Pharmacokinetic profiles of the analgesic flupirtine in dogs after the administration of four pharmaceutical formulations

Agomelatine: A novel melatonergic antidepressant. Method validation and first exploratory pharmacokinetic study in fasted and fed dogs

Agomelatine is a novel melatonergic antidepressant, with a non-monoaminergic mechanism of action. The aim of this study was to evaluate its plasma concentrations after a single oral dose of 300 mg/dog in fasted and fed status. The research was carried out in 6 adult healthy Labrador dogs according to a randomized open, single-dose, two-treatment, two-phase, paired 2 × 2 cross-over study. At the end of the study all the animals had received the drug in fasted and fed conditions. The drug concentrations were detected in plasma by a validated LC-MS/MS analytical method. The plasma concentrations of agomelatine were found to be extremely variable in both groups as well as the pharmacokinetic profiles. Due to these variable findings the only reliable pharmacokinetic parameters were assessed as C_max (31.8 vs 15.7 ng/mL), T_max (0.75 vs 4 h) and AUC (155 vs 52 ng h/mL) in fasted and fed status, respectively. Unfortunately, as a pioneer study, the small animal sample size used along with the unanticipated variability did not allow to neither statistically estimate if food can affect the pharmacokinetics of agomelatine nor recommend agomelatine for off-label therapies in canine species. Further studies are warranted to clarify this issue.

Comparative single-dose pharmacokinetics of sildenafil after oral and rectal administration in healthy beagle dogs

BACKGROUND

Sildenafil citrate, a highly selective phosphodiesterase type 5 inhibitor, is used to treat pulmonary hypertension (PH) in veterinary medicine. The objective of this study was to investigate pharmacokinetic profiles by oral administration of orally disintegrating film (ODF) and film coated tablet (FCT) formulations and rectal administration of ODF formulation in healthy dogs. Twelve healthy beagle dogs were administered four separate doses of sildenafil: FCT formulation 2 mg/kg orally, ODF formulation 2 mg/kg orally, ODF formulation 2 mg/kg rectally, and ODF formulation 10 mg/kg rectally. For 24 hours following administration, blood samples were collected and the plasma concentrations of sildenafil were assayed by liquid chromatography-tandem mass spectrometry.

RESULTS

There were no significant differences in all the pharmacokinetic parameters between FCT and ODF formulations when administrated orally. C_max at the time of rectal administration was lower when the same dose was given as that orally administered. No serious systemic adverse events (AEs) were observed.

CONCLUSIONS

These findings suggest that sildenafil ODF formulation can be used as an alternative to FCT formulation in the treatment of canine PH patients; additionally, rectal administration of sildenafil ODF may be a beneficial treatment option for canine patients who are unable to receive medication orally.

Synergistic interaction between tapentadol and flupirtine in the rat orafacial formalin test

Combination therapy with two or more analgesics is widely used for conditions associated with moderate to severe pain. Combinations of diverse analgesics with different modes of action can improve the risk-benefit ratio of analgesic treatments. The aim of this study is to evaluate the antinociceptive effect of tapentadol (TAP) and flupirtine (FLP), when administered separately or in combination, as well as their synergistic interaction in the orofacial formalin test in rats. After i.p. injection of TAP at different doses (2, 5, 10 and 15mg/kg), the biphasic nociceptive behavior was reduced in a dose-dependent manner in both phase I and II. Conversely, i.p. injection of FLP at different doses (0.6, 1.6, 3.3, 6.6, 16.6 and 22.2mg/kg) induced a dose-dependent antinociceptive effect in phase II only. TAP was found to be more effective than FLP. The interaction between TAP and FLP was synergistic in phase II with an interaction index (γ) of 0.50±0.24. The data reported in this study indicate that FLP enhances the antinociceptive effect of TAP and this drug combination might be potentially useful in the treatment of chronic pain.