Grounds of pharmacoresistance epilepsy
Several mechanisms have been proposed to explain pharmacoresistance like disease related mechanisms, drug related mechanisms and genetics. The transporter hypothesis relates to pharmacokinetic aspects, which
suggests that over expressed efflux transporters at the BBB limits brain penetration of AED’s.10,11 One of the glycoprotein active efflux systems i.e. P-glycoprotein (P-gp) consists group of closely related intrinsic membrane proteins which are involved in multidrug resistance and encoded by a small family of multidrug resistance are encoded by MDR1 and mdr1a genes in human and rodent respectively.12 Preclinical study reveals that the absence of its substituent (mdr1a or mdr1b genes) shows a significant increase in-uptake of various lipophilic drugs in brain.13 Fig. 1A illustrate ATP dependent multi drug transporters such as P-gp or MRP2 located at the apical cell membrane of the endothelial cells acts as an active efflux pump by transferring part of drug back into the blood, thus limiting penetration of many lipophilic drugs into brain parenchyma. By lowering the concentration of drug in endothelial cells, multidrug transporter proteins also promotes flux from brain extracellular space into endothelial cells. Moreover, as Fig. 1B shows these transporters are over expressed and may contribute to barrier function. Hence, AED concentrations would be insufficient to cause antiepileptic potential.14–21