Pharmacokinetics of tildipirosin in porcine plasma, lung tissue, and bronchial fluid and effects of test conditions on in vitro activity against reference strains and field isolates of Actinobacillus pleuropneumoniae.

The pharmacokinetics of tildipirosin (Zuprevo(®) 40 mg/mL solution for injection for pigs), a novel 16-membered-ring macrolide for the treatment for swine respiratory disease (SRD), was investigated in studies collecting blood plasma and postmortem samples of lung tissue and bronchial fluid (BF) from swine. In view of factors influencing the in vitro activity of macrolides, and for the interpretation of tildipirosin pharmacokinetics in relation to minimum inhibitory concentrations (MIC), additional experiments were conducted to study the effects of pH, carbon dioxide-enriched atmosphere, buffers, and serum on tildipirosin MICs for various reference strains and Actinobacillus (A.) pleuropneumoniae field isolates. After single intramuscular (i.m.) injection at 4 mg/kg body weight, maximum plasma concentration (Cmax) was 0.9 µg/mL observed within 23 min (Tmax ). Mean residence time from the time of dosing to the time of last measurable concentration (MRTlast) and terminal half-life (T1/2) both were about 4 days. A dose-response relationship with no significant sex effect is observed for area under the plasma concentration-time curve from time 0 to the last sampling time with a quantifiable drug concentration (AUClast) over the range of doses up to 6 mg/kg. However, linear dose proportionality could not be proven with statistical methods. The time-concentration profile of tildipirosin in BF and lung far exceeded that in blood plasma. In lung, tildipirosin concentrations reached 3.1 µg/g at 2 h, peaked at 4.3 µg/g at day 1, and slowly declined to 0.8 µg/g at day 17. In BF, tildipirosin levels were 14.3, 7.0, and 6.5 µg/g at days 5, 10, and 14. T1/2 in lung was ∼7 days. Tildipirosin is rapidly and extensively distributed to the respiratory tract followed by slow elimination. Culture media pH and carbon dioxide-enriched atmosphere (CO2 -EA) had a marked impact on in vitro activity of tildipirosin in reference strains of various rapidly growing aerobic and fastidious bacteria including Histophilus (H.) somni ATCC 700025 and A. pleuropneumoniae ATCC 27090. For A. pleuropneumoniae ATCC 27090 testing conditions without CO2 -EA resulted in reduced acidification of culture media pH and a reduction in the minimum inhibitory concentrations compared to standard in vitro test conditions by 2 log2 dilution steps (4-fold) from 8 to 2 µg/mL. Supplementary buffering of standard culture media resulted in a reduction in the A. pleuropneumoniae (n = 8) MIC range by 4 log2 dilution steps (16-fold) from 8-16 to 0.5-1 µg/mL. Incremental supplementation of culture media with 50% serum resulted in noticeable shifts to lower minimum or maximum MICs by at least 2 log2 dilution steps (≥4-fold) in all aerobic and fastidious reference strains tested except for Pasteurella (P.) multocida. The MIC of A. pleuropneumoniae ATCC 27090 decreased by 2-4 log2 dilution steps (4 to 16-fold) from 8 to 0.5-2 µg/mL when 50% serum was added to the standard assay. Considering a higher presence of serum and the rather neutral pH conditions maintained in vivo, it is suggested to take the influence of these factors on in vitro activity into account when interpreting tildipirosin MICs for A. pleuropneumoniae in relation to pharmacokinetics.

Pharmacokinetics of tildipirosin in bovine plasma, lung tissue, and bronchial fluid (from live, nonanesthetized cattle).

The pharmacokinetics of tildipirosin (Zuprevo(®) 180 mg/mL solution for injection for cattle), a novel 16-membered macrolide for treatment, control, and prevention of bovine respiratory disease, were investigated in studies collecting blood plasma, lung tissue, and in vivo samples of bronchial fluid (BF) from cattle. After single subcutaneous (s.c.) injection at 4 mg/kg body weight, maximum plasma concentration (C(max)) was 0.7 µg/mL. T(max) was 23 min. Mean residence time from the time of dosing to the time of last measurable concentration (MRT(last)) and terminal half-life (T(1/2) ) was 6 and 9 days, respectively. A strong dose-response relationship with no significant sex effect was shown for both C(max) and area under the plasma concentration-time curve from time 0 to the last sampling time with a quantifiable drug concentration (AUC(last) ) over the range of doses up to 6 mg/kg. Absolute bioavailability was 78.9%. The volume of distribution based on the terminal phase (V(z)) was 49.4 L/kg, and the plasma clearance was 144 mL/h/kg. The time-concentration profile of tildipirosin in BF and lung far exceeded those in blood plasma. In lung, tildipirosin concentrations reached 9.2 µg/g at 4 h, peaked at 14.8 µg/g at day 1, and slowly declined to 2.0 µg/g at day 28. In BF, the concentration of tildipirosin reached 1.5 and 3.0 µg/g at 4 and 10 h, maintained a plateau of about 3.5 µg/g between day 1 and 3, and slowly declined to 1.0 at day 21. T(1/2) in lung and BF was approximately 10 and 11 days. Tildipirosin is rapidly and extensively distributed to the respiratory tract followed by slow elimination.

Differential Induction of Lipoxygenase Isoforms in Wheat upon Treatment with Rust Fungus Elicitor, Chitin Oligosaccharides, Chitosan, and Methyl Jasmonate.

A glycopeptide elicitor prepared from germ tubes of the rust fungus Puccinia graminis Pers. f. sp. tritici Erikss. & Henn (Pgt), as well as chitin oligosaccharides, chitosan, and methyl jasmonate (MJ) stimulated lipoxygenase (LOX) activity (E.C. 1.13.11.12) in wheat (Triticum aestivum) leaves. Immunoblot analysis using anti-LOX antibodies revealed the induction of 92- and 103-kD LOX species after Pgt elicitor treatment. In contrast, MJ treatment led to a significant increase of a 100-kD LOX species, which was also detected at lower levels in control plants. The effects of chitin oligomers and chitosan resembled those caused by MJ. In conjunction with other observations the results suggest that separate reaction cascades exist, and that jasmonates may not be involved in Pgt elicitor action. LOX-92 appears to be mainly responsible for the increase in LOX activity after Pgt elicitor treatment because its appearance on western blots coincided with high LOX activity in distinct anion-exchange chromatography fractions. It is most active at pH 5.5 to 6.0, and product formation from linoleic and [alpha]-linolenic acid is clearly in favor of the 9-LOOHs. It is interesting that a 92-kD LOX species, which seems to correspond to the Pgt elicitor-induced LOX species, was also detected in rust-inoculated leaves.