In vitro binding of cefovecin to plasma proteins in Australian marsupials and plasma concentrations of cefovecin following single subcutaneous administration to koalas (Phascolarctos cinereus)

CEFOVECIN PROTEIN BINDING AS A PREDICTOR FOR EXTENDED DURATION OF ACTION: A REVIEW OF CURRENT LITERATURE AND IN VITRO ANALYSIS IN MULTIPLE ZOOLOGICAL SPECIES

Cefovecin is a third-generation cephalosporin antibiotic with an efficacy of 2 wk following a single injection in domestic dogs and cats. A high degree of plasma protein binding to cefovecin has been proposed as one of the mechanisms responsible for the long elimination half-life, but protein binding has not been evaluated extensively in nondomestic species. In this study, a review of the current literature was conducted, and pharmacokinetic data were compiled for species in which cefovecin has been evaluated thus far. Additionally, in vitro cefovecin protein binding was evaluated in plasma from 22 nondomestic species representing a broad range of taxa. Animals of the order Carnivora demonstrated protein-binding levels of >98%, which is supportive of the long elimination half-life seen in related species. Protein binding was highly variable in Artiodactyl and Perissodactyl species, with dolphins (Tursiops truncatus) and barasingha (Rucervus duvaucelii) displaying high protein binding (99.12% to >99%), but not gazelles (Eudorcas thomsonii) or equids (91.76-92.70%). Cefovecin was not highly bound in any reptiles or birds, corresponding to short half-lives reported for these taxa. These results suggest that a high percentage of plasma protein binding in vitro may predict in which species cefovecin may exhibit a long half-life and duration of action in vivo. These findings may aid in selecting species for cefovecin pharmacokinetic research and for empirical treatment of infections caused by susceptible bacteria.

Pharmacokinetic profile of injectable tramadol in the koala (Phascolarctos cinereus) and prediction of its analgesic efficacy

Tramadol is used as an analgesic in humans and some animal species. When tramadol is administered to most species it undergoes metabolism to its main metabolites M1 or O-desmethyltramadol, and M2 or N-desmethyltramadol, and many other metabolites. This study describes the pharmacokinetic profile of tramadol when a single subcutaneous bolus of 2 mg/kg was initially administered to two koalas. Based on the results of these two koalas, subsequently 4 mg/kg as a single subcutaneous injection, was administered to an additional four koalas. M1 is recognised as an active metabolite and has greater analgesic activity than tramadol, while M2 is considered inactive. A liquid chromatography assay to quantify tramadol, M1 and M2 in koala plasma was developed and validated. Liquid chromatography-mass spectrometry confirmed that M1 had been identified. Additionally, the metabolite didesmethyltramadol was identified in chromatograms of two of the male koalas. When 4 mg/kg tramadol was administered, the median half-life of tramadol and M1 were 2.89 h and 24.69 h, respectively. The M1 plasma concentration remained well above the minimally effective M1 plasma concentration in humans (approximately 36 ng/mL) over 12 hours. The M1 plasma concentration, when tramadol was administered at 2 mg/kg, did not exceed 36 ng/mL at any time-point. When tramadol was administered at 2 mg/kg and 4 mg/kg the area under the curve M1: tramadol ratios were 0.33 and 0.50, respectively. Tramadol and M1 binding to plasma protein were determined using thawed, frozen koala plasma and the mean binding was 20% and 75%, respectively. It is concluded that when tramadol is administered at 4 mg/kg as a subcutaneous injection to the koala, it is predicted to have some analgesic activity.

Assay validation and determination of in vitro binding of mefloquine to plasma proteins from clinically normal and FIP-affected cats

The antimalarial agent mefloquine is currently being investigated for its potential to inhibit feline coronavirus and feline calicivirus infections. A simple, high pressure liquid chromatography assay was developed to detect mefloquine plasma concentrations in feline plasma. The assay’s lower limit of quantification was 250 ng/mL. The mean ± standard deviation intra- and inter-day precision expressed as coefficients of variation were 6.83 ± 1.75 and 5.33 ± 1.37%, respectively, whereas intra- and inter-day accuracy expressed as a percentage of the bias were 11.40 ± 3.73 and 10.59 ± 3.88%, respectively. Accordingly, this validated assay should prove valuable for future in vivo clinical trials of mefloquine as an antiviral agent against feline coronavirus and feline calicivirus. However, the proportion of mefloquine binding to feline plasma proteins has not been reported. The proportion of drug bound to plasma protein binding is an important concept when developing drug dosing regimens. As cats with feline infectious peritonitis (FIP) demonstrate altered concentrations of plasma proteins, the proportion of mefloquine binding to plasma proteins in both clinically normal cats and FIP-affected cats was also investigated. An in vitro method using rapid equilibrium dialysis demonstrated that mefloquine was highly plasma protein bound in both populations (on average > 99%).