Overdose and Poisoning

Dr Tom Leach

8 years ago

Contents

Opiates
Benzodiazepines
Paracetamol
Aspirin (salicylic acid)
- Investigations
- Management
β – blockers
Cannabis
Sympathomimetics e.g. cocaine, amphetamines
Carbon Monoxide

Antidotes
- Related Articles

Opiates

Naloxone will reverse the effect of opiate overdose, typically in the presence of CNS and respiratory depression.

It competitively binds opioid receptors, causing a blockade
Usually given IV for fastest action (<1 min)
Opioid overdose typically seen in heroin users who have been incarcerated / ‘gone cold turkey’ who subsequently return to heroin abuse. Upon returning to opioid use they often take the same dose they were taking before cessation, which, in the absence of tolerance, can be fatal.
CAUTION – the half-life of naloxone is shorter than that of opiates, thus the naloxone can wear off, and the patient can go back into a state of opiate overdose.

Benzodiazepines

symptoms: agitation, euphoria, blurred vision, slurred speech, ataxia, slate-grey cyanosis
Flumazenil – can reverse the effect of benzodiazepines, however, is not always recommended. It is mainly used to reduce the sedative / drowsiness effects of benzodiazepines

In long-term benzo abusers, it can induce withdrawal (including seizures), thus use is not recommended
It competitively binds benzodiazepines
Its half-life is shorter than benzodiazepines, so multiple doses may need to be administered

Paracetamol

Paracetamol overdose is considered separately in its own article.

Aspirin (salicylic acid)

Note that Pepto-Bismol(R) is very high in salicylate!
<125mg/Kg is not toxic
250mg/Kg is mildly toxic. Signs and symptoms include:

Tinnitus
Lethargy
Dizziness
Nausea / vomiting

500mg/Kg is severe. Signs and symptoms include (as well as the above)

Dehydration
Sweating / warm extremities
Bounding pulse
Deafness
Breathlessness
Glucose disturbance (hypo or hyper)
Confusion / disorientation, rarely coma

Other features indicating a life-threatening attack include:

pulmonary oedema
metabolic acidosis
salicylate conc >700mg/L

Investigations

Salicylate concentration should be measured, but unlike paracetomal is not an indication of the severity of poisoning

It is most accurate >4 hours after ingestion. Repeat after a further 2 hours to asses for rising levels

Renal function (U+E’s)
Glucose
Plasma Potassium – hypokalaemia likely, correct with IV KCl
Urine pH + ABG – Check hourly – severity of poisoning can be asses using blood pH and urine pH:

Stage I – blood >7.4, urine >6.0
Stage II – blood >7.4, urine <6.0
Stage III – blood < 7.4, urine <6.0

Management

Activated charcoal – if >125mg/Kg ingested <1hr ago
Gastric lavage – if >500mg/Kg ingested <1hr ago
Aggressive rehydration
Consider glucose – intracellular glucose is often depleted even if blood glucose remains normal
Increase alkalinity of urine – can increase excretion of salicylate

Give sodium bicarbonate if >500mg/Kg ingested. Optimum urine pH is 7.5 – 8.5
Hypokalaemia reduces the effectiveness of urine alkalisation

CAUTION – forced dieresis is not effective at increasing salicylate excretion and may cause pulmonary oedema.
HAEMODIALYSIS is the treatment of choice for severe cases (also continue alkalisation or urine providing no oliguria). Consider in:

Plasma salicylate >700mg/Kg
- Lower if patient <10 or >70 years
Renal failure
Heart failure
Coma
Convulsions
Non-resolution of CNS symptoms, despite correction of acidosis
Severe metabolic acidosis (pH <7.2)

β – blockers

Positively inotropic agents (e.g. dobutamine, or catecholamines, e.g. dopamine, noradrenaline, adrenaline) are often not effective in β-blockade. Glucagon is usually the treatment of choice.
Hypocalcaemia may also be present, and should be corrected with calcium.

Cannabis

Dry cough, increased appetite, social withdrawal and paranoia, altered perception of time

Sympathomimetics e.g. cocaine, amphetamines

Tachycardia, mydriasis, euphoria, formication- insects crawling, agitation, tremor, dilated pupils, tachycardia, arrhythmias, convulsions.

Treatment: Benzodiazepine e.g. diazepam

Carbon Monoxide

Inebriation, coma, reduced reflexes, tachycardia, pulmonary oedema, shock, met acidosis, flushed cherry pink skin. headache.

Treatment – hyperbaric oxygen

Antidotes

Anti-freeze (ethylene glycol) poisoning – Ethanol
Cyanide poisoning – Dicobalt edetate
Lead poisoning – Sodium calcium edetate
Organophosphate poisoning – Atropine
Heparin overdose – Protamine sulphate