Overdose and toxicity

Question 1

What are some general measures to treating overdoses? (7)

Answer 1

Preventing absorption

• Activated charcoal ingestion within 1 hour
• Pt must be alert and cooperative
• Does not work for drugs that do not bind to charcoal, eg alcohol

Increasing elimination

• Haemodialysis
• Requires drug with low volume of distribution, such as aspirin, sodium valproate and lithium

Question 2

How does paracetamol toxicity occur and what are its treatment options? (4)

Answer 2

Paracetamol toxicity- >150mg/kg
Normally: paracetamol forms conjugates with glucuronide. Sometimes NAPQI pathway, but this is eliminated via glutathione.
Toxicity: Glutathione is depleted/ overwhelmed, so NAPQI pathway leads to hepatoxicity

Treatment:
Nomogram- looks at plasma concentration of paracetamol vs time since overdose
If above treatment line: IV N-acetylcysteine- replenishes glutathione.

Question 3

What are the symptoms of aspirin overdose and how is it treated? (4)

Answer 3

Aspirin overdose- >500mg/kg
Symptoms: n+v, hyperglycaemia, pulmonary oedema, coma

Treatment
Activated charcoal, within an hour
IV Sodium bicarbonate- increases urinary excretion
Severe cases- haemodialysis

Question 4

What are the symptoms of an opioid overdose and how is it treated? (5)

Answer 4

Symptom:
depressed respiratory system, depressed consciousness, low blood pressure

Treatment: naloxone- opioid antagonist
IV, muscarinic, nasal
Short half life- so requires observation.

Question 5

What are the symptoms of tricyclic antidepressants overdose, and how is it treated? (5)

Answer 5

Antimuscarinic- confusion, tachycardia, urinary retention, dry mouth
Na channel block- Broad QRS, arrhythmias,
CNS effects, confusion, seizures

No antidote. Treatment is supportive. Hence why it is important to assess suicidal risk.

Question 6

What drugs can cause serotonin syndrome, what are the symptoms of it and how is it treated? (6)

Answer 6

Serotonin syndrome is caused by multiple drugs targeting serotonergic pathways.
Antidepressants: MAOs, SNRIs, SSRIs, TCAs
Recreational: amphetamine, cocaine, MDMA

Symptoms:
Neuromuscular- increased reflexes, tremor
CNS- agitation, confusion, seizures
Autonomic- Hypothermia, bladder instability, fluctuating blood pressure, flushing

Treatment is largely supportive, and sometimes benzodiazepines

Question 7

What drugs can cause QTc prolongation?

Answer 7

Can cause severe arrhytmias

Drugs:
- Antihistamines, some antibiotics, antipsychotics, cocaine, morphine

Now a crucial part of pre-clinical studies