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Prolonged analgesia and decreased toxicity with liposomal morphine in a mouse model
G J Grant1, K Vermeulen, M I Zakowski
1Department of Anesthesiology, New York University Medical Center, New York 10016.
Abstract:
Inadequate control of postoperative pain remains a major clinical problem. A reliable method of providing long-lasting postoperative analgesia with a single dose would be very useful. We synthesized a liposomal morphine formulation and compared it to free morphine with regard to duration of analgesia in the mouse. Analgesia was assessed after intraperitoneal injection using the tail-flick test. The systemic toxicity after administration of liposomal and free morphine was compared. The release rate of morphine from liposomes in vitro was also evaluated. The lethal intraperitoneal dose of free morphine in 50% of mice (LD50) was 400 mg/kg. The maximum safe (non-lethal) dose of free morphine was 130 mg/kg. The highest dose of liposomal morphine administered (1650 mg/kg) did not cause death in any animal. Duration of analgesia was significantly prolonged with the highest dose of liposomal morphine (21.5 +/- 5.3 h) compared to the maximum safe dose of free morphine (3.7 +/- 0.75 h), P < 0.01. In vitro experiments showed a slow release rate of morphine from the liposome depot. Prolonged analgesia and decreased systemic toxicity for liposomal morphine are explained by sustained release of morphine from the liposomal depot. These results suggest that liposomal narcotic formulations may provide prolonged analgesia with single-dose administration.
Insights
New liposomal morphine offers extended pain relief after surgery. This formulation provides longer-lasting analgesia with reduced toxicity compared to traditional morphine, suggesting a promising single-dose treatment option.
Area of Science:
- Pharmacology
- Drug Delivery Systems
- Pain Management
Background:
- Postoperative pain management remains a significant clinical challenge.
- Effective, long-lasting analgesia from a single dose is highly desirable.
Purpose of the Study:
- To develop and evaluate a liposomal morphine formulation for prolonged postoperative analgesia.
- To compare the efficacy and safety of liposomal morphine against free morphine in a mouse model.
Main Methods:
- Liposomal morphine and free morphine were administered intraperitoneally to mice.
- Analgesia was assessed using the tail-flick test.
- Systemic toxicity and in vitro morphine release rates were evaluated.
Main Results:
- Liposomal morphine demonstrated significantly prolonged analgesia (21.5 h) compared to free morphine (3.7 h).
- Liposomal morphine exhibited reduced systemic toxicity, with no mortality at doses up to 1650 mg/kg.
- In vitro studies confirmed a slow release rate of morphine from the liposomal formulation.
Conclusions:
- Liposomal morphine provides sustained release, leading to prolonged analgesia and decreased toxicity.
- This liposomal formulation represents a promising approach for single-dose, long-lasting postoperative pain management.