Toxicology Flashcards
What bloods would you check in someone who has overdosed on paracetamol
Paracetamol level
LFT
Clotting - INR
What is the antidote to paracetamol overdose
N-acetylcysteine
You should take a paracetamol level immediately after overdose - true or false
False
4 hours is the cut off for a blood test, will not get an accurate level until this point as takes a while to absorb
How does N-acetylcysteine work
Glutathione stores in the liver are used to break down paracetamol safely by conjugating with the toxic metabolite NAPQI
If you exceed your stores, such as in OD, the NAPQI builds up which causes the liver damage.
The NAC acts as a substrate to glutathione so prevents this damage
What should you do if someone develops a rash on N-acetylcysteine
Some people can be allergic to NAC
They develop an anaphylactoid reaction in the form of urticarial rash NOT true allergy/anaphylaxis
Stop the infusion, give antihistamine, wait for symptoms to settle then restart. It is not a true allergy so can continue
The dose of N-acetylcysteine is dependent on what
The patient’s weight
What are the criteria for discharge following a paracetamol overdose
INR must be <1.4
ALT okay
No signs of toxicity
Paracetamol level <10mg/L
How can you reverse a benzo overdose
Give flumazinil
Only licensed for iatrogenic overdose
Why can flumazinil not be used for deliberate or personal benzo overdose
If the person is a regular user they can be benzo dependent
By reversing you send them into withdrawal with seizures that you need benzos to treat!
These people are treated supportively
What is a toxidrome
A collection of signs and symptoms signs caused by a toxin
What are the 5 major toxidromes
Anticholinergic Cholinergic Opiate Sympathomametic Sedative/hypnotic
Which drugs can cause the sympathomametic toxidrome
Ecstasy Amphetamines and methamphetamines Cocaine LSD Theophylline Ritalin
Describe the basis of the sympathomametic toxidrome
Mimics the effects of the sympathetic nervous system
List common symptoms of the sympathomametic toxidrome
Tachycardia - may cause arrhythmia Increased RR Raised BP Pyrexia - sweating Dilated pupils Tremor Hyperreflexia
Can be fatal via multi-organ failure or seizures
Which drugs can cause the opiate toxidrome
Heroin Morphine Codeine Fentanyl Tramadol etc etc
List common symptoms of the opiate toxidrome
Pin-point pupils Reduced RR, BP and HR Reduced temperature Absent/decreased bowel sounds Reduced conscious level
Resp depression can cause death
Which drugs can cause the anticholinergic toxidrome
Tricyclic antidepressants Atropine Anti-psychotics Antihistamines Antiemetics
Belladonna - very rare!!
List common symptoms of the anticholinergic toxidrome
Tachycardia - can cause arrhythmias, VT or VF Pyrexia and flushed skin Dry mouth Urinary Retention Dilated pupils Absent bowel sounds Confusion Ataxia Dysarthria May have hallucinations/psychosis/seizures
Which drugs can cause the sedative/hypnotic toxidrome
Benzodiazepines
Zopiclone
Barbituates
Muscle relaxants
List common symptoms of the sedative/hypnotic toxidrome
Reduced GCS
Reduced RR and HR
Hypoxia - due to reduced resp effort
Reduced temperature
List common symptoms of the cholinergic toxidrome
Pinpoint pupils Sweating Lacrimation Rhinorrhea Salivation Bradycardia Urination Vomiting and diarrhoea
Can lead to resp failure - oedema, spasm, failure
Also convulsions or coma
Which drugs can cause the cholinergic toxidrome
Organic phosphate compounds - insecticide Sarin gas Pilocarpine Mushrooms
Which drugs can have their blood levels directly measured
Paracetamol = 4 hours after ingestion Salicylates = at least 2 hours after ingestion if symptomatic and 4 hours if asymp.
How do you calculate the anion gap
(Na + K) - (Cl + HCO3)
When do you calculate the anion gap
If you need to determine the cause of a metabolic acidosis
List causes of a raised anion gap
MUDPILES Methanol Uraemia Paraaldehyde Diabetic ketoacidosis Iron overdose Lactic acid Ethylene glycol Salicylate
How is activated charcoal used in overdose
Can be given within an hour of ingestion
Typically give 50g as a solution
It can reduce the absorption of the substance by binding to the toxin
Only works with certain drugs and is poorly tolerated
What is the most common cause of overdose in the West
Paracetamol
What is considered a safe dose of paracetamol
75mg/kg or less
75-100 is potentially toxic
and over this is likely toxic
N-actylcysteine is a fast acting treatment - true or false
False
Takes up to 21 hours to deliver a dose
What is the antidote to tricyclic antidepressant overdose
Sodium bicarbonate
What is the antidote to beta blocker overdose
Glucagon - IV 5-10mg
What is the antidote to opioid overdose
Naloxone
IM or IV
Titrate up to response - look for a rise in RR
What is the antidote to ethylene glycol or methanol overdose
Ethanol
Fomepizole - inhibits dehydrogenase
Give sodium bicarb if acidotic
What is the antidote to iron salts overdose
Desferrioxamine
What is the antidote to organophosphate overdose
Atropine - to reduce bronchial secretions/spasm
Pralidoxime mesylate
How can you enhance the elimination of a toxic substance
Enhance or augment renal function
- urinary alkalinisation (give IV sodium bicarbonate to cause K+ depletion)
- haemodialysis
- haemofiltration
What is the antidote to cyanide
Dicobalt edentate
Hydroxycobalamin
Nitrates
Which patients are at higher risk of liver damage from paracetamol
Those with existing glutathione deficiency such as malnourished or co-existing liver disease
Enhanced cytochrome p450 system - alcoholics, St John’s Wort, Phenytoin, carbemazipine etc.
