PK-PD Modeling and Optimal Dosing Regimen of Acetylkitasamycin against Streptococcus suis in Piglets

Streptococcus suis (S. suis) causes severe respiratory diseases in pigs and is also an important pathogen causing hidden dangers to public health and safety. Acetylkitasamycin is a new macrolide agent that has shown good activity to Gram-positive cocci such as Streptococcus. The purpose of this study was to perform pharmacokinetic–pharmacodynamic (PK-PD) modeling to formulate a dosing regimen of acetylkitasamycin for treatment of S. suis and to decrease the emergence of acetylkitasamycin-resistant S. suis. The minimal inhibitory concentration (MIC) of 110 S. suis isolates was determined by broth micro dilution method. The MIC(50) of the 55 sensitive S. suis isolates was 1.21 μg/mL. The strain HB1607 with MIC close to MIC(50) and high pathogenicity was used for the PK-PD experiments. The MIC and MBC of HB1607 in both MH broth and pulmonary epithelial lining fluid (PELF) was 1 and 2 μg/mL, respectively. The liquid chromatography–tandem mass spectrometry (LC-MS/MS) method was used to determine the concentration change of acetylkitasamycin in piglet plasma and PELF after intragastric administration of a single dose of 50 mg/kg b.w. acetylkitasamycin. The PK parameters were calculated by WinNolin software. The PK data showed that the maximum concentration (C(max)), peak time (T(max)), and area under the concentration–time curve (AUC) were 9.84 ± 0.39 μg/mL, 4.27 ± 0.19 h and 248.58 ± 21.17 h·μg/mL, respectively. Integration of the in vivo PK data and ex vivo PD data, an inhibition sigmoid E(max) equation was established. The dosing regimen of acetylkitasamycin for the treatment S. suis infection established as 33.12 mg/kg b.w. every 12 h for 3 days. This study provided a reasonable dosing regimen for a new drug used in clinical treatment, which can effectively be used to treat S. suis infection and slow down the generation of drug resistance.