Time effect of experimental infection on Rainbow trout (Oncorhynchus mykiss) by immersion with Aeromonas salmonicida subsp. salmonicida.

Furunculosis caused by Aeromonas salmonicida subsp salmonicida (Ass) is a medically and economically important bacterial disease in salmonid farms that requires therapeutic measures to prevent and control the disease. Evaluation of the effectiveness of traditional measures such as antibiotics or vaccines usually requires infecting fish experimentally. The objective of this study is to develop a method of infectious challenge of large (250-g) Rainbow trout by immersion close to natural infection conditions. We compare mortality, morbidity and anti-Ass antibody production of Rainbow trout following different bathing times (2, 4, 8 and 24 h) at a final bacterial concentration of 106 CFU/mL. One hundred sixty fish divided in five groups corresponding to the 4 bathing times and the non-challenged group were studied. The 24 h contact duration resulted in the infection of all fish, with a mortality rate of 53.25%. The challenged fish developed acute infection with symptoms and lesions (inappetance, altering of swimming behaviour, presence of boils) similar to those observed in furunculosis, and produced antibodies against the bacterium at 4 weeks after challenging, in contrast with the non-challenged group.

Evaluation of the efficacy of enrofloxacin in rainbow trout (Oncorhynchus mykiss) following experimental challenge with Yersinia ruckeri.

BACKGROUND: Use of enrofloxacin in trout farms is reported, especially for the treatment of yersiniosis, albeit various dosing regimens have been used. Therefore, optimal doses should be investigated. METHODS: Five groups of 15 fish were challenged with Y. ruckeri. Two days later, three groups received feed containing enrofloxacin (ENR) at 1, 2.5 and 5 mg/kg fish respectively, during 7 days; one group received a single intraperitoneal injection of ENR at 10 mg/kg; and one group was left untreated. On day 15, surviving fish were euthanized. RESULTS: All fish survived in the group treated by injection, compared to 53%, 60% and 40% of the fish treated with 1, 2.5 and 5 mg/kg oral ENR, respectively, and 53% in the infected untreated group. CONCLUSION: A single intraperitoneal injection of ENR at 10 mg/kg seems more relevant than repeated oral administrations. The ENR oral doses used in trout farms should be revised.

Pharmacokinetics of low-dose methotrexate in horses.

This study aimed to investigate both the pharmacokinetic behavior and tolerance of methotrexate (MTX) in horses to design a specific dosing regimen as a new immunomodulatory drug for long-term treatment. To determine the primary plasma pharmacokinetic variables after single intravenous, subcutaneous or oral administration, six horses were administered 0.3 mg/kg MTX in a crossover design study. After a 10-week washout, MTX was administered subcutaneously to three of the six previously treated horses at a dose of 0.3 mg/kg once per week for 3 months. In both studies, MTX and metabolite concentrations were measured using LC-MS/MS. The absolute bioavailability of MTX was 73% following subcutaneous administration but less than 1% following oral administration. The plasma clearance was 1.54 ml min-1  kg-1 (extraction ratio = 2%). After 24 hr, plasma concentrations were below the LOQ. No adverse effects were noted except for a moderate reversible elevation in liver enzymes (GLDH). With regards to the main metabolites of MTX, very low concentrations of 7-hydroxy-MTX were found, whereas polyglutamated forms (mainly short chains) were found in red blood cells. A subcutaneous dose of 0.2 mg kg-1  week-1 may be safe and relevant in horses, although this has yet to be clinically confirmed.

Review of the Eprinomectin effective doses required for dairy goats: Where do we go from here?

Eprinomectin (EPM) has been recently granted a marketing authorisation in the European Union for use in goats, with a zero-day milk withdrawal period. Considering the high prevalence of benzimidazole resistance worldwide and the economic implications of managing milk residues, EPM may today be considered the main (or even the only) affordable treatment option, at least in dairy goats in the EU. However, the chosen dose (1 mg/kg) seems to be suboptimal, especially for lactating goats, and the chosen route of administration (Pour-on) highly subject to inter-individual variability. Considering the scarcity of anthelmintic resources, such a dosage regimen might threat the sustainability of this crucial drug in goat milk production and needs to be urgently discussed and reassessed.

Pharmacokinetics of low-dose methotrexate in healthy beagle dogs.

Methotrexate may be an alternative to ciclosporin in the treatment of canine atopic dermatitis (cAD) as suggested by recent data. The aim of the study was to investigate both the tolerance and the pharmacokinetic behavior of methotrexate (MTX) in plasma, following intravenous (i.v.), subcutaneous (s.c.) or oral (OR) administration over several weeks. Six healthy dogs were given oral MTX once a week, respectively, per dog at 2.5 mg/1 week, 5 mg/4 weeks, 7.5 mg/3 weeks, 10 mg/6 weeks and 12.5 mg/5 weeks. No clinically relevant abnormalities of laboratory parameters were noticed. A high inter-individual variation of MTX plasma concentration was observed with a suspicion of saturation phenomenon in absorption. To compare with other routes of administration, six healthy beagle dogs followed a crossover design study at 7.5 mg per dog MTX. The absolute bioavailability was 93% for SC injection and 30% for the oral route. The inter-individual variability was quite low following SC administration compared to oral route. Just as in human, given the substantial variability of oral absorption, clinicians cannot assume consistent oral bioavailability of MTX. Therefore, they may consider switching dogs to the SC route in case of absence of clinical response with a weekly oral dose.