Cerebrovascular permeability and delivery of gentamicin to normal brain and experimental brain abscess in rats.

Antibiotics vary widely in their ability to penetrate the blood-brain barrier. In studies of 70 rats, the permeability of the normal blood-brain barrier to gentamicin was shown to be poor. In experimental brain abscesses, during the cerebritic stage of development, the penetration of intravenous antibiotics was increased compared to normal brain but was very inconsistent. Antibiotic delivery to brain abscess was not significantly altered with the administration of high-dose steroids, but the macrophage and glial response was markedly decreased with high-dose steroid therapy. Reversible osmotic blood-brain barrier modification with mannitol increased the delivery of gentamicin both to brain abscess and to the surrounding brain. It also resulted in more consistent tissue drug levels. The clinical implications of these studies suggest that, because of the inconsistent delivery of gentamicin to brain abscess, the therapeutic efficacy of medical management alone may be quite variable. This mode of therapy could possibly increase the efficacy of medical management of brain abscesses, especially in patients with multiple or surgically inaccessible brain abscesses.