PGP and cancer: Based on the fact that dCK could convert GEM into dFdCTP and P-gp could play a critical role in the acquired resistance of cancer to GEM, we believe that the co-administration of DBD alters the GEM metabolism by regulating the expression and activity of dCK and P-gp, which could be a reasonable explanation for the significantly heightened Cmax and AUC0–t of dFdCTP in pharmacokinetic results.