PGP and inflammatory bowel disease: Loss or dysfunction of P-gp is associated with increased susceptibility to intestinal inflammation, as evidenced both by the link of single nucleotide polymorphisms (SNPs) in mdr1 and risk of inflammatory bowel disease (IBD) (7, –, 9) and observed development of spontaneous colitis in P-gp knockout (mdr1a−/−) mice (6, 10, 11).