PGP and epilepsy: [11C]Metoclopramide is a weak P-gp substrate, which shows higher baseline brain uptake than previously described “avid” P-gp substrates and may thus possess better sensitivity to measure P-gp activity at the BBB, in particular in conditions in which the activity of P-gp is upregulated (e.g. drug-resistant epilepsy) [8–12].