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Department of Anesthesiology; Wayne State University; Detroit, MI; rkbaumgarten{at}comcast.net
To the Editor:
The editor should be commended for closing the door on research involving neuraxial administration of medications before adequate tissue toxicity screening (1). The off-label intrathecal use of medications approved for epidural use is another matter entirely. Anesthesiologists take great care when placing needles and catheters in the epidural space. But our best efforts are still "blind," so we can never be absolutely sure that we are not injecting intravascularly or intrathecally. In the early 1980s, there were a number of reports of serious complications after attempted epidural injection of large doses of local anesthetics. In response, the FDA changed the labeling of epidural local anesthetics. For epidurals, the FDA package insert recommends incremental injection of 3–5 mL of solution with subsequent careful monitoring for "manifestations of unintentional intravascular or intrathecal injection." This incremental dose is 90–150 mg for 3% 2-chloroprocaine, 15–25 mg for 0.5% bupivacaine and 0.5% ropivacaine. These are greater than the doses used for intentional spinal anesthesia (2). If there is any chance that these small doses can produce tissue toxicity to the delicate, unmyelinated nerves in the CSF, we should not be using them for epidural anesthesia in the first place.
By endorsing an intrathecal test dose, the FDA certified that small doses of these drugs are not neurotoxic. Despite this assurance, 2-chloroprocaine and bupivacaine retain the "Not for Spinal Anesthesia" caveat, while ropivacaine has no warning. This is an example of the haphazard manner in which package inserts are modified. Unlike textbooks, there is no mechanism for systematically updating package inserts with newer medical knowledge (3,4).
The use of 2-chloroprocaine, isobaric bupivacaine, ropivacaine, and mepivacaine for spinal anesthesia is off-label. However, this is because no one is prepared to finance a formal FDA application for this clinical application. It is not related to any concern about tissue toxicity. Therefore, I believe the journal should still accept spinal anesthesia research with drugs that are approved for epidural use.
REFERENCES
This article has been cited by other articles:
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  S. L. Shafer Spinal Anesthesia Research: Let's Not Be Hasty Anesth. Analg., December 1, 2007; 105(6): 1862 - 1863. [Full Text] [PDF]
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