Vitamin D is also known as cholecalciferol and is a fat soluble vitamin. Toxicity occurs when excessive amounts of cholecalciferol are ingested. Most commonly, this occurs as a result of ingestion of choleciferol-containing rodenticides or vitamin supplements. Less commonly, vitamin D toxicity may also occur as a result of an improperly balanced diet.
Effects of Excessive Amounts of Vitamin D in the Dog and Cat
Cholecalciferol, when ingested, is metabolized in the liver to 25-hydroxycholecalciferol, which in turn is metabolized by the kidneys to calcitriol. Calcitriol enhances calcium resorption from the bones and the uptake of calcium from the intestinal tract. When excessive amounts of calcitriol are present, as happens in vitamin D toxicity, hypercalcemia (abnormally high levels of calcium in the blood) occurs because:
- excessive amounts of calcium are absorbed from the intestinal tract
- calcium resorption from bone is stimulated
- the kidneys increase the reabsorption of calcium
Symptoms of Vitamin D Toxicity and Hypercalcemia in the Dog and Cat
The symptoms seen in cases of vitamin D toxicity are a result of the hypercalcemia that develops due to excessive amounts of cholecalciferol being metabolized to calcitriol. Hypercalcemia results in abnormal calcification in the kidneys, gastrointestinal tract and cardiovascular system as well as neurological dysfunction.
The symptoms seen with hypervitaminosis D (vitamin D toxicity) include:
- vomiting
- diarrhea
- increased water consumption
- increased urine volume
- lethargy
- lack of appetite
- hemorrhage in the gastrointestinal tract and/or lungs, in some animals
- pain from the kidney area
- abnormal heart rhythms
- bone pain
- limping
Treatment of Vitamin D Toxicity and Resulting Hypercalcemia in Dogs and Cats
When possible, decontamination of the gastrointestinal tract can help mitigate the effects of ingestion of excessive amounts of vitamin D. If ingestion of cholecaliferol-containing rodenticides or vitamin supplements has occurred or is suspected, initial treatment should include:
- administration of an emetic to induce vomiting and reduce the amount of cholecalciferol in the gastrointestinal tract, if the exposure is recent
- administration of activated charcoal to adsorb the toxin in the gastrointestinal tract
- administration of a saline or osmotic cathartic to speed passage of the toxin through the gastrointestinal tract
- fluid therapy as necessary to correct fluid and electrolyte abnormalities
If the pet is experiencing seizure activity, administration of an emetic is contraindicated, as this increases the chance of aspiration pneumonia or choking.
If the animal is already suffering from hypercalcemia, potential treatments include:
- furosemide
- prednisone or prednisolone
- calcitonin
Additional treatment to control the symptoms resulting from hypercalcemia may be necessary also.
- Peritoneal dialysis to treat extreme uremia should be considered. Peritoneal dialysis with a calcium-free dialysate may also be effective in lowering blood calcium levels.
- Anti-convulsant medications may be necessary to treat seizure activity.
- Cardiac arrhythmias may also need to be treated with appropriate medications.
Hypercalcemia resulting from vitamin D toxicity in dogs and cats can persist for weeks and may require long-term therapy. Maintenance dosage of furosemide and prednisone (prednisolone) may be necessary. A diet low in calcium will be necessary during the recovery period. Milk and other dairy products as well as supplements containing calcium should be avoided as well.
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