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. To avoid toxicity, the maintenance dosages of aminoglycosides in patients with renal insufficiency must be modified by either decreasing the dose or increasing the interval between doses or both. In patients with excessive ECF, as in edema, the dose should be calculated based on total body weight. Patients with burns and cystic fibrosis have decreased plasma levels and may require higher doses.
Anemia tends to increase plasma levels.
In vivo inactivation of the aminoglycoside can occur in patients with renal failure receiving both a penicillin and an aminoglycoside with long intervals between doses of aminoglycoside. Indications With the exception of streptomycin, which has a more limited antibiotic spectrum, all aminoglycosides have good activity against gram-negative aerobic bacilli but lack activity against anaerobes. Streptomycin, neomycin, and kanamycin lack activity against P. aeruginosa, whereas gentamicin, tobramycin, amikacin, and netilmicin have good activity against this organism. The aminoglycosides are active against staphylococci but not against streptococci, including pneumococci. An aminoglycoside should always be added to a -lactam antibiotic when treating serious P. aeruginosa infection.