro. By challenging pulmonary host defenses with various bacterial species as probes, we were able to evaluate clindamycin-phagocyte interaction in vivo. A murine model was developed using an implanted mini-osmotic pump to maintain constant clindamycin blood levels at 1/4 MIC (1 microgram/ml). Mice pretreated for 24 h with clindamycin killed a significantly greater percentage of intratracheally inoculated Bacteroides thetaiotaomicron in 4 h than did control animals (37 +/- 2% versus 7 +/- 5%). The enhancing effects of clindamycin on pulmonary defenses could not be duplicated by a 1-h preincubation of B. theta in 1/4 MIC of clindamycin before inoculation into untreated mice. Clindamycin blood levels of 1 microgram/ml did not alter the rate at which Pseudomonas aeruginosa (clindamycin-resistant) was killed by pulmonary defenses, suggesting that clindamycin did not cause nonspecific activation of phagocytic defenses. Both PMNs and alveolar macrophages lavaged from the lungs of clindamycin-treated mice contained bioassayable concentrated intracellular antibiotic. The presence of intracellular antibiotic was further supported by experiments in which the intrapulmonary killing of large numbers of Staphylococcus aureus (sensitive, but not resistant organisms) was significantly enhanced (89 +/- 5 versus 70 +/- 5%) by clindamycin pretreatment. In contrast, phagocytes lavaged from mice with constant 1/4 MIC (4 micrograms/ml) blood levels of penicillin G had no detectable intracellular antibiotic activity and did not augment the intrapulmonary killing of B. theta.(ABSTRACT TRUNCATED AT 250 WORDS)