Toxic Dose Calculation

Question 1

What are the 4 basic tenets of toxicology?

Answer 1

1. the dose makes the poison
2. exposure does not equal poisoning
3. for most toxicants, there is a dose-response relationship and a threshold dose
4. many factors influence toxicity

Question 2

What does “the dose makes the poison” mean?

Answer 2

• virtually all substances are toxic if given at a high enough dose
• virtually all substances can be safe if given at a low enough dose

Question 3

What must occur for an agent to cause a toxic effect?

Answer 3

must reach its site of action at a high enough concentration and for a sufficient time —> this is why treatment includes decontamination —> can get rid of agent after exposure, but before it causes toxicosis

Question 4

What is a threshold dose?

Answer 4

highest dose at which there is no response
- toxicosis = dose higher than threshold

Question 5

What factors influence toxicity?

Answer 5

• characteristics of the animal exposed: age, species, strain, sex, nutritional status, pre-existing conditions, reproductive status, medication history, exposure to other toxicants
• characteristics of toxicant: formulation, concentration, kind of toxicant
• route of exposure
• frequency and duration of exposure
• environmental status: snakes more common in warm places

Question 6

Why do we calculate dosage?

Answer 6

(amount of toxicant/BW) —> dose = total toxicant exposed

decides how to proceed with a case
- Is the exposure going to cause adverse effects?
- What clinical signs may develop?
- Is any treatment needed?
- What decontamination should be performed?
- Should the patient be hospitalized for monitoring?
- Is there an antidote?
- What are the likely costs of treatment?

Question 7

Why do we not just treat any exposure to a toxicant?

Answer 7

risks (and expenses) of treatment may outweigh risks of poisoning

Question 8

How is a treatment regimen for a potential toxicosis decided upon?

Answer 8

severity of poisoning

• aggressive treatment for lethal exposure
• risk from poison must outweigh risk of treatment with sublethal doses

Question 9

What is necessary for diagnosis of toxicoses?

Answer 9

history

• What toxicant was exposed to the animal?
• What is the active ingredient?
• What is the toxicity of the active ingredient?
• Is the amount of ingested active ingredient of concern?
• Should it be treated?

Question 10

Why is diagnosis of toxicoses hard to arrive at?

Answer 10

exposure is usually not witnessed - animal presents with sudden illness and other possibilities must be ruled out

Question 11

What is important to consider?

Answer 11

What kind of chocolate did Tusia ingest?
- different types have different concentrations of theobromine
- solid milk chocolate

How much chocolate was ingested?
- 10 to 20 eggs (always choose worst case scenario!)
- size/weight —> 9 kisses weigh 41 g

Did she eat enough to cause poisoning?

Question 12

Tusia’s owner believes she ate 10-20 eggs. How much chocolate did Tusia ingest? Theobromine and caffeine?

Hershey’s website states that 9 kisses weigh 41 grams and contains 61 mg of theobromine and 9 mg of caffeine.

Answer 12

Question 13

Tusia’s owner believes she ate 10-20 eggs. How much theobromine and caffeine was Tusia exposed to in ounces? What was the dosage of total methylxanthines?

Hershey’s website states that 9 kisses weigh 41 grams and contains 61 mg of theobromine and 9 mg of caffeine.

Answer 13

(41g/9 kisses) = 4.55 g/kiss
20 kisses x (4.55 g/kiss) = 91 g milk chocolate

Question 14

When is treatment for toxicoses indicated?

Answer 14

when exposure dose/dosage is greater than the MTD

Question 15

Owner states that the puppy ate three 3-oz throw bags. How much bait did the puppy eat?

The active ingredient in the bait is diphacinone and makes up 0.005% content. How much diphacinone did the puppy eat?

If the puppy weighs 20 punds, how many mg of diphacinone per kg of body weight did the puppy ingest?

Answer 15

3 oz x (28g/oz) = 84 g per pack
3 packs x (84g/pack) = 252 g bait

20lb/2.2 = 9 kg
(12.6mg)/(9kg) = 1.4 mg/kg (dosage)

Question 16

Answer 16

33lb/2.2 = 15 kg
15 kg x (5.5mL/kg) = 82.5 mL of 20% solution per dose

Question 17

What are equivalents (Eq)?

Answer 17

number of univalent counter ions needed to react with a molecule of a substance - the amount of ions required to cancel out the electrical charge of an oppositely charged ion (amount of charge on an ion = valence)

• Na+ requires 1 negative charge
• Ca2+ requires 2 negative charges
• HCO3- requires 1 positive charge

Question 18

How do you convert mmol/L to mEq/L?

Answer 18

mEq/L = (concentration (mmol/L)/MW) x valence

MONOVALENT IONS: 1 mmol/L = 1 mEq/L
DIVALENT IONS: 1 mmol/L = 2 mEq/L

Question 19

How many grams are in an ounce?

Answer 19

28g/oz

Question 20

What does ppm equate to?

Answer 20

mg/L