Topical insulin in wound healing: a randomised, double-blind, placebo-controlled trial

Two studies were carried out to assess the relative roles of insulin and zinc in the acceleration of wound healing. In the first study, six diabetic and five non-diabetic human volunteers had two uniform cuts created, one on each forearm. One forearm wound was treated with topical regular insulin (Iletin-II) and the other with normal saline four times a day until healed. Treatment was double-blind and forearms were assigned randomly. The wounds treated with insulin healed 2.4 +/- 0.8 days faster than the wounds treated with saline (P < 0.001 by paired t-test). Zinc is used to crystallise insulin. When wounds are treated with insulin, they are therefore also being treated with zinc. If insulin accelerates wound healing, it is not clear if the increase in the rate of healing would be due to insulin (a known growth factor), the zinc it contains, or a combination of the two. The second study used a randomised, double-blind, placebo-controlled design to compare the efficacy of insulin with that of a solution containing the same amount of zinc in accelerating the healing of standardised wounds in rats and humans. Although these pilot investigations did not have the power to define the relative roles of insulin and zinc with accuracy, the results suggest that zinc does play a role in the wound healing process. It is concluded that topical insulin accelerates wound healing in humans. More importantly, however, this study describes a method of creating uniform wounds in humans acceptable to an institutional review board, thus solving one of the major impediments to the scientific evaluation of human wound healing.