Poisoning and Toxicosis in Dogs


Understanding Pet poisoning and Toxicosis

It is not unusual at our practice for a pet owner to bring in an obviously ill pet with the predetermined notion that it has been deliberately poisoned by a neighbor. In almost all of these types of cases it turns out the pet is ill for some other reason. Accidental poisonings, on the other hand, are not highly unusual in veterinary medicine. This month I am going to try to cover the poisonings we see most commonly in our practice and to also cover some of the nonpoisonous substances that have an unjustified bad reputation as a possible poison. There are a number of terms that are used when discussing toxicology and it is important to know at least a few of them:

A poison is a substance that has the potential to harm an animal by interfering with the normal processes for maintaining life.

A toxin is a poison that is produced by a biologic process. The distinction between a poison and a toxin is subtle and the term toxin is often used as a substitute name for any type of poison. Technically, though, a chemical or compound that does not come from a plant or animal is not a toxin. Recently, to make matters even more confusing it has become common in the literature for toxins to be referred to as biotoxins. This term would be redundant except for the tendency to use the words poison and toxin interchangeably. Toxicity is a measurement of the ability of a poison to cause an adverse effect or the dosage of the poison necessary to cause adverse effects.

Toxicosis is a disease state that has been induced by a poison. It is important to note that it is entirely possible to have a toxicosis that will not result in death. Any adverse effect on an animal is regarded as a toxicosis. This can be a real sticking point when trying to evaluate information about poisonous substances. Most people assume that when there is a report of a poisoning there was at least some risk of death to the pet during the poisoning episode. This is not necessarily true, though. A substance that causes vomiting but no more serious symptom than that will still be considered to be a poison by a toxicologist.

The lethal dose of a poison is the dose that causes death. Most of the time this is broken down further and reported as the dosage that causes death in some percentage of patients. The LD50 would be the dose of a poison which would kill 50% of the animals exposed to it. An LD10 would the dose that kills 10% of the animals exposed to it. Sometimes this is also called the lethal concentration, usually for poisons that are meant to mixed with water or with foods prior to use.

There are two terms used to describe the levels at which poisons cause an observed adverse effect. They are the NOAEL or "no observed adverse effect level" and the LOAEL, or "lowest observed adverse effect level". The difference between these might be easiest to envision by thinking about walking towards the edge of a cliff. If it takes 20 steps to get right the cliff edge then the NOAEL is 20 steps. The 21st step would the LOAEL in this example. That would be the point that you stepped off the cliff.

While the LD50, NOAEL and LOAEL are useful in assessing the possible risk to a pet from exposure to a known poison it is important to remember that individual pets vary widely in their susceptibility to the effects of a poison . For this reason it is not uncommon for veterinarians to react cautiously when poisonings are possible and to advise treatment even when the risk of death is not especially high.

It is really very important to understand the difference between the lowest observed adverse effect level and the lethal dose when discussing poisons. Frequently veterinarians advise treatment for toxicoses when it seems likely that the toxin has exceeded the LOAEL even when the risk of death is extremely low. This can cause confusion about the seriousness of a toxicosis and lead to undue worry after exposure to poisons that are quite capable of causing adverse effects but are very unlikely to actually cause death.

It is possible for a substance to be both a medication and a poison or toxin. In fact, most medications are poisonous if enough of the medication is administered. This might not a common problem if humans were not a great deal larger than many of their pets. When a 5 lb. poodle ingests thirty 5mg enalapril tablets it is more likely he or she will have an adverse effect than the owner would if a similar number of pills were ingested by the owner.

Medications that are safe to use for humans may not be safe for dogs or cats. Medications that are safe to use in dogs may not be safe to use in cats. It is critically important to understand that different species of animals have different reactions to many substances and that a substance may be a poison in one species and non-harmful or even beneficial in another species. Lots of people kill their pets every year by making the mistake of using their own medications or over the counter medications to treat suspected illnesses.

There are a number of poisons whose ability to cause harm depends on how the pet is exposed to the medication. Some poisons must be inhaled to cause toxicosis while others have to be ingested or applied to the skin in order to cause harm. Whenever it is possible to tell, it is important to let your veterinarian know the possible route of exposure when a poisoning is suspected.

