For pediatric patients with PIK3CD mutation-related immunodeficiency disease without posaconazole, the probabilities of exceeding the upper limit of the target concentration were less than 9%, 8%, 6%, and 1%, for the dosages of sirolimus, 0.07, 0.06, 0.05, and 0.04 mg/kg/day respectively. Here, PIK3CD is linked to immunodeficiency disease.