Pharmacology & Poisoning
Question 58 of 180
A 15 year old girl is brought to the Emergency Department by her parents following an intentional overdose. She has taken approximately fifty 300 mg aspirin tablets. What antidote, if required, would be used in this case?
Answer:
Once the serum potassium concentration is within the normal range, start to correct metabolic acidosis in an adult with intravenous sodium bicarbonate 50-100 mmoL given over 30 minutes. Administration of sodium bicarbonate will reduce transfer of salicylate into the central nervous system and hence reduce toxicity.Salicylate Toxicity
Pharmacology & Poisoning
Last Updated: 31st January 2021
Salicylates are highly toxic in large overdose. Patients are more likely to die if they are aged over 70 years, or if they develop coma, convulsions, confusion, agitation, pulmonary oedema, severe metabolic acidosis, or hyperpyrexia. Ventricular arrhythmias and asystole can occur, leading to fatalities.
Clinical features
- Mild (usually associated with a peak salicylate concentration of less than 300 mg/L (2.2 mmol/L))
- Lethargy
- Nausea
- Vomiting
- Tinnitus
- Dizziness
- Deafness
- Moderate (usually associated with a salicylate concentration of 300 - 700 mg/L (2.2 - 5.1 mmol/L))
- Dehydration
- Restlessness
- Sweating
- Warm extremities with bounding pulses
- Increased respiratory rate and hyperventilation
- Respiratory alkalosis (may also be a metabolic acidosis)
- Severe (usually associated with a peak salicylate concentration of more than 700 mg/L (5.1 mmol/L))
- Cardiac dysrhythmias
- Acute non-cardiogenic pulmonary oedema
- Cerebral oedema
- Convulsions
- Confusion
- Coma
- Hyperpyrexia
- Heart failure
- Renal failure
- Worsening metabolic and lactic acidosis
Management
- Maintain a clear airway and ensure adequate ventilation. Avoid intubation unless there is evidence of respiratory failure (worsening respiratory acidosis, severe hypoxemia). Loss of hyperventilatory drive can result in sudden decompensation and death.
- The benefit of gastric decontamination is uncertain. Consider activated charcoal (charcoal dose: 50 g for adults; 1 g/kg for children) if the patient presents within 1 hour of ingestion of 125 mg/kg or more salicylate, or any amount of methyl salicylate, providing it is safe to do so and the airway can be protected. Efficacy declines rapidly with time since ingestion but there may be some potential benefit from later use, especially following large ingestions. A second dose of charcoal may be warranted in patients whose plasma salicylate concentration continues to rise, suggesting delayed gastric emptying, or who have taken enteric coated preparations where absorption may be slower.
- Where the practical expertise exists, consider gastric lavage in adults within 1 hour of a potentially life-threatening overdose (suggested dose 500 mg/kg salicylate or more), providing the airway can be protected.
- An urgent plasma salicylate concentration should be taken at least 2 hours (symptomatic patients) or 4 hours (asymptomatic patients) after ingestion, since it may take several hours for peak plasma concentrations to occur with enteric-coated preparations. Repeat salicylate concentrations every 2 hours in all patients who are symptomatic, or those with initial plasma salicylate concentrations of 200 mg/L or more until concentrations are falling and any clinical features have improved.
- Asymptomatic patients with normal acid-base status can be considered for discharge after observation for 6 hours following the overdose, provided their plasma salicylate concentration is below 300 mg/L (2.2 mmol/L).
- Treat hypokalaemia urgently; this will reduce the risk of severe hypokalaemia with bicarbonate therapy if this becomes necessary later.
- Give fluids intravenously (with added potassium if necessary) to replace fluid losses which may be substantial.
- Once the serum potassium concentration is within the normal range, start to correct metabolic acidosis in an adult with intravenous sodium bicarbonate 50-100 mmoL given over 30 minutes. Administration of sodium bicarbonate will reduce transfer of salicylate into the central nervous system and hence reduce toxicity.
- The elimination of salicylate may be increased by alkalinisation of the urine. Consider urine alkalinisation if the plasma salicylate concentration is above 500 mg/L (3.6 mmol/L) in adults and 350 mg/L (2.5 mmol/L) in children. The optimum urine pH is 7.5-8.5. The urinary pH should be checked hourly. Plasma sodium and potassium should also be checked 1-2 hourly, and potassium replaced IV, if necessary, to maintain plasma potassium around 4-4.5 mmol/L.
- Haemodialysis (or haemodiafiltration) is the treatment of choice for severe poisoning.
- Indications:
- Salicylate concentration of 900 mg/L (6.4 mmol/L) or more
- Salicylate concentrations greater than 700 mg/L (5.1 mmol/L) with a metabolic acidosis
- Coma due to salicylate poisoning
- It should also be considered for patients with a plasma salicylate concentration greater than 700 mg/L (5.1 mmol/L).
- Dialysis may also benefit those with severe acidosis, renal failure, congestive cardiac failure, or non-cardiogenic pulmonary oedema
- Indications:
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
