An aqueous or powder composition includes anti-gram-negative antibiotic or salt thereof being present at an amount ranging from about 100 mg/ml to about 200 mg/ml. Another aqueous or powder composition includes anti-gram-positive antibiotic or salt thereof being present at a concentration ranging from about 0.6 to about 0.9 of the water solubility limit, at 25° C. and 1.0 atmosphere, of the anti-gram-positive antibiotic or salt thereof. Other embodiments include unit doses, kits, and methods.
