AssessmentIs the cause toxicological?
Introduction
Poisoning is a common reason for presentation to hospital; for example, there were 154,000 accident and emergency presentations in England with poisoning (including drug overdose) in the 2012/13 reporting year.1 The peak age groups are infants and young adults. In most cases, a history of drug overdose, accidental ingestion or illicit drug administration is provided by the patient, parent, other witness or ambulance staff, so the correct diagnosis is not difficult to make. Sometimes, however, the diagnosis may not be straightforward, such as when the patient is unable to give a history or, less commonly, when exposure to potential toxins is concealed.
In patients with unexplained clinical features, it is essential to take a detailed history from the patient and other witnesses and to perform a careful clinical examination. Clues such as tablet bottles or recreational drug paraphernalia may also be found in the patient's property.
The following are situations where poisoning is likely or possible and should be excluded.
Section snippets
Unexplained coma
Unexplained coma is commonly caused by drug toxicity,2 particularly in young adults. The substances most frequently implicated are opioids (check the pupils and search for needle marks, consider using naloxone), sedatives such as benzodiazepines or antihistamines and tricyclic antidepressants (check the electrocardiograph (ECG) for QRS interval prolongation). Less commonly, γ-hydroxybutyrate (GHB), or the related substances γ-butyrolactone (GBL) or 1,4-butanediol, may be responsible. Alcohol is
Acute confusional states
Intoxication with drugs or chemicals is a common cause of acute confusion, especially when it presents in young adults. The substances commonly involved are those that reduce conscious level (as above), but confusion may also occur with recreational stimulants or hallucinogens,3 both traditional drugs (e.g. amphetamines, ecstasy, cocaine) or so-called novel psychoactive substances (e.g. cathinones such as mephedrone or synthetic cannabinoid receptor agonists), anticholinergics (e.g. toxic
Hypoglycaemia
Hypoglycaemia is a common complication of insulin treatment in patients with diabetes mellitus (look for stigmata such as lipoatrophy or hypertrophy, and for diabetes-related paraphernalia among the patient's property), but may also occur following sulphonylurea or meglitinide overdose or with alcohol intoxication. Uncommon toxic causes include salicylates, sodium valproate and β-adrenoceptor antagonists. Occult drug-induced hypoglycaemia should be considered in healthcare workers because of
Abnormal liver function
Abnormal liver function (particularly markedly elevated transaminases associated with prolongation of prothrombin time) should prompt exclusion of paracetamol ingestion during the previous few days. Associated clinical features include hepatic tenderness, vomiting and renal impairment. At this stage, paracetamol is unlikely to persist in the plasma. Less common toxic causes of hepatotoxicity include carbon tetrachloride, Amanita sp. mushrooms, iron, sulphonamides and tetracyclines. Abnormal
Unexplained convulsions
Convulsions may be caused by drug toxicity (e.g. tricyclic antidepressants, bupropion, antipsychotic drugs, monoamine oxidase inhibitors, selective serotonin reuptake inhibitors, venlafaxine, theophylline, lithium, mefenamic acid, anticonvulsants, antiarrhythmic drugs, tramadol, isoniazid, amfetamines, cathinones, ecstasy, cocaine) or by withdrawal from alcohol, benzodiazepines or GHB/GBL.6 A history of exposure can usually be obtained from witnesses or from the patient following recovery. A
Unexplained metabolic acidosis
Poisoning is a common cause of metabolic acidosis; when this is present, calculation of the anion gap and measurement of plasma lactate is helpful (see also Metabolic effects of poisoning on pages 87–90 of this issue). A raised anion gap with lactic acidosis occurs in poisoning with ethylene glycol, methanol, sodium valproate, iron, carbon monoxide and cyanide, as well as with poor tissue perfusion from any cause. Poisoning with salicylates or formaldehyde causes a high anion gap acidosis,
Abnormal bleeding
Clotting may be affected by a number of mechanisms in poisoning8 and result in abnormal bleeding, for example haematuria in an individual with a normal urinary tract. Substances involved include warfarin, novel oral anticoagulants such as dabigatran, apixaban and rivaroxaban, and rodenticides such as difenacoum. When these are suspected, a full blood count and coagulation screen are indicated. In warfarin and difenacoum poisoning, the prothrombin time and international normalized ratio are
Several individuals presenting with similar clinical features
Air, water and food-borne poisoning should be considered when clustering of cases occurs. Non-specific neurological signs, such as headache and confusion, affecting several family members may be caused by carbon monoxide poisoning, perhaps from a faulty gas appliance, which is a leading cause of death from accidental poisoning. An elevated blood carboxyhaemoglobin concentration confirms recent carbon monoxide exposure, but this is not excluded if it was several hours previously.10
Recurrent or chronic unexplained symptoms in children
Accidental chronic poisoning may occur in childhood (e.g. lead poisoning from exposure to lead-based paint). Deliberate poisoning, as a form of Munchausen syndrome by proxy, is rare but early recognition is important.11 Sedative drugs are often implicated, and further episodes may occur while the child is in hospital. In this situation, blood or urine toxicology may provide the diagnosis.
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