New Approach Could Transform Local Anesthesia

A new study predicts that magnet-directed nanoparticles (MNPs) containing an anesthetic could one day provide a successful alternative to nerve block for local anesthesia.

Researchers at the of University of Pittsburgh School of Medicine (PA, USA) conducted an experimental pilot study to evaluate the use of MNP complexes containing 0.7% ropivacaine (R) and 12% magnetite (Fe₃O₄). The MNP/R complexes were injected intravenously (IV) into anesthetized rats. The researchers then placed magnets around the ankle of the right paw of the rats for 15, 30, or 60 minutes to draw the MNP/R complexes; once there, they would release the anesthetic, numbing the nerves around the ankle. Sensation was assessed by comparing the right paw to the left paw.

The results showed that the MNP/R complexes followed by magnet application produced significant nerve block in the right ankle, similar to a standard nerve block; the left ankle remained unaffected. The researchers found that the ankle block anesthesia produced was greatest when the magnet was applied for a period 30 minutes, likely reflecting the time of maximum ropivacaine release, leading to a high concentration build up by local sequestration via magnet use.

The researchers also discovered that in rats receiving MNP/R, the nanoparticles contained a total of 14 milligrams of ropivacaine, a dose high enough to cause potentially fatal toxic effects. Yet none of the animals in the study group had apparent adverse effects of ropivacaine and showed similar toxicity to rats in the control group that received one milligram of plain ropivacaine. Thus the safe dose of the MNP/R complex could be at least 14 times higher, compared to IV ropivacaine alone. The study was published in the April 2014 issue of Anesthesia & Analgesia.

“We have established proof of principle that it is possible to produce ankle block in the rat by intravenous injection of magnetic nanoparticles associated with ropivacaine and magnet application at the ankle,” concluded lead author Venkat Mantha, MD, and colleagues of the department of anesthesiology. “If proved safe, the magnet-directed approach could provide a useful new alternative for regional anesthesia, delivering high concentrations of local anesthetics directly to the desired area, without increasing toxic effects.”

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University of Pittsburgh School of Medicine