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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:
- agitation, anxiety, sweating, hyper-reflexia, mydriasis, tremor
- confusion, fever, hyperactivity, hypertension, tachycardia, tachypnoea
- delirium, hallucinations, hyperpyrexia, tachyarrhythmias
- coma, cardiovascular collapse, seizures
Depressant poisoning
Features of increasing toxicity:
- ataxia, confusion, lethargy, weakness but able to obey commands and to
make verbal response
- mild coma. No verbal response but motor response to pain. Brainstem and
deep tendon reflexes intact
- moderate coma. Respiratory depression, unresponsive to pain. Some but
not all reflexes absent
- deep coma. Apnoea, cardiovascular depression. All reflexes absent
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