Pharmacokinetics of the novel atypical opioid tapentadol following oral and intravenous administration in dogs

Tapentadol (TAP) is a novel opioid pain reliever drug with a dual mechanism of action (mu opioid receptor agonist and noradrenaline reuptake inhibitor). It is used as an analgesic in humans, but could be of interest for veterinary species if it has a suitable pharmacokinetic profile. Six dogs were randomly assigned to two treatment groups, using an open, single-dose, two-treatment, two-period, and randomised cross-over design. Each subject received TAP at 50 and 200mg by intravenous (IV) and oral route, respectively, with a 1-week wash-out period between administrations. Blood was collected at regular intervals and the plasma concentration of TAP in each sample was measured using a validated HPLC-FL method. After IV administration, concentrations of TAP were detectable in plasma for up to 6h with a half-life in the range 38–68min. After oral administration, drug absorption was rapid (Tmax, time required to reach the maximum concentration of 47.5min), but its bioavailability was low (4.4%). Some dose-related adverse effects, including salivation and sedation, were observed, particularly following IV administration. In summary, this study showed that TAP may be useful as an analgesic in the dog, but further studies, including in dogs requiring analgesia, are required to confirm efficacy.