Background and Objective: Morphine is the most effective analgesic in the treatment of moderate to severe pain, but animal studies have reported a short analgesic effect for the drug after a single injection. Sufficient level of morphine concentration for an extended period of time is necessary to provide effective treatment with the drug. Chitosan has the desired properties for safe use as a pharmaceutical recipient. We aimed to use a chitosan-based molecular imprinted polymer (CS-MIP) nanogel to extend duration of morphine (10 mg/kg) analgesic effect in mice. Materials and Methods: A chitosan-based molecular imprinted polymer (CS-MIP) nanogel was synthesized in the presence of morphine template and fully characterized. Duration of analgesic effect of morphine-loaded CS-MIP after a single injection was assessed in male albino NMRI mice on a hotplate test. Control mice received morphine (10 mg/kg) dissolved in normal saline. Findings: The CS-MIP nanogel particles with 25 nm size range exhibited 98% loading efficiency. In vitro release results showed an initial burst followed by an extended slow release of morphine. The results of hotplate test showed that subcutaneous injection of morphine-loaded CS-MIP induced lasting analgesia for 270 min after injection compared to 150 min in mice receiving morphine (10 mg/kg) dissolved in normal saline. Conclusion: The results suggest that CS-MIP nanogel can be a possible strategy as morphine carrier for controlled release and extension of its analgesic efficacy.
