Production of Edema in Rats by Local Anesthetics

¹ Department of Pharmacology, West Virginia University Medical Center Morgantown, West Virginia

The edema-producing action of local anesthetic solutions was studied. One flank of a rat was injected subcutaneously with 0.25 cc. of the drug to be tested, the other flank was injected with a similar volume of isotonic saline (control). Biopsies (11 x 10 mm.) were taken down to muscle 24 hours after injection. The degree of 24-hour edema was expressed quantitatively as the per cent weight loss of the biopsy after drying 20 hours at 105° C.

The following conclusions were drawn from the data: (1) Certain local anesthetic solutions produced edema when small quantities were injected subcutaneously in rats. (2) Statistically significant edema was produced by commercial 2 per cent lidocaine, mepivacaine, and procaine solutions containing preservatives and vasoconstrictors and by 2 per cent lidocaine HCl, mepivacaine HCl, and procaine HCl in isotonic saline. (3) Commercial NPN solution and 0.15 per cent tetracaine HCl, 1:50,000 epinephrine, 1:100,000 epinephrine, 1:20,000 l-nordefrin, 0.05 per cent sodium pyrosulfite, 0.2 per cent sodium bisulfite, and 0.1 per cent methylparaben did not produce statistically significant edema. (4) The degrees of edema produced by the lidocaine and mepivacaine solutions were similar, that is, they were three times as potent in this regard as the procaine solution. (5) The agents in the local anesthetic solutions that were responsible for the production of edema were determined to be the anesthetic drugs and not the vasoconstrictors or preservatives.