Fentanyl Transdermal Therapeutic System Provides Rapid Systemic Fentanyl Absorption in Two Ball Pythons (Python regius)

Abstract Although our understanding of reptile analgesia continues to develop, μ-opioid receptor agonists are currently the most effective analgesics in a variety of reptile species. Fentanyl, a potent, short-acting, μ- and δ-opioid receptor agonist, is formulated for use as a transdermal therapeutic system (TTS) and was shown to be absorbed across the skin of prehensile-tailed skinks (Corucia zebrata). Snakes, which possess highly permeable skin, seem to be ideal candidates for effective transdermal analgesia. Fentanyl TTS (12 μg/h) was applied to the midbody, dorsal surface of two ball pythons (Python regius). Specimen mean body weight was 2.60 kg (2.20–2.99 kg). Cardiac blood samples were collected for 7 days, and plasma fentanyl concentrations were determined using high-performance liquid chromatography–mass spectroscopy. Therapeutic concentrations, as defined in mammals (1 ng/ml), were reached within 4 h of patch application, and they were sustained throughout the study. Plasma fentanyl steady-state (8.68–10.3 ng/ml) and maximum (11.7–17.6 ng/ml) concentrations were substantially higher than those demonstrated to attain analgesia in mammals, suggesting the potential to use smaller dosages. Patches remained well adhered throughout the study. Snakes exhibited no adverse side effects during the experiment. Data from this study suggest that the TTS delivers quantifiable fentanyl concentrations in ball python plasma and may serve as a route for prolonged analgesia administration to snakes. Additional research is needed to further determine treatment efficacy and safety and to optimize the dosing regimen.