MODE OF ACTION AND EFFECTS ON TISSUES OF LONG-ACTING LOCAL ANESTHETICS

The search for satisfactory long-lasting local anesthetics for nerve blocking continues. The advent of each new drug or preparation appears to be a step toward a goal that has not yet been attained. A recently introduced and apparently a prematurely acclaimed preparation known as Efocaine has aroused our interest. Efocaine contains procaine base (1% ), butyl-p-aminobenzoate (Butesin) (5%), and procaine hydrochloride (0.25%) in a mixture of polyethylene glycol (2%), propylene glycol (78%), and water (20%). Butyl-p-aminobenzoate is insoluble in water (1 gm. dissolves in 7 liters of water at 20 C) but soluble in organic solvents. Contact with an aqueous medium causes the procaine base and butyl-p-aminobenzoate to precipitate. Presumably the drugs are slowly absorbed when injected perineurally, and a long-lasting anesthetic effect is obtained. The possibility of depositing crystalline substances in the tissues on contact with water and a subsequent foreign body reaction has