In vivo pharmacokinetic interaction by ethanolic extract of Gymnema sylvestre with CYP2C9 (Tolbutamide), CYP3A4 (Amlodipine) and CYP1A2 (Phenacetin) in rats.

Gymnema sylvestre (GS) is a medicinal herb used for diabetes mellitus (DM). Herbs are gaining popularity as medicines in DM for its safety purpose. The aim of the present study was to evaluate in vivo pharmacokinetic (PK) interaction between allopathic drugs tolbutamide (TOLBU), amlodipine (AMLO), and phenacetin (PHENA) at low (L) and high (H) doses with ethanolic extract (EL) from GS. EL was extracted and subjected to TLC, total triterpenoid content (19.76 ± 0.02 W/W) and sterol content (0.1837 ± 0.0046 W/W) estimation followed by identification of phytoconstituents using HRLC-MS and GC-MS. PK interaction study with CYP2C9, CYP3A4 and CYP1A2 enzymes were assessed using TOLBU, AMLO and PHENA respectively to index cytochrome (CYP) mediated interaction in rats after concomitant administration of EL extract (400 mg/kg) from GS for 7 days. The rats were divided into four groups for each PK study where, group I and II were positive control for low and high dose of test drugs (CYP substrates) while group II and IV were orally administered EL. The PK study result of PHENA indicated that area under the plasma concentration-time curve (AUC) was significantly (P < 0.0001) increased by 1.4 (L) and 1.3-fold (H), plasma concentration (C) was significantly (P < 0.001) increased by 1.6 (L) and 1.4-fold (H). Whereas for TOLBU; clearance rate (CL) was significantly (P < 0.0001) decreased by 2.4 (L) and 2.3-fold (H), C was significantly (P < 0.001) decreased by 26.5% (L) and 50.4% (H) and AUC was significantly (P < 0.0001) decreased by 59.8% (L) and 57.5% (H). Thus, EL is seen to be interacting with CYP1A2 by inhibiting its metabolic activity. HRLC-MS and GC-MS helped identify the presence of gymnemic acid (GA), triterpenoids and steroids in EL which could be the reason for PK interaction of CYP1A2 and CYP2C9. Also, in silico structure based site of metabolism study showed Fe accessibility and intrinsic activity for GA-IV, GA-VI, GA-VII and GA-X with CYP2C9. PK parameters of AMLO were not significantly affected by pre-treatment of EL. Thereby our findings indicate that co-administration of GS with drugs that are metabolized by CYP2C9 and CYP1A2 could lead to potential HDI.