Local anesthesia in otolaryngology. A re-evaluation

Abstract

Almost a half century following attempts to ban its use, cocaine remains at the pinnacle of topical anesthesia in otolaryngology. To understand how nonaddicting synthetic substitutes such as procaine, dibucaine, tetracaine and lidocaine have not totally supplanted cocaine, requires an in-depth analysis of its unique pharmological properties, untoward effects and potential substitutes. Almost all of the reported cocaine deaths occurred after subcutaneous injection; when used topically, cocaine's toxicity has been confined to an occasional reaction. Certain variables under physician control may be manipulated to reduce the chance of reaction to a minimum. For example, intermittent application of a particular dosage results in lower blood levels, and allowing sufficient time between doses reduces the amount necessary to obtain the desired anesthesia. If total dosage is kept below 200 mg there are few reactions. A singular advantage of cocaine over other topical anesthetics is its inherent ability to cause vasoconstriction, thus retarding its own absorption. The addition of a topical vasoconstrictor such as epinephrine is thus redundant, and may actually be harmful as cocaine sensitizes the patient to exogenous epinephrine. Finally, the usual preoperative dosages of barbiturates are entirely inadequate to prevent or treat cocaine reactions. Why, then, have synthetic local anesthetics not replaced cocaine? Inherent differences in topical effectiveness, duration of anesthesia and toxicity provide the answer. Of other local anesthetics possessing topical effectiveness tetracaine is about six times more toxic than cocaine. Dibucaine is as toxic as tetracaine, and lidocaine, while relatively nontoxic, provides only a 15 minute duration of topical anesthesia. A review of cocaine and its potential substitutes thus leads to the conclusion that cocaine is still a vital and necessary instrument in the otolaryngologist's armamentarium, singularly providing excellent topical anesthesia of usable duration, vasoconstriction, and shrinkage of mucous membranes, all with a quite acceptable margin of safety.