A series of researches concerning the relationship between multidrug transporters and drug resistance in medically intractable epilepsy have been done. There is accumulating evidence demonstrating that P-glycoprotein (PGP) is a candidate to cause AEDs resistance. The effect of PGP inhibitor-verapamil on the intracellular AEDs accumulation in a MDR(multidrug resistant) K562 was investigated. The multidrug resistant (overexpression of PGP) cell line K562/Dox was established and the intracellular PHT and CBZ accumulation in multidrug resistant cell line and non- multidrug resistant cell line was observed. After PGP inhibitor-verapamil was applied to the two cell lines, the concentration change of PHT and CBZ in MDR cell was observed. The results were found: compared with non-MDR cell line K562, which IC₅₀ was significantly increased in MDR cell line K562/Dox after PHT and CBZ was applied; verapamil could decrease significantly the level of IC₅₀ in MDR cell line K562/Dox, and the reversal index were 2.5 and 1.5. The concentration of PHT and CBZ in MDR cell line K562/Dox was lower than that in non-MDR cell line K562, and verapamil significantly increased the concentration of PHT and CBZ in MDR cell line K562/Dox(P < 0.05). It is obvious that overexpression of PGP are concerned with drug resistance of medically intractable epilepsy.