Poisoning and STOPP-START Flashcards

1
Q

Explain why most pharmacological toxicity is often predictable

A

Most toxicity is due to an extension of the desired drug effect

e.g.

  • Warfarin - causes bleeding
  • Insulin- can cause hypoglycaemia
  • Loop diuretics - hypotension, hyperkalaemia, hyponatraemia
  • AChE inhibitors - sludge side effects
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2
Q

What are secondary toxicity effects?

A

Side effects that are not related to the primary aim of treatment

Occur at or above normal therapeutic dose

e.g.

  • Statins- causing rhabdomyelisis
  • Thalidomide- birth defects
  • Beta agonists- tachycardia
  • Beta blockers - bronchoconstriction, bradycardia
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3
Q

Give some examples of how poor prescribing can lead to drug toxicity due to a large difference between therapuetic window and toxic response

A
  • Beta blockers - myocardial depression
  • Opiods- respiratory depression
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4
Q

Give some examples of how drug toxicity can occur when there is only a small difference between therapuetic window and toxic response

A
  • Theophylline (asthma drug) - arrhythmias and convulsions
  • Phenobarbitol and carbamezapine (anti-epileptics) can cause respiratory depression
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5
Q

Explain how paracetamol toxicty can be overcome

A
  • In paracetamol overdose - glutathione which converts paracetamol to non-toxic metabolites gets overwhelmed causing the build up of NAPQI
  • N-Acetylcysteine can be given which donates a thiol group to paracetamol forming non-toxic metabolite that can excreted in urine
  • Needs to be given as 3 successive infusions over 21 hours
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6
Q

Explain the use of Mesna in overcoming toxicity in patients taking cyclophospamide that has caused haemorrhagic cystitis

A

Cyclophosphamide used to treat severe rhematoid arthritis but can cause haemorrhagic cystitis

Mesna as a thiol group for cytoprotection and a polar group to help it get to the kidneys and into the urinary system

Given 2 hours before or with cyclophosphamide as a protective mechanism

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7
Q

What are the basic management principles of treating a overdose?

A
  • Immediate action
  • Give supportive measures
  • Enhance elimination to try and get rid of the drug
  • Give antidotes if possible
  • Prevent absorption if possible
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8
Q

What immediate actions should be taken if someone has overdosed?

A
  • remove them from contact with poison
  • Check vital signs and for injury
  • Take a history if you can from patient or their chaperone, check for evidence; packaging, written notes
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9
Q

How can doctors prevent absorption in the case of overdose

A
  • Gastric lavage almost never reccommended (risk of aspiration)
  • Activated charcoal- needs to be given within 1 hour (often don’t see patients that quick), not suitable if patient is drosy or comatose as taken orally
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10
Q

How can drugs be eliminated in overdose?

A
  • Continued activated charcoal for up to 36hrs useful for some drugs; benzos and phenobarbitol
  • Sodium bicarbonate - increases urine pH for alkaline diuresis if patient has weak acid poisoning e.g. aspiring overdoes (not a common presentation)
  • Foreced diuresis is not recommended- causes serious electrolyte imbalances
  • Haemodialysis in seriously ill patients - only if drug has a small Vd
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11
Q

What types of antidotes are available?

A
  • Competitive antagonists
    • Naloxone (opiod receptor antagonist)
    • Atropine
  • Chelating agents
  • Agents that manipulate drug metabolism
  • Antibodies
    • antivenoms
    • digoxin specific antibodies
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12
Q

Explain how fomepizole is used to overcome methanol and ethylene glycol (anti-freeze) poisoning

A

Methanol and Ethylene glycol both converted to toxic metabolites by alcohol dehydrogenase

Fomepizole acts as a competitive inhibitor of alcohol dehydrogenase so that toxic metabolites can’t be formed whilst the toxic drug is renally eliminated

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13
Q

What are some of the main things to check during a patient drug review?

A
  • Is the medication right for the patient
  • Are there any time limits on medications
  • Age-life expectancy and risk benefit
  • Is medication effective?
  • Cost- can generics be used?
  • Can any appropriate tests be done to support decisions e.g. Hba1c
  • Are there any drug interactions?
  • Any contraindications?
  • Side effects
  • Lifestyle modifications - medication may no longer be needed
  • Any over the counter medications?
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14
Q

What does STOPP START stand for?

A

Screening Tool of Older People’s Prescriptions and Screening Tool to Alert Right Treatment

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