They are active only against aerobic gram-negative bacilli and staphylococci. Activity against streptococci and anaerobes is poor. Aminoglycosides may be used in combination with a penicillin in staphylococcal, streptococcal, and especially enterococcal endocarditis. Neomycin and kanamycin have a limited antibacterial spectrum and are more toxic than the other aminoglycosides. These two drugs should only be used topically or orally.
Protein binding is low.
Even with inflammation, concentrations in tissues and secretions are much less than those in plasma levels. The major exceptions are urine, otic perilymph, and renal cortical tissue, which selectively bind aminoglycosides, resulting in concentrations higher than in plasma. Penetration of aminoglycosides into the eye, CSF, and respiratory secretions is poor, even with inflammation. When aminoglycosides are used to treat meningitis, intrathecal injections, in addition to IV administration, are often necessary to achieve adequate CSF levels. Aminoglycosides are excreted unchanged into the urine by glomerular filtration.