Tandospirone ameliorates fentanyl-induced respiratory depression and potentiates analgesic and sedative effects

To evaluate the effect of tandospirone (TS) on fentanyl (FEN)-induced respiratory depression and its impact on fentanyl's analgesic and sedative effects, a rat model of respiratory depression was established using FEN. After drug administration, respiratory frequency (F), tidal volume (TV), expiratory volume (EV), and enhanced pause (PENH) were measured using plethysmography. Blood oxygen saturation (SaO₂) was measured using a non-invasive pulse meter. The acetic acid writhing test, hot-plate test, and spontaneous activity test were used to evaluate the number of writhes, reaction time, and locomotor activity in mice. The righting reflex test was used to measure the loss rate and immobility time in rats this experiment was approved by the Institute of Military Medicine Experimental Animal Management and Utilization Committee (approval number: IACUC-2023-001C). Compared with the respiratory depression model group (FEN 160 μg·kg^-1), the changes of F, TV, EV, PENH, SaO₂ in rats at the same time points after pre-treatment and treatment of different doses of TS were improved. TS (2 mg·kg^-1) and TS+FEN groups reduced the number of writhing movements, total distance of spontaneous activity and increased the maximmal possible effect (MPE), indicating that TS has its own analgesic and sedative effect and enhances the analgesic and sedative effect of FEN. The increase in the median effective concentration (EC₅₀) of loss of the righting reflex (LORR) and the reduction in immobilization time confirm that preconditioning with TS has a protective effect against FEN poisoning. In conclusion, TS ameliorates FEN-induced respiratory depression, and it possesses inherent sedative and analgesic effects. When co-administered with FEN, TS can enhance the analgesic and sedative effects of FEN. TS could serve as a non-opioid medication to improve opioid-induced respiratory depression and warrants further development and research.