Pharmacokinetics of the Novel Cyclooxygenase 2 Inhibitor Cimicoxib in Donkeys

A preli­minary study of endoscopic diagnosis of gastric ulcer in Egyptian donkeys (Equus asinus) pa­ra­sitised by Gasterophilus intestinalis (Diptera: Oestridae)

Equine gastric ulcer syndrome (EGUS) is a communal broad problem in equines but in donkeys, the disease is a subclinical disorder which leads to economic losses. Gasterophilus intestinalis larvae are the most predominant parasitic infestation in donkeys. The present study was planned to facilitate the early and efficient diagnosis of gastric ulceration in donkeys through gastroscopic examination. The study was conducted on 120 adult Egyptian donkeys (Equus asinus) from both sexes after a one-month acclimatisation period. Gastroscopic examination was used to evaluate the presence of gastric lesions. In the majority of infested donkeys, G. intestinalis larvae were in the non-glandular part of the stomach. The prevalence of Gastrophilus larvae in animals reached 96.66%. The infestation percentage among jennets (97.5%) was slightly higher than that among jacks (96.25%). After morphological identification of the 3rd instar of larvae, all donkeys were found to be infested by G. intestinalis larvae. The histopathological examination of the affected stomach revealed severe necrosis of the gastric mucosa. Gastroscopic examination is the main diagnostic tool for examination of gastric lesions in the donkeys, so it is necessary as a routine diagnostic tool in donkeys’ examinations.

Clinical Pharmacology in Donkeys and Mules

Donkeys and mules show several pharmacodynamic and pharmacokinetic idiosyncrasies that have to be fully considered by any clinician dealing with these species. Because they possess an increased metabolic rate and cellular water content compared with horses, higher doses (or shorter dosing intervals) are usually recommended for those drugs where pharmacologic studies have been performed. Nonetheless, owing to the lack of species-specific information, this assumption cannot be arbitrarily applied. Thus, when a drug protocol published for horses is extrapolated to a donkey or a mule, a close monitoring is required to detect any secondary effect or subdosing.

Evaluation of pharmacokinetic properties of vitacoxib in fasted and fed horses

The pharmacokinetic properties of vitacoxib have not been established completely; current dosage recommendations are based on clinical experiences. The primary objective of this study was to describe plasma concentrations and characterize the pharmacokinetics of vitacoxib formulation following oral administrations in horses. Also, the effect of the state of stomach contents on the absorption of vitacoxib was investigated in fed/fasted horses. Blood samples were collected prior to and at various times up to 72 hr post-administration. Drug concentrations were measured using ultra high-performance liquid chromatography-tandem mass spectrometry. Pharmacokinetic parameters were calculated using Non-Compartmental Analysis Model 200 in WinNonlin™ software. No complications resulting from the vitacoxib administration were noted. All procedures were tolerated well by the horses throughout the study. C_max was 17.5 ± 9.36 ng/ml (fasted) and 9.47 ± 3.53 ng/ml (fed) following oral administrations. AUC_last was 173.7 ± 137.9 ng hr/ml (fasted) and 113.2 ± 70.8 ng h/ml (fed). No significant differences in pharmacokinetic parameters were noted and the results from the pharmacokinetic analysis were similar between the studies, regardless of precision of dosage and fasted and fed conditions. The study extends previous studies describing the pharmacokinetics of vitacoxib following p.o. administration to the horses. Further studies investigating the pharmacokinetics/pharmacodynamics of vitacoxib are necessary to establish adequate therapeutic protocols (optimal dosage and frequency of administration) in horses.

Plasma profile of cimicoxib in sheep after oral administration at two different rates

Sheep are often subjected to painful procedures and thus they need to be treated with analgesics. Nevertheless, knowledges about pharmacokinetic features of these drugs in this species are poor. The aim of this study was to evaluate plasma behaviour of cimicoxib in sheep after a single oral administration at two different dose rates (4 and 6 mg/kg). Maximum plasma concentrations of cimicoxib were equal to 273.78 (median value; range 189.00-567.32) and 565.01 (range 308.27-822.59) ng/mL after treatment with 4 and 6 mg/kg, respectively. The time of maximum concentration (Tmax) was achieved between 4 and 10 hours following treatment at the lower dose, and between 6 and 10 hours after the administration of the higher dose, with one sheep achieving the concentration peak at 0.75 hours. The slow absorption and the great individual variability in plasma concentration, probably due to ruminal effects, suggest that cimicoxib is not suitable for oral treatment in sheep.

