Clinical efficacy of florfenicol administered in the drinking water against Ornithobacterium rhinotracheale in turkeys housed in different environmental conditions: a pharmacokinetic/pharmacodynamic approach

Oral pharmacokinetics of a pharmaceutical preparation of florfenicol in broiler chickens

Introduction

The use of florfenicol must follow particular pharmacokinetic/pharmacodynamic (PK/PD) ratios, i.e., it requires achieving serum concentrations at or slightly above the pathogen's minimum inhibitory concentration (MIC) during the dosing interval and that the ratio of area under the concentration vs. time curve (AUC)/MIC should be as high as possible (still undetermined for poultry). As an alternative to the standard soluble florfenicol that is administered to the flock through drinking water, florfenicol premix is often recommended as feed medication in Latin America. However, no particular pharmaceutical design has been proposed.

Methods

This study compared the PK of two preparations of florfenicol in broiler chickens and pondered the possibility of each covering the referred PK-PD ratios as predictors of clinical efficacy. The preparations comprise a pharmaceutical form as FOLA pellets (F = bioavailability; O = optimum; and LA = long-acting) and the premix formulation. The former are small colored pellets with vehicles and absorption enhancers of florfenicol designed for long action, and the latter is the reference premix of the antibiotic. First, these two pharmaceutical forms of florfenicol were administered as oral boluses (30 mg/kg), aided by a probe. In a second trial of the dosing form, both pharmaceutical preparations of florfenicol were administered in feed and ad libitum (110 ppm; ~30 mg/kg).

Results

In both cases, FOLA-florfenicol presented much higher relative bioavailability (3.27 times higher) and mean better residence time than florfenicol premix (two times high when forced as bolus dose). Consequently, FOLA-florfenicol possesses better PK/PD ratios than less sensitive pathogens, i.e., E. coli. It is proposed that if a metaphylactic treatment of a bacterial outbreak in poultry is implemented with florfenicol prepared as FOLA, better PK/PD ratios will be obtained than those of standard florfenicol premix.

Discussion

Clinicians must confirm that feed consumption in the flock has not been affected by the particular disease if FOLA pellets of florfenicol are used.

The influence of the site of drug administration on florfenicol pharmacokinetics in turkeys

Florfenicol is a broad-spectrum antibacterial drug used in the treatment of farm animals, including poultry. This drug is poorly soluble in water, therefore, administration in drinking water may lead to high variability of concentrations in treated individuals. The use of injection preparations, however, requires individual administration and may have a negative effect on the quality of the carcass. In addition, the renal portal system in birds may reduce the bioavailability of the drug administered in the caudofemoral region of the body. The aim of this study was to compare the pharmacokinetics of florfenicol in turkeys after a single intravenous, intramuscular, and subcutaneous administration at a dose of 15 mg/kg body weight. Additionally, to evaluate the effect of renal portal system on drug kinetics, the intramuscular administration was divided into pectoral and caudofemoral administration. The study showed that the area under the concentration-time curve (AUC) was similar regardless of the route of administration. The mean values for clearance and volume of distribution were 0.33 L/kg/h and 0.92 L/kg, respectively. The mean residence time (MRT) was 2.87 h for an intravenous bolus, while for the extravascular administrations it was approx. 5.5 h. The elimination half-life was approx. 4 h regardless of the route of administration. The maximum plasma concentration did not differ statistically between intramuscular (approx. 6.8 mg/L) and subcutaneous (8.2 mg/L) administrations, while the time to appear for this concentration was the longest for caudofemoral administration (1.5 h). The bioavailability was 88.64% for subcutaneous administration, 77.95% for pectoral administration and 85.30% for caudofemoral administration. Overall, all 3 routes of extravascular administration allowed for efficient drug absorption. There was no evidence of an influence of the renal portal system on the kinetic parameters of the drug administered to the lower extremities of the body.

