Herb–Drug Interaction and Antidiabetic Drug Development: A Spectroscopic and Pharmacokinetics Investigation of Polyalthia Longifolia Versus Metformin

Abstract

Diabetes mellitus is a chronic metabolic condition characterized by consistently high blood sugar levels, resulting from problems with insulin production, insulin function, or both. Metformin remains the most widely recommended first-line treatment for type 2 diabetes because of its proven effectiveness, good safety profile, and ability to improve the body’s response to insulin. Despite its benefits, many diabetic patients now combine metformin with herbal remedies, such as Polyalthia longifolia, in hopes of gaining additional health advantages. While this practice is increasingly common, it also raises important concerns about possible herb–drug interactions, especially since there is limited scientific evidence on how Polyalthia longifolia may affect the pharmaceutical performance of metformin. Understanding these interactions is essential to ensure safe co-administration, preserve therapeutic effectiveness, and prevent unwanted changes in drug absorption or availability. In this study, the effect of methanolic extract of Polyalthia longifolia on the in-vitro dissolution profile of different brands of metformin tablets was investigated. The selected metformin brands were first evaluated for key physicochemical properties according to pharmacopeia standards. Findings showed that all brands met the required quality specifications, including friability values below 1%, weight variation within ±5%, disintegration times under 15 minutes, and hardness values ranging from 4–10 kg/F. These results indicate that the tablets possessed satisfactory quality, strength, and formulation stability. Further phytochemical screening of the plant extract revealed the presence of important bioactive compounds such as alkaloids, flavonoids, saponins, terpenoids, steroids, and cardiac glycosides, all of which may influence drug dissolution and absorption. To assess potential interactions, dissolution studies were conducted in phosphate buffer (pH 6.8) to simulate intestinal conditions, both in the absence and presence of the plant extract. The results demonstrated that Polyalthia longifolia extract significantly increased the apparent dissolution rate of metformin, with some tablet brands achieving complete drug release of up to 100%. This increase may be due to physicochemical interactions between the extract and the drug, enhanced solubilization, or possible analytical interference from phytochemical constituents present in the extract. In summary, methanolic extract of Polyalthia longifolia significantly altered the dissolution behavior of metformin tablets, suggesting a potential herb–drug interaction that may influence the drug’s bioavailability and therapeutic response. These findings highlight the importance of exercising caution when Polyalthia longifolia is used alongside metformin and reinforce the need for further in-vivo studies to determine the real clinical significance of this interaction.