Safety Study of Long-Acting Local Anesthetic

Currently available amino amide local anesthetics (e.g. bupivacaine, levobupivacaine, ropivacaine) do not reliably provide analgesia beyond roughly 8 hours following subcutaneous infiltration. In addition, they can cause systemic toxicities such as seizures, arrhythmias, and cardiac arrest, as well as local tissue toxicities to muscle, cartilage and nerve. Therefore, there is a need for safe local anesthetics that can provide longer duration analgesia with low systemic and local tissue toxicities.

The investigator team previously reported that tetrodotoxin, saxitoxin, and NeoSTX could produce prolonged sensory blockade (numbness) and motor blockade (weakness) following injection near the sciatic nerves in rats. In these studies, combining the site 1 toxin with either bupivacaine or epinephrine dramatically improved efficacy (duration of sensory blockade) and reduced systemic toxicity.

NeoSTX is the most potent member of the STX series identified to date. In preliminary studies, investigators at the University of Chile, Santiago, and with a small biotech company, Proteus S.A, developed a bioreactor process to produce clinical grade NeoSTX efficiently, with excellent purity, stability, sterility and non-pyrogenicity. A series of preclinical safety and toxicologic studies in mice, rats, and sheep were performed at CHB and Toxikon, Inc.

In this proposal, the investigators plan to conduct a Phase I study to be performed under an Investigator-Initiated FDA IND to further establish the systemic and local safety of escalating doses of NeoSTX via sub-cutaneous infiltration in healthy and awake young adult male human volunteer subjects.

The primary aim of this Phase 1 study is to evaluate the systemic safety of a novel prolonged-duration local anesthetic, neosaxitoxin (NeoSTX), given by subcutaneous injection, either alone or in combination with the commonly used local anesthetic, bupivacaine, and epinephrine. The hypothesis is that, using adverse events as endpoints, a "minimal adverse effect threshold" NeoSTX dose for subcutaneous administration in combination with bupivacaine 0.2% and epinephrine 5mcg/ml respectively, can be defined for awake, young adult healthy volunteer subjects.

In double blind fashion, each subject will receive two injections simultaneously in a 3 cm x 3cm square area on skin of the posterior aspect of the lower leg (calf), one on each side. Each subject receives one injection with bupivacaine 0.2% alone on one side. On other side, they will receive one of 4 possible solutions: (1) saline placebo, (2) NeoSTX in saline or (3) NeoSTX in combination with bupivacaine or (4) NeoSTX in combination with bupivacaine 0.2% and epinephrine 5mcg/ml.

In each dose group, only one of the injections involves placebo. Prior to each dose increase, there is a safety review and confirmation that no stopping rule has been reached.

Specific Aims

1. Measure the dose dependence of FDA-AEs and SD-AEs from NeoSTX in saline;
2. Measure the dose dependence of FDA-AEs and SD-AEs from NeoSTX in bupivacaine 0.2%;
3. Measure the dose dependence of FDA-AEs and SD-AEs from NeoSTX in bupivacaine 0.2% with epinephrine 5mcg/ml;
4. Measure the serum and urine concentrations of NeoSTX following injections of NeoSTX alone or with bupivacaine 0.2% with and without epinephrine; and correlate the serum concentrations with the "Systemic Effects";
5. Evaluate skin integrity and other potential local reactions (edema, numbness, and paresthesia, erythema) in treated limbs receiving NeoSTX-saline, NeoSTX-bupivacaine, NeoSTX-bupivacaine-epinephrine or plain bupivacaine.
6. Using QST, establish the dependence of sensory blockade intensity and duration on NeoSTX dose and on presence or absence of bupivacaine and epinephrine;