Ornithobacterium rhinotracheale: An Update Review about An Emerging Poultry Pathogen

Respiratory diseases in birds generate sanitary and economic impacts and may be related to the environment and climate. Mycoplasma gallisepticum, Ornithobacterium rhinotracheale (ORT), Pasteurella multocida, Avibacterium paragallinarum, Escherichia coli, Riemerella anatipestifer, and Bordetella avium are among the most important avian respiratory pathogens. ORT is responsible for causing ornitobacteriosis, a disease characterized by clinical signs ranging from mild to severe respiratory conditions, with high mortality rates, mainly affecting turkeys and chickens. The first report of ornitobacteriosis was in 1981 in Germany. Despite its importance, few studies on ORT have been published. In addition, the presence of this pathogen has been neglected in poultry farms, mainly due to the lack of appropriate diagnostic protocols. The lack of correct isolation and diagnostic protocols along with inappropriate use of antimicrobial agents have been contributing to treatment failure. Due to its economic importance to the poultry industry, ornitobacteriosis should be monitored and included in national programs for the prevention and control of avian respiratory diseases. This review aimed to update and discuss important issues related to ORT since this pathogen has great economic and sanitary implications for the chicken production chain.

Efficacy of gamithromycin against Ornithobacterium rhinotracheale in turkey poults pre-infected with avian metapneumovirus

Ornithobacterium rhinotracheale is an avian respiratory pathogen that affects turkeys. The objective of this study was to evaluate the clinical efficacy of gamithromycin (GAM) against O. rhinotracheale in turkeys. The birds were inoculated oculonasally with 10(8) colony-forming units (cfu) of O. rhinotracheale, preceded by infection with avian metapneumovirus. In addition to a negative (CONTR-) and a positive control group (CONTR+) there were two treated groups administered GAM (6 mg/kg) either subcutaneously (GAM SC) or orally (GAM PO) by administration as a single bolus at one-day post-bacterial infection (p.b.i.). From the start of the avian metapneumovirus infection until the end of the experiment, the turkeys were examined clinically and scored daily. In addition, tracheal swabs were collected at several days p.b.i. Necropsy was performed at 4, 8 and 12 days p.b.i. to evaluate the presence of gross lesions, and to collect trachea and lung tissue samples and air sac swabs for O. rhinotracheale quantification. The clinical score of the GAM SC group showed slightly lower values and birds recovered earlier than those in the GAM PO and CONTR+ groups. O. rhinotracheale cfus were significantly reduced in tracheal swabs of the SC group between 2 and 4 days p.b.i. At necropsy, CONTR+ showed higher O. rhinotracheale cfu in lung tissues compared to the treated groups. Moreover, at 8 days p.b.i. only the lung samples of CONTR+ were positive. In conclusion, the efficacy of GAM against O. rhinotracheale was demonstrated, especially in the lung tissue. However, the PO bolus administration of the commercially available product was not as efficacious as the SC bolus.

Pharmacokinetic and pharmacodynamic properties of gamithromycin in turkey poults with respect to Ornithobacterium rhinotracheale

The macrolide gamithromycin (GAM) has the ability to accumulate in tissues of the respiratory tract. Consequently, GAM might be a suitable antibiotic to treat bacterial respiratory infections in poultry, such as Ornithobacterium rhinotracheale. As O. rhinotracheale infections are common in turkey flocks, the aim of this study was to determine the pharmacokinetic (PK) parameters of GAM in plasma, lung tissue, and pulmonary epithelial lining fluid (PELF) of turkeys and to correlate them with pharmacodynamic (PD) characteristics (PK/PD). The animal experiment was performed with 64 turkeys, which received either a subcutaneous (SC, n=32) or an oral (PO, n=32) bolus of 6 mg GAM/kg body weight (BW). GAM concentrations in plasma, lung tissue, and PELF were measured at different time points post administration (p.a.), and PK characteristics were determined using non-compartmental modeling. The maximum plasma concentration after PO administration was ten-fold lower than after SC injection (0.087 and 0.89 μg/mL, respectively), whereas there was no difference in lung concentrations between both routes of administration. However, lung concentrations at day 1 p.a. were significantly higher than plasma levels for both routes of administration (2.22 and 3.66 μg/g for PO and SC, respectively). Consequently, lung/plasma ratios were high, up to 50 and 80 after PO and SC administration, respectively. GAM could not be detected in PELF, although this might be attributed to the collection method of PELF in birds. The GAM minimum inhibitory concentration (MIC) was determined for 38 O. rhinotracheale strains; MIC50 and MIC90 were 2 and >32 μg/mL, respectively. PK/PD correlation for lung tissue demonstrated that the time above the MIC90 of the susceptible population (2 μg/mL) was 1 day after PO bolus and 3.5 days after SC administration. The area under the curve (AUClast)/MIC ratios for lung tissue after SC and PO administration were 233 and 90, respectively. To conclude, GAM is highly distributed to lung tissue in turkey poults, suggesting that it has the potential to be used to treat respiratory infections such as O. rhinotracheale.