Just a thought. If I were to catch on of my cats eating a plant that I know is poisonous to cats (e.g. travelling over christmas and they found a poinsettia). Is there something that I should do to immediately to try and mitigate the problem before going to the vet?
My first-aid manual1 has a few tips for immediate aid:
Immediately call your vet or an emergency veterinary hospital depending on time of day. This is a medical emergency and needs swift resolution.
Inducing vomiting only if the cat is fully awake and in control of their body and you know what they ate. If there's any doubt that they are not then don't do it as it they may inhale it coming up. Also, do not do this if they ate a caustic poison! (see below) In any event, 3% hydrogen peroxide solution with a dosage of 1 teaspoon (real measure don't wing it from your cutlery) per 10 pounds of pet. Cats are not as susceptible to it as dogs are, but the foaming action will tend to induce vomiting. Keep any vomit for analysis by the vet.
Dilute it. If you can get them to eat something, even treats, then the food can dilute and delay the absorption of the poisonous material.
Be prepared to give artificial respiration and/or CPR. This can be tricky when it comes to animals, so I'd really suggest getting your vet to show you how to do this so you can respond in an emergency. A bit of training ahead of time may help save the life of your pet.
When going to the vet, take any samples of the poisonous material and any vomit that your pet has produced.
For caustic poisons like ammonia or bleach and with petroleum products like kerosene and the like, you can try and feed them bread that has been soaked in mineral or vegetable oil. The oil will help protect the stomach lining and intestines. As noted above, never induce vomiting in this situation.
If the poison is caustic, it's unlikely they have swallowed it, unless it was in something that prevented tasting, and so may have only burned their mouths on it. Treat that with milk and/or water to help cool the burns, but you'll still need to get to the vet.
1 The First Aid Companion for Dogs and Cats. - Amy D. Shojai
The are veterinary poison control centers. Keep the number for one handy, and call them before either panicking or doing anything that might make matters worse. Or call your vet.