Pain & Sedation
A 23 year old woman presents to the Emergency Department complaining of a frontal headache. The triage nurse administers paracetamol. Regarding paracetamol, which of the following statements is CORRECT?
Answer:
Paracetamol is a non-opioid analgesic, similar in efficacy to aspirin, with antipyretic properties but no anti-inflammatory properties. It can be given orally, rectally or intravenously. Paracetamol is a suitable first-line choice for most people with mild-to-moderate pain, and for combination therapy. There are no contraindications to the use of paracetamol.Paracetamol Pharmacology
Pain & Sedation
Last Updated: 12th February 2021
Mechanism of Action
Paracetamol is a non-opioid analgesic, similar in efficacy to aspirin, with antipyretic properties but no anti-inflammatory properties. It can be given orally, rectally or intravenously.
Indications
Paracetamol is a suitable first-line choice for most people with mild-to-moderate pain, and for combination therapy.
Paracetamol is the analgesic of choice for women who are trying to conceive, or who are pregnant. It can be used at the standard dose at any stage of pregnancy. Paracetamol is also suitable for use during breastfeeding.
Contraindications and Cautions
There are no contraindications to the use of paracetamol.
Paracetamol should be used with caution in:
- Chronic alcohol consumption
- Chronic dehydration
- Chronic malnutrition
- Hepatic impairment
- People who weigh < 50 kg (clinical judgment should be used to adjust the dose)
Side Effects
Adverse effects are rare with paracetamol. There have been very rare reports of blood dyscrasias (including thrombocytopenia and agranulocytosis) in people taking paracetamol, but it is not clear that these were directly caused by the paracetamol.
Overdose
Paracetamol doses greater than the maximum daily dose of 4 grams can lead to hepatotoxicity (and, less frequently, acute kidney injury). In some people this may be fatal.
People who have taken an overdose of paracetamol (accidentally or intentionally) may require urgent admission to hospital, depending on the quantity of paracetamol taken and the presence of risk factors for liver damage, including: alcohol dependence, pre-existing liver disease, malnutrition, and the use of liver enzyme inducing drugs (such as rifampicin, carbamazepine, and phenytoin).
Early symptoms of paracetamol toxicity are nausea, vomiting, and abdominal pain which usually settle within 24 hours. Symptoms of liver damage include right subcostal pain and tenderness. Liver damage peaks 3 to 4 days after paracetamol ingestion. The person may develop encephalopathy, bleeding, hypoglycaemia, and cerebral oedema.
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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 |
