Anaphylaxis in a cat can go from 1 swollen eyelid to a closed airway in 5 minutes. Three things in the first 10 minutes matter more than anything done later: epinephrine at 0.01 mg/kg as prescribed by your vet, the cat flat on its side with the hind legs raised, and a car already moving. Sitting still for 20 minutes to see whether it settles is the mistake behind almost every bad outcome.
What happens in the first 5 minutes
This is a whole-body mast cell dump. Histamine dilates blood vessels, blood pressure falls, fluid leaks into tissue, and the airway lining swells. Cats hide the first 2-3 minutes well, then crash fast, which is why the clock starts at the first symptom and not at the first obvious emergency.
Expect 2 or 3 of these 6 signs at once: sudden vomiting, 2-3 explosive diarrhea episodes, heavy drooling, loud gum clicking, itching around the face and ears, and a cat that lies flat and will not get up. Breathing signs come next: over 40 breaths per minute at rest, then wheeze, then open-mouth breathing, which is never normal in a cat at any age.
What to do at home first
Minute 0-1: stop the exposure and call the clinic on speaker. Say the 1 word that changes triage, anaphylaxis, then give the cat's weight in kilograms, because every drug dose is calculated from it.
Minute 1-2: if your vet has already sent home an epinephrine kit, give 0.01 mg/kg into the thigh muscle, exactly as the label reads. It is prescription only: never borrow a dog's ampoule and never estimate a dose by eye. Keep the ampoule out of sunlight, because epinephrine turns pink-brown and loses potency 6-12 months past the expiry date.
Minute 2-3: lay the cat flat on its side and raise the hind legs 15-20 cm on a folded towel. This is not comfort, it is blood pressure. Pooling blood in the legs pushes 200-300 mL back toward the heart in a 4 kg cat, which buys 3-5 minutes of perfusion to the brain.
Minute 3-5: nothing by mouth. No water, no food, no oral drug. A cat in this state cannot swallow safely, and 1 mL of water in the airway is worse than 12 hours of thirst.
Minute by minute: the first 20
| Minute | Do | Number that matters |
|---|---|---|
| 0-1 | Stop exposure, call clinic on speaker | Weight in kg; time 0 written down |
| 1-2 | Epinephrine into thigh muscle | 0.01 mg/kg, prescription only |
| 2-3 | Flat on side, hind legs up | 15-20 cm raise; 3-5 min of pressure |
| 3-5 | Nothing by mouth, clear the carrier | 0 mL oral |
| 5-10 | Carrier flat in the car, drive | Breathing under 40 per minute |
| 10-20 | Call ahead, hand over the timeline | 3 monitors logged every 2 min |
Epinephrine: the dose that decides the night
0.01 mg/kg is the number to remember, and the volume is what confuses people at 2 a.m. With the 1 mg/mL (1:1000) solution, 0.01 mg/kg equals 0.01 mL/kg, so a 4 kg cat gets 0.04 mg in 0.04 mL. Clinic staff often dilute to 1:10,000 (0.1 mg/mL), which turns that same 0.04 mg into a 0.4 mL syringe, 10 times easier to measure.
If your vet supplied a pre-filled syringe, the label should show 3 things: mg, mL and your cat's weight. If it shows only mL, ask for the mg figure in writing before you need it. Repeat dosing is a veterinary decision, usually not before 5-15 minutes, and never in a cat that is already twitching or barely breathing.
When you must go to the clinic
Go now, not in an hour, if any 1 of these is true: facial or throat swelling with vomiting, breathing over 40 per minute, open-mouth breathing, gums that are pale, grey or blue, collapse, or a sting inside the mouth. A cat that improves after epinephrine still goes in, because the drug wears off in 15-20 minutes while the reaction can run 8-24 hours.
Call while you drive and say 3 things: anaphylaxis, weight in kg, and minutes since the first sign. Clinics can draw up drugs and set up oxygen in the 10 minutes you are on the road, and a 10-minute head start is the difference between treating a stable cat and resuscitating a crashing one.
What to bring to the clinic
- 1 item of evidence: the insect in a closed jar, the vaccine box with its lot number, or the drug packet.
- Time zero on paper: the minute the first sign appeared, plus the minute you gave epinephrine.
- Weight in kg and the exact dose given, in mg and mL.
- Phone photos at 0, 5 and 10 minutes, because swelling is easier to grade on a screen than from memory.
- The medication list, including 2x daily insulin or a 3-weekly flea product (toxin and product lookup).
Three things to monitor in the car
| Monitor | Normal | Act now |
|---|---|---|
| Breathing rate | 20-30 per min, mouth closed | 40+ per min, or open mouth |
| Gum color and refill | Pink, refill under 2 sec | White or blue, refill over 3 sec |
| Awareness | Looks at you, ears move | Unresponsive, twitching, seizure |
| Body temperature | 37.5-39.2 C | Under 37 C, or shivering stops |
Say the numbers out loud every 2 minutes to whoever is driving. A second pair of hands is worth more than a second opinion at this stage, and 3 logged numbers let the vet skip 10 minutes of questions.
The second wave, 8-24 hours later
Most emergency protocols keep the cat for 8-24 hours even after a good response, because a quiet 2-6 hours can be followed by a second wave of swelling with no new exposure. Do not accept a discharge without 3 written items: drug name, dose, and the exact hour of the next dose.
A cat whose urinary catheter came out 24-48 hours earlier is a higher-risk patient: dehydration concentrates the reaction, and urine output is already low (catheter aftercare). The full reaction map is in the anaphylaxis guide.
Four steps to prepare today
- Ask your vet for a written anaphylaxis plan with mg, mL and the weight it was calculated for.
- Keep 1 epinephrine kit, 2 syringes and the clinic number in the carrier, not in a kitchen drawer.
- Weigh the cat once a month and write the kg figure on the carrier lid.
- Rehearse the flat-with-legs-up position once, so nobody argues about it at minute 3.
Anaphylaxis is one of the few cat emergencies where 5 correct minutes at home outweigh everything done in the clinic afterward.
Frequently asked
What exactly is the epinephrine dose for a cat in anaphylaxis?
The standard figure is 0.01 mg/kg, given by prescription only. With the 1 mg/mL solution that equals 0.01 mL/kg, so a 4 kg cat gets 0.04 mg in 0.04 mL, which is why clinics often dilute to 1:10,000 so the same dose becomes a 0.4 mL syringe. Give it into the thigh muscle and never guess a dose from a dog's ampoule.
Why does the cat have to lie flat with the hind legs raised?
Because the emergency is a blood pressure crash, not a skin problem. Raising the hind legs 15-20 cm returns 200-300 mL of pooled blood toward the heart in a 4 kg cat and buys 3-5 minutes of brain perfusion. Sitting the cat up, or letting it stand and walk to the car, drops pressure further and is how cats collapse in doorways.
How long after a reaction is the cat actually safe?
Not at 30 minutes. Most protocols keep the cat 8-24 hours because a quiet 2-6 hours can be followed by a second wave with no new exposure, and the epinephrine itself wears off in 15-20 minutes. Leave with three written items: drug name, dose, and the exact hour of the next dose. A cat with a recent urinary catheter needs closer monitoring because dehydration concentrates the reaction.