Ropivacaine combined with MNP in mouse anesthesia

It was to study the preparation of magnetic nanoparticles (MNP)-encapsulated ropivacaine (RP) anesthesia and to explore its metabolism in mice and its effect on the function of various organs in mice. Fe₃O₄ MNP gel-encapsulated RP complex (RP–MNP) was prepared, and the content and release characteristics of RP were determined in vitro using the ultraviolet–visible spectroscopy. 30 BALB/c mice were randomly divided into 3 groups: RP-I (0.05% RP), RP-NG (1% RP encapsulated 1% RP, no Fe₃O₄ MNP), and RP-MNP (RP–MNP complex), all were injected into the tail vein with the volume of 2 mL, and there were 10 mice in each group. All mice were covered with ring and round magnets in their right paws instead of left paws. The thermal nociception test was used to detect the withdrawal latency of the left and right paws of each group of mice, and to detect the concentration of RP in plasma and ankle tissues and the cardiopulmonary function, serum biochemical indicators, and pharmacokinetic indicators of the mice in each group. The release efficiency of RP was the best at 37 °C. The withdrawal latency of right hind paw of mice in the RP-NG group was significantly lower than that in the RP-I group and the RP-MNP group in 10–80 min (P < 0.05). The withdrawal latency of right hind paw of mice in the RP-MNP group was significantly higher than that in the RP-I group in 10–60 min (P < 0.05). Compared with RP-I group, RP concentration in plasma and ankle tissue of mice in RP-NG group and RP-MNP group were significantly reduced (P < 0.05). Compared with the RP-I group and the RP-NG group, the heart rate, systolic blood pressure, diastolic blood pressure, and mean arterial pressure of the RP-MNP group were significantly reduced (P < 0.05). Compared with RP-I group and RP-MNP group, PeCO₂ and PaO₂ in RP-NG group were significantly reduced (P < 0.05). There were no significant differences in serum biochemical indicators and pharmacokinetic indicators between the three groups, such as blood urea nitrogen, alanine aminotransferase, creatine kinase, and creatinine. The drug-loaded magnetic nanoparticle RP–MNP complex, injected into mice via the tail vein and applied magnets to the ankle, can produce local anesthesia block in the ankle of mice, and its security and efficacy were higher than intravenous injection of ropivacaine alone.