What are common symptoms of poisoning
Nausea
Vomiting
Abdominal pain
How soon after overdose should n-acetylcysteine be started
Within 8 hours if possible
How do you manage a staggered paracetamol overdose
If they’ve taken over 75 mg/kg within the last 24 hour period, they should be treated with acetylcysteine
If it has been more than 24hrs since ingestion and their ALT and INR are fine, so are they
If abnormal - treat
How does salicylate poisoning present
Overdose of aspirin Respiratory alkalosis and metabolic acidosis N and V and haematemesis Tinnitus Epigastric pain Sweating High HR, RR and temperature Non-cardiogenic pulmonary oedema Reduced conscious level / seizures
Hypoglycaemia in children
How do you treat salicylate overdose
Mild - Fluids
Moderate - Urinary alkalinisation
Severe - Haemodialysis
Why should you not discharge someone immediately after giving naloxone
Naloxone’s half life is much shorter than that of opiates/oids
Therefore, once it wears off the person can go back into toxicity
How do you treat cocaine toxicity
Benzos
How do you treat amphetamine toxicity
Supportive to ensure adequate hydration
Benzodiazepines can be used for treatment of excitation, agitation or convulsions
Why might somone who has taken ecstasy present with hyponatreamia
It causes hyperthermia and sweating so people drink a lot more
Some do this prophylactically
Worsened by the SIADH effect of ecstasy
Can activated charcoal be used for alcohol poisoning
No
It does not absorb alcohol
How do you manage ethanol poisoning
Supportive
Will recover once ingestion has ceased
List symptoms and signs of methanol poisoning
Initial CNS effects which are similar to ethanol
Vertigo
Headache
Paraesthesia
Reduced visual acuity - driving in a snowstorm
Nausea, vomiting and abdominal pain
Eventual reduced consciousness and coma
Where is ethylene glycol found
Common ingredient in commercial products such as coolants and antifreeze
Serotonin syndrome is more likely if a patient is exposed to 2 or more drugs which cause increased stimulation of serotonergic synapses - true or false
True
e.g. SSRIs, MAOIs, tricyclics, cocaine etc
List signs and symptoms of serotonin syndrome
Agitation Tremor Hypertonia Diaphoresis Tachycardia Hyperpyrexia
Severe cases may be complicated with severe hyperthermia, rhabdomyolysis, renal failure and coagulopathies
Why is it important to check U&Es in anticholinergic overdose
Risk of renal impairment and rhabdomyolysis
Organophosphates can be absorbed through the skin - true or false
True
Must wear PPE when dealing with skin exposure and throughly decontaminate the patient
How does carbon monoxide poisoning present
Headache Cherry red discoloration - only if very severe Malaise, lethargy Nausea SOB Tachycardia Neurological signs Reduced consciousness Seizures
A carbon monoxide level of up to 15% is normal in smokers - true or false
False
Only up to 10%
Over 15% is indicative of significant exposure to CO
How do you treat CO poisoning
Oxygen - as high a conc as possible
How does b-blocker overdose present
Reduced BP and HR which may be severe enough to result in cardiogenic shock
Bronchospasm
CNS effects - convulsions, coma, resp depression
How does calcium channel blocker overdose present
Myocardial depression, bradycardia and peripheral vasodilation producing profound hypotension and cardiogenic shock
Metabolic effects = acidosis, hyperglycaemia and kalaemia
How do you treat calcium channel blocker overdose
Supportive
IV calcium chlroide
Insulin and dextrose infusion
What can cause methaemoglobinaemia
Local anaesthetics
Antibiotics
Nitrites and nitrates
What is methaemoglobin
An oxidised form of haemoglobin which is incapable of carrying O2
How does methaemoglobinaemia present
Persistant cyanosis despite adequate O2 delivery Slate-grey colouration Headache, nausea Raised HR and RR Coma Chocolate brown arterial blood
What is the antidote to methaemoglobinaemia
Methylene blue solution
Which type of drug typically causes acute dystonias
Antipsychotic or antiemetic drugs
Which type of drug typically causes neuroleptic malignant syndrome
Antipsychotics
Doesnt need to be an overdose to occur
How does neuroleptic malignant syndrome present
Confusion Rigidity Tremor Autonomic instability Sweating and hyperpyrexia
What is rhabdomyolysis
Breakdown of skeletal muscle causing the release of myoglobin
This can damage the kidneys
What can cause rhabdomyolysis
Prolonged immobilisation secondary to reduced consciousness Status epilepticus or repeated seizures Muscle hypertonicity Hyperpyrexia Excessive exercise Direct effect of toxin i.e. colchicine
What is the antidote to lignocaine overdose
Lipid emulsion
