Zonampanel inhibits the human MRP4-mediated transport of [H]oestradiol 17-D-glucuronide in a concentration-dependent manner. In contrast, Zonampanel (up to 1000 mM) does not inhibit the human MRP2- or BCRP-mediated transport of [H]oestradiol 17-D-glucuronide or [H]methotrexate. Zonampanel inhibits the uptake of typical substrates by Oat1, Oat2, and Oat3 with inhibition constant (Ki) values of 7.02 to 10.4 μM. A time- and saturable concentration-dependent increase in [C]Zonampanel uptake is observed in these cells [Km values: 13.4 to 53.6 μM].