Pharmacokinetic/pharmacodynamic (PK/PD) evaluation of tulathromycin against Haemophilus parasuis in an experimental neutropenic guinea pig model

Abstract

The objective of the study was to develop an ex-vivo PK/PD model of intramuscular (IM) administration of tulathromycin and to test its efficacy against Haemophilus parasuis (H. parasuis) infection in intraperitoneal-inoculated neutropenic guinea pigs. The pharmacokinetics (PKs) of tulathromycin at doses of 1 and 10 mg/kg in H. parasuis-infected neutropenic guinea pig were studied by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). In vitro minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), mutant prevention concentration (MPC), post-antibiotic effect (PAE) and dynamic time-kill curve experiments were carried out using H. parasuis strain 13R. Tulathromycin exhibited concentration-dependent activity and PAE persisted long after administration of the antibiotic. The ratio of the 24-h area under the concentration-time curve (AUC) to MIC in serum (AUC24h/MICserum) was recognized as an important PK/PD parameter that positively correlated with the in vitro antibacterial effectiveness of tulathromycin (R2 = 0.9961 or R2 = 1). For the 1 and 10 mg/kg treatments with tulathromycin, the values of AUC24h/MIC for H. parasuis bacteriostatic action, bactericidal action and virtual bacterial eradication were respectively 22.73, 34.5 and 88.03 h for the 1 mg/kg treatment and respectively 24.94, 30.94 and 49.92 h for the 10 mg/kg treatment. In addition, we demonstrated that doses of 7.2-8.0 mg/kg of tulathromycin resulted in high eradication rates (99.99%). Using a previously published conversion factor of 0.296, we were able to estimate an approximate dose, 2.1-2.4 mg/kg, that should also obtain high eradication rates in the target animal, pigs. This study can help optimize tulathromycin efficacy against H. parasuis infections in swine farming.

Fig 1. Clinical symptoms after H. parasuis-infection in guinea pigs.

Top left panel, guinea pigs group together and exhibit immunocompromised; top right panel, a guinea pig’s head droops with closed eyes; bottom left panel, celiac effusion and intestinal mucosal hemorrhage; and bottom right panel, liver swelling, necrosis and hemorrhage.

Fig 2. The concentration-time curve of tulathromycin in guinea pig serum after a single dose intramuscular administration at 1 or 10 mg/kg in a H. parasuis infection model (inset depicts the serum concentrations in the first 8-h post-administration) (n = 8/time point).

Fig 3. In vitro time-kill curves of tulathromycin against H. parasuis 13R in CAMHB medium (MIC_CAMHB = 0.5 μg/mL).

Fig 4. Ex-vivo antibacterial activity of tulathromycin against H. parasuis 13R in blank guinea pig serum samples with added tulathromycin (MIC_serum = 0.03 μg/mL).

Fig 5. Ex-vivo antibacterial activity of tulathromycin in serum of guinea pigs against H. parasuis after IM administration (1 mg/kg.b.w., n = 8/per time point).

Fig 6. Ex-vivo antibacterial activity of tulathromycin in serum of guinea pigs against H. parasuis after IM administration (10 mg/kg.b.w., n = 8/per time point).

Fig 7. Sigmoid E_max relationship between anti-Haemophilus parasuis effect (E, log₁₀ CFU/serum) and ex vivo AUC_24h/MIC ratio in the serum of guinea pigs based on a single dose of 1 mg/kg of tulathromycin.

Fig 8. Sigmoid E_max relationship between anti-Haemophilus parasuis effect (E, log₁₀ CFU/serum) and ex vivo AUC_24h/MIC ratio in the serum of guinea pigs based on a single dose of 10 mg/kg of tulathromycin.