Salicylate poisoning is potentially fatal. Salicylates are present in aspirin medications, Pepto-Bismol® and in high concentrations of oil of wintergreen (methyl salicylate: 1 teaspoon = 7 g of salicylate). The local poisons service should be contacted for advice:
- UK National Poisons Information Service - www.npis.org - Tel: 0844 892 0111.
- Toxbase (see below for link): provides information about routine diagnosis, treatment and management of patients exposed to drugs, household products, and industrial and agricultural chemicals.
Children and adults who have ingested less than 125 mg/kg aspirin and have no symptoms do not require hospital admission but ingestion of more than 250 mg/kg aspirin is likely to cause moderate toxicity and ingestion of more than 500 mg/kg aspirin causes severe and possibly fatal toxicity. Risk factors for death include:
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- Mild poisoning causes nausea, vomiting, tinnitus, lethargy or dizziness.
- More severe poisoning causes dehydration, restlessness, sweating, warm extremities with bounding pulses, increased respiratory rate, hyperventilation and deafness.
- A degree of disturbance of acid-base balance is present in most cases.
- Hyperglycaemia, normoglycaemia or hypoglycaemia (all with intracellular glucose depletion) may occur.
- Uncommon features include haematemesis, hypokalaemia, hyponatraemia/hypernatraemia, hypocalcaemia, thrombocytopenia, abnormal blood coagulation (increased prothrombin ratio/INR), disseminated intravascular coagulation, renal failure and non-cardiac pulmonary oedema.
- CNS: confusion, disorientation, coma and convulsions (less common in adults than in children).
- Plasma salicylate concentrations:
- The severity of poisoning cannot be assessed from plasma salicylate concentrations alone and the clinical and biochemical features should also be considered.
- Should be measured urgently for patients who are thought to have ingested more than 125 mg/kg of aspirin as well as those who have taken methyl salicylate or salicylamide.
- The sample should be taken at least 2 hours (symptomatic patients) or 4 hours (asymptomatic patients) following ingestion as it may take several hours for peak plasma concentrations to occur.
- A repeat sample should be taken after a further 2 hours because of the possibility of continuing absorption. Measurements should be repeated every 3 hours until concentrations are falling.
- Renal function and electrolytes, full blood count, coagulation studies (raised INR/PTR), urinary pH, and blood glucose.
- Plasma potassium should be checked every 3 hours and plasma potassium levels maintained at between 4.0-4.5 mmol/L.
- Arterial blood gases (capillary gases or venous blood gases are alternatives in children): some degree of acid-base disturbance is present in most cases:
- Adults and older children over the age of 4 years: mixed respiratory alkalosis and metabolic acidosis, with normal or high arterial pH.
- Young children: metabolic acidosis is common.
The likelihood of toxicity can be gauged to a degree by:
- The ingested dose:
- Greater than 125 mg/kg body weight: likely toxicity is mild.
- Greater than 250 mg/kg body weight: likely toxicity is moderate.
- Greater than 500 mg/kg body weight: likely toxicity is severe, possibly fatal.
- Salicylate concentration:
- Severity of poisoning cannot be assessed from plasma salicylate concentrations alone but salicylate intoxication is usually associated with plasma concentrations greater than 350 mg/L (2.5 mmol/L). Most adult deaths occur in patients whose concentrations exceed 700 mg/L (5.1 mmol/L).
- Clinical grading:
- Acid-base staging:
- Stage I: blood pH>7.4, urine pH>6.0 - respiratory alkalosis, increased urinary excretion of bicarbonate.
- Stage II: blood pH>7.4, urine pH<6.0 - metabolic acidosis with compensating respiratory alkalosis, urinary hydrogen excretion, intracellular potassium depletion.
- Stage III: blood pH<7.4, urine pH<6.0 - severe metabolic acidosis and hypokalaemia.
Treatment must be in hospital where plasma salicylate, pH and electrolytes can be measured. Absorption of aspirin may be slow and the plasma-salicylate concentration may continue to rise for several hours, requiring repeated measurement of plasma-salicylate concentration.
- General measures for poisoning.
- Consider oral activated charcoal (50 g for an adult, 1 g/kg for a child) if ingested more than 125 mg/kg body weight salicylate less than 1 hour previously.
- A second dose of charcoal may be required in patients whose plasma salicylate level continues to rise or who have taken enteric coated preparations (absorption may be slower).
- Gastric lavage if the patient has ingested more than 500 mg/kg body weight salicylate within 1 hour.
- Aggressive rehydration.
- Have a low threshold to give glucose as intracellular glucose depletion may not be reflected in the blood glucose level.
- Urinary alkalinisation:
- Elimination of salicylate may be increased by alkalinisation of the urine. The optimum urine pH is 7.5-8.5.
- If the salicylate concentration in an adult is above 500 mg/L (3.6 mmol/L): 225 mmol sodium bicarbonate (225 mL of 8.4% over 60 minutes or 1.5 L of 1.26% over 2 hours).
- If the salicylate concentration in a child is above 350 mg/L (2.5 mmol/L): 1 mL/kg 8.4% bicarbonate diluted in 0.5L 5% dextrose or normal saline at 2-3 mL/kg/hour.
- The urinary pH should be checked hourly. Further amounts of sodium bicarbonate (8.4%) may be required to maintain the urine pH at 7.5-8.5.
- The plasma salicylate concentration should be repeated 1-2 hourly to ensure that treatment has been effective.
- Hypokalaemia may make alkalinisation of the urine less effective and it is important to recheck the plasma potassium 1 to 2-hourly and to give potassium if the plasma potassium falls below 4.0 mmol/L.
- Urinary alkalinisation does not need to be delayed while awaiting haemodialysis but volume overload must be avoided in a patient who is oliguric.
- Forced diuresis: should not be used as it does not enhance salicylate excretion and may cause pulmonary oedema.
- Haemodialysis is the treatment of choice for severe poisoning and should be seriously considered in patients with:
- Plasma concentrations greater than 700 mg/L (5.1 mmol/L)
- Renal failure
- Congestive cardiac failure
- Non-cardiogenic pulmonary oedema
- CNS effects not resolved by correction of acidosis
- Persistently high salicylate concentrations unresponsive to urinary alkalinisation
- Severe metabolic acidosis (pH below 7.2)
- Patients aged under 10 years or over 70 years have increased risk of salicylate toxicity and may require dialysis at an earlier stage.
- Haemofiltration is much less efficient than haemodialysis or haemodiafiltration, but may be an alternative in hospitals without dialysis facilities, especially if transfer is likely to be delayed.
- Small retail pack size.
- Measures to prevent accidental overdose by children, eg safe storage, child-proof caps.
Further reading & references
- Toxbase®; (Registration is free for doctors who are employed by an NHS practice.)
- Hawton K, Townsend E, Deeks J, et al; Effects of legislation restricting pack sizes of paracetamol and salicylate on self poisoning in the United Kingdom: before and after study. BMJ. 2001 May 19;322(7296):1203-7.
|Original Author: Dr Colin Tidy||Current Version: Dr Colin Tidy|
|Last Checked: 20/04/2011||Document ID: 2744 Version: 22||© EMIS|
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