Intravenous vitamin K (phytomenadione) is a synthetic form of vitamin K1 administered directly into the bloodstream to rapidly restore blood clotting function. It is primarily used in UK hospitals for urgent reversal of warfarin anticoagulation in patients experiencing major or life-threatening bleeding, such as intracranial haemorrhage or significant gastrointestinal bleeding. By enabling the liver to synthesise essential clotting factors (II, VII, IX, and X), IV vitamin K can reduce the International Normalised Ratio (INR) within 4–6 hours. The modern UK-licensed preparation (Konakion MM) uses a mixed micelle formulation to minimise the risk of serious allergic reactions, though slow administration and close monitoring remain essential for patient safety.

What Is Intravenous Vitamin K and When Is It Used?

Intravenous vitamin K, also known as phytomenadione, is a synthetic form of vitamin K1 administered directly into the bloodstream. Vitamin K plays an essential role in the synthesis of clotting factors II, VII, IX, and X in the liver, as well as anticoagulant proteins C and S, which are crucial for normal blood coagulation. When given intravenously, vitamin K can restore the body's ability to produce these clotting factors, making it a vital intervention in emergency situations involving serious bleeding or dangerously prolonged clotting times.

The intravenous route is reserved for specific clinical scenarios where rapid correction of coagulopathy is required. This typically includes life-threatening or major bleeding in patients taking warfarin or other vitamin K antagonists, situations where oral administration is not feasible (such as in unconscious patients or those with severe gastrointestinal disorders), and cases of vitamin K deficiency causing significant haemorrhage. The IV formulation allows for faster onset of action compared to oral or intramuscular routes, with initial INR reduction typically within 4-6 hours and full effect by 12-24 hours.

Importantly, intravenous vitamin K is effective only for reversing vitamin K antagonists like warfarin and has no effect on direct oral anticoagulants (DOACs).

In the UK, intravenous vitamin K is primarily used in hospital settings under close medical supervision. The UK-licensed preparation (Konakion MM) is formulated with a mixed micelle vehicle to reduce the risk of anaphylactoid reactions that were associated with earlier formulations. Healthcare professionals must carefully assess each patient to determine whether the benefits of rapid vitamin K administration outweigh the potential risks, particularly given that slower routes of administration may be safer in non-emergency situations.

Indications for IV Vitamin K: Bleeding and Warfarin Reversal

The primary indication for intravenous vitamin K is the urgent reversal of warfarin anticoagulation in patients experiencing major or life-threatening bleeding. This includes intracranial haemorrhage, significant gastrointestinal bleeding, haemothorax, retroperitoneal haemorrhage, or any bleeding that is haemodynamically compromising. In these critical situations, IV vitamin K is administered alongside other reversal agents such as prothrombin complex concentrate (PCC) to achieve rapid normalisation of the International Normalised Ratio (INR).

According to British Society for Haematology (BSH) guidelines, intravenous vitamin K is also indicated when patients on warfarin have an INR greater than 8.0 with minor bleeding, or when there is serious bleeding at any INR level. The urgency of the clinical situation determines whether vitamin K alone is sufficient or whether additional clotting factor replacement is required. For patients with major bleeding, the combination of IV vitamin K (5–10 mg) and four-factor prothrombin complex concentrate provides the most rapid and effective reversal.

Other indications include vitamin K deficiency bleeding in neonates (previously called haemorrhagic disease of the newborn) when treatment is required. This is distinct from the routine prophylactic vitamin K given to newborns, which is typically administered via the intramuscular route. In adults, IV vitamin K may be used for severe vitamin K deficiency with active bleeding due to malabsorption syndromes. Patients with obstructive jaundice, coeliac disease, or those on prolonged antibiotic therapy may develop vitamin K deficiency, though bleeding complications requiring IV administration are relatively uncommon.

It is important to note that IV vitamin K is not indicated for routine over-anticoagulation without bleeding. In such cases, withholding warfarin and administering oral vitamin K (if INR >8.0) is usually sufficient and carries fewer risks than intravenous administration. Additionally, vitamin K may have limited effect in coagulopathy from advanced liver failure unless vitamin K deficiency is present.

Dosage and Administration Guidelines for Intravenous Vitamin K

The dosage of intravenous vitamin K varies according to the clinical indication and severity of bleeding. For major or life-threatening bleeding in warfarin-treated patients, the standard adult dose is 5–10 mg of phytomenadione given by slow intravenous injection. This should be administered at a rate not exceeding 1 mg per minute to minimise the risk of anaphylactoid reactions. The dose may be repeated if the INR remains elevated after 12–24 hours, though this is rarely necessary when used in combination with prothrombin complex concentrate.

