Effect of Acetaminophen Alone and in Combination with Morphine and Tramadol on the Minimum Alveolar Concentration of Isoflurane in Rats

Abstract

BackgroundIt has been observed that acetaminophen potentiates the analgesic effect of morphine and tramadol in postoperative pain management. Its capacity as an analgesic drug or in combinations thereof to reduce the minimum alveolar concentration (MAC) of inhalational anesthetics represents an objective measure of this effect during general anesthesia. In this study, the effect of acetaminophen with and without morphine or tramadol was evaluated on the isoflurane MAC.MethodsForty-eight male Wistar rats were anesthetized with isoflurane in oxygen. MACISO was determined from alveolar gas samples at the time of tail clamping without the drug, after administering acetaminophen (300 mg/kg), morphine (3 mg/kg), tramadol (10 mg/kg), acetaminophen (300 mg/kg) + morphine (3 mg/kg), and acetaminophen (300 mg/kg) + tramadol (10 mg/kg).ResultsThe control and acetaminophen groups did not present statistically significant differences (p = 0.98). The values determined for MACISO after treatment with acetaminophen + morphine, acetaminophen + tramadol, morphine, and tramadol were 0.98% ± 0.04%, 0.99% ± 0.009%, 0.97% ± 0.02%, and 0.99% ± 0.01%, respectively.ConclusionsThe administration of acetaminophen did not reduce the MAC of isoflurane and did not potentiate the reduction in MACISO by morphine and tramadol in rats, and therefore does not present a sparing effect of morphine or tramadol in rats anesthetized with isoflurane.

Minimum Alveolar Concentration of Isoflurane in Rats Chronically Treated with the Synthetic Cannabinoid WIN 55,212-2

“…Once instrumentation was performed, and prior to assessing MAC isoflurane, Fe Iso was adjusted to 1.32%, which is a value close to the isoflurane MAC previously reported by the authors [ 15 ]. Once this concentration was achieved, it was maintained for 15 min in order to achieve the equilibrium of isoflurane partial pressure between alveolar gas, arterial blood, and the spinal cord.…”

Perioperative Opioid Administration

“…3,40,41 However, the amount of intraoperative opioid sparing could differ between surgical procedures, and not all analgesics may be safe in all procedures or patients. 4,42,43…”

Clinical evaluation of postoperative analgesia, cardiorespiratory parameters and changes in liver and renal function tests of paracetamol compared to meloxicam and carprofen in dogs undergoing ovariohysterectomy

“…In part, the varying physiological interactions that paracetamol has may be in part to do with its potentiation of the analgesic effects of morphine [32] and tramadol in the management of postoperative pain in humans. This interaction likely varies with veterinary application as the use of analgesic drugs to reduce the minimum alveolar concentration of inhaled anaesthetics has not been proven [33]. However, clinically, the analgesic efficacy of the combined use of hydrocodone and paracetamol leads to similar responses to tramadol as does a single agent for the treatment of postoperative pain in dogs undergoing tibial plateau levelling osteotomy [34].…”