Vitamin K1 for Dogs and Cats

Updated Jun. 27, 2024
white fluffy dog waits for injection of medication at vet exam.

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PetMD’s medications content was written and reviewed by veterinary professionals to answer your most common questions about how medications function, their side effects, and what species they are prescribed for. This content shouldn’t take the place of advice by your vet.

What Is Vitamin K1 for Dogs and Cats?

Vitamin K1 is a vitamin prescribed in veterinary medicine as the antidote for vitamin K deficiency associated with rat poisoning in dogs and cats.

Vitamin K is essential for normal blood clotting, and certain ingredients in some rat poisons (anticoagulant rodenticides) cause a severe deficiency of vitamin K that prevents blood from clotting normally, resulting in internal bleeding.

Veterinarians may also prescribe oral vitamin K1 for less common causes of severe vitamin K deficiency in dogs and cats, including certain conditions of the liver (intrahepatic cholestasis), gallbladder (obstruction of the bile duct), intestine (intestinal malabsorption), and chronic oral antibiotic administration.

The injectable form of vitamin K1 is administered under the skin (subcutaneously) by a veterinarian while your pet is hospitalized because the injection works faster than the oral formulation to help your pet’s blood regain its normal clotting abilities.

When your pet’s bleeding condition is stable, your vet will generally prescribe the oral form of vitamin K1 for your pet for a few weeks. Your vet may frequently perform bloodwork to assess how well your pet’s blood is clotting to determine their response to treatment.

Vitamin K1 is FDA-approved for human use in various oral tablet and capsule formulations, under the brand name Mephyton® and as generic phytonadione or vitamin K1. Injectable vitamin K1 is available as generic phytonadione or vitamin K1.

Vitamin K1 is currently not FDA-approved as a veterinary medication. However, it is readily utilized in the veterinary field, and veterinarians can legally prescribe certain human drugs in animals in certain circumstances. This is called extra-label or off-label use because this use isn’t described on the drug label.

In certain circumstances, your vet may recommend a compounded formulation of vitamin K1. Compounded medications are prescribed if there’s a specific reason your pet’s health can’t be managed by an FDA-approved drug, such as if your pet has trouble taking pills in capsule form, the dosage strength is not commercially available, or the pet is allergic to an ingredient in the FDA-approved medication.

Compounded medications are not FDA-approved. They are created by either a veterinarian or a licensed pharmacist on an individual basis to best suit a patient’s particular needs. You can learn more about compounded medications here.

How Vitamin K1 Works in Dogs and Cats

Vitamin K1 is the cure for the harmful anti-clotting (anticoagulant) effects of certain rat poisons. Replenishing vitamin K levels restores the function of the substances in the blood that are essential to normal clotting (clotting factors).

Vitamin K1 Directions for Dogs and Cats

Follow the directions on the drug label or as provided by your veterinarian.

Generally, your vet will instruct you to give vitamin K1 by mouth to your pet twice a day with fat-containing foods for around four to six weeks. 

The dosage of vitamin K1 and length of treatment time your vet prescribes depends on the type and amount of rat poison your pet ingested, the severity of your pet’s toxicity and symptoms, and their medical needs.

Missed a Dose?

Speak with your veterinarian about what to do if you forget to give a dose of vitamin K1. Generally, they may instruct you to give it when you remember, or if it is almost time for your pet’s next dose, to skip the missed dose and resume your normal dosing schedule. Do not give extra or double doses.

Possible Side Effects of Vitamin K1 for Dogs and Cats

A subcutaneous (under the skin) injection of vitamin K1 may cause symptoms including:

  • Pain, swelling, and tenderness at the injection site

  • Allergic reaction (rare)

The oral form of vitamin K1 is generally well tolerated in dogs and cats.

Human Side Effects

Vitamin K1 is also a prescription medication for humans, frequently with dosages different from those prescribed for your pet by a veterinarian. Due to possible side effects, humans should never use medicine dispensed for their pets and pets should not be given any medicine dispensed for a human’s use.

If you accidentally ingest this medication, immediately call your physician or the national Poison Control Center hotline at 800-222-1222.

Call Your Vet If:

  • Severe side effects are seen (see above)

  • Your pet’s condition worsens or does not improve with treatment

  • You see or suspect an overdose

  • You have additional questions or concerns about the use of vitamin K1

Vitamin K1 Overdose Information for Dogs and Cats

An overdose of vitamin K1 is unlikely to cause toxicity or symptoms in a dog or cat.

If you suspect an overdose, immediately contact your veterinarian or an animal poison control center. Consultation fees often apply.

Pet Poison Helpline (855) 764-7661

ASPCA Animal Poison Control (888) 426-4435

Vitamin K1 Storage for Dogs and Cats

Always confirm storage requirements by reading the prescription label.

Vitamin K1 tablets and capsules should be stored at controlled temperatures between 59–86 F. Keep the container tightly closed in order to protect its contents from moisture and light.

Compounded medications should be stored according to the compounding pharmacy’s label.

Keep out of reach of children and pets.


Do you need a prescription for vitamin K1 for dogs and cats?

Yes, the dosage form of vitamin K1 needed to treat rat poisoning for dogs and cats is only available by prescription through your veterinarian.

How long does it take for vitamin K1 to work in dogs?

Vitamin K1 starts reversing the harmful blood thinning effect of rat poisons within 24–48 hours from the beginning of treatment. Since the poisons can remain in the body for a long period of time, veterinarians generally prescribe 30 days of vitamin K1 to make sure the pet is safe from internal bleeding

No vet writer or qualified reviewer has received any compensation from the manufacturer of the medication as part of creating this article. All content contained in this article is sourced from public sources or the manufacturer.


Plumb DC. Vitamin K1. Plumb’s Veterinary Drugs. Updated July 2022. Accessed May 1, 2024


Molly Price, DVM


Molly Price, DVM


Dr. Molly Price has practiced small animal medicine for over 20 years and is a graduate of Texas A&M College of Veterinary Medicine. She...

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