Pharmacokinetics and disposition of flupirtine in the horse

Flupirtine (FLU) is a non-opioid analgesic drug, with no antipyretic or anti-inflammatory effects, used in the treatment of a wide range of pain states in human beings. It does not induce the side effects associated with the classical drugs used as pain relievers. The aim of this study was to evaluate the pharmacokinetic profiles of FLU after IV and PO administration in healthy horses. Six mixed breed adult mares were randomly assigned to two treatment groups using an open, single-dose, two-treatment, two-phase, paired, cross-over design (2 × 2 Latin-square). Group 1 (n = 3) received a single dose of 1 mg/kg of FLU injected IV into the jugular vein. Group 2 (n = 3) received FLU (5 mg/kg) via nasogastric tube. The animals then swapped groups after a 1-week wash-out period and the doses were repeated. Blood samples (5 mL) were collected at 0.25, 0.5, 0.75, 1, 1.5, 2, 4, 6, 8, 10, 24, 36 and 48 h and plasma was then analysed by a validated HPLC method. Some mild and transient adverse effects (that spontaneously resolved within 5 min) were observed in 2/6 animals after IV administration. No adverse effects were noticed in the PO administration group. After IV and PO administrations, FLU was detectable in plasma for up to 36 h. The mean elimination half-life was longer after PO (10.27 h) than after IV (3.02 h) administration. The oral bioavailability was 71.4 ± 33.1%. After compartmental simulation/modelling, an oral dose of 2.6 mg/kg was calculated to give Cmax and AUC values in horses similar to those reported in humans after a clinical dose administration with a theoretical FLU effective plasma concentration of 187 ng/mL. These findings may form the basis for further studies concerning this active ingredient in equine medicine.

Disposition of cimicoxib in plasma and milk of whelping bitches and in their puppies

BACKGROUND

Caesarean section of bitches is a well recognized painful condition in dogs and it can be classified as a soft tissue surgery. Cimicoxib, a newly registered NSAID in European Union has a claim for the relief of pain in peri-operative conditions. However, in case of caesarean section, the main concerns of using NSAIDs are the transfer of the drugs into milk and its impact on the suckling pups. Thus, the aim of the present work was to evaluate the transfer of cimicoxib into the milk of 6 lactating bitches after a single oral administration of the drug on day 0 (just after whelping) and on day 28 at the target dose of 2 mg/kg. Another aim of the study was to evaluate the transfer of the drug from the milk into the suckling pups. Blood and milk samples were collected from the bitches after each administration on day 0 and day 28 and blood samples were drawn from the pups after suckling on day 28.

RESULTS

All bitches whelped without any complication and gave birth to 38 pups. After administration on D0, the mean observed plasma Cmax in bitches was 0.5323 μg/mL and the mean area under the concentration-time curve extrapolated to the infinity, AUCINF, was 2.411 μg.h/mL. After administration on D28, only AUCINF was significantly higher with a value of 3.747 μg.h/mL. In milk, after administration on D0, the mean observed Cmax was 0.9974 μg/mL and the mean area under the concentration-time curve until the last measurable time point, AUClast, was 4.205 μg.h/mL. Out of 24 sampled pups on D28, only 2 animals had a sample with very low cimicoxib concentrations slightly above the limit of quantification (0.01 μg/mL).

CONCLUSION

The presented data show that cimicoxib given by oral route to lactating bitches at a single dose of 2 mg/kg had a high transfer rate into the milk with a milk to plasma ratio of 1.7 to 1.9. The transfer rate to the suckling pups was low and no clinical abnormalities were detected in both bitches and pups.