Pharmacokinetics and bioavailability of tildipirosin in rabbits following single-dose intravenous and intramuscular administration

Pharmacokinetics of tildipirosin in estuarine (Crocodylus porosus) and freshwater (Crocodylus siamensis) crocodiles

Tildipirosin is a macrolide antimicrobial. It is authorised for the treatment and prevention of respiratory disease in cattle and pigs. There are no data on its administration in crocodiles. Therefore, this study evaluated the disposition kinetics of tildipirosin after intravenous (dose: 2 mg/kg) and intramuscular (doses: 2 and 4 mg/kg) administration in two crocodilian species (estuarine and freshwater; n = 5). Tildipirosin plasma concentrations were quantified by a validated HPLC method. Plasma concentrations obtained at each extraction time were analysed by non-compartmental methods. In the estuarine and freshwater crocodiles, the apparent volumes of distribution of tildipirosin after intravenous administration were 0.36 ± 0.10 and 1.48 ± 0.26 L/kg, respectively. These values, suggesting poorer tissue distribution, were much lower than those obtained in mammals. There was complete bioavailability of tildipirosin after intramuscular route at a dose of 2 mg/kg; however, at a dose of 4 mg/kg the bioavailability decreased by about 20-25 %. Furthermore, the pharmacokinetics of tildipirosin were markedly different in the two crocodilian species. Considering a MIC of 0.5 µg/mL, the surrogate marker AUC0-24/MIC indicates that tildipirosin would greatly exceed the value of 65 h for both crocodile species and dose levels tested. This suggests that both doses (2 and 4 mg/kg) may provide a bactericidal effect. Therefore, based on the absence of adverse reactions following the administration of tildipirosin in both crocodilian species, and considering its favourable pharmacokinetic properties, tildipirosin may be useful in treating infections in these reptiles.

Pharmacokinetics of tildipirosin in horses after intravenous and intramuscular administration and its potential muscle damage

Tildipirosin is a novel semisynthetic macrolide antibiotic exclusively used in veterinary practice to treat respiratory infections. There are no pharmacokinetic or safety information available regarding the use of tildipirosin after intramuscular administration in horses. Thus, the objective of this work was to determine the disposition kinetics of tildipirosin after intravenous (IV) and intramuscular (IM) administration in horses and its potential muscle damage and cardiotoxicity. Six mature, Spanish-breed horses were used in a crossover study with a washout period of 30 days. Tildipirosin (18%) was administered at single doses by IV (2 mg/kg) and IM (4 mg/kg) routes. Tildipirosin plasma concentrations were determined by HPLC assay with ultraviolet detection. Muscle damage and inflammation were assessed by creatine kinase (CK) and haptoglobin (Hp), respectively. Creatine kinase myocardial band (CK-MB) and troponin (Tn) were used to evaluate cardiotoxicity. Tildipirosin in horses reached peak concentrations (C_max = 1.13 μg/mL) at 0.60 h (t_max) after IM administration with an absolute bioavailability of 109.2%. Steady-state volume of distribution and clearance were 3.31 ± 0.57 L/kg and 0.22 ± 0.02 L/h/kg, respectively. Tildipirosin did not cause cardiotoxicity since CK-MB and Tn basal levels were not significantly different from those obtained after several days post-administration. Mild local reactions were observed after IM administration. This local inflammation was associated with mild myolysis (CK 239-837 UI/L), which was detectable for 48 h. In brief, tildipirosin could help to treat respiratory infections in horses because it showed extensive distribution, high bioavailability and did not provoke general adverse reactions.

Development and Validation of an Improved HPLC-UV Method for the Determination of Tildipirosin in Horse Plasma

A simple, rapid, low-cost, and sensitive high-performance liquid chromatographic method was developed to determine tildipirosin in horse plasma. Plasma samples were extracted with diethyl ether, and after evaporation, tildipirosin was determined by reverse-phase chromatography with an ultraviolet detector set at a wavelength of 289 nm. Tildipirosin was separated on a Zorbax Eclipse XDB-C18 column, 150 x 3.0 mm, 5 μm with gradient chromatographic elution. The retention times were 3.0 min and 6.4 min for tildipirosin and tylosin tartrate, respectively. The total run time was 9 minutes in this method.