An antidote is a substance that counteracts the effect of a specific toxin or poison. There are specific antidotes for a number of toxicoses. If a specific antidote is not available there are also substances that help a great deal in the treatment of pets who have been poisoned in more general ways. The best example of one of these latter substances is activated charcoal, which is given orally and absorbs many toxins or poisons, safely transporting them out of the digestive tract. It is more likely that an emergency clinic (EVC) will have some of the specific antidotes than a general veterinary practice so in a true emergency it is best to go to the EVC directly than to try to get in contact with your vet in many instances.

Dr Mike Richards, DVM


General information on exposure to poisons

General information on exposure to poisons

When a poisoning is suspected the best possible situation is to know what poison a pet was exposed to, the amount that it ingested (or was exposed to by other means), the time the exposure occurred and when symptoms on poisoning started, if they have started already. There is no substitute for keeping your wits about you when dealing with a suspected poisoning and gathering up the container the poison came in, if available, looking around just enough to make a good guess as to how much of the poison the pet was exposed to or getting the phone number of anyone who might have inadvertently poisoned a pet, such as an exterminator, who may be able to provide additional information on the substance the pet was exposed to.

The labels of many substances that can be poisonous have warnings or information to use in case of accidentally exposure to the chemical. Read the label. If it says to induce vomiting there are several ways to do this at home. Syrup of ipecac can be given to pets to induce vomiting. The dosage for dogs is 1 to 2 ml per kilogram of body weight or about 0.5 to 1ml per pound of body weight. This also works out to 1 teaspoonful per 5 to 10 lbs. of body weight. The dosage for cats is 3.3 ml/kg or about 1 teaspoonful per 4 pounds of body weight. Administering hydrogen peroxide will cause most pets to vomit if enough of it is given. The recommended dosage for dogs is 1 to 2 ml/kg or 0.5 to 1ml/lb. It is usually necessary to repeat the dosage once or twice to get vomiting to occur. The same dosage of hydrogen peroxide works for cats but the dosage should only be repeated once in this species.

If it is not possible to identify a specific poison your vet may only be able to treat the symptoms of the poisoning and hope for the best. In some cases the signs of a toxicosis are distinct enough to allow identification of the poison without prior knowledge of what it was but don't count on this. In situations in which it really seems likely that a poisoning has occurred but it is unclear what the poison it is still possible to treat symptomatically successfully in many cases.

One situation that often catches people unprepared is the sudden death of a pet. Often in this circumstance there is some worry over the possibility of poisoning. My best advice in this circumstance is to ask for a post mortem exam (necropsy exam) in order to determine a cause of death, if possible. It is best to be prepared to make this decision in advance because many people have a very hard time with the emotional aspects of having a necropsy exam done while also dealing with the sudden loss of a valued friend. Over the long term, though, many people have expressed regret over not pursuing an accurate diagnosis at the time of death. It just helps to know what happened. This is particularly important when there is more than one pet in a household and there is any chance of exposure to a poison that might affect more than one pet.

It is important when discussing necropsy examination as a diagnostic tool to point out that most general practice veterinarians are not going to be able to determine whether a specific poison was responsible for the death of a pet. In most cases this doesn't cause problems because in most cases in which poisoning is suspected another cause of death can be identified on necropsy examination. If it is certain, or near certain, that a poison caused a pet's death and it is important to know exactly which poison was involved it is best to ask that the pet's necropsy examination be performed by a board certified veterinary pathologist. It is almost always possible to find veterinary pathologists at veterinary schools but there are also a number of veterinary pathologists who work for commercial laboratories that provide necropsy examination services. If it is necessary to test serum or tissues for poisons the cost can be quite high so it is important to get some idea of the cost in advance when making arrangements for testing. If the cost is prohibitive you can always elect to have just the post mortem examination done and hope that a cause for death is found.

Knowing where your local emergency clinic is, or being aware of the emergency options available to you if an emergency clinic is not within a reasonable driving distance before an emergency occurs is extremely important. Time can be the most critical factor in the success of treatment for several poisonings and is important in almost all poisonings. If activated charcoal can be given within an hour of the ingestion of a poison it can absorb it is nearly twice as effective if given within the first hour as it is when started more than an hour after the ingestion of a poison. Several types of poisoning can only be successfully treated if treatment starts within a specific time period. Make sure that you know where to go after your vet's regular hours or on weekends or holidays.

Dr Mike Richards, DVM 2/16/2007

Last edited 02/16/07


Michael Richards, D.V.M. co-owns a small animal general veterinary practice in rural tidewater Virginia. Dr. Richards graduated from Iowa State University's College of Veterinary Medicine in 1979, and has been in private practice ever since. Dr. Richards has been the director of the PetCare Forum...