This action has been demonstrated in animals and humans.
The medical use of the NSTX anesthetic effect is supported by three reasons:
#NSTX anesthetic duration:
#* Any current available local anesthetic hardly produces clinical effects 12 hours after a single injection. Then, in cases of severe or prolonged pain, some patients need repeated injections, catheters, pumps and opioids to feel comfortable, with different kinds of side effects, costs and risks.
#* On the other hand, NSTX local infiltration produces long lasting anesthesia, well over all the current available local anesthetics. Some investigations demonstrated anesthetic effect lasting over one week after single injection in rodents, using extended release formulation, without histologic or functional sequelae.
#* Additionally, two human reports demonstrated strong potentiation between NSTX anesthetic effect, bupivacaine and epinephrine.
#NSTX local safety:
#* All available local anesthetic are associated with local damage in different models. This undesired effect could be enhanced by sustained release formulations.
#* On the contrary, several investigations show local safety of saxitoxin-related neurotoxins, including very sensitive models, and there is no reason to presume otherwise for NSTX.
#NSTX systemic safety:
#* In spite of advances of ultrasound guided injections, acute systemic local anesthetic toxicity is still an unsolved clinical problem, and can produce devastating consequences, related to the neurologic and cardiovascular effects of all available local anesthetics.
#* Otherwise, clinical experience and animal models shows the relative safety of accidental and experimental NSTX intoxication (when appropriate support therapy is provided in a timely manner).
#* Recent investigation in sheep shows a safe limit, due to motor block, over 1 µg/kg for intravenous injection of NSTX, with full recovery after a brief course of mechanical ventilation.
#* Regarding systemic safety, saxitoxins diffuse through the blood–brain barrier, but, because of Nav channel specificity, acute toxicity is associated to a very low risk of seizures. This establishes an important difference with current local anesthetic toxicity.
#* As could be predicted from its ion channel selectivity, NSTX intoxication clinical picture is almost devoid of arrhythmias, establishing another difference with available local anesthetic's numerous cardiac effects.
#* And last but not least, some degree of improving in therapeutic index of NSTX can be observed when is mixed with bupivacaine and/or epinephrine.
In conclusion, NSTX is a well defined molecule with a long-lasting and sometimes dangerous relationship with human subjects. Recent investigations suggest a clinical application as a new local anesthetic that sounds "too good to be true", but more investigation is required.