Dose: How much is too much for Your Animal?

Dose determines the level of toxicity

For the vast majority of poisons, the amount of poison controls the signs we see. Similarly, poisonous amounts will be different for every substance. For example, The amount of ibuprofen it takes to cause kidney failure is larger than the amount of naproxen it takes. This article will help you understand what a toxicologist does to calculate toxicity.

Anything can be toxic  

Anything.  Even water. Thus, any substance on the planet can make you ill or kill you. An excellent veterinary toxicity professional will be able to provide you with the answer to several pieces of information.

These definitions will help you understand your vet:

• Your pet’s dose:  We express this in milligrams per kilogram.
  
• The therapeutic dosage (if applicable): We use this dose in veterinary medicine to treat various diseases.
  • For example, a vet may give your pet 1-2 milligrams per pound of diphenhydramine to therapeutically treat allergies. Anything over that dose is an overdose.
    
• A threshold dose is the lowest dose for a specific substance that will cause signs of illness.
  • However, even therapeutic doses can cause certain signs. We call these “side effects”.
    
• LD50 is a fancy term in toxicology that you frequently see to measure the relative danger of a particular substance.  It indicates the specific dose at which 50% of the test population died after exposure to something.
  • We often call this the “lethal dose”. But, this is just a mathematical mean, not the SMALLEST amount that will kill a pet.
    
• The margin of safety: This compares the therapeutic and threshold doses. If there is a large difference between the therapeutic and threshold doses, a drug has a wide margin of safety. The reverse also applies. Drugs with a wide margin of safety are safer than drugs with a narrow margin of safety.
  
• The serum or plasma half-life is the amount of time it takes the body to get rid of half of a substance.

Other considerations

While this all sounds pretty straightforward, there are several other factors that influence a poison’s effect on the body:

• Other medications a pet is taking – Some medications will enhance or hinder each other. A medication that would normally be safe might be lethal in combination with another medication.
  
• The pet’s health history – Certain diseases will affect how a pet metabolizes a medication. This makes it more difficult for them to clear it out of their body.
  
• Formulation – some medications come in both instant-release and extended-release forms. Extended-release medications take longer to take effect and will last longer in the body.

All of this information is necessary for a veterinarian to be able to determine how something will affect your pet!  

This is often why a practicing vet will not know how to treat a case of poisoning.  Since toxicology is a specialized field, it is not extensively covered in vet school. So, veterinarians will often refer an owner to a poison control center to assess all of this information. This assessment is what you pay for when you call an animal poison control center. It is not just a recommendation of whether to take your pet to the vet.

Additionally, there are other important things a poison control center or toxicologist will be able to tell you or your vet:

• If it is safe to induce vomiting – if something is expected to cause signs quickly, we do not induce vomiting
  
• What signs we can see at any specific dose
  
• What medication can reverse or control specific signs
  
• How long before a poison takes effect
  
• How long the effects will last
  
• What long-term effects may occur

So, how do I tell how much my pet has ingested?

Calculating a dose can be very complicated.  Information on toxicity is presented in a milligram per kilogram format (mg/kg). So, the key to seeing if something is toxic lays in determining how many milligrams of a specific poison is any food, medication, plant, or other substance.

If the lethal dose of a medication is 25 mg/kg, this does not necessarily mean that giving 25 milligrams is lethal!

We use body weight to determine how much of a medication is poisonous. For a simple example, let’s see how much sugar a pet gets from a pill:

A 10-pound dog swallows a 25-milligram sugar pill:

• 10 pounds is equal to 4.55 kilograms
• 25 milligrams divided by 4.55 kilograms equals 5.49 milligrams per kilogram (5.49 mg/kg) of sugar per dog

A 65-pound dog swallows the same 25-milligram sugar pill:

• 65 pounds is equal to 29.55 kilograms
• 25 milligrams divided by 29.55 kilograms equals 0.85 milligrams per kilogram (0.85 mg/kg) of sugar per dog

Sounds easy, right?  Let’s make it a bit more complicated:

A 10-pound dog swallows 10 ounces of chocolate that contains 25 milligrams of sugar per ounce. (This is a made-up number):

• 10 pounds still equals 4.55 kilograms
• 10 ounces of chocolate times 25 milligrams of sugar per ounce equals 250 milligrams of sugar
• 250 milligrams divided by 4.55 kilograms equals 54.95 milligrams per kilogram (54.95 mg/kg) of sugar per dog

Keep in mind that in the above example, we calculated how much sugar the pet ingested, NOT how much chocolate.

If I haven’t lost you yet, let’s do one final bit of work to make you especially confused:

A 10-pound dog swallows 15 cookies, each containing 10 ounces of chocolate with 25 milligrams of sugar per ounce. (Let’s see if I’ve managed to confuse even myself!):

• 10 pounds of dog will always equal 4.55 kilograms of dog. (To amuse veterinary professionals, this is 4,550,000 milligrams of dog).
  
• 15 cookies times 10 ounces of chocolate per cookie equals 150 ounces of chocolate in total.
  
• 150 ounces of chocolate times 25 milligrams of sugar per ounce equals 3,750 milligrams of sugar per 10 ounces or per 15 cookies.
  
• 3,750 milligrams of sugar divided by 4.55 kilograms of dog equals 824.18 milligrams per kilogram of sugar per dog (824.18 mg/kg).

While we could continue to complicate things, it gets more confusing when we’re dealing with substances that have milligrams per milliliter, percentage of concentration, or parts per million (ppm).

Please don’t try to do this all yourself at home if your pet swallows something.  Even in the veterinary field, we want other people checking our math to make sure our numbers are free of error.  

Your pet’s life could be at stake.  

So please call someone who does this daily, and can do it quickly.

_{(I’m sorry for all the math)}