In vitro and in vivo activity of first generation cephalosporins against Leptospira.

Third generation cephalosporins are commonly used in the treatment of leptospirosis. The efficacy of first generation cephalosporins has been less well-studied. Susceptibility testing of 13 Leptospira strains (11 serovars) to cefazolin and cephalexin was conducted using broth microdilution. Median minimal inhibitory concentration (MIC) for cefazolin and cephalexin ranged from < 0.016 to 2 μg/mL (MIC(90) = 0.5 μg/mL) and from 1 to 8 μg/mL (MIC(90) = 8 μg/mL), respectively. Efficacy of cefazolin and cephalexin in an acute lethal hamster model of leptospirosis was studied. Survival rates for cefazolin were 80%, 100%, and 100%, and survival rates for cephalexin were 50%, 80%, and 100% (treated with 5, 25, and 50 mg/kg per day for 5 days, respectively). Each treatment group showed improved survival compared with no treatment (P < 0.01), and none of the therapies, regardless of dose, was statistically significantly different than doxycycline. These results support a potential role for first generation cephalosporins as alternative therapies for leptospirosis.