Feline Pharmacokinetics of Oral Transmucosal and Intramuscular Dexmedetomidine and Buprenorphine

Introduction
Plasma concentrations and pharmacokinetics of dexmedetomidine and buprenorphine after oral transmucosal (otM) and intramuscular (iM) administration in cats were evalu- ated. the aim was to compare systemic absorption of this sedative-analgesic combina- tion following otM and iM administration.

Material and Methods
According to a cross-over protocol (1 month wash-out), a combination of dexmedeto- midine (40 μg/kg) and buprenorphine (20 μg/kg) was given otM (buccal cavity)(1) or iM (quadriceps muscle) in 6 female neutered cats. plasma samples were collected through a jugular catheter during a 24-hour period. plasma dexmedetomidine and buprenor- phine concentrations were determined by liquid chromatography-tandem mass spec- trometry. plasma concentration-time data were fitted to compartmental models (MW/ pharm, Mediware). Wilcoxon signed rank tests were performed (p < 0.05).

Results
For dexmedetomidine, the area under the plasma concentration-time curve from 0 to 12 h was significantly different between otM (9.59 ± 3.88 ng·h/ml) (mean ± SD) and iM administration (38.56 ± 8.66 ng·h/ml). Maximum plasma concentration of dexmedeto- midine was significantly lower after otM (3.59 ± 2.02 ng/ml) than after iM route (22.07 ± 8.91 ng/ml). for buprenorphine, the area under the plasma concentration-time curve from 0 to 6 h was significantly different between otM (16.91 ± 7.68 ng·h/ml) and iM (178.63 ± 71.50 ng·h/ml) administration. Buprenorphine achieved maximum plasma concentrations of 5.19 ± 3.09 ng/ml at 1.18 ± 0.34 h after otM administration and of 104.31 ± 0.52 ng/ml at 0.15 ± 0.15 h after iM injection with a significant difference between both treatments. Dexmedetomidine and buprenorphine relative bioavailabili- ties after otM compared to iM administration were 25.9 ± 11.2 % and 11 ± 6.4 %, respectively.

Conclusions
These data suggest that absorption of combined dexmedetomidine and buprenor- phine is less after otM administration compared to iM injection in cats. Clinical efficacy of this sedative-analgesic regimen after otM administration is questionable.