Use of the novel atypical opioid tapentadol in goats (Capra hircus): pharmacokinetics after intravenous, and intramuscular administration

The objective of the present study was to assess the pharmacokinetics of the novel atypical drug tapentadol (TAP) after intravenous (I.V.) and intramuscular (I.M.) injections in clinically healthy goats. A 2x2 cross-over design study was carried out. Six local adult Nubian nonlactating, nonpregnant female goats, were given 5mg/kg body weight of TAP by I.V. and I.M. routes. The concentrations of TAP in plasma were evaluated using a validated HPLC method. Transient adverse effects were noticed in some animals, especially after I.V. administration (tremors and ataxia). Three days after drug administration, severe hair loss was also recorded. The plasma concentrations after the two routes of administration were best described by a bi-compartmental model. After I.M. injection, TAP showed a very fast absorption (T-max=0.17h) and a short half-life (1.29h). The I.M. bioavailability was quite high, despite being variable (87.8 +/- 35.6%). This is the first pharmacokinetic study of TAP in goats but due to its unknown safety profile and efficacy, it is premature to recommend the use of this drug in clinical ovine practice.