Toxicology Flashcards
What are the 4 types of poisoning?
Acute
Chronic
Accidental
Intentional
What is A toxidrome?
• Overdose on a certain type of drug gives symptoms/clinical features which can be seen on examination, a way to distinguish what type of drug they have overdosed on
What are the toxidromes of opioid poisoning?
- Pinpoint pupils
- Reduced GCS – drowsy/unconscious
- Reduced RR (respiratory rate)
What are the toxidromes of Serotonergic - Any drug that stimulates serotonin release, stimulates the receptor or blocks metabolism of serotonin i.e. SSRIs (sertraline), ecstasy, MDMA?
- Agitation/anxious
- Delirium
- Tremor
- Tachycardia
- Labile BP – high/low blood pressure
- Sweating
- Hypertonia
- Brisk reflexes
- Clonus
- Fever
- Serotonin syndrome
What are the toxidromes of anticholinergics?
- Dilated pupils
- Warm, dry skin
- Confusion, restlessness, hallucinations
- Brisk reflexes, myoclonic jerks
- Tachycardia
- Urine retention
What are the toxidromes of cholinergics?
- Miosis
- Bradycardia
- Sweating
- Excessive secretions from pretty much any orifice
- Hypersalivation
- Lacrimation
- Rhinorrhoea
- Bronchorrhoea
- Diarrhoea
What are the toxidromes of
Sympathomimetic
- Hypertension, tachycardia
- Mydriasis
- Sweating
- Agitation, paranoia, psychosis
- Hyperreflexia
- Stereotypy doing the same thing over and over again?
- Hyperpyrexia high temp that doesn’t go down (just keeps going up) leads to multiple organ failure if not treated
What lab tests need to be done after an overdose?
− Routine blood tests
− ABG
• COHb carboxyHb i.e. smokers may have higher levels of this
• MetHb sign of “poppers” (alkyl nitrites – illegal drug) use, dapsone (immunosuppressant) use (legal drug)
− Anion gap + osmolal gap
• Can be calculated easily, measure osmolality of the plasma and the can calculate osmolality based on blood gas and work out what the gap is
− Analytical toxicology
• Emergency measurement
• Salicylate (aspirin), iron, theophylline, methanol, ethyleneglycol, lithium, phenytoin, carbamazepine
• Can get fast results from tests of these drugs
• Can’t always get fast results with other drugs
− Screening
• Paracetamol
• Always screen for paracetamol in anyone who has overdose cuz ppl may be asymptomatic and may not disclose that they’ve taken paracetamol
• Drugs of abuse
• This just gives +ves or -ves on a limited number of drugs
• Can do more detailed screening tests time of flight, can screen for any drug with this (even drugs that haven’t been detected before)
What are the causes of a raised Anion gap? (added acid)
- Ketoacidosis check ketones via fingerprick
- Lactic acidosis
- Salicylate overdose
- Alcohols: ethanol, methanol, ethylene glycol
- Can measure ethanol easily
- Methanol, ethylene glycol take longer to get readings for
- Renal failure check kidney functions
- Rhabdomyolysis check CK (creatinine kinase)
- Muscle break down from a crush injury, release of chemicals in blood i.e. creatinine kinase, K+, can cause AKI
What are the causes of an increased osmolal gap?
- Ethanol
- Methanol
- Ethylene glycol
- Acetone
- Isopropanol
General management: How can you prevent further absorption?
− Emetics – i.e. ipecac, not recommended
o Risk of aspiration
− Gastric lavage – very rarely used, pumping stomach, putting tube down stomach
o Risk increasing absorption of poison
− Activated charcoal - commonly used
o Pt shouldn’t be drowsy (low GCS), pt needs to be alert enough to take it, needs to be swallowed properly otherwise it can go to lungs further problem
− Whole bowel irrigation - using nasogastric tube to put down loads of klean prep (polyethylene glycol electrolyte solution), used for bowel prep to empty the bowel
o Need to use a lot of it to empty bowel
o Can be used for
-Modified release
medications
-Body packers = someone trying to swallow packets of drug
WEAG
General management: hOW CAN YOU ENHANCE elimination?
