Optimizing tylosin dosage for co-infection of Actinobacillus pleuropneumoniae and Pasteurella multocida in pigs using pharmacokinetic/pharmacodynamic modeling

Abstract

Formulating a therapeutic strategy that can effectively combat concurrent infections of Actinobacillus pleuropneumoniae (A. pleuropneumoniae) and Pasteurella multocida (P. multocida) can be challenging. This study aimed to 1) establish minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), time kill curve, and post-antibiotic effect (PAE) of tylosin against A. pleuropneumoniae and P. multocida pig isolates and employ the MIC data for the development of epidemiological cutoff (ECOFF) values; 2) estimate the pharmacokinetics (PKs) of tylosin following its intramuscular (IM) administration (20 mg/kg) in healthy and infected pigs; and 3) establish a PK-pharmacodynamic (PD) integrated model and predict optimal dosing regimens and PK/PD cutoff values for tylosin in healthy and infected pigs. The MIC of tylosin against both 89 and 363 isolates of A. pleuropneumoniae and P. multocida strains spread widely, ranging from 1 to 256 μg/mL and from 0.5 to 128 μg/mL, respectively. According to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) ECOFFinder analysis ECOFF value (≤64 µg/mL), 97.75% (87 strains) of the A. pleuropnumoniae isolates were wild-type, whereas with the same ECOFF value (≤64 µg/mL), 99.72% (363 strains) of the P. multicoda isolates were considered wild-type to tylosin. Area under the concentration time curve (AUC), T_1/2, and C_max values were significantly greater in healthy pigs than those in infected pigs (13.33 h × μg/mL, 1.99 h, and 5.79 μg/mL vs. 10.46 h × μg/mL, 1.83 h, and 3.59 μg/mL, respectively) (p < 0.05). In healthy pigs, AUC_{24 h}/MIC values for the bacteriostatic activity were 0.98 and 1.10 h; for the bactericidal activity, AUC_{24 h}/MIC values were 1.97 and 1.99 h for A. pleuropneumoniae and P. multocida, respectively. In infected pigs, AUC_{24 h}/MIC values for the bacteriostatic activity were 1.03 and 1.12 h; for bactericidal activity, AUC_{24 h}/MIC values were 2.54 and 2.36 h for A. pleuropneumoniae and P. multocida, respectively. Monte Carlo simulation lead to a 2 μg/mL calculated PK/PD cutoff. Managing co-infections can present challenges, as it often demands the administration of multiple antibiotics to address diverse pathogens. However, using tylosin, which effectively targets both A. pleuropneumoniae and P. multocida in pigs, may enhance the control of bacterial burden. By employing an optimized dosage of 11.94-15.37 mg/kg and 25.17-27.79 mg/kg of tylosin can result in achieving bacteriostatic and bactericidal effects in 90% of co-infected pigs.

Keywords: Actinobacillus pleuropneumoniae; Monte Carlo simulation; Pasteurella multocida; dosage optimization; pharmacokinetic/pharmacodynamic modeling.

FIGURE 1

Fitted minimum inhibitory concentration (MIC) distribution for tylosin against Actinobacillus pleuropneumoniae (A. pleuropneumoniae) (n = 89) (A) and Pasteurella multocida (P. multocida) (n = 363) (B) by ECOFFinder. Insert graphs represent observed MIC distribution with MIC₉₀.

FIGURE 2

Pharmacodynamic (PD) study of tylosin against A. pleuropneumoniae and P. multocida. (A) In vitro time kill curves of tylosin against A. pleuropneumoniae at 0-, 1-, 2-, 4-, 8-, 12-, and 24-h time points and turbidity observations of tubes containing 1/2×, 1×, 2×, and 4× MIC of tylosin and control (without drug) following 24-h incubation, (B) post-antibiotic effect (PAE) following exposure to tylosin against A. pleuropneumoniae. (C) In vitro time kill curves of tylosin against P. Multocida at 0-, 1-, 2-, 4-, 8-, 12-, and 24-h time points. (D) PAE following exposure to tylosin against P. multocida.

FIGURE 3

Ex vivo time kill curves of tylosin plasma against A. pleuropneumoniae ((A), healthy; (B), infected) and P. multocida ((C), healthy; (D), infected) at 0-, 1-, 2-, 4-, 8-, 12-, and 24-h time points.

FIGURE 4

Plots of tylosin concentration–time in plasma following IM administration (20 mg/kg).

FIGURE 5

Sigmoidal Emax model of ex vivo AUC_24 h/MIC ratios versus LogE (CFU/mL) of tylosin against A. pleuropneumoniae ((A), healthy; (B), infected) and P. multocida ((C), healthy; (D), infected) within 24 h. Dotted lines represent bacteriostatic (E = 0) and bactericidal (E = −3) activities.

FIGURE 6

Predicted doses of tylosin for treating A. pleuropneumoniae at 50% and 90% target ratios in healthy and infected pigs. (A ₁ ) The predicted population dose for the bacteriostatic activity at 50% target in healthy pigs; (A ₂ ) the predicted population dose for the bacteriostatic activity at 90% target in healthy pigs; (B ₁ ) the predicted population dose for the bactericidal activity at 50% target in healthy pigs; (B ₂ ) the predicted population dose for the bactericidal activity at 90% target in healthy pigs; (C ₁ ) the predicted population dose for the bacteriostatic activity at 50% target in infected pigs; (C ₂ ) the predicted population dose for the bacteriostatic activity at 90% target in infected pigs; (D ₁ ) the predicted population dose for the bactericidal activity at 50% target in infected pigs; (D ₂ ) the predicted population dose for the bactericidal activity at 90% target in infected pigs.

FIGURE 7

Predicted doses of tylosin for treating P. multocida at 50% and 90% target ratios in healthy and infected pigs. (A ₁ ) The predicted population dose for the bacteriostatic activity at 50% target in healthy pigs; (A ₂ ) the predicted population dose for the bacteriostatic activity at 90% target in healthy pigs,; (B ₁ ) the predicted population dose for the bactericidal activity at 50% target in healthy pigs; (B ₂ ) the predicted population dose for the bactericidal activity at 90% target in healthy pigs; (C ₁ ) the predicted population dose for the bacteriostatic activity at 50% target in infected pigs; (C ₂ ) the predicted population dose for the bacteriostatic activity at 90% target in infected pigs; (D ₁ ) the predicted population dose for the bactericidal activity at 50% target in infected pigs; (D ₂ ) the predicted population dose for the bactericidal activity at 90% target in infected pigs.

FIGURE 8

Probability of target attainment for treating with single-dose tylosin at 20 mg/kg for A. pleuropneumoniae ((A), healthy; (B), infected) and P. multocida ((C), healthy; (D), infected). Dotted lines represent 90% target.