Efficacy of ceftriaxone and gentamicin in an abscess model.

The therapeutic efficacy of ceftriaxone and gentamicin was investigated in a foreign body induced abscess model in the rat by implanting a dialysis tube contaminated with Klebsiella pneumoniae into the subcutaneous tissue. Animals were treated for four days with ceftriaxone, gentamicin, and their combination starting immediately following or 48 h after the implantation. Peak free ceftriaxone and gentamicin abscess fluid levels were 4.3 and 2.6 mcg/ml, which were 7.3% and 37.5% of peak blood levels respectively. Both agents persisted longer in abscess fluid than in blood. Ceftriaxone inhibited the development of abscess formation when administered shortly after the implantation of the contaminated foreign body whereas gentamicin alone was without beneficial effect. When administered after 48 h ceftriaxone was less effective than immediately after implantation and gentamicin was again without any therapeutic effect. The effect of the combination of ceftriaxone and gentamicin was slightly better than ceftriaxone alone. Low oxygen tension may be an explanation for the lack of bactericidal effect of gentamicin. Ceftriaxone may be more suitable for the therapy of closed space infections caused by susceptible microorganisms than gentamicin.