Lipids as excipient in sustained release insulin implants

When implanted in Wistar rats with streptozotocin-induced diabetes, the release of insulin from an admixture with cholesterol which had been compressed into a pellet disc was previously found to continue for about 30 days. Several common fatty acids, their anhydrides, and glycerides were evaluated for similar suitability as a component of the implant in this study. Stearic acid and palmitic acid were found to be very promising. Especially with palmitic acid, a 25 mg piece containing 20% insulin reduced hyperglycemia to 3.7 ± 0.8 mmol/1 for 43.5 ± 6.5 days when implanted subcutaneously in diabetic rats. The stable blood glucose leve followed a regular food consumption pattern. But under scheduled feeding, the level varied from 2.4 ± 0.3 to 6.2 ± 0.5 mmol/1. However, hypoglycemic convulsion did not occur even after fasting for 16 h. Therefore, the rat model study indicates that palmitic acid can be a useful adjunct in sustaining the release of insulin from an implant.