TOXICOLOGY Poisoning may be:
Accidental – cyanide from burning furniture, an accumulation of toxic levels of a prescription drug, accidentally ingested by a child
Social drug use
Deliberate self harm
Attempts to harm others What are the important questions you need to ask when taking a history from a patient with poisoning ? HISTORY
What have they taken ? Type of preparation taken ? Any other substances taken ? Route of poisoning ? Time taken ?
Previous poisoning attempts Psychiatric history Description of the event Intended results of poisoning
SAD PERSONS score
Be cynical – don’t presume they are being completely truthful – there may be social, family or mental health issues at play
WHAT SHOULD YOU BE LOOKING FOR IN YOUR EXAMINATION ? EXAMINATION
Should focus on:
Identifying the underlying cause - Opioid overdose – small pupils, ↓ resp rate
Identifying any complications from the overdose - GCS - Temp - Cardiovascular compromise - Inadequate respiration WHAT TOXIDROMES CAN YOU LOOK FOR ? TOXIDROMES
A toxidrome :
describe signs/symptoms that consistently result from particular toxins
Groups drugs together according to these signs/symptoms
Vital signs and end organ manifestations SYMPATHOMIMETIC TOXIDROME
Drugs – caffeine, cocaine, amphetamines, Ritalin, LSD, theophylline, MDMA
Mimics fight or flight
Characteristics: Tachycardia, dysrhythmias Hypertension Delusions, paranoia Diaphoresis Seizures Hyperthermia Dilated pupils ANTICHLINERGIC TOXIDROME Drugs:
Anticholinergics –Atropine, glycopyrrolate
Antipsychotics – Chlorpromazine, Clozapine, Olanzapine, Quetiapine
Cyclic antidepressants –Amitriptyline, Nortriptyline
Mydriatics – Cyclopentolate, Tropicamide
Also carbamazepine, class 1A antiarrhythmics, certain plants - belladonna
ANTICHLINERGIC TOXIDROME
Anticholinergic poisoning commonly occurs but is frequently unrecognized
The degree of central and peripheral anticholinergic effects vary depending on the drug or toxin involved
There is a marked individual variation in response to the anticholinergic agents
Children: particularly sensitive to anticholinergic agents due to receptor sensitivity
Children with Down syndrome commonly have a genetically determined hypersensitivity to anticholinergic agents ANTICHLINERGIC TOXIDROME
A mnemonic for recalling some of the signs and symptoms of anticholinergic poisoning:
– Mad as a hatter
–Blind as a bat – very dilated pupils
– Dry as a bone - Blockade of cholinergic tone to salivary glands – ↓ salivation, dry mouth, intense thirst and difficulty swallowing
– Red as a beetroot – flushing of the skin
– Hot as a pistol – hyperthermia, sweat glands are blocked Symphatomimetic Anticholinergic
Mydriasis Mydriasis Tachycardia/HTN Tachycardia/HTN Hyperthermia Hyperthermia Disorientation Disorientation Agitation Hallucinations Hallucinations
Bowel sounds present Decreased bowel Diaphoresis sounds (unreliable) Dry skin/mucous membranes
CHOLINERGIC TOXIDROME DRUGS: ORGANOPHOSPHATES, CERTAIN MUSHROOMS, PESTICIDES
Muscarinic efects Nicotinic effects
Defecation Tachycardia Urination Hypertension Miosis Muscle fasticulation Bradycardia paralysis Emesis Lacrimation Increased secretions sweating OPIOID TOXIDROME
Drugs: morphine, codeine, tramadol, methadone, fentanyl, heroin, oxycodone
Pin point pupils Altered mental status Decreased bowel sounds Respiratory depression WHAT OTHER DIAGNOSES DO YOU NEED TO BE WORRIED ABOUT ? SEROTONIN TOXICITY
Drugs: MAOIs, SSRIs, SNRIs, cocaine, amphetamines, MDMA, levodopa, tramadol, TCAs, ondansetron, maxalon, lithium, fentanyl, carbamazepine
Leads to neuroexcitation spectrum of toxicity
