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Up Agents & syndromes Elimination Organ support Severity

Charles Gomersall

First posted July 2006

Prediction of potential toxicity

  • requires knowledge of agent, dose and time of exposure
  • labelling (although often inaccurate or incomplete) may give some indication of toxicity:
    • weak irritant ⇒ may damage mucosal surfaces following topical exposure
    • strong irritant ⇒ may damage skin as well as mucosa following topical exposure
    • corrosive ⇒ can cause permanent tissue damage or death following topical exposure
    • moderately toxic ⇒ oral LD50 50-500 mg/kg
    • highly toxic ⇒ oral LD50 1-50 mg/kg
    • extremely toxic ⇒ oral LD50 <1 mg/kg
  • dose
    • tablets/capsules. Dose can be estimated from number swallowed. If the history is thought to be unreliable (which in common in deliberate self-poisoning) or is unknown assume the worst case-scenario and assume maximum possible dose
    • liquids. Estimate can be obtained from history:
      • teaspoon: 3-7 ml
      • tablespoon: 7-14 ml (non-calibrated tablespoon)
      • volume of a sip or swallow depends on age, height, weight and sex of patient, orifice size of container and viscosity of liquid
        • infant: 1-5 ml
        • adult: 4-40 ml
    • for any given dose assume maximal toxicity will develop and treat accordingly
  • timing
    • for most agents maximal toxicity develops within 4-6 hours of ingestion
    • exceptions include:
      • exposure to corrosives
      • irritant gas aspiration
      • pulmonary aspiration of agent (eg hydrocarbon pneumonitis)
      • agents with slow GI absorption. eg carbamazepine, digitalis preparations, enteric coated preparations, salicylates, slow release preparations, Lomotil
      • agents that form gastric concretions. eg barbiturates, heavy metals (eg iron), lithium, salicylates
      • agents with slow distribution. eg digitalis derivatives, heavy metals, lithium, salicylates
      • agents that undergo metabolic activation. eg paracetamol (acetaminophen), chlorinated hydrocarbons, ethylene glycol, methanol, paraquat, some methaemoglobin inducers
      • agents that inhibit nucleic acid synthesis: Amanita phalloides and related mushrooms, cancer chemotherapy and immunosuppressants, anti-virals
      • agents that inhibit metabolic pathways. eg disulfiram, monoamine oxidase inhibitors, salicylates, thyroid hormone synthesis inhibitors
  • serum concentrations can be used to predict toxicity associated with some agents, eg paracetamol (acetaminophen), ethylene glycol, salicylates, alcohols, paraquat, heavy metals, anti-arrhythmics, barbiturates, carbon monoxide, digoxin, electrolytes, lithium, theophylline

Assessment of severity

This is based predominantly on the findings of physical examination, which should concentrate initially on cardiovascular stability, respiratory function and neurological status. Measurement of core temperature is also important and often forgotten. Frequent re-evaluation is necessary as the clinical state may change rapidly.

Stimulant poisoning

Features of increasing toxicity:

  1. agitation, anxiety, sweating, hyper-reflexia, mydriasis, tremor
  2. confusion, fever, hyperactivity, hypertension, tachycardia, tachypnoea
  3. delirium, hallucinations, hyperpyrexia, tachyarrhythmias
  4. coma, cardiovascular collapse, seizures

Depressant poisoning

Features of increasing toxicity:

  1. ataxia, confusion, lethargy, weakness but able to obey commands and to make verbal response
  2. mild coma. No verbal response but motor response to pain. Brainstem and deep tendon reflexes intact
  3. moderate coma. Respiratory depression, unresponsive to pain. Some but not all reflexes absent
  4. deep coma. Apnoea, cardiovascular depression. All reflexes absent

©Charles Gomersall, April, 2014 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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