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Long duration local anesthesia with lecithin-coated microdroplets of methoxyflurane: studies with rat skin
A F Kirkpatrick1, M Lavallee-Grey, D H Haynes
1Department of Anesthesiology, University of South Florida College Medicine, Tampa 33612-4799.
Abstract:
Lecithin-coated microdroplets of methoxyflurane (MOF) are shown to produce local anesthesia of three- to six-day duration in the skin with a single intradermal injection in rats. Anesthesia was quantitated by elevation of the threshold (milliampere) for shock vocalization with intradermal electrodes. Intradermal injection of 0.1 ml 0.5% MOF gave moderate (2.1 mA) anesthesia of approximately three-day duration for a 10-12-mm diameter area, with no damage to the tissue. Higher concentrations gave six-day duration anesthesia at very high level (7 to 12 mA) anesthesia of three- to five-day duration with some damage to the tissue. At 4.4% MOF, ulcers formed in the center of the injection site with maximal dimensions of 1.3 mm (11-13% of the site diameter). Phenol, a widely used neurolytic agent, was tested as a control in the same concentration range. Phenol at 4.4% gave very high level (8 mA) anesthesia for longer than seven-day duration and caused formation of ulcers with maximal dimensions of 3.8 mm (31-38% of the site diameter). Analysis showed that MOF produced less damage than phenol for any given degree of anesthesia. Systemic toxicity and pharmacokinetic data are also presented. Phenol produced a hypothermic reaction and behavioral changes, whereas MOF was without systemic effect. The plasma concentrations of phenol were four to five times greater than those of MOF. These results suggest that MOF may have clinical advantages over phenol.
Insights
Methoxyflurane (MOF) microdroplets offer prolonged local anesthesia in rats, lasting up to six days with minimal tissue damage compared to phenol. This novel approach shows potential clinical advantages for pain management.
Area of Science:
- Anesthesiology
- Pharmacology
- Biomaterials
Background:
- Local anesthesia is crucial for pain management.
- Phenol is a neurolytic agent but can cause significant tissue damage.
- Novel anesthetic agents with improved safety profiles are needed.
Purpose of the Study:
- To evaluate the efficacy and safety of lecithin-coated methoxyflurane (MOF) microdroplets for local anesthesia.
- To compare the anesthetic effects and tissue toxicity of MOF with phenol in rats.
Main Methods:
- Intradermal injections of MOF microdroplets and phenol were administered to rats.
- Anesthesia was quantified by measuring the threshold for shock vocalization.
- Tissue damage, systemic toxicity, and pharmacokinetic profiles were assessed.
Main Results:
- MOF provided local anesthesia lasting three to six days with minimal tissue damage.
- Higher MOF concentrations caused some tissue damage, including ulcers.
- Phenol induced anesthesia of longer duration but with significantly greater tissue damage and systemic effects.
Conclusions:
- Lecithin-coated MOF microdroplets demonstrate effective and prolonged local anesthesia in rats.
- MOF exhibits a more favorable safety profile with less tissue damage and systemic toxicity compared to phenol.
- MOF holds potential for clinical applications as a safer alternative to phenol for local anesthesia.