Eugenol for anesthesia of African clawed frogs (Xenopus laevis)

Objective To determine the level of anesthesia attained in Xenopus laevis frogs with eugenol at different doses and by different routes of administration. Study design Prospective experimental trial. Animals Sixty X. laevis nonbreeding female frogs weighing between 90 and 140 g. Methods Three different routes of administration were tested - subcutaneous injections into the dorsal lymph sacs, topical administration using a gauze patch, and immersion in a bath containing eugenol. Following the determination of the best route of administration, the acetic acid test, the withdrawal reflex, righting reflex, heart rate, and respiratory frequency were used to evaluate central nervous system depression following eugenol bath administration. In an additional group, the response to a surgical incision of the abdominal wall was evaluated. The pharmacokinetics of eugenol were determined following bath immersion administration, and pharmacokinetic parameters were calculated following blood concentration determination by tandem liquid chromatography/mass spectrometry analyses. Results It was not possible to induce anethesia with subcutaneous and patch administration, independent of the eugenol dose administered. The immersion bath was the only efficacious route for anesthesia inducing surgical anesthesia for at least 30 minutes with postoperative analgesia. Histopathology of selected tissues (heart, lung, liver, kidneys, eyes) showed no evidence of lesions 24 hours following bath immersion. The elimination half-life (T-1/2) was 4 hours. Conclusions When administered as a single-bath immersion (dose 350 mg L-1) for 15 minutes, eugenol may serve as an effective anesthetic in X. laevis frogs for short surgical procedures.