Overdose and Poisoning

Original article by Tom Leach | Last updated on 17/1/2015
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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

Overdose Signs + Symptoms

  • Nausea / vomiting
  • Hepatic necrosis causes:
  • Renal failure
  • Oliguria
  • Metabolic Acidosis
  • Often asymptomatic, until 24-72 hours after when acute liver failure occurs
 

Investigations

  • Paracetamol (+ salicylate) level - Only accurate if >4 hours after ingestion
  • LFT’s
  • Glucose
  • U+E’s
  • Prothrombin time is a very good measure of acute renal failure
  • ABG – checking for metabolic acidosis
 

Management if <8 hours after ingestion

Activated Charcoal

  • Not suitable in all instances. Only if:
  • >12g or 150mg/Kg paracetamol
  • <2hrs (most effective if <1hr) after overdose

Acetylcysteine

  • Promotes conjugation of circulating paracetamol. Should only be administered if you have a plasma paracetamol level. Then, look at the treatment graph. Patients above the treatment line (or above the high risk line if they are high risk) should receive acetylcysteine.
  • Greatest effect if given <12 hours after ingestion
  • Once administration has begun, it usually continues for 24 hours regardless of plasma level of paracetamol
 

Management if >8 hours after ingestion

Give acetylcystiene if >12g or >150mg/Kg has been ingested, regardless of current plasma level (don’t wait for blood result)

  • Proven to decrease mortality in late presentations even if liver failure is present
  • Administer with 5% dextrose
  • 5% of patients will have allergic rash
 

Management if >24 hours after ingestion

  • Controversial, seek expert advice
  • Often Toxobase is used
 
 

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)

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 Potassiumhypokalaemia 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