Assessment of antiepileptic drugs as substrates for canine P-glycoprotein.
OBJECTIVE
To determine whether antiepileptic drugs (AEDs) are substrates for canine P-glycoprotein (P-gp). Sample Population-OS2.4/Doxo cells (canine osteosarcoma cells induced via exposure to doxorubicin to highly express P-gp).


METHODS
Competitive inhibition of rhodamine 123 efflux from OS2.4/Doxo cells was used to determine whether AEDs were substrates for canine P-gp. Flow cytometry was used to quantify mean fluorescence intensity of cells treated with rhodamine alone and in combination with each experimental drug.


RESULTS
Known P-gp substrate drugs ivermectin and cyclosporin A altered rhodamine efflux by 90% and 95%, respectively. Experimental drugs altered rhodamine efflux weakly (diazepam, gabapentin, lamotrigine, levetiracetam, and phenobarbital) or not at all (carbamazepine, felbamate, phenytoin, topirimate, and zonisamide).


CONCLUSIONS
At clinically relevant doses, it appeared that AEDs were weak substrates (diazepam, gabapentin, lamotrigine, levetiracetam, and phenobarbital) or were not substrates (carbamazepine, felbamate, phenytoin, topirimate, and zonisamide) for canine P-gp. Therefore, it seems unlikely that efficacy of these AEDs is affected by P-gp expression at the blood-brain barrier in dogs.
West
Chadwick L
CL
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-6610, USA.
Mealey
Katrina L
KL
D018435:ATP Binding Cassette Transporter, Subfamily B / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D000927:Anticonvulsants / Q000493:pharmacokinetics*; D001812:Blood-Brain Barrier; D045744:Cell Line, Tumor; D016572:Cyclosporine / Q000494:pharmacology; D004285:Dogs; D005434:Flow Cytometry; D015151:Immunoblotting; D007559:Ivermectin / Q000494:pharmacology; D012516:Osteosarcoma; D020112:Rhodamine 123 / Q000493:pharmacokinetics; D013379:Substrate Specificity
D018435:ATP Binding Cassette Transporter, Subfamily B; D000927:Anticonvulsants; D020112:Rhodamine 123; D007559:Ivermectin; D016572:Cyclosporine