Overdose Flashcards
1
Q
N-AcetylCysteine (NAC)
Common indications
A
- Antidote for paracetamol poisoning
- Prevent renal injury due to radiographic contrast material (Contrast nephropathy)
- To reduce the viscosity of respiratory secretions (acting as a mucloytic)
2
Q
NAC
MOA
A
- In therapeutic doses, paracetamol is metabolisde mainly by conjugation with glucuronic acid and sulfate
- A small amount is converted to N-acetyl-q-benzoquinone (NAPQI), which is hepatotoxic
- Normally, this is quickly detoxicified by conjugation with glutathione
- However, in paracetamol poisoning, the body’s supply of glutathione is overwhelmed and NAPQI is free to cause liver damage
- NAC replenishes the body’s supply of glutathione. It also has antioxidant effects, which may contribute to it’s effect in preventing contrast nephropathy, although this is not completely understood.
- If acetylcysteine is brought into contact with mucus, it causes it to liquefy
- For patients who have tenacious respiratory secretions (e.g. bronchiectasis), this may aid sputum clearance
3
Q
NAC
Important adverse effects
A
- When administered IV can cause anaphylactoid reaction
- This is similar to an anaphylactic reaction (presenting with nausea, tachy, rash and wheeze) but involves histamine release independent of IgE Abs
- Therefore, once the reaction has settled (by stopping the NAC and giving antihistamine), it is usually safe to restart NAC, but a lower rate of infusion.
- When administered in nebulised form as a mucolytic, NAC may cause bronchospasm. Therefore a bronchodilator is often given prior to adminstration
4
Q
NAC
Warnings
A
- History of anaphylactoid reactions to acetylcysteine does not contraindicate its future use if still needed
- It is important that such reactions are not labelled as allergic, which may lead to effective treatment for paracetamol poisoning being inappropriately denied
- However, it is essential to obtain specialist advice if there is any doubt
5
Q
Interactions
A
- No significant adverse drug reaction
6
Q
NAC prescription
A
- Paracetamol overdose (IV infusion, 3 components, over 21 hours)
- Prophylaxis of contrast nephropathy (600-1200mg PO 12hrly for 2/7)
- Respiratory secretions (2.5-5mL of 10% solution 6H)
7
Q
Activated charcoal
Common indications
A
- A single dose of activated charcoal may be used to reduce absorption of certain poisons (including drugs in overdose) from the gut
- Multiple doses of activated charcoal may also be used to increase the elimination of certain poisons
8
Q
Activated Charcoal
MOA
A
- Van der Waals forces are responsible for the MOA.
- Molecules are adsorbed onto the surface of the charcoal as they travel through the gut, reducing the absorption into the circulation
- However, activated charcoal is only useful in cases where the poison ingested is likely to be absorbed onto it
- The affinity of a substance of activated charcoal is determined by its ionic status and its solubility in water
- Weakly ionic, hydrophobic substances (e.g. BZ, MTX) are well absorbed. Hydrophillic (Li, Fe, alcohols, acid/base) not well absorbed
- Multiple administrations cause more rapid diffusion back into the gut, by causing a concentration gradient (high in circ, low in gut)
9
Q
Activated charcoal
Adverse effects
A
- Aspiration of activated charcoal can lead to pneumonitis, bronchospasm and airway obstruction
- It can also precipitate intestinal obstruction
- Most common: Black stools and vomiting
10
Q
Activated Charcoal
Warnings
A
- Activated charcoal should not be used in patients with a reduced level of counsciousness, unless their airway is protected via intubation
- Caution is required when prescribing activated charcoal to patients with persistent vomiting, as there is a risk of aspiration
- Those with reduced GI motility have an increased risk of intestinal obstruction
11
Q
Activated Charcoal
Interactions
A
- Prevents absorption of many drugs (mainly hydrophobic)
12
Q
Activated charcoal
Prescription
A
- Only for patients presenting within 1 hours of ingestion of clinically significant amount of substance that is absorbed by charcoal
- For drugs that delay gastric emptying (Aspirin, Opioids, TCA) AC can be administered upto 2hrs following ingestion
- AC should be prescribed on the once-only section of the drug chart
- For multiple doses 50g 4H with pre-emptive anti-emetic and laxatives
13
Q
A