For less severe bleeding or asymptomatic over-anticoagulation with an INR above 8.0, a lower dose of 1–3 mg IV may be appropriate, though the oral route is generally preferred if the patient can swallow safely and there is no active bleeding. In neonates with vitamin K deficiency bleeding, the typical dose is 1 mg for term infants and 0.5 mg for preterm infants, using the Konakion MM Paediatric formulation, given by slow intravenous injection.

Administration technique is crucial for patient safety. The injection must be given slowly—ideally diluted in glucose 5% or sodium chloride 0.9% and infused at a rate not exceeding 1 mg per minute, as specified in the SmPC. Rapid injection significantly increases the risk of severe hypersensitivity reactions. The intravenous route should only be used when absolutely necessary; intramuscular administration should be avoided in anticoagulated patients due to haematoma risk, and the subcutaneous route is not recommended due to variable absorption.

Healthcare professionals should ensure resuscitation facilities are immediately available during administration, as anaphylactoid reactions, though rare with modern formulations, can occur. The patient should be monitored continuously during infusion and for at least 30 minutes afterwards. If PCC has also been administered, the INR should be checked 30-60 minutes after administration, then again at 4-6 hours. Documentation should include the indication, dose, rate of administration, and any adverse reactions observed.

Side Effects and Risks of Intravenous Vitamin K

While intravenous vitamin K is generally well-tolerated when administered correctly, it carries several important risks that necessitate careful patient monitoring. The most serious adverse effect is anaphylactoid or hypersensitivity reactions, which can range from mild flushing and dyspnoea to severe bronchospasm, cardiovascular collapse, and cardiac arrest. Modern mixed micelle formulations (Konakion MM) have significantly reduced this risk compared to older preparations, but reactions can still occur, particularly with rapid injection. This is why slow administration (no faster than 1 mg per minute) is absolutely essential.

Patients with known hypersensitivity to vitamin K or any component of the formulation should not receive IV vitamin K unless the benefits clearly outweigh the risks and alternative treatments are unavailable. The Konakion MM formulation contains ingredients derived from soya, so patients with soya or peanut allergies may be at increased risk of hypersensitivity reactions.

Other acute reactions include facial flushing, chest tightness, tachycardia, and hypotension. These symptoms typically occur during or immediately after injection and may resolve with slowing or temporarily stopping the infusion. In rare cases, patients may experience pain or phlebitis at the injection site, particularly if the drug is not adequately diluted.

A significant clinical consideration is the risk of resistance to subsequent warfarin therapy. High doses of vitamin K (particularly above 5 mg) can make patients relatively resistant to warfarin for several days or even weeks, which may complicate re-anticoagulation in patients who require ongoing thromboprophylaxis. This is particularly relevant in patients with mechanical heart valves or recurrent venous thromboembolism, where maintaining therapeutic anticoagulation is critical.

Healthcare professionals should always weigh the urgency of reversal against the potential risks of intravenous administration. Suspected adverse reactions should be reported via the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk).

Monitoring and Follow-Up After IV Vitamin K Treatment

Appropriate monitoring following intravenous vitamin K administration is essential to ensure therapeutic efficacy and patient safety. If prothrombin complex concentrate (PCC) has been administered, the INR should be checked 30-60 minutes after administration, then again at 4-6 hours. If vitamin K has been given alone, the INR should be checked 4–6 hours after administration to assess the response to treatment. If the INR remains elevated or bleeding continues, further doses of vitamin K or additional clotting factor replacement may be required. Serial INR measurements should continue at regular intervals (typically every 6–12 hours initially) until stable and within the target range.

Immediate post-administration monitoring should include continuous observation for at least 30 minutes to detect any hypersensitivity reactions. Vital signs including blood pressure, heart rate, respiratory rate, and oxygen saturation should be recorded before, during, and after the infusion. Any signs of allergic reaction, chest pain, or respiratory distress require immediate medical intervention and cessation of the infusion.

For patients who were receiving warfarin for a valid indication (such as atrial fibrillation, mechanical heart valves, or previous venous thromboembolism), careful consideration must be given to when and how to restart anticoagulation. The timing depends on the indication for anticoagulation, the severity of the bleeding episode, and the dose of vitamin K administered. Patients should be reviewed by a haematologist or anticoagulation specialist to develop an appropriate re-anticoagulation plan, which may involve bridging therapy with low-molecular-weight heparin, particularly if higher doses of vitamin K have been given.

Patients should be advised to call 999 or attend emergency services immediately if they experience severe recurrent bleeding, chest pain, or new neurological symptoms. For less urgent concerns, they should contact their GP or return to hospital. Clear written information should be provided about their anticoagulation status and any changes to their medication regimen. Follow-up appointments should be arranged to monitor INR levels during warfarin re-initiation and to review the circumstances that led to over-anticoagulation, addressing any modifiable factors such as drug interactions or dosing errors.

Frequently Asked Questions