Why the oily liquid is worse than the capsule shell
The gel cap itself is harmless gelatin, but the oil inside is pure, highly absorbable vitamin D3—no barriers slow its uptake. For a 3 kg cat, licking that oil means rapid absorption through the mouth's mucous membranes, bypassing slower stomach processing. This direct route can spike blood calcium faster than eating a whole capsule would.
Check where your cat bit the capsule—if it burst near the end, she may not have ingested all 5000 IU, but even half is dangerously high. Oily residues on her fur or paws increase exposure through grooming; wipe her gently with a damp cloth while awaiting veterinary instructions.
How small cats process vitamin D differently
A cat's liver can't metabolize excess vitamin D as efficiently as larger animals. That 5000 IU dose, designed for humans, overwhelms her system's ability to regulate calcium. Within hours, calcium begins leaching from bones into her bloodstream, while her kidneys struggle to filter it out—this dual assault risks acute kidney injury.
The oil's consistency also matters—it sticks to the throat and stomach lining, prolonging absorption. Your vet may recommend hospitalization for IV fluids to dilute the calcium surge and protect her kidneys. Blood tests at 12 and 24 hours post-ingestion are critical to catch rising levels before damage occurs.
Why you might not see immediate symptoms
Early signs like slight lethargy or decreased appetite are easy to miss in cats. More obvious vomiting or excessive urination often appear only after significant calcium buildup. By day two or three, she might show muscle twitching or constipation—these signal advanced toxicity requiring aggressive treatment.
Monitor her water intake closely—increased thirst means her kidneys are under stress. Use the same bowl to measure consumption, and note litter box output. Save any vomit or stool samples for the vet; they can test for calcium crystals that confirm systemic overload.
Longer-term risks after one gel cap
Even if initial treatment succeeds, your cat may need follow-up bloodwork for months. High calcium can cause lasting kidney changes or heart rhythm abnormalities. Your vet might prescribe a low-calcium diet temporarily and recommend frequent water intake checks.
Store all supplements in childproof containers cats can't bat open—gel caps are especially tempting because they roll. Consider switching to solid tablets if you use vitamin D yourself; they're harder for pets to accidentally ingest. Always check floors after taking supplements; oily leaks from punctured capsules leave invisible hazards.
For a dose worked out against your pet's weight, use the Vitamin D (Cholecalciferol) Toxicity Calculator.