College of Pharmacy & Health Sciences, Des Moines, IA, USA.
Ann Pharmacother. 2011 Jan;45(1):e2. doi: 10.1345/aph.1P461. Epub 2011 Jan 4.
To report a case of a critically elevated international normalized ratio (INR) following discontinuation of a vitamin K supplement in a patient receiving warfarin.
A 64-year-old man with atrial fibrillation received warfarin for primary stroke prevention. He was initiated on low-dose vitamin K supplementation therapy secondary to a high level of INR variability. The patient was stabilized on this therapy for approximately 9 months with a mean INR of 2.02 and a warfarin dose ranging from 6.5 to 7.5 mg/week. At a visit with his primary care physician, the patient's INR was subtherapeutic at 1.5. He had not been taking his vitamin K supplement for nearly a week, but had not missed any doses of warfarin. The vitamin K supplement was discontinued and his warfarin dose was increased by 14.3%. Nearly 2 weeks later the patient presented with a critically elevated INR of 8.5, but no acute bleeding. No other factors affecting the INR could be determined. After a dose of 2.5 mg of vitamin K was administered and warfarin was withheld for 2 days, the patient's INR returned to 2.9. Low-dose vitamin K supplementation and warfarin at a lower dose of 7 mg/week were restarted. His INR remained relatively stable, with no ensuing critical INR changes or other sequelae.
Vitamin K supplement removal was believed to be a major contributor to the critically elevated INR. While the warfarin dose had been increased according to the clinic protocol (14.3% for an INR of 1.5), the timing of the INR elevation following supplement removal follows pharmacodynamic expectations of clotting factor synthesis. This case is labeled a category D error.
Discontinuation of vitamin K supplementation therapy might result in elevation of INR.
报告 1 例在停止服用华法林期间接受维生素 K 补充剂的患者，国际标准化比值（INR）显著升高。
1 例 64 岁男性，因心房颤动接受华法林治疗以预防原发性中风。由于 INR 变异性高，他开始接受低剂量维生素 K 补充剂治疗。该患者在这种治疗方案下稳定了大约 9 个月，平均 INR 为 2.02，华法林剂量为 6.5 至 7.5mg/周。在与初级保健医生的就诊中，患者的 INR 处于治疗范围以下，为 1.5。他已经将近一周没有服用维生素 K 补充剂，但没有漏服华法林。停止服用维生素 K 补充剂，并将华法林剂量增加 14.3%。近 2 周后，患者出现了严重的 INR 升高至 8.5，但没有急性出血。无法确定其他影响 INR 的因素。给予 2.5mg 维生素 K 后，停用华法林 2 天，患者的 INR 恢复至 2.9。开始低剂量维生素 K 补充剂和华法林（7mg/周）治疗。他的 INR 相对稳定，没有随后出现的 INR 显著升高或其他并发症。
维生素 K 补充剂的停用被认为是 INR 显著升高的主要原因。虽然根据临床方案（INR 为 1.5 时增加 14.3%）增加了华法林剂量，但在停止补充剂后 INR 升高的时间符合凝血因子合成的药效学预期。该病例被标记为 D 类错误。
停止维生素 K 补充剂治疗可能导致 INR 升高。
