The therapeutic schemes with magnesium sulfate for the treatment to severe criteria preeclampsia haven't had changes since the last century; they don't take into account the medicine's pharmacokinetics, resulting in variations on the Magnesium's serum levels.There is local research which evidenced that the use of current schemes is associated with subtherapeutic serum levels.Looking at factors that influenced creatinine's serum levels, body mass index (BMI) and the therapeutic scheme used.In this prospective study made in a third level hospital.We studied 90 pregnant women diagnosed with severe criteria preeclampsia, who were treated in the University Hospital of Santander from 2018 to 2019 and who started a prophylactic scheme with magnesium sulfate by 24 hours.josha.org