Ergocalciferol

What is ergocalciferol?

Ergocalciferol is a form of vitamin D that is sometimes used in veterinary medicine to treat low calcium blood levels that result from a condition called hypoparathyroidism. Another form of vitamin D, calcitriol, is usually recommended first, but ergocalciferol is sometimes substituted because it is less expensive.

Compared to calcitriol, ergocalciferol requires large initial doses, effects take longer to be seen, and if hypercalcemia (excess blood calcium) develops, it takes longer recover from (up to 18 weeks).

Ergocalciferol is used off-label in dogs and cats as there are no veterinary formulations available, and products intended for human consumption are used. Many drugs are commonly prescribed for off-label use in veterinary medicine. 

“Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions very carefully, as their directions may be significantly different from those on the label.

How do I give my pet ergocalciferol?

• Ergocalciferol is given orally (by mouth) in the form of a capsule, tablet, or liquid solution.
• It may be given with or without food.
• If vomiting occurs when dosed on an empty stomach, give future doses with food or a treat.
• Follow the instructions on the product label, in conjunction with your veterinarian’s directions.

This medication should take effect 5 to 14 days after treatment begins, and improvement in clinical signs should follow.

What if I miss giving my pet the medication?

If you miss a dose of ergocalciferol, give it as soon as you remember, and then continue with the regular dosing schedule. However, if it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.

Are there any potential side effects from ergocalciferol?

Ergocalciferol may cause the following side effects:

• Nausea, vomiting, diarrhea
• Oral ulceration

Serious adverse reactions may occur. If any of the following signs develop, stop giving ergocalciferol and contact your veterinarian immediately:

• Severe skin lesions such as ulcers, crusts and weeping wounds
• Seizures
• Unusual behavior
• Changes in blood cell numbers, identified through blood work (low red blood cell, white blood cell, and platelet counts)

Drug sensitivities can develop over time with repeated exposure. Your pet may have no reaction after the first few doses but may develop a sensitivity later. It is important to watch for signs of an allergic reaction over the entire course of treatment. Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately.

Excessive ergocalciferol doses can cause calcium concentrations in the blood to become too high. This effect can last for many weeks, even after the medication is discontinued.

Are there any risk factors for this medication?

DO NOT USE ergocalciferol in:

• Pets with a known hypersensitivity to this medication or to vitamin D
• Pets with hypercalcemia (high blood calcium levels)
• Pets with vitamin D toxicity
• Pets with malabsorption syndrome

USE WITH EXTREME CAUTION in:

• Pets with hyperphosphatemia (high blood phosphorus levels)

USE WITH CAUTION in:

• Pets with kidney dysfunction or impairment (calcitriol or dihydrotachysterol [DHT] would be preferred because those drugs do not require activation by the kidney)

Are there any drug interactions I should be aware of?

Certain medications may interact with ergocalciferol and so it is important to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking before starting any new treatment. 

Several medications should be used with caution when given with ergocalciferol, including:

• Cholestyramine
• Cimetidine
• Corticosteroids
• Digoxin or verapamil
• Mineral oil
• Phenobarbital
• Thiazide diuretics

Is any monitoring needed with this medication?

• Blood calcium levels must be monitored to ensure this drug is working.
• Pets should remain hospitalized until blood calcium levels are stable without extra calcium therapy.
• Weekly blood calcium levels should be measured and the dose of ergocalciferol should be adjusted accordingly based on blood results.
• Once the pet is stable, monthly blood rechecks are recommended for 6 months and then every 2–3 months thereafter.
• At home, monitor for any side effects such as those noted above. If any side effects occur, discontinue use of the medication and contact your veterinarian.
• Your veterinarian will let you know when they want to reassess your pet to ensure the medication is working and not causing side effects.

Lifelong treatment and regular laboratory monitoring is required for vitamin D drug treatment. Chronic therapy should not be initiated unless owners are willing to commit to ongoing patient monitoring.

How do I store ergocalciferol?

• Ergocalciferol is sensitive to light, heat, and air.
• Store capsules or liquid at room temperature (59°F–86°F or 15°C–30°C).
• Store in an airtight container and protect from light.
• Keep medication out of reach of children and pets.

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. Be prepared to provide information about the product and your pet's weight and symptoms.