Poisons and poisoning

Question 1

What is the difference between acute overdose and chronic exposure?

Answer 1

Acute overdose results in adverse effects within 24 hours usually after single dose. Chronic exposure results in adverse effects after an accumulation of a drug after taking it for a considerable amount of time.

Question 2

What are the 4 main signs you can look for to try and determine if an overdose has occured or not and what overdose has occured?

Answer 2

1. Pupils
   If constricted then drug has caused decreased sympathetic activity (such as opiates - strong analgesics) whereas if pupils are dilated it indicates the drug has cause increased sympathetic activity (eg antidepressants, party pills, MDMA, atropine).
2. Skin
   Sweating indicated increased amphetimine and decreased atropine.
3. Odour
   Skin/the patients breath may smell like ethanol (alcohol poisoning), Garlic (arsenic poisoning), Almonds (cyanide poisoning)
4. Clinical chemistry
   The blood and the urine can be tested for the conc of various drugs present.

Question 3

What is the first line treatment for someone that has had an ovedose/poisoning?

Answer 3

Doc’s ABC’s

airways, breathing, circulation

Question 4

What is the next step in treatment?

Answer 4

Decrease the absorption of the drug in the stomach and increase the elimination.

Increase absorption by:

• emesis (give syrup of ipecac to make them vom)
• gastric lavage (stomach pump)
• activated charcoal (binds to drugs in the gut)
• Fullers earth

Increase elimination by:

• activated charcoal (binds to drug in the gut to prevent absoprtion but then this also makes conc of drug int he gut lower so it moves out from the blood down conc gradient into the gut to be eliminated)
• Haemoperfusion/ haemodialysis
• diuresis

Question 5

What does naloxone do?

Answer 5

Blocks the effects of opioids and reverses an overdose. Eg it competed for the binding sites of morphine

Question 6

Specific antidotes to treat overdoses are rare but an example of one is paracetamol. Discuss how paracetamol can cause damage both in the short term and long term?

Answer 6

Paracetamol poisoning is one of the most common acute overdoses in industrialized countries.

1. Interaction with ethanol.
   Ethanol induces the enzyme CYP2EI which converts ehtanol to NAPQI its toxic metabolite. However as long as ethanol is in the body it will occupy the CYP2EI enzyme binding sites so hepatocellular damage wont occur. This inducing effect of alcohol lasts a week. When an alcoholic stops drinking and takes paracetamol that is often when damage occurs.
2. Interaction with Glutathione.
   NAPQI is inactivated by Glutathione which is naturally produced in the bod. However there are limited stores so when when the glutathione stores are used up by large doses of paracetamol patients are often given N-Acetyl-Cysteine which is used to make more glutathione in the bod.
   Note this drug cause nausea and vomitting and must be administered intravenously so shouldnt be given unless paracetamol overdose confirmed.