Keegan Mark T, Bondy Lois R, Blackshear Joseph L, Lanier William L
Department of Anesthesiology, Mayo Clinic, Rochester, Minn 55905, USA.
Mayo Clin Proc. 2002 Jun;77(6):584-6. doi: 10.4065/77.6.584.
Fosphenytoin is a prodrug that is metabolized by phosphatases to yield the antiepileptic drug phenytoin plus inorganic phosphate. Thus, fosphenytoin can theoretically alter the electrocardiogram by 2 mechanisms: the direct effects of phenytoin on cardiac conduction and on phosphate binding of calcium, which could indirectly alter cardiac conduction as a result of hypocalcemia. We report the case of a 23-year-old man, weight 73 kg, with a known but untreated seizure disorder who was given prophylactic fosphenytoin, 1500-mg phenytoin equivalents over 85 minutes by intravenous infusion. The patient was normocalcemic before drug infusion. Fosphenytoin produced electrocardiographic changes (prolongation of the ST segment and the QT interval and merging of the T and P waves) consistent with hypocalcemia, and these changes were associated with new-onset reductions in both total and ionized serum calcium concentrations. Plasma phenytoin concentrations were within the therapeutic range during the electrocardiographic changes, and the patient's blood pressure was stable. We interpret these findings as fosphenytoin-related electrocardiographic changes likely attributable to inorganic phosphate-induced hypocalcemia.
磷苯妥英是一种前体药物，可被磷酸酶代谢生成抗癫痫药物苯妥英和无机磷酸盐。因此，磷苯妥英理论上可通过两种机制改变心电图：苯妥英对心脏传导以及钙的磷酸盐结合的直接作用，这可能因低钙血症而间接改变心脏传导。我们报告一例23岁男性病例，体重73千克，患有已知但未治疗的癫痫疾病，通过静脉输注在85分钟内给予预防性磷苯妥英1500毫克苯妥英等效物。药物输注前患者血钙正常。磷苯妥英引起了与低钙血症一致的心电图变化（ST段和QT间期延长以及T波与P波融合），并且这些变化与血清总钙和离子钙浓度的新发降低有关。在心电图变化期间血浆苯妥英浓度在治疗范围内，且患者血压稳定。我们将这些发现解释为可能归因于无机磷酸盐诱导的低钙血症的磷苯妥英相关心电图变化。
