The long term objective of these studies is to use aerosols to deliver antitubercular drugs in microparticles to alveolar macrophages (AMs) in the lung. The lungs, specifically the population of AMs, are a major site of Mycobacterium tuberculosis infection. Targeted drug delivery to the lungs will maintain local therapeutic concentrations and minimize systemic exposure. Slowly dissolving polymeric microparticles, administered as aerosols, will exhibit extended residence times in the lungs and may improve drug delivery to AMs. Biodegradable microparticulate aerosols will be used to deliver rifampicin to the lungs of M. tuberculosis infected guinea pigs. These particles will remain within the lungs by virtue of their size and relatively slow dissolution rate. They will be phagocytosed by macrophages, a primary site of M. tuberculosis in the early stages of infection. Slowly degrading microparticles will be transported to lymph nodes, a principal site of M. tuberculosis in the later stages of infection. Therapeutic targeting may be demonstrated by delivering microparticles containing antitubercular agents as aerosols to macrophages in the lungs of diseased animals and evaluating their action. The first objective is to prepare and characterize microparticles, containing antitubercular drug, in respirable sizes (less than 5 Mm). Microparticles will be manufactured by an emulsion evaporation/solvent extraction technique. FITC-dextran (50KD) will be incorporated as a marker in poly(lactide-coglycolide)(PLGA) microparticles. The second objective is to evaluate the quantitative interaction of these microparticles with AMs. The uptake of fluorescent microparticles by adhered cell cultures of AMs will be monitored after 6 hours of exposure by fluorescence microscopy. The third objective is to quantify the phagocytosis by alveolar macrophages and the disposition of fluorescent microparticles in normal guinea pigs following aqueous suspension aerosol delivery. Performing broncho-alveolar lavage and histological examination of the lungs and lymph node tissues will verify the location/distribution of the microparticles. The final objective is to determine the efficacy of rifampicin microparticles with different residence times and different drug release rates (delivered as dry powder aerosols) in a guinea pig model of tuberculosis. Completion of these studies will significantly advance the prospect of achieving therapeutic drug concentrations in the vicinity of invading micro-organisms.