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Long duration local anesthesia with lecithin-coated microdroplets of methoxyflurane: studies with human skin
1Department of Pharmacology, University of Miami, School of Medicine, Florida.
Abstract:
Lecithin-coated microdroplets of methoxyflurane (MOF) have been reported to produce local anesthesia of long duration in rats. The present study was conducted in two phases. The first phase was open label studies in two human volunteers aimed at determining the effective concentration of MOF in human skin. Over the concentration range of 0.3-2.4%, MOF produced local anesthesia to pinprick and cold stimuli within 15 seconds. The duration of the anesthesia effect of 2.4% MOF in the skin of the buttock, forearm and leg was five to eight days. Microdroplets containing isoflurane, a more volatile agent, gave an anesthetic effect that reversed within two to five hours. In the second phase of the study, the safety and efficacy of MOF were compared to phenol in placebo-controlled and blinded studies using indwelling stimulating electrodes. Phenol was destructive to skin at a concentration necessary to obtain a degree of local anesthesia comparable to MOF. The greater part of the anesthetic effect produced by phenol at this "toxic" concentration was transient (approximately one hour). In contrast to phenol, MOF produced an anesthetic effect lasting four to seven days without producing visible damage to skin. These results suggest that MOF is safer and more efficacious than phenol for producing long-lasting local anesthesia of human skin.
Insights
Methoxyflurane (MOF) microdroplets provide long-lasting local anesthesia in human skin, lasting up to eight days. MOF demonstrated superior safety and efficacy compared to phenol for sustained pain relief.
Area of Science:
- Anesthesiology
- Dermatology
- Pharmacology
Background:
- Methoxyflurane (MOF) has shown potential for prolonged local anesthesia in animal models.
- Previous research indicates MOF microdroplets may offer extended anesthetic effects.
Purpose of the Study:
- To determine the effective concentration and duration of methoxyflurane (MOF) for local anesthesia in human skin.
- To compare the safety and efficacy of MOF with phenol for long-lasting skin anesthesia.
Main Methods:
- Phase 1: Open-label studies in human volunteers to assess MOF concentration and anesthetic effect duration.
- Phase 2: Placebo-controlled, blinded studies comparing MOF and phenol using stimulating electrodes.
- Evaluated skin response, anesthetic duration, and visible tissue damage.
Main Results:
- MOF achieved local anesthesia within 15 seconds at concentrations of 0.3-2.4%.
- Anesthetic effects of 2.4% MOF lasted five to eight days without visible skin damage.
- Phenol required toxic concentrations for comparable anesthesia, with effects lasting only one hour and causing skin damage.
Conclusions:
- Methoxyflurane (MOF) is a safer and more effective agent than phenol for achieving long-lasting local anesthesia in human skin.
- MOF offers a promising alternative for sustained pain management without adverse tissue effects.