In vitro concentration dependent transport of phenytoin and phenobarbital, but not ethosuximide, by human P-glycoprotein

Chunbo Zhang, Patrick Kwan, Zhong Zuo, Larry Baum

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54 Citations (Scopus)


Aims: One possible mechanism for epilepsy drug resistance is overexpression of P-glycoprotein in the blood-brain barrier, but whether (or which) antiepileptic drugs (AEDs) are transported by P-gp remains unclear. We evaluated AEDs as P-gp substrates using cell monolayers. Main methods: Bi-directional transport assays and concentration equilibrium transport assays (CETAs) were performed for phenytoin (PHT), phenobarbital (PB), and ethosuximide (ESM) using wildtype Madin-Darby Canine Kidney II cell line MDCKII and porcine renal endothelial cell line LLC-PK1 cells and these cells transfected with human MDR1 cDNA to express P-gp. Key findings: Wildtype cells demonstrated no efflux transport of PHT, PB, or ESM. In CETAs, both MDR1-transfected cell lines transported PHT from basolateral to apical when PHT loading concentrations were 5 or 10, but not 20μg/ml. MDCK-MDR1 cells transported PB when initial concentrations were 10 or 20, but not 5μg/ml. LLC-MDR1 did not transport PB. P-gp inhibitor verapamil blocked efflux transport. MDR1-transfected cells did not transport ESM at 5.6 or 56μg/ml. Bi-directional transport assays demonstrated weak transport for PHT but not PB or ESM. Significance: Human P-gp transports PHT and PB, but not ESM, in a concentration dependent manner. CETA may be more sensitive than bi-directional assays to detect transport of drugs with high passive diffusion. Potential P-gp substrates should be tested at clinically relevant concentration ranges.

Original languageEnglish
Pages (from-to)899-905
Number of pages7
JournalLife Sciences
Issue number23-24
Publication statusPublished - 1 Jan 2010
Externally publishedYes


  • Antiepileptic drugs
  • Blood-brain barrier
  • Drug transport
  • Ethosuximide
  • P-glycoprotein
  • Phenobarbital
  • Phenytoin

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