The intensity of linical findings reflects the degree of serotonergic activity
Abnormalities of: mental state – agitation, restlessness, confusion
Motor system – clonus, myoclonus, tremor, hyperreflexia, hypertonia
Autonomic nervous system – Diaphoresis / tachycardia / flushing / mydriasis SEROTONIN TOXICITY
Majority present within 24 hours and most within six hours of a change in dose or initiation of a drug
Intentional O.Ds often develop greater toxicity than accidental cases
Clinical diagnosis
Neuromuscular findings more pronounced in lower limbs
Tachycardia, ↑BP, hyperthermia
Complications – ARDS, DIC, rhabdomylosis, metabolic acidosis, AKI HUNTER SEROTONIN TOXICITY CRITERIA
WHAT IS YOUR INITIAL MANAGEMENT GOING TO BE ? MANAGEMENT
Airway
Breathing
Circulation
Disability – GCS, pupils, neuro
E - temperature Supportive measures
Measures to reduce absorption Charcoal Whole bowel irrigation – iron, lithium, lead, drug packers, SR preps, ingestion of transdermal patches
Antidotes – beware of Short half lifes Consider length of infusion and hospital suppies Can precipitate withdrawal Can be dangerous in themselves Some don’t act against any toxic metabolites already present e.g ethanol
Toxbase
ANTIDOTES
Antidote Toxin Metabolism of action
Acetylcysteine Paracetamol By production of cysteine which acts as a glutathione precursor. It also supplys additional thiol groups which bind directly with NAPQI – the reactive metabolite. Atropine Organophosphates Blocks the action of acetylcholine at muscarinic receptors
Glucagon Beta blockers Stimulates adenyl cyclase to produce cAMP at a site distant from the beta receptor – produces effects similar to those of beta agonists resulting in ↑ myocardial contractility and heart rate Desferrioxamine Iron Binds free circulating iron in the plasma to form the octahedral iron complex ferrioxamine
Dicobalt edetate Cyanide Forms relatively non toxic stable ion complexes (cobaltocyanides, cobalti- cyanides) with cyanide which are then excreted in the urine
Digoxin specific Digoxin Has a greater affinity for digoxin than the tissue binding sites. The Fab antibody fragments fragments bind the intravascular free digoxin & then diffuse into the interstitial space binding free digoxin there Ethanol Ethylene glycol & Both metabolised by alcohol dehydrogenase. Ethanol is a competitive methanol antagonist for ADH and possesses a far greater affinity for the enzyme Antidote Toxin Metabolism of action
Flumazenil Benzodiazepines A competitive inhibitor of drugs which act via the benzodiazepine receptors, specifically blocking their central effects. Fomepizole Ethylene glycol & A competitive inhibitor of alcohol dehydrogenase methanol Methionine Paracetamol Acts as glutathione precursor and replenishes glutathione stores which have been depleted due to paracetamol poisoning Naloxone Opioids A specific antagonist the acts competively at opioid receptors
Penicillamine Heavy metals A chelation agent for certain heavy metals – copper, lead, mercury
Pralidoxime Organophosphates Organophosphates inhibit acetylcholinesterase (AC-ase). Pralidoxime restores AC-ase activityby removing the bulky phosphate moiety from the phosphorylated AC-ase Protamine Heparin Has a greater affinity for heparin than AT III and is able to cause a dissociation of the heparin AT III complex in favour of the stable and inactive heparin protamine complex Sodium Thiosulphate Cyanide Acts as a substrate for the enzyme rhodanase which catalyses the conversion of cyanide to the relatively non toxic thiocyante WHAT INVESTIGATIONS SHOULD YOU REQUEST ? HOW USEFUL ARE THE LABORATORY LEVELS ?