Cholecalciferol toxicity

Buzz's story is a cautionary tale to keep pest baits and toxins locked safely out of reach of our companion animal pets.

Buzz - a 7-year-old male neutered Labrador, affectionately known as ‘Buzz Lightyear' by the veterinary staff at Totally Vets Ltd -  was brought to the clinic with suspected cholecalciferol poisoning after ingesting ‘Kiwicare - No possums gel bait®'.  Although Buzz was a picture of innocence, the evidence was stacked against him with the discovery of a half-chewed packet of bait, and green faeces. 

Cholecalciferol (Vitamin D3) is used as a possum or rodent poison in products including Kiwicare®, Feratox® and Feracol®, and acts by increasing calcium and phosphorus absorption from the gut, mobilising stores of calcium from bone and decreasing excretion of calcium from the kidneys.  Sufficiently high levels of calcium (hypercalcaemia) can result in calcium deposits throughout body tissues - heart, blood vessels, kidney and lungs. In severe cases, untreated pets can die of heart failure or kidney failure.

Signs of poisoning can include a lack of appetite, vomiting, dehydration, constipation, drinking and urinating lots, blood in the vomit and/or faeces, slow or irregular heart rate, difficulty breathing due to bleeding in to the lungs, and neurological signs (twitching, depression and less commonly seizures).  In patients who are not showing any clinical signs the prognosis is good, but in cases like Buzz, who was showing clinical signs of vomiting, lethargy and a slow heart rate, the prognosis is guarded.  Treatment can take several weeks as cholecalciferol remains in the body for a long time.

Blood samples confirmed Buzz had an elevated blood calcium level. Buzz was admitted to hospital to begin immediate treatment with a diuretic (furesomide) and fluid diuresis (an intravenous drip). At twice his normal fluid maintenance, he required 3 litres of fluid a day with a compound that was specifically lacking in calcium (0.9% NaCl).  Buzz was also given activated charcoal, which binds to toxic compounds and makes them inactive. His diet needed to be calcium restricted - so there was cooked mince or chicken and pasta on the menu. 

Blood tests repeated 48 hours later showed elevations in kidney parameters and a further rise in calcium levels. Clinically Buzz had started to vomit in earnest, likely as a result of progressing kidney disease. As well as continued diuresis therapy, Buzz was started on anti-vomit and gut-protectant drugs, and corticosteroids to prevent uptake of calcium from bone, reduce intestinal calcium absorption and promote kidney excretion of calcium. 

The breakthrough came with sourcing Pamisol® (Disodium pamidronate).  This hard-to-obtain drug works by preventing calcium stores from being mobilised from bone. Within 24 hours of administration, Buzz's calcium levels had returned to normal.

Buzz remained in hospital for a total of 12 days to manage his kidney disease and concurrent gut bleed that had developed despite the vet team's best efforts. However, after appearing to be on the mend, he re-presented to the clinic in a state of near collapse from vomiting and dehydration.  Repeat blood tests indicated both liver and kidney damage. Buzz was referred to Massey University Veterinary Teaching Hospital (MUVTH) for ultrasound analysis of his liver, as this was an unexpected turn of events given that cholecalciferol toxicity has not been documented to cause liver damage.  A complete work-up concluded he may have had a drug reaction as a side-effect to the life-saving drug cocktail he had received.

Buzz has continued to improve clinically following further supportive care, and regular blood tests show improved liver and kidney function.  His journey has not been devoid of further hiccups however, with a recent urinary tract infection followed by an uncommon allergic reaction to the prescribed antibiotic.

Although not out of the woods yet, we are quietly hopeful that Buzz's liver and kidney parameters will continue to improve. We join his owners in being big fans of Buzz - although they joke that he is no longer eligible for his inheritance - and hope his mischievous Labrador nature doesn't get him into any further trouble.