Patients carrying two copies of the CYP3A4*22 allele or one copy of the *22 allele in combination with the *1 allele may have decreased metabolism of tacrolimus as compared to patients with two copies of the CYP3A4*1 allele. However, conflicting evidence has been reported. This annotation only covers the pharmacokinetic relationship between CYP3A4 and tacrolimus and does not include evidence about clinical outcomes. Other genetic and clinical factors may also influence tacrolimus metabolism.