Implanted tissue-cages: a critical evaluation of their relevance in measuring tissue concentrations of antibiotics.

In several species of laboratory animals, the concurrent serum and tissue-cage fluid levels of several antibiotics after a single parenteral dose have markedly different profiles. New work has shown that these differences are mainly due to the relatively impermeable granulomatous sheath which develops around the implanted tissue chambers. The concentrations of an antibiotic in tissue-cage fluid are therefore not representative of its concentration in "interstitial fluid" or extravascular fluid in general. Tissue-cage levels are probably more representative of antibiotic levels to be found inside abscesses, in chronic disease situations, or relatively avascular sites in the body.