Some authors have compared serum levels of proinflammatory cytokines and pharmacokinetic parameters of drugs–substrates of CYP3A enzymes between healthy individuals and patients with ulcerative colitis or Crohn’s disease [419,420]; it has been demonstrated there that higher baseline serum levels of proinflammatory cytokines (TNF, IL-1β, IL-6, and IL-8) in the patients do not cause a change in CYP3A4 activity, as evidenced by the pharmacokinetic parameters of the drugs–substrates of CYP3A enzymes in such patients. This evidence concerns the gene CYP3A4 and Crohn disease.