Epinephrine anesthetic combinations

Epinephrine is not directly anesthetic either alone or in combination with cocaine for it does not increase the anesthetic effect when the circulation has previously been arrested. It also does not lower the threshold concentration in wheals, although the duration of the anesthesia is greater for a given concentration. 

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These agents are often combined with a vasoconstrictant such as epinephrine [51-43-4]. By using such a combination, the local anesthetic is held in the area for a longer period of time and its effect extended hemorrhage is minimized, blood loss prevented, and a better surgical repair obtained. 

TAC (tetracaine, adrenalin [epinephrine], and cocaine) is a combination topical anesthetic frequently used in pediatric emergency departments for repair of minor lacerations. The usual mixture is tetracaine 0.5%, epinephrine 1 2,000, and cocaine 11.8%. Because of potential complications (seizures), lower concentrations of cocaine and epinephrine in a tetracaine 1% solution have been suggested (TAC III). 

Beta-blockers interact with a large number of other medications. The combination of beta-blockers with calcium antagonists should be avoided, given the risk for hypotension and cardiac arrhythmias. Cimetidine, hydralazine, and alcohol all increase blood levels of beta-blockers, whereas rifampicin decreases their concentrations. Beta-blockers may increase blood levels of phenothiazines and other neuroleptics, clonidine, phen-ytoin, anesthetics, lidocaine, epinephrine, monoamine oxidase inhibitors and other antidepressants, benzodiazepines, and thyroxine. Beta-blockers decrease the effects of insulin and oral hypoglycemic agents. Smoking, oral contraceptives, carbamazepine, and nonsteroidal anti-inflammatory analgesics decrease the effects of beta-blockers (Coffey, 1990). 

Combining agonists with some local anesthetics greatly prolongs the duration of infiltration nerve block the total dose of local anesthetic (and the probability of toxicity) can therefore be reduced. Epinephrine, 1 200,000, is the favored agent for this application, but norepinephrine, phenylephrine, and other agonists have also been used. Systemic effects on the heart and peripheral vasculature may occur even with local drug administration but are usually minimal. 

Epinephrine or other vasoconstrictors have no significant effect on the duration of topical anesthesia and should never be combined with commercially available topical anesthetics. 

Lidocaine (lignocaine) is an amide local anesthetic that is approved (2% solution, 20mg/ml) for use in horses. This agent is also used widely in humans and is available as 1% and 2% solutions also in combination with epinephrine (adrenaline) at a concentration of 1 in 200 000. 

Hyaluronidase has found applications as an additive to the anesthetic agents used for peribulbar anesthesia for vitreoretinal surgery. Combinations of hyaluronidase with bupivacaine [119], lidocaine and epinephrine [120], lignocaine and adrenaline [121], or lidocaine and bupivacaine [122] were judged very... 

Although the intrinsic potency of procaine was low and its duration of action relatively short compared with that of cocaine, it was found that these deficiencies could be remedied when procaine was combined with a vasoconstrictor, such as epinephrine. Apparently, a vasoconstrictor agent reduces the local blood supply and, thereby, prolongs the residence time of the local anesthetic. 

Lidocaine [2-(diethylamino)-N-(2, 6-dimethylphenyl) acetamide monohydrochloride] is the most commonly used amino amide-type local anesthetic. Lidocaine is very lipid soluble and, thus, has a more rapid onset and a longer duration of action than most amino ester-type local anesthetics, such as procaine and tetracaine. It can be administered parenterally (with or without epinephrine) or topically either by itself or in combination with prilocaine or etidocaine as a eutectic mixture that is very popular with pediatric patients. The use of lidocaine-epinephrine mixtures should be avoided, however, in areas with limited vascular supply to prevent tissue necrosis. Lidocaine also frequently is used as a class IB antiarrhythmic agent for the treatment of ventricular arrhythmias, both because it binds and inhibits sodium channels in the cardiac muscle and because of its longer duration of action than amino ester-type local anesthetics. 

The first topical anesthetic agent was TAC, which is a combination of tetracaine, adrenaline (epinephrine), and cocaine, and was used for face and scalp lacerations. A version of TAC called LET is used today. LET is a combination of lidocaine, epinephrine, and tetracaine. Lidocaine replaced cocaine. LET gel is... 

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