Poisoning and STOPP-START Flashcards
Explain why most pharmacological toxicity is often predictable
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
What are secondary toxicity effects?
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
Give some examples of how poor prescribing can lead to drug toxicity due to a large difference between therapuetic window and toxic response
- Beta blockers - myocardial depression
- Opiods- respiratory depression
Give some examples of how drug toxicity can occur when there is only a small difference between therapuetic window and toxic response
- Theophylline (asthma drug) - arrhythmias and convulsions
- Phenobarbitol and carbamezapine (anti-epileptics) can cause respiratory depression
Explain how paracetamol toxicty can be overcome
- 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
Explain the use of Mesna in overcoming toxicity in patients taking cyclophospamide that has caused haemorrhagic cystitis
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
What are the basic management principles of treating a overdose?
- Immediate action
- Give supportive measures
- Enhance elimination to try and get rid of the drug
- Give antidotes if possible
- Prevent absorption if possible
What immediate actions should be taken if someone has overdosed?
- 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
How can doctors prevent absorption in the case of overdose
- 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
How can drugs be eliminated in overdose?
- 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
What types of antidotes are available?
-
Competitive antagonists
- Naloxone (opiod receptor antagonist)
- Atropine
- Chelating agents
- Agents that manipulate drug metabolism
-
Antibodies
- antivenoms
- digoxin specific antibodies
Explain how fomepizole is used to overcome methanol and ethylene glycol (anti-freeze) poisoning
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
What are some of the main things to check during a patient drug review?
- 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?
What does STOPP START stand for?
Screening Tool of Older People’s Prescriptions and Screening Tool to Alert Right Treatment
