A Safer Alternative to Marcaine and Other Local Anesthetics?
In my last post, I discussed a 2008 research article which found a relationship (in both duration of exposure and concentration) between Bupivacaine and muscle damage. In a prior post, I sought to summarize some earlier articles which also discuss local anesthetics and myotoxicity. Given the significant evidence that seems to support this troubling relationship, I've wondered if there are any efforts to develop alternatives to existing local anesthetics, especially Bupivacaine.
In "Prolonged Duration Local Anesthesia With Minimal Toxicity," (2009) Hila Epstein-Barash and colleagues (which include Dr. Daniel S. Kohane, one of the authors of the above 2008 article) describe a compound which has powerful anesthetic properties but with causes little damage to human cells. The authors explain the motivation behind their research:
The development of local anesthetics to provide prolonged analgesia from a single injection has encountered 3 principal challenges: inadequate duration of action, systemic toxicity, and adverse local tissue reaction. The purpose of this research was to produce a local anesthetic lasting many days without those detrimental sequelae.
Conventional local anesthetics are intrinsically myotoxic. They are also myotoxic when released from a wide range of delivery systems, even when the delivery systems themselves are minimally toxic. The myotoxicity of bupivacaine increases dramatically over extended durations of exposure, suggesting that myotoxicity may be an inevitable consequence of sustained release of such compounds. (citations omitted)
The article is quite technical and I don't begin to understand all of its complexities. What I do grasp, however, is that the researchers developed a formulation called STX (saxitoxin) which is a site 1 sodium-channel blocker, which blocks nerves in a different manner than conventional local anesthetics. Site 1 sodium channel blockers are known not to cause myo- or neuro-toxicity. The authors were interested in providing a controlled release of STX over an extended period of time in order to attempt a prolonged nerve block, so they used liposomes--tiny bubbles made of the same material as cell membranes--as a delivery vehicle for the medication. The authors reported that in cell cultures of rats, Bupivacaine but not STX was myo- and neuro-toxic in both time and concentration dependent manners. The authors state these results suggest that controlled release of STX and similar compounds can provide very prolonged nerve blocks with minimal systemic and local toxicity.
I have no idea how far in the future STX might be approved and available for human use. However, it is encouraging to know that there are scientists concerned enough about the shortcomings of Bupivacaine and other conventional local anesthetics who are working to create safer alternatives.
