Intravenous vitamin K1 injections: dangerous prophylaxis

Management and dosing of warfarin therapy

When initiating warfarin therapy, clinicians should avoid loading doses that can raise the International Normalized Ratio (INR) excessively; instead, warfarin should be initiated with a 5-mg dose (or 2 to 4 mg in the very elderly). With a 5-mg initial dose, the INR will not rise appreciably in the first 24 hours, except in rare patients who will ultimately require a very small daily dose (0.5 to 2.0 mg). Adjusting a steady-state warfarin dose depends on the measured INR values and clinical factors: the dose does not need to be adjusted for a single INR that is slightly out of range, and most changes should alter the total weekly dose by 5% to 20%. The INR should be monitored frequently (eg, 2 to 4 times per week) immediately after initiation of warfarin; subsequently, the interval between INR tests can be lengthened gradually (up to a maximum of 4 to 6 weeks) in patients with stable INR values. Patients who have an elevated INR will need more frequent testing and may also require vitamin K1. For example, a nonbleeding patient with an INR of 9 can be given low-dose vitamin K1 (eg, 2.5 mg phytonadione, by mouth). Patients who have an excessive INR with clinically important bleeding require clotting factors (eg, fresh-frozen plasma) as well as vitamin K1.

Phytonadione therapy in a multiple-drug overdose involving warfarin

We cared for a patient who ingested an unknown amount of acetaminophen with zopiclone and warfarin. The only liver function test that was abnormal was an increased international normalized ratio (INR), which remained elevated despite treatment with subcutaneous phytonadione and a prolonged infusion of N-acetylcysteine. An interaction between acetaminophen and warfarin may have decreased the hepatic metabolism of warfarin. The patient received numerous antibiotics that may have contributed to the increased INR. The prolonged elevation of INR also may have been due to infrequent administration of phytonadione.

Cutaneous allergic reaction to intramuscular vitamin K1

A 40-year-old woman with no pre-existing hepatic disease developed a cutaneous allergic reaction to intramuscular vitamin K1. She received this medication prophylactically prior to surgery, developed severe localized, and subsequently generalized, dermatitis, beginning 5 days after administration of the Konakion Cremophor-EL form of vitamin K1 by intramuscular injection at four sites on her thighs. Investigation by patch and intradermal testing revealed delayed-type hypersensitivity to Konakion Cremophor-EL, Konakion Mixed Micelles and pure vitamin K1, but not Cremophor-EL vehicle alone. This case is unusual because the patient was also shown to be patch test positive to vitamin K3 sodium bisulfite.