Calibration curves ranged from 0.1 to 3 μg/mL. The lower limit of detection for plasma was0.035μg/mL, and the lower limit of quantitation was 0.1 μg/mL. Both accuracy and precision were always < 12% exce pt for LLOQ < 20%. Mean recovery was 99.5 %. This procedure can be applied to determine tildipirosin concentrations in plasma and be useful to perform pharmacokinetic studies.

Evaluating parameters affecting drug fate at the intramuscular injection site

Intramuscular (IM) injections are a well-established method of delivering a variety of therapeutics formulated for parenteral administration. While the wide range of commercial IM pharmaceuticals provide a wealth of pharmacokinetic (PK) information following injection, there remains an inadequate understanding of drug fate at the IM injection site that could dictate these PK outcomes. An improved understanding of injection site events could improve approaches taken by formulation scientists to identify therapeutically effective and consistent drug PK outcomes. Interplay between the typically non-physiological aspects of drug formulations and the homeostatic IM environment may provide insights into the fate of drugs at the IM injection site, leading to predictions of how a drug will behave post-injection in vivo. Immune responses occur by design after e.g. vaccine administration, however immune responses post-injection are not in the scope of this article. Taking cues from existing in vitro modelling technologies, the purpose of this article is to propose "critical parameters" of the IM environment that could be examined in hypothesis-driven studies. Outcomes of such studies might ultimately be useful in predicting and improving in vivo PK performance of IM injected drugs.

Pharmacokinetics of Tildipirosin in Ewes after Intravenous, Intramuscular and Subcutaneous Administration

Simple Summary

Pneumonia is a significant cause of death in sheep flocks. Thus, antibiotics are essential for the treatment of bacterial pneumonia to reduce morbidity and mortality, but few drugs are specifically labeled for clinical use in sheep. Many of the antimicrobial clinical prescriptions that occur in sheep are classified as extra-label use, with dosage, administration frequency, indications, and drug withdrawal times usually being extrapolated from information reported in other species. Thus, the objective of this study was to determine the disposition kinetics of tildipirosin after intravenous, intramuscular, and subcutaneous administration in sheep. Throughout the experiment, all ewes were healthy and no adverse reactions were recorded. The apparent volume of distribution was high, indicating a wide distribution in the body, which can be attributed to a significant fraction of tildipirosin inside the cells, and its expected activity against intracellular bacteria. Following intramuscular administration, tildipirosin was rapidly absorbed even to a greater extent when compared to subcutaneous administration. Most of the adsorbed tildipirosin after intramuscular and subcutaneous administrations were available in the body (>70%). In brief, the excellent tolerability of this formulation and the suitable disposition of tildipirosin in the body makes it an alternative for sheep use, in conditions where the administration of antibiotics is needed to observe desired effects with the benefits of scant manipulation of animals.

Abstract

A single-dose disposition kinetics for tildipirosin was evaluated in clinically healthy ewes (n = 6) after intravenous (IV), intramuscular (IM), and subcutaneous (SC) administration of a commercial formulation. Tildipirosin concentrations were determined by high-performance liquid chromatography with ultraviolet detection. Plasma concentration-time data was calculated by non-compartmental pharmacokinetic methods. The apparent volume of distribution (Vz) of tildipirosin after IV administration was 5.36 ± 0.57 L/kg suggesting a wide distribution in tissues and inside the cells. The elimination half-life (t½λz) was 17.16 ± 2.25, 23.90 ± 6.99 and 43.19 ± 5.17 h after IV, IM and SC administration, respectively. Following IM administration, tildipirosin was rapidly absorbed (tmax = 0.62 ± 0.10 h) even to a greater extent than after SC administration. Time to reach peak concentration (tmax) and peak plasma concentrations (Cmax) differed significantly, but both parameters showed a more significant variability after SC than after IM administration. Bioavailabilities after extravascular administration were high (>70%). Therefore, given general adverse reactions that were not observed in any ewe and favourable pharmacokinetics, tildipirosin could be effective in treating bacterial infections in sheep.