Counting the missing tablets is your first priority
Right now, every minute matters in determining how much levothyroxine your 6 kg cat ingested. Empty the bottle onto a clean surface and tally any broken or crushed tablets—even small fragments can contain significant hormone doses for a cat. While doing this, keep the exposed cat confined where you can observe tremors or agitation starting.
If more than half a tablet is unaccounted for, assume your cat ate a dangerous amount. Cats process thyroid hormones differently than dogs, and their smaller size makes them far more vulnerable to overdose effects like rapid heart rate and hyperthermia.
Your other cats need mouth checks, not panic
Though your two unaffected cats didn’t directly eat from the bottle, run a finger along their gums and under their tongues to check for sticky pill residue. Levothyroxine tablets often crumble easily, and curious cats might lick traces off each other’s fur.
No fragments? Isolate them in another room with water but no food for two hours—this prevents shared grooming. Watch for dilated pupils or excessive vocalization, though with no observed ingestion, symptoms are unlikely.
Why the 6 kg cat can’t wait
A 25 mcg tablet might seem tiny, but for a 6 kg cat, even one whole tablet exceeds safe thresholds. The hormone will peak in their bloodstream within 4-6 hours, potentially causing dangerous spikes in blood pressure and body temperature.
Don’t wait for panting or restlessness—those are late signs. Your vet will likely administer IV fluids and medications to protect the heart, which is far more effective when started early.
Handling multiple pets in a medication scare
With three cats, focus shifts quickly: the exposed one needs a vet now, while the others need observation. Confine the exposed cat in a carrier (stress is preferable to roaming with a racing heart). For the others, note their normal resting respiratory rates now—counting breaths per minute helps spot subtle changes later.
Wipe down any surfaces the bottle touched with a damp cloth—levothyroxine powder can linger on countertops. Store future medications in high cabinets; cats can chew through childproof caps given time.
The step-by-step response, from the first minute to the vet visit, is in our Thyroid Medicines (Levothyroxine) emergency guide.