Metformin Potentiates the Antidiabetic Properties of Annona muricata and Tapinanthus globiferus Leaf Extracts in Diabetic Rats

Background: There is paucity of experimental evidence on the complementary use of standard anti-diabetic drugs with herbal formulations. Materials and Methods: In this study, extracts of Annona muricata (AME) and Tapinanthus globiferus (TGE) were administered with metformin to diabetic rats in order to study the potential complementary effects. Diabetes was induced by a single intraperitoneal (i.p) injection of alloxan (150 mg/kg BW). AME and TGE (200 mg/ kg BW each) and Metformin (100 mg/kg BW) was administered to diabetic rats orally for 21 days. At the end of the study, rats were sacrificed; blood was collected for assessment of lipid profile and kidney function. Results: Treatment of diabetic rats with AME and TGE caused a significant decrease (p < 0.05) in the concentrations of total cholesterol (TC), triglyceride (TG) and Coronary Risk Index (CRI) with a concomitant increase in High Density Lipoprotein (HDL). Similarly, urea and creatinine concentration decreased in diabetic rats administered plant extracts. Co-administration of the plant extracts with metformin significantly improved lipid profiles and kidney function relative to rats administered metformin alone. Co-administration of AME and TGE extracts with metformin produced significant improvement in biochemical indices of diabetic rats. Conclusion: The results suggest potential synergistic interaction between the plant extracts and metformin. Furthermore, this work provides scientific support for the concomitant use of the plants used in the study with orthodox drugs for the management of diabetes.