The Pharmacokinetics of a Long-acting Oxytetracycline Formulation in Healthy Dogs and in Dogs Infected with Ehrlichia canis

The pharmacokinetic properties of oxytetracycline were studied following a single injection of a long-acting formulation (20 mg/kg body weight) into the semimembranosus muscle of healthy dogs and of dogs that had been experimentally infected with Ehrlichia canis. The disposition curves of the long-acting oxytetracycline formulation before and after infection were best described by a bi-exponential decline after a first-order absorption. The mean maximum serum concentration (C _max) following infection was significantly lower and the time taken to attain this concentration (t _max) was significantly shorter than that in the healthy dogs. The mean apparent elimination half-life (t _1/2) was significantly increased following infection. The corresponding rate constant () was significantly decreased. The absorption half-life (t _1/2ab) was significantly decreased after infection. The volume of distribution at steady state (V _dss) increased significantly following infection. It was concluded that the pharmacokinetic behaviour of a long-acting oxytetracycline in dogs after intramuscular administration is characterized by a two-compartment model with a slow elimination phase. This could be due to flip-flop kinetics. The febrile reaction in experimental E. canis infection affected some pharmacokinetic parameters of oxytetracycline.     

Measurement of Faecal Cortisol Metabolites in Cats and Dogs: A Non-invasive Method for Evaluating Adrenocortical Function

The aim of this comparative study was to gain more information about the metabolism and excretion of glucocorticoids in cats and dogs in order to establish non-invasive methods for evaluating stressful conditions. Therefore, in a first experiment, [¹⁴C]cortisol was administered intravenously to 8 animals (two of each sex and species). Over a period of 6 days, faeces and urine were collected immediately after spontaneous defecation and urination. Marked species differences were found, as cats mainly excreted cortisol in the faeces (82%±4% of the total recovered radioactivity), whereas in dogs only a small portion was found there (23%±4%). The highest urinary radioactivity was observed after 9±3 h in cats and 3±1 h in dogs. Peak concentrations in the faeces occurred after 22±6 h in cats and after 24±4 h in dogs. Most of the radioactivity was not extractable with diethyl ether, indicating that the metabolites excreted in urine and faeces were mainly of the conjugated or polar unconjugated types. This was confirmed by RP-HPLC, which also revealed marked differences between cats and dogs concerning the metabolites formed. In addition, the immunoreactivity of the metabolites was tested in cortisol, corticosterone and 11-oxoaetiocholanolone EIAs. The latter, measuring 11,17-dioxoandrostanes (11,17-DOA) detected the highest quantities of immunoreactive metabolites in cats, but not in dogs. In a second experiment, the adrenal cortex of both species was stimulated by ACTH and, three weeks later, suppressed by dexamethasone. In this study, only faeces were collected over a period of 7 days. In both species, inter-animal variability in the basal and maximal/minimal faecal cortisol metabolite concentrations and the time course was observed. The 11-oxoaetiocholanolone EIA in cats and the cortisol EIA in dogs proved best suited for monitoring changes in adrenocortical activity. ACTH injections resulted in an increase above baseline values of 355% (median) in 11,17-DOA concentrations in cats and of 702% in the concentrations of cortisol equivalents in dogs by about 25 h and 22 h (median) after injection, respectively. Minimal concentrations after dexamethasone administration were about 17% in cats and 31% in dogs (in relation to baseline values) and were reached in 66 h and 72 h, respectively. It was concluded that measuring cortisol metabolites in faeces should be a useful non-invasive tool for monitoring stress in carnivores.     

The validity of some haematological and elisa methods for the diagnosis of canine heartworm disease

Examinations for heartworm (Dirofilaria immitis) were performed on 175 impounded dogs from a hyperendemic area of the Po Valley (Italy). Each blood sample was used wiht five haematological diagnostic methods (filtration, direct smear, modified Knott, clotted blood and capillary tube) and three commercial ELISA kits (PetChek, Diasystems, Uni-Tec). The results were compared with the true infection status obtained from post-mortem examination of the heart, pulmonary arteries, thoracic venae cavae and lungs. The prevalence of the infection by adult worms at necropsy was 63%. The sensitivity of the tests ranged from 60% (capillary tube) to 81% (Diasystems) and the specificity from 88% (filtration) to 98% (PetChek). The results of all the tests differed significantly (p<0.01) from those obtained at necropsy. The sensitivity of the tests was also assessed with respect to the differing numbers of worms in the hosts. A positive correlation between the worm burden and the sensitivity was observed in all the tests. It is apparent that the ELISA methods were better able to detect cases with a low number of worms than the haematological tests.Abbreviations AC accuracy - CB clotted blood - CT capillary tube - DI Diasystems - DS direct smear - ELISA enzyme-linked immunosorbent assay - FI filtration - MK modified Knott - NPV negative predictive value - PE PetChek - PPV positive predictive value - SE sensitivity - SP specificity - UN Uni-Tec