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Phytonadione (Vitamin K1)

By Rania Gollakner, BS, DVM, MPH

Medications

What is phytonadione?

Phytonadione (brand names: Mephyton®, Phytomenadione®, Aqua-Mephyton®, K-Caps®, Konakion®) is a vitamin supplement (also called vitamin K1) that is used as an antidote to treat anticoagulant rodenticide, sweet clover, dicumarol, or sulfaquinoxaline toxicities. It is also used to treat bleeding disorders caused by conditions such as liver failure. It is used in cats, dogs, horses, birds, and rabbits.

Dietary supplements are substances that can be used to supplement the diet, such as vitamins, minerals, amino acids, herbs, botanicals, enzymes, and probiotics. While many supplements are sold over the counter, they still contain ingredients that have biological effects that should be managed by your veterinarian. Follow your veterinarian’s directions and cautions very carefully as their directions may be significantly different from those on the label.

There are differences in how countries regulate supplements. In the United States, the over the counter forms of these substances are not as vigorously regulated by the FDA as other medications, which means they can be sold without the manufacturer proving their effectiveness, safety, and without a guarantee of consistent or accurately reported ingredients. In Canada, products that have been evaluated for quality, safety, and effectiveness by Health Canada and authorized for sale will have a license number on the label.

Why is vitamin K1 important?

The liver makes certain compounds in the body to aid in blood clotting and coagulation. Vitamin K1 is required to make these compounds functional. Deficiencies in vitamin K1 leads to uncontrolled bleeding.

How effective is phytonadione?

Phytonadione is very effective when used to treat a vitamin K1 deficiency; however, it does not appear to have an effect when used in normal, healthy pets.

How is phytonadione given?

Phytonadione is given by mouth in the form of a tablet, chewable, capsule, or compounded liquid. It can also be given by injection in the hospital setting. Give with food, ideally a fatty meal. Measure liquid forms carefully.

This medication should take effect within 1 to 2 hours; however, effects may not be visibly obvious and therefore laboratory tests may need to be done to evaluate this medication’s effectiveness.

What if I miss giving my pet the supplement?

If you miss a dose, give it when you remember. If it is close to the time for the next dose, give both doses at the same time, and then return to the regular dosing schedule. Do not skip doses.

Are there any potential side effects?

Side effects are uncommon and this vitamin is generally well tolerated when given by mouth. Serious side effects include allergic reactions when the vitamin is administered as an injection; therefore, it is preferred to give this medication by mouth.

This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this supplement?

Do not use in pets that are allergic to it unless the benefits outweigh the risks. Use cautiously in pregnant or lactating pets, as safety has not been established.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with phytonadione: oral antibiotics, mineral oil, or warfarin.

Vitamins, herbal therapies, and supplements have the potential to interact with each other, as well as with prescription and over the counter medications. It is important to tell your veterinarian about any medications (including all vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this supplement?

Your veterinarian will monitor your pet to be sure that the medication is working. Clotting tests should be monitored in cases of anticoagulant poisoning, as this is how to evaluate when your pet can discontinue supplementation.

How do I store phytonadione?

Tablets and capsules should be stored at room temperature between 59°F and 86°F (15°C and 30°C), in a light-resistant container. Protect from light at all times. Follow the storage instructions on the label for compounded liquid forms of this supplement.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

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