Overdosing and Poisoning

What do you need to ask when taking a poisoned patients history?

Which tablets?
Are they your own?
Any other drugs/alcohol?
Timing of the ingestion?

What can small pupils (miosis) be from?

Opiates

What can large pupils mydriasis be from?

sympathomimetics and anticholinergics

What can jaundice eyes be from?

Late presentation of paracetamol OD / alcoholic liver disease

What other things to look out for in the poisoned patient?

Self-harm
Track marks → IV drug use
Injuries suggested violence/abuse
Extensive bruising from long lie risk of rhabdomyolysis

What investigations need to be done for a poisoned patient?

Pulse rate, BP, RR, oxygen saturations, temperature, 12 lead ECG/cardiac monitor

What drugs can cause hyperthermia?

• Cocaine

• Amfetamines

• Ecstasy

• Serotonergic drugs - SSRIs

How often should check temperature?

15 minutes → temps is 39-40 degrees

What blood tests need to be done?

Urea

Electrolytes
Creatinine
Glucose
Clotting → paracetamol
Creatine Kinase activity → shows muscle breakdown
Specific drug assays → save blood and urine if unsure

Examples of specific toxin blood concentrations?

• Paracetamol

• Salicylate

• Iron

• Lithium

• Methanol/ethylene glycol

• Ethanol

• Theophylline

• Digoxin

• Valproic acid

• Carbamazepine

When should you use toxicological analysis?

• Useful for drugs of abuse screening

• Unknown overdose in comatose or delirious patient

• Results only as good as the method allows

• Specialist advice is available

Describe immunoassay based tests?

Limited value risk of false positives and negative
Useless for synthetic cannabinoids

Describe UPLC/MS?

The classic drug screen
Highly sensitive urine/blood testing
As comprehensive as test library

Describe time of flight test?

• unknown drug screen

  • Less sensitive but highly specific

  • Software predicts compounds present from fragments identified

What is imaging used for?

• Primarily for secondary complications e.g. aspiration pneumonia

• Ingested objects (body packers, body stuffers)

• Rarely show up on plain Xrays

What would be the cluster/toxidromes for opiates?

Coma, miosis, reduced respiratory rate, hypoxia

What would be the cluster/toxidromes for stimulates?

Agitation, delirium, mydriasis, hypertension hyperthermia, tachycardia, arrhythmias

What would be the cluster/toxidromes for anticholinergic syndrome?

Drowsiness, confusion, mydriasis, tachycardia, urinary retention

Examples of drugs that cause Drowsiness, confusion, mydriasis, tachycardia, urinary retention?

diphenhydramine, hyoscine, promethazine mirtazapine, TCA

What would be the cluster/toxidromes for salicylates?

Nausea, vomiting, tinnitus, deafness, hyperpyrexia, hyperventilation metabolic acidosis

What are the 4 main points of management for poisoned patients?

• Symptomatic and supportive measures

• Reducing absorption

• Enhancing elimination

• Specific antidotes

What is the ABC of resuscitation?

• Airway – clear obstruction

• Breathing – oxygen – assisted ventilation

• Circulation – skin colour and temperature, Intravenous access / fluids

What are the main 3 ways to reduce absorption of the substances?

Gastric lavage

Single dose activated charcoal

Whole bowel irrigation

Describe gastric lavage?

• V.rarely undertaken

• Potential benefit only if within 1 hr of ingestion

When is single dose of activated charcoal used?

• Usually patients presenting within one hour of a substantial overdose

• Charcoal does not bind alcohols, glycols, acids/alkalis, iron or lithium

Describe whole bowel irrigation?

• Body packer

• Occasionally sustained release preparations

• 2 litres per hour orally until bowel effluent clear

What are the main 4 ways of enhancing elimination?

Multiple dose activated charcoal (MDAC)

Urine alkalinization

Extracorporeal elimination

Chelating agents

Describe what Multiple dose activated charcoal (MDAC) can be used for?

• distinct to single dose AC for reducing absorption

• Confirmed evidence of benefit in OD with carbamazepine, quinine, theophylline or dapsone

• May be beneficial in drugs with enterohepatic circulation e.g. colchicine

How does MDAC work?

Activated charcoal binds drug to maintain low concentration of free drug
Absorbed drug moves by diffusion along concentration gradients

Describe urine alkalinization?

• Administration of intravenous sodium bicarbonate to achieve urine pH of 7.5-8.5

• Enhances salicylate clearance by favouring ionisation

• Requires adequate fluid resuscitation, close monitoring of systemic pH and serum potassium

Describe Extracorporeal elimination?

• Haemodialysis / haemodiafiltration

• Poisoning complicated by renal failure

• Specifically enhances elimination of ethanol, ethylene glycol, methanol, salicylates, lithium, metformin, valproic acid

Describe chelating agents?

• For heavy metal poisoning

• Sodium calcium edetate for Pb

What is the specific antidote for paracetamol overdose?

Acetylcysteine: glutathione precursor for paracetamol poisoning
Most common overdose in UK

What is the specific antidote for opiate overdoses?

Naloxone opiate antagonist

What is the specific antidote for benzodiazepine?

Flumazenil: GABA receptor antagonist

What is the specific antidote for alcohol?

Fomepizole: Alcohol dehydrogenase inhibitor for treatment of toxic alcohol poisoning

What is the specific antidote for methaemoglobinaemia?

Methylthioninium chloride / Methylene Blue:

What factors influence overdose and hepatotoxicity with paracetamol?

Dose of paracetamol ingested

• Plasma paracetamol concentration

• Time to antidote administration

• Nature of the overdose – single (over less than 1 hour) or staggered / therapeutic excess

What dose a paracetamol is unlikely to cause overdose?

less than 75mg/kg

What dose a paracetamol is rare to cause overdose?

75-150mg/kg

What dose of paracetamol is possible to cause overdose?

above 150mg/kg

What can affect paracetamol overdose?

Weight of patients

When should you take bloods in paracetamol overdose?

• Do not take blood before 4 hours

• After 16 hours can be a bit hit or miss if above or below

  • Treat on side of caution

Why do patients need to be treated within 8 hours in paracetamol overdose?

Provided a patient is treated within 8 hours of overdose they are extremely unlikely to develop significant liver damage

What are antidotes for paracetamol poisoning?

glutathione precursors

Why not use 12 hour regimen of glutathione in paracetamol overdose?

• Not endorsed by MHRA

• Results in a lower peak concentration

• Reduction in anaphylactoid reactions