Connective tissue reactions to 3% tetracycline ointment in rat skin

The connective tissue reactions to 3% tetracycline ointment were studied in 14 Sprague-Dawley white male rats. Using polyethylene tubes, the ointment was implanted subcutaneously in the pouches surgically created on the backs of the experimental group. Empty tube implants, tubes with the vehicle (vaseline/lanolin), and a sham operation (surgical pouches with no implant) served as controls. The animals were killed on day 14 and tissue blocks were taken containing the tubes and a generous amount of the peripheral connective tissue. The connective tissue surrounding the tube opening furthest from the surgical incision was histologically examined for the severity of tissue reaction (STR), the number of inflammatory cell infiltrates (II), and the spread of the reaction area (RSI). The data were statistically analyzed. The sham operation group showed minimal inflammatory response. All three parameters (STR, II, RSI) were significantly greater in the tetracycline group when compared with the empty tube group at 0.05 level of significance. There were significant differences between the mean values of the STR and RSI scores in the tetracycline and vehicle groups (groups 1 and 2). The vehicle group (group 2) had significantly higher STR and II values than the empty tube group (group 3); however, the RSI scores were not statistically different. Necrosis was observed in the reaction site in group 1 and vacuole-containing macrophages were noted in groups 1 and 2. This study, although an animal investigation, questions the use of topical 3% tetracycline ointment on sutured surgical flaps.