Liquid vitamin K is a fat-soluble vitamin preparation essential for blood clotting and bone health, available as oral drops or injectable solutions. In the UK, it is most commonly used for newborn prophylaxis to prevent vitamin K deficiency bleeding, a potentially serious condition affecting infants with limited vitamin K stores at birth. Liquid formulations offer advantages for those unable to swallow tablets or requiring precise dosing, including individuals with malabsorption disorders or chronic liver disease. This article explores how liquid vitamin K works, who requires supplementation, appropriate dosing, and important safety considerations for UK patients.

What Is Liquid Vitamin K and How Does It Work?

Vitamin K is a fat-soluble vitamin essential for blood clotting and bone health. It exists in several forms, primarily vitamin K1 (phylloquinone) found in green leafy vegetables, and vitamin K2 (menaquinone) produced by gut bacteria and present in fermented foods. Liquid vitamin K formulations typically contain vitamin K1 (phytomenadione) and are available as oral drops or injectable solutions, offering an alternative to tablet forms for those who have difficulty swallowing or require precise dosing.

The primary mechanism of action involves the carboxylation of clotting factors. Vitamin K acts as a cofactor for the enzyme gamma-glutamyl carboxylase, which activates several proteins essential for coagulation, including factors II (prothrombin), VII, IX, and X. Without adequate vitamin K, these clotting factors remain inactive, leading to impaired blood coagulation and increased bleeding risk. This process is particularly critical in newborns, who have limited vitamin K stores at birth.

Beyond haemostasis, vitamin K plays a role in bone metabolism by activating osteocalcin, a protein that binds calcium to the bone matrix. Some research suggests a potential role in cardiovascular health, though this remains an area of ongoing investigation and is not currently a basis for supplementation in UK clinical practice.

Absorption of vitamin K occurs primarily in the small intestine and requires bile salts and pancreatic enzymes. In the UK, oral liquid vitamin K for neonates is typically available as a mixed-micelle formulation (Konakion MM Paediatric), which may improve absorption in some circumstances. However, in conditions like cholestasis where bile flow is impaired, parenteral (injectable) administration is preferred as oral absorption becomes unreliable.

Who Needs Liquid Vitamin K Supplementation?

Newborn infants represent the most common group requiring vitamin K supplementation. The NHS recommends that all newborns receive vitamin K prophylaxis to prevent vitamin K deficiency bleeding (VKDB), previously known as haemorrhagic disease of the newborn. Babies are born with low vitamin K stores because the vitamin crosses the placenta poorly, and breast milk contains relatively low amounts. A single intramuscular injection of 1mg vitamin K is offered at birth, or alternatively, oral doses can be administered according to a specific schedule. Liquid oral preparations are used when parents decline the injection, but are unsuitable for babies with cholestasis, liver disease or significant vomiting. Preterm or ill infants may require different regimens according to local protocols or BNFC guidance.

Individuals with malabsorption disorders may require vitamin K supplementation. Conditions affecting fat absorption—such as coeliac disease, Crohn's disease, ulcerative colitis, cystic fibrosis, and chronic pancreatitis—can impair vitamin K uptake. Patients who have undergone bariatric surgery or have short bowel syndrome may also develop deficiency. In these cases, mixed-micelle formulations may offer advantages, though severe malabsorption may still require parenteral administration.

Patients on long-term antibiotic therapy may experience reduced vitamin K production by gut bacteria, though clinical deficiency is uncommon unless other risk factors are present. Those taking certain medications, particularly anticoagulants like warfarin, require careful monitoring but generally should not take vitamin K supplements without medical supervision, as it can interfere with anticoagulation control.

Other groups who may benefit include:

• Individuals with chronic liver disease, where vitamin K-dependent clotting factor synthesis is impaired and cholestasis may reduce absorption

• Patients with biliary obstruction affecting bile salt secretion

• Elderly individuals with poor dietary intake

• Those on long-term parenteral nutrition without adequate vitamin K supplementation

Anyone considering vitamin K supplementation should consult their GP or healthcare professional to determine appropriateness and correct dosing.

