Activities of Vernonia amygdalina on the fate of metformin in rabbits

The use of herbal preparations in parallel with conventional drugs is on the increase, thus a great concern has arisen. From the leaf of Vernonia amygdalina (VA), several flavones have been isolated:- luteolin, luteolin 7-O-β-glucoside and luteolin 7-O-β-glucuronoside. It is one of the most widely used herbal remedies by diabetic patient with an encouraging safety profile and has been claimed by herbal practitioners to increase the efficacy of an anti-diabetic drug, metformin (MET). Thus we investigated the effect of the aqueous extract of VA on the fate of MET in rabbits. The Pharmacokinetics of MET (100 mg/kg b.wt., o.r.) was studied in rabbits with or without co-administration of the extract of VA (500 mg/kg b.wt., o.r.). Blood samples were drawn at 0h and at 0.5 to 24h post dosing from the retro orbital plexus into sodium heparin bottles and centrifuged to separate plasma. The animals were allowed food after 4h post dose. The plasma samples were assayed for MET levels using validated HPLC method. SPSS 15 statistical package with P set at 0.05 was used to analyzed data. Following VA co-administration, MET showed significantly higher K_a, F, C_max, AUC_0-∞ and T_max than the control group. No significant difference was seen in t_1/2el between the groups. These results indicated that VA enhanced absorption constant K_a thus increasing C_max. Therefore patients on MET therapy should consume VA with caution as life threatening interaction may occur.