Warfarin and Superwarfarin Toxicity Workup
- Author: Kent R Olson, MD, FACEP; Chief Editor: Asim Tarabar, MD more...
Blood levels of warfarin are neither readily available nor helpful. Specific levels of superwarfarin rodenticides (eg, brodifacoum) may be useful in cases in which the ingestion is denied or for purposes of estimating the necessary duration of vitamin K1 therapy. However, most reference laboratories do not perform this analysis. (National Medical Laboratory [NMS] in Willow Grove, Pa, offers a qualitative screen for anticoagulant rodenticides and a quantitative analysis for brodifacoum.)
The anticoagulant effect is best quantified by baseline and daily repeated measurement of the PT and the INR, which may not be elevated until 1-2 days postingestion. A normal PT 48-72 hours after ingestion rules out significant ingestion.
Blood levels of vitamin K–dependent clotting factors (II, VII, IX, and X) are decreased if measured, but these are rarely available in a timely fashion and usually do not aid in clinical management. However, depressed levels may provide supporting evidence for suspected poisoning by warfarin or superwarfarins.
Note that a "mixing study" using an aliquot of normal serum mixed with the patient's serum will restore an abnormal PT to normal. This may be useful when trying to distinguish anticoagulation caused by warfarin or a superwarfarin from that caused by a factor inhibitor (eg, lupus anticoagulant) or antifactor antibodies.
Other laboratory tests that may be indicated include a blood count for baseline hemoglobin and/or hematocrit to assess for anemia if the ingestion is more remote. A blood type and crossmatch or antibody screening is indicated if substantial blood loss is suggested.
In addition, other laboratory tests (eg, acetaminophen level) or toxicology screening may be indicated to rule out co-ingestions. If intracranial bleeding is suspected, obtain a noncontrast computed tomography (CT) scan of the head.
Anderson IB. Warfarin and related rodenticides. Olson KR. Poisoning and Drug Overdose. 5th ed. Appleton & Lange; 2007. 379-381.
Su M, Hoffman RS. Anticoagulants. Goldfrank's Toxicologic Emergencies. 8th ed. McGraw-Hill; 2006. 887-902.
Hirsh J, Dalen J, Anderson DR, Poller L, Bussey H, Ansell J, et al. Oral anticoagulants: mechanism of action, clinical effectiveness, and optimal therapeutic range. Chest. 2001 Jan. 119(1 Suppl):8S-21S. [Medline].
Olmos V, Lopez CM. Brodifacoum poisoning with toxicokinetic data. Clin Toxicol (Phila). 2007. 45(5):487-9. [Medline].
Baillargeon J, Holmes HM, Lin YL, Raji MA, Sharma G, Kuo YF. Concurrent use of warfarin and antibiotics and the risk of bleeding in older adults. Am J Med. 2012 Feb. 125(2):183-9. [Medline].
Mowry JB, Spyker DA, Brooks DE, McMillan N, Schauben JL. 2014 Annual Report of the American Association of Poison Control Centers' National Poison Data System (NPDS): 32nd Annual Report. Clin Toxicol (Phila). 2015 Dec. 53 (10):962-1147. [Medline]. [Full Text].
Ingels M, Lai C, Tai W, Manning BH, Rangan C, Williams SR, et al. A prospective study of acute, unintentional, pediatric superwarfarin ingestions managed without decontamination. Ann Emerg Med. 2002 Jul. 40(1):73-8. [Medline].
Gitter MJ, Jaeger TM, Petterson TM, et al. Bleeding and thromboembolism during anticoagulant therapy: a population- based study in Rochester, Minnesota. Mayo Clin Proc. 1995 Aug. 70(8):725-33. [Medline].
[Guideline] Caravati EM, Erdman AR, Scharman EJ, Woolf AD, Chyka PA, Cobaugh DJ. Long-acting anticoagulant rodenticide poisoning: an evidence-based consensus guideline for out-of-hospital management. Clin Toxicol (Phila). 2007. 45(1):1-22. [Medline].
Shah M, Avgil Tsadok M, Jackevicius CA, Essebag V, Eisenberg MJ, Rahme E, et al. Warfarin use and the risk for stroke and bleeding in patients with atrial fibrillation undergoing dialysis. Circulation. 2014 Mar 18. 129(11):1196-203. [Medline].
Miller MA, Levy PD, Hile D. Rapid identification of surreptitious brodifacoum poisoning by analysis of vitamin K-dependent factor activity. Am J Emerg Med. 2006 May. 24(3):383. [Medline].
Spahr JE, Maul JS, Rodgers GM. Superwarfarin poisoning: a report of two cases and review of the literature. Am J Hematol. 2007 Jul. 82(7):656-60. [Medline].
Tsutaoka BT, Miller M, Fung SM, et.al. Superwarfarin and glass ingestion with prolonged coagulopathy requiring high-dose vitamin K1 therapy. Pharmacotherapy. 2003 Sep. 23(9):1186-9. [Medline].
Chua JD, Friedenberg WR. Superwarfarin poisoning. Arch Intern Med. 1998 Sep 28. 158(17):1929-32. [Medline].
Schulman S, Parpia S, Stewart C, Rudd-Scott L, Julian JA, Levine M. Warfarin dose assessment every 4 weeks versus every 12 weeks in patients with stable international normalized ratios: a randomized trial. Ann Intern Med. 2011 Nov 15. 155(10):653-9. [Medline].
Mullins ME, Brands CL, Daya MR. Unintentional pediatric superwarfarin exposures: do we really need a prothrombin time?. Pediatrics. 2000 Feb. 105(2):402-4. [Medline].
Smolinske SC, Scherger DL, Kearns PS, et al. Superwarfarin poisoning in children: a prospective study. Pediatrics. 1989 Sep. 84(3):490-4. [Medline].
Bershad EM, Suarez JI. Prothrombin complex concentrates for oral anticoagulant therapy-related intracranial hemorrhage: a review of the literature. Neurocrit Care. 2010 Jun. 12(3):403-13. [Medline].
Deveras RA, Kessler CM. Reversal of warfarin-induced excessive anticoagulation with recombinant human factor VIIa. Ann Intern Med. 2002. 137(11):884-888. [Medline].
Ilyas C, Beyer GM, Dutton RP, Scalea TM, Hess JR. Recombinant factor VIIa for warfarin-associated intracranial bleeding. J Clin Anesth. 2008 Jun. 20(4):276-9. [Medline].
Nishijima DK, Dager WE, Schrot RJ, Holmes JF. The efficacy of factor VIIa in emergency department patients with warfarin use and traumatic intracranial hemorrhage. Acad Emerg Med. 2010 Mar. 17(3):244-51. [Medline].
Huttner HB, Schellinger PD, Hartmann M, Köhrmann M, Juettler E, Wikner J, et al. Hematoma growth and outcome in treated neurocritical care patients with intracerebral hemorrhage related to oral anticoagulant therapy: comparison of acute treatment strategies using vitamin K, fresh frozen plasma, and prothrombin complex concentrates. Stroke. 2006 Jun. 37(6):1465-70. [Medline].
Kalina M, Tinkoff G, Gbadebo A, Veneri P, Fulda G. A protocol for the rapid normalization of INR in trauma patients with intracranial hemorrhage on prescribed warfarin therapy. Am Surg. 2008 Sep. 74(9):858-61. [Medline].
Dezee KJ, Shimeall WT, Douglas KM, Shumway NM, O'malley PG. Treatment of excessive anticoagulation with phytonadione (vitamin K): a meta-analysis. Arch Intern Med. 2006 Feb 27. 166(4):391-7. [Medline].