Dosage and Administration of Liquid Vitamin K

Dosage recommendations for liquid vitamin K vary considerably depending on the indication, age, and clinical context. For newborn prophylaxis, the standard regimen involves either a single intramuscular injection of 1mg at birth, or an oral schedule consisting of 2mg at birth, followed by 2mg at 4–7 days, and a final 2mg dose at one month for exclusively breastfed infants. Formula-fed babies typically require only the first two doses if taking adequate amounts of formula, as infant formula is supplemented with vitamin K. Local neonatal protocols should be followed, and preterm or ill infants require specialist regimens.

For adults with deficiency or malabsorption, dosing should be determined by a healthcare professional based on individual circumstances and laboratory monitoring. Routine vitamin K intake for adults is measured in micrograms, with the UK reference nutrient intake being approximately 1 microgram per kg body weight daily. Higher doses in the milligram range are used only for treating deficiency or reversing warfarin effects under medical supervision. The MHRA-approved preparations provide specific dosing guidance that should be followed carefully.

Administration technique for liquid vitamin K is straightforward but requires attention to detail. Oral drops should be measured using the calibrated dropper provided with the product. The liquid can be administered directly into the mouth, ideally placed on the inside of the cheek rather than at the back of the throat to reduce choking risk. For infants, the dose can be given during or immediately after feeding. The liquid should not be mixed with large volumes of milk or formula, as this may result in incomplete dosing if the feed is not finished.

When taking vitamin K alongside medications that affect absorption, such as bile acid sequestrants (cholestyramine, colestipol) or orlistat, separate the doses by at least 2-3 hours to improve absorption.

Storage of liquid vitamin K preparations should follow manufacturer instructions, typically requiring protection from light and storage at room temperature. Once opened, products may have limited shelf life, and expiry dates should be checked regularly. Patients should be advised to:

• Shake the bottle gently before use if instructed

• Use the measuring device provided rather than household spoons

• Administer doses at consistent times when taking regular supplementation

• Not exceed recommended doses without medical advice

For those on warfarin or other anticoagulants, vitamin K supplementation should only occur under specialist guidance, as even small amounts can significantly affect INR (International Normalised Ratio) and anticoagulation control.

Side Effects and Safety Considerations

Liquid vitamin K is generally well-tolerated with a favourable safety profile when used at recommended doses. Unlike some vitamins, vitamin K1 (phylloquinone) has no established upper tolerable limit because toxicity from oral supplementation is extremely rare. However, certain adverse effects and safety considerations warrant attention.

Common side effects from oral liquid vitamin K are uncommon but may include:

• Mild gastrointestinal disturbances such as nausea or upset stomach

• Unpleasant taste, which can be minimised by taking with food

These effects are typically mild and transient. More significant reactions are rare with oral preparations but can occur with injectable forms, including pain at injection sites or, very rarely, anaphylactic reactions. This is one reason why oral liquid formulations are preferred when clinically appropriate.

Drug interactions represent the most clinically significant safety concern. Vitamin K directly antagonises warfarin and other coumarin anticoagulants, which work by inhibiting vitamin K-dependent clotting factor synthesis. Patients on warfarin should maintain consistent vitamin K intake and avoid supplementation unless specifically directed by their anticoagulation clinic, as fluctuations can lead to dangerous variations in INR. Conversely, vitamin K may be used therapeutically to reverse warfarin over-anticoagulation in controlled settings. Importantly, vitamin K does not reverse the effects of direct oral anticoagulants (DOACs) such as apixaban or rivaroxaban.

Other medications that may interact include:

• Antibiotics (particularly broad-spectrum types) that reduce gut bacteria producing vitamin K2

• Bile acid sequestrants (cholestyramine, colestipol) that may impair absorption

• Orlistat and other fat-absorption inhibitors

Contraindications are limited but include known hypersensitivity to vitamin K or formulation excipients.

When to seek medical advice: Patients should contact their GP if they experience unusual bleeding or bruising while taking vitamin K supplements. For severe bleeding or signs of allergic reaction (rash, swelling, difficulty breathing), call 999 or attend A&E immediately. Those taking anticoagulant medications should consult their anticoagulation clinic before taking any vitamin K supplements.

Suspected adverse reactions to vitamin K preparations should be reported via the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk or the Yellow Card app).

Frequently Asked Questions