Poisons and Poisoning Flashcards Preview

Toxicology and Pharmacology > Poisons and Poisoning > Flashcards

Flashcards in Poisons and Poisoning Deck (33):
1

Define a poison:

Any substance which destroys life or injures health

2

Define an antidote

A medicine given to counteract the influence of poison, or an attack of disease

3

What are the stratagies to counteract poisoning?

Using Pharmacodynamics and pharmacokinetics:
- Decrease absorption
- 'Neutralize' the chemical or metabolite so it cannot react with endogenous targets
- Enhance elimination
- Antagonize the effect
- Replace the activity

Usually used in combination i.e attempt to decrease absoprtion and neutralize activity

4

Whats a drug that attempts to decrease absorption?

Ipecac:
- Ipecac consists of Cephaeline which stimulates the central vomiting center
- Bad cause vomiting is damaging
- Not proven to improve patient outcome
- Increases risk of aspiration
Will affect the absorption of other antidotes

5

Whats another example of a drug that decreases absorption?

Activated charcoal
- Charcoal may absorb drug
- Can create concentration gradient across mesenteric vasculature so that the drug is eliminated faster
- Useful on drugs that undergo enterohepatic recirculation, small volume of distribution, low protein binding
- Dose 1-2g/kg orally or nasogastric tube
Multiple doses may be given

6

What is an example of a drug used to neutralize the chemical?

Ingestion of large amounts of iron is toxic (60mg/kg) is life threatening

- When serum binding levels exceed the capacity of the binding protein transferrin, severe toxicity may occur, secondary to deposition of iron in soft tissue.

Deferoxamine is used to treat

7

How does deferoxamine work?

Free iron generates oxygen free radicals which are severely damaging.

stage one = vomiting and diarrhea + tachycardia
stage two = major organ failure

Deferoxamine chelates the free iron to form feroxamine but does not remove iron from proteins (great!) i.e transferrin, ferritin, cytochromes and haemoglobin

Feroxamine is excreted in the urine

8

Which drug is most commonly seen in overdoses?

Paracetamol

9

What are the stats of paracetamol overdose in NZ?

172/879 overdoses are paracetamol related
- 86.2% self harm, of these 80% female

10

How is paracetamol overdose treated?

N-actetyl cysteine

11

What is the action of N-actetyl cysteine in paracetamol overdose?

precursor for glutathione synthesis and so boosts resynthesis allowing deactivation of metabolite

or

The sulfhydryl group of N-actetyl cysteine may bind and detoxify the metabolite directly

or

Act as an antioxidant and block reactive oxygen species dependent cell death

12

What is an example of enhanced elimination?

Salicylate is excreted more by urinary alkalisation

13

What is salicylate and why is it a problem?

Aspirin is readily hydrolyzed to salicylate which,
- Stimulates medullary resp center = resp akalosis and eventually metabolic acidosis
- Produces tinnitus, nausea, vomiting, ataxia, coma and hyperthermia

14

How much aspirin must be ingested to be toxic?

>300mg/kg serious toxic reactions
>500mg/Kg potentially toxic

15

How is aspiring overdose treated/

Salicylate toxicity is remedied by:
- Sodium Bicarbonate is used to raise urinary pH (>7.5)
- Weak acids that undergo renal excretion become trapped
- Useful for salicylate, herbicide
- Used in conjunction with activated charcoal

16

What may happen with poor perfusions of sodium bicarbonate?

May produce too higher pH which impairs cardiac contractility, hypernatremia, and fluid overload may occur.

17

Whats an example of pharmacodynamic intervention?

Heroin and Naloxone

18

How is heroin generally toxic?

When overdoses, used normally in conjunction with alcohol, benzodiazapines, cannabis and anphetamine

19

What does heroin do?

Heroin produces typical narcotic effects as it is converted into morphine
- euphoria

Associated with coma, seizures, and delayed encephelopathy in overdose.

20

Can the lethal dose of heroin be defined?

No its hard to define
- death may be sudden in massive overdose
- Complicated by administration of other drugs

21

What is often the cause of heroin related death?

Friends-

- Advise sleeping it off = coma and resp depression
- Give milk as antidote
- Use cold shower potential hypotension
- Using more drugs

22

What is naloxone?

An antagonist at the beta, K and delta opoid receptors

23

How is nalaxone administered?

I.m
S.C
endotracheal etc

24

What is bad about nalaxone?

It has a shorter half life than heroin therefore relapse may occur.

May also precipitate heroin withdrawl

25

Whats an example of replace activity poison + antidote?

Warfarin and vitamin K

26

What is warfarin?

Used in the prophylaxis and treatment of venous thrombosis + Pulmonary embolism
- Inhibits the synthesis of vitamin K dependent coagulation factors
- This results in a sequential depression of factors

27

How does warfarin overdose present?

Blood in stools, urine, excessive menstrual bleeding

Can lead to gangrene necrosis

Death

28

Whats the normal dose of vitmamin K?

1microgram

29

What happens at higher vitamin K dosing?

At higher concentrations Vitamin k is reduced to hydroquinone by another warfarin- insensitive liver reductase

30

How is warfarin overdose countered?

Vitamin K therapy may be required for weeks or months until prothrombrin time (coagulation) returns to normal

31

What receptors do organophosphate poisons act on?

Nicotinic receptors:
- Muscle weakness
- Hypertension
- tachycardia

CNS effects:
- Confusion
- Seizures

Muscunaric effects
- Salivation
- Urination
- Defacation

32

What method is used to relieve organophosphate poisoning?

Regenerate effect

33

What does the regenerate effect involve and whats an example?

Give a combination of drugs to prevent symtoms i.e

Give atropine to antagonise ACh then pralidoxime.

Pralidoxime can remove a phosphate group from ACh esterase, to regenerate catalytic activity
- effects at nicotinic>muscunaric
- Effect is great if erythrocyte esterase is given soon after toxicity
- Reactivation of plasma cholinesterase is minimal