Antimicrobial tissue penetration in a rat model of E. coli epididymitis

Following induction of unilateral epididymitis by intratesticular injection of E. coli, a single intraperitoneal dose of amdinocillin, ampicillin, doxycycline, tobramycin, or trimethoprim/sulfamethoxazole was administered to five groups of rats. The animal was sacrificed serially and concentrations of antibiotic in serum, infected epididymides, and non-infected epididymides were determined by high performance liquid chromatography. The ratio of infected to non-infected tissue area under the curve values was 1.05 for trimethoprim, 1.58 for sulfamethoxazole, 1.67 for amdinocillin, 2.01 for tobramycin, 2.25 for doxycycline, and 2.58 for ampicillin. Except for trimethoprim, infected tissue concentrations were significantly greater than compared to uninfected epididymal levels (p less than 0.05). Antibiotic concentrations in infected epididymides compared to serum revealed overall penetration of 34% for amdinocillin, 66% for sulfamethoxazole, 70% for ampicillin, 76% for tobramycin, 256% for trimethoprim, and 257% for doxycycline. In a rat model of epididymitis, trimethoprim and doxycycline demonstrated the greatest degree of epididymal penetration compared to serum. All antibiotics except trimethoprim had significantly greater penetration into infected tissue when compared to non-infected epididymal tissue.