Given the knowledge that trough levels above 1% of FVIII prevent spontaneous bleeding and therefore joint disease, in haemophilia A, 1 IU of FVIII modifies the factor concentration by 2%, which seeks to normalise haemostasis; the higher the dose, the higher the percentage of factor in the blood, which is why the concept of pharmacokinetics becomes a priority in the schemes of prophylaxis dosages defined as changes in concentration as a function of time [11]. The gene discussed is F8; the disease is arthropathy.