New Anesthetic Delivery System Targets Pain Fibers Exclusively-Pain Medicine News

March 1, 2010 at 4:56 pm 2 comments

New Anesthetic Delivery System Targets Pain Fibers Exclusively.

New Anesthetic Delivery System Targets Pain Fibers Exclusively

Clayton Simmons

New York—A new delivery system for local anesthetics that can specifically target pain-transmitting neurons appears to eliminate the disruption of motor function and tactile sensation that is characteristic of current drugs and may improve outcomes after procedures. Human trials of the delivery system, to date studied only in animals, may begin this year.

The delivery system exploits a characteristic unique to nociceptive neurons, the only cells in the peripheral nervous system that express the receptor TRPV1. Capsaicin opens this receptor, and TRPV1 is large enough to allow lidocaine—and other local anesthetics—into the cell.

One of the developers, Clifford Woolf, MD, PhD, chair of anesthesia research at Massachusetts General Hospital in Boston, began his research using QX-314, a derivative of lidocaine. Because it is aquaphilic, QX-314 cannot permeate cell membranes and thus produces no effect when delivered alone. Until now, its use has been relegated to experiments in petri dishes and animals. But by injecting it with capsaicin, Dr. Woolf and colleagues were able to open TRPV1 receptors, which in turn enabled QX-314 to target pain neurons.

Published in Nature in 2007 (449:607-610), these test tube studies confirmed the ability of QX-314 to create a pain-specific block, but a practical issue remained—capsaicin caused tremendous burning that eliminated any clinical benefits the combination might have. Fortunately, an unrelated research group found that lidocaine alone can open the TRPV1 receptor (J Clin Invest 2008;118:763-776).

Investigated in rats, the combination of QX-314 and lidocaine seems promising, Dr. Woolf said at the World Institute of Pain’s recent biannual meeting. The lidocaine blocks all nerve activity for approximately 30 minutes, after which QX-314 maintains a block on nociceptive neurons lasting at least six hours, producing a long-lasting anesthetic that preserves mobility and tactile sensation.

Future Promise

Such a drug combination promises to make local anesthesia more comfortable and may improve postprocedural outcomes, explained Dr. Woolf. The drug would eliminate the feeling of “fat lips” that accompanies dental surgery. But more importantly, it would also allow patients to return to mobility faster than with current drugs. Women in labor who receive an epidural would retain muscle control and would be able to stand soon after birth. Patients undergoing joint replacements might be able to ambulate sooner, a factor associated with better outcomes. Although this research will take time to reach the bedside, Dr. Woolf said that his laboratory is collaborating with Endo Pharmaceuticals to develop the drug.

QX-314 has yet to undergo toxicity testing in humans, noted James P. Rathmell, chief of pain medicine at Massachusetts General Hospital and a collaborator with Dr. Woolf. As a result, it will be years before it can be studied in large clinical trials.

In the meantime, researchers want to experiment with other compounds that might achieve similar effects but that could come to market sooner. Human trials using such compounds may start this year. Peter Gerner, MD, assistant professor of anesthesiology at Harvard Medical School and another collaborator in this research, is investigating the combination of bupivacaine and capsaicin. In rats, bupivacaine eliminates the burning from capsaicin, and even though bupivacaine temporarily blocks all nerve function, the pain neurons remain dormant for longer, Dr. Gerner told Pain Medicine News.

In the future, Dr. Gerner suggested that researchers may be able to develop a delivery system for QX-314 that would eliminate the motor block entirely. Researchers have investigated more specific local anesthetic delivery systems for years without much success, Dr. Gerner acknowledged. However, “this one is really different,” he said. “The experimental work is much stronger.”


Entry filed under: Allodynia, Analgesia, Anesthesia, C-Fibers, Chief Complaint, Cold, Complaints, Daubert Test, Drugs, False Diagnosis, Hot, Medical, Nerve, Nocioception, Pain, Pain Fibers, Peer-Review, Perjury, Pin-Prick, Proprioception, Racism, Repeated Mistakes, Scientific, Sensory, Signs, Slander, Smith County, Symptoms, Temperature, Vibration.

New Anesthetic Delivery System Targets Pain Fibers Exclusively Cognitive effects of pregabalin in healthy volunteers: A double-blind, placebo-controlled trial — Salinsky et al. 74 (9): 755 — Neurology

2 Comments Add your own

  • 1. steve  |  January 30, 2011 at 9:24 am

    I would love to be a part of the human trials on this med. I suffer CP and would love some relief of pain i have tried it all and need something that works.

    • 2. grussell903  |  February 13, 2011 at 4:27 pm

      Sorry I don’t do Clinical Trials I just quoted this from The Pain Medicine News you need to find the Original Authors at Harved Dept of Pain Medicne


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