Antimicrobial effects of amikacin therapy on experimentally induced Salmonella typhimurium infection in fowls

The antimicrobial effects of amikacin on Salmonella Typhimurium were investigated in fowls using pharmacokinetic parameters of amikacin and the minimum inhibitory concentration (MIG) of the drug for the bacteria. Pharmacokinetic parameters of amikacin after the intramuscular administration into the fowls were measured using the fluorescence polarization immunoassay. As there was no protein binding amikacin, the total concentration was identical to the free concentration. After inoculation of the bacteria, the following intramuscular dosage regimens were carried out to test the antimicrobial effects: injection with 20 mg/kg of amikacin sulfate every 9 hr for 72 hr, injection with 20 mg/kg every 18 hr for 72 hr, injection with 20 mg/kg every 36 hr for 72 hr, and injection with 10 mg/kg every 12 hr for 72 hr. The control birds were not injected with amikacin. Abdominal organs were collected from each bird after the treatment ended. The organs were cultured and the number of colonies on each plate was calculated. No significant differences were detected among the four amikacin-treated groups, whereas the number of colonies in the control group was significantly higher than that in the amikacin-treated groups. An antimicrobial drug concentration exceeding the bacterium's MIC for at least 1/4 of the administration interval might be effective for the treatment of the infection, and the degree of peak drug concentration had no effect on antibacterial activity as long as the duration of the drug concentration above the MIC value remained the same.