- Multiple dose activated charcoal
o Useful for drugs that undergo entero-hepatic recirculation
o Carbamazepine, colchicine, quinine, theophylline, phenobarbital - Entero-hepatic recirculation = drugs that are absorbed and then recirculated into the bowel
- Used QDS (four times a day)
- Urine alkalinisation
o Aspirin
o Aiming for high pH in urine = increases excretion of certain drugs - Extracorporeal
o Haemofiltration
o Haemodialysis- Lithium, salicylates, ethylene glycol, methanol
General management: Specific Antidotes for specific poisons
− A therapeutic substance administered to counteract the adverse effects of a xenobiotic.
What Drugs that should be available immediately in A&E?
− Acetylcystine = every hospital will have this
− Cyanide antidotes = needed immediately
− Procyclidine = for dystonic reactions, not always used for overdose, can be used for idiosyncratic reactions to drugs i.e. metoclopramide
− Dantrolene = smooth muscle relaxant, every hospital will have this
Used to treat NMS = rare hereditary condition adverse reaction to inhaled anaesthetic, get hyperthermia due to rigidity of the muscle
− Desferrioxamine = for iron overdose
− Fomepizole = for toxic alcohol i.e. ethylene glycol, methanol
− Idarucizumab = for dabigatran overdose
What are the mechanism of actions of antidotes?
Mechanisms 1
− Forms an inert complex with poison: CHELATION – drug binds with poison and then is excreted
− Issue in poor kidney function = drug + poison won’t get excreted so can circulate around the body risk that poison can separate therefore pt may need dialysis
o Desferrioxamine (iron)
o Dicobalt edetate (cyanide)
o Digoxin-specific antibody fragments (digoxin)
o Protamine (heparin)
Mechanisms 2
− Accelerates detoxification of the poison, it’s metabolite or toxic moiety:
o Acetylcysteine for paracetamol
♣ Gives body more glutathione which allows liver to metabolise the metabolites of paracetamol
o Methylene blue for methaemoglobinaemia
♣ Used in surgery to highlight parathyroid glands/ lymph nodes in breast surgery
♣ Used for methaemoglobinaemia
o Sodium thiosulphate for cyanide
Mechanisms 3
− Reduces rate of conversion to a more toxic compound:
o Fomepizole for ethylene glycol and methanol poisoning
o Ethylene glycol and methanol not toxic themselves, metabolites are toxic
o Prevent conversion of these substances into their toxic metabolites = prevent toxicity
Mechanism 4
− Competes with toxic substances for essential receptor sites:
o Flumazenil = Competes with BZDs for GABA receptor
o Naloxone = Competes with opioids for opioid receptor
o Vitamin K = Competes with warfarin for Vit K receptors
Mechanisms 5
− Blocks essential receptors through which the toxic effects are mediated:
− Toxic effects of these below are mediated through ACh receptors
− Can’t block nicotinic ACh receptors but can block the muscarinic ACh receptors
o Atropine = mACh receptor antagonist
♣ Nerve agents
♣ Organophosphate insecticides
♣ Drugs for myasthenia gravis e.g. pyridostigmine
♣ Clitocybe mushrooms (muscarine)
♣ Can block some of the effects of the poison but not all due to effects of poison at the NACh receptors
Mechanisms 6
− Bypasses the effect of the poison:
− Beta blocker overdose = blocks generation of cyclic AMP and reduce contractility of heart muscle
o Glucagon for beta blockers
♣ Glucagon bypasses beta receptors
♣ When used for hypoglycaemic events, only give 1mg IM but for beta blocker overdose, need to use higher doses
♣ Needs to be given as a constant infusion = problem cuz it crystallises if its in a syringe for more than 2hrs
♣ Can only make a 2hour worth syringe
