Overdose Flashcards

1
Q

N-AcetylCysteine (NAC)

Common indications

A
  1. Antidote for paracetamol poisoning
  2. Prevent renal injury due to radiographic contrast material (Contrast nephropathy)
  3. To reduce the viscosity of respiratory secretions (acting as a mucloytic)
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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
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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
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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
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5
Q

Interactions

A
  • No significant adverse drug reaction
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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)
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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
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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)
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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
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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
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11
Q

Activated Charcoal

Interactions

A
  • Prevents absorption of many drugs (mainly hydrophobic)
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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
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13
Q
A
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