Clinical Pharmacology of Local Anesthetics
Local and regional anesthesia and analgesia appear to be under going a renaissance, as judged by attendance at specialty meetings and substantial increase in research activity, as evidenced by growing number of scientific publications. In contrast to general anesthesia, in which the molecular mechanism remains the subject of speculation, the site at which local anesthetic (LA) drugs bind to produce nerve blocks has been cloned and mutated. This chapter focuses on mechanisms of anesthesia and toxicity, especially as knowledge of these mechanisms will assist the clinician in conducting safer and more effective regional anesthesia.
The Incas regarded coca as a gift from the son of the sun God and limited its use to the “upper crust” of society.1 They recognized and used the medicinal properties of cocaine long before the compound was brought to Europe for its properties to be “discovered.” The Incas sometimes treated persistent headaches with trepanation, and coca was occasionally used to facilitate this procedure. Local anesthesia was accomplished by having the operator chew coca leaves and apply the macerated pulp to the skin and wound edges while using a tumi knife to bore through the bone.
By the sixteenth century, having disrupted Incan society, the conquistadors began paying laborers with cocaine paste. The laborers generally rolled the cocaine leaves into balls (called cocadas), bound together by guano or cornstarch.1,2 These cocadas released the free-base cocaine as a consequence of the alkalinity of the guano and of the practice of chewing the cocadas with ash or lime (such alkaline compounds increase pH, favoring the free-base cocaine form over the positively charged hydrochloride salt). This practice probably marks the birth of “free-basing” cocaine and is the historic antecedent of the “rock” or “crack” cocaine so often abused in Western societies.
Cocaine was brought back to Vienna by an explorer/physician named Scherzer.1 In Vienna, the chemist Albert Niemann isolated and crystallized pure cocaine hydrochloride in 1860. The Merck Company distributed batches of this agent to physicians for investigational purposes. Sigmund Freud was the most prominent of these cocaine experimenters. Freud reviewed his experimental work in a monograph devoted to cocaine, Über Coca. Freud and Carl Koller (an ophthalmology trainee) took cocaine orally and noticed that the drug rendered their tongues insensible.
Koller and Joseph Gartner began a series of experiments using cocaine to produce topical anesthesia of the conjunctiva. The birth of local and regional anesthesia dates from 1884, when Koller and Gartner reported their success at producing topical cocaine anesthesia of the eye in the frog, rabbit, dog, and human.2,3,4
The use of local anesthesia quickly spread around the world. The American surgeon William Halsted at Roosevelt Hospital in New York reported using cocaine to produce mandibular nerve ...