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Written on 1st March 2022 by Susan Brown

Healthcare watchdog, HSIB has published its latest report, Unintentional overdose of paracetamol in adults with low bodyweight.

The report follows HSIB’s national investigation into the safety risk to adult patients with low bodyweight of liver toxicity (poisoning) from being overdosed in hospital with oral paracetamol. The national investigation was triggered by the death of an elderly woman who suffered liver toxicity from excessive doses of paracetamol in hospital, after an inquest identified liver toxicity as one of the causes of her death.

Paracetamol is one of the most commonly prescribed painkillers in the world. The public can buy it over the counter, and in hospitals it is a first-line treatment for mild to moderate pain.  Paracetamol is widely regarded, even by hospital doctors and nurses, as low risk medication, but can quickly cause liver failure, leading to death or serious injury, when prescribed and taken in excess. The risks are increased where the patient has existing health conditions or lifestyle habits which increase their vulnerability to liver damage, including low bodyweight, below 50kg.

Commenting on the investigation, HSIB National Investigator, Keely Galloway described the impact of liver toxicity as “devastating, leading to death or significant harm such as acute liver failure, jaundice, bleeding, and neurological and psychological issues. This is exacerbated in patients who are already unwell and vulnerable to infection, as we saw in [the patient’s] case…”

HSIB’s report aims to raise awareness of unintentional paracetamol overdose in patients with low bodyweight in hospitals as “a safety issue [that is] known about and documented but not always recognised and addressed as it should be.”


Paracetamol is dangerous in excess

The British Liver Trust warns that the maximum dose [of paracetamol] within a 24-hour period must never be exceeded. This is because too much paracetamol can damage the liver. Even small overdoses of this widely available over-the-counter painkiller can lead to serious harm.

Liver toxicity is a known risk of paracetamol, particularly where the patient is already at risk of impaired liver function from other conditions, such as chronic dehydration, malnutrition or alcohol consumption, or from taking paracetamol over an extended period of time.  The British National Formulary (BNF], which provides information and advice to doctors about prescribing medication, advises doctors prescribing paracetamol to use clinical judgement to adjust the dose, as some patients may be at increased risk of toxicity even at therapeutic doses, particularly where their bodyweight is below 50 kg.

However, HSIB found that where low bodyweight is the patient’s only risk factor, the risk of paracetamol toxicity is not fully understood. Guidance for prescribers is limited and inconsistent. The BNF gives suggested dose adjustments for IV (injectable) paracetamol for adults weighing less than 50kg, but not for oral or rectal paracetamol, whereas clinical knowledge summaries commissioned by NICE (based on MHRA advice) suggest that bodyweight below 50kg alone is not an indication to reduce the dose of oral paracetamol.

How paracetamol overdose in hospital caused liver toxicity – HSIB’s reference event

HSIB’s national investigation was triggered by the experience of an 83-year-old woman who was admitted to hospital after a fall. She weighed less than 50 kg, and for years had had a co-codamol (codeine and paracetamol) prescription from her GP. Her existing health conditions made her vulnerable to infection.  She had knee pain but no other injuries from the fall but x-rays revealed an infection in her lungs, so she was admitted to a ward for antibiotic treatment. On the ward, her medication chart included a prescription by a junior doctor for paracetamol four times a day. She received her first oral dose the next morning and her medication chart was reviewed by a pharmacy technician. No mistakes were identified.

During the month she spent in hospital her condition deteriorated. She developed acute kidney injury and her antibiotics were changed when she developed signs of sepsis. She was weighed on day 12 after concerns were raised about her food intake. She continued to lose weight. She was regularly prescribed paracetamol and codeine for her knee pain. After experiencing nausea and vomiting blood, tests revealed abnormal liver function. When her further weight loss was noted on her medication chart pharmacy staff noted her low bodyweight and asked for her heparin (blood thinning medication) to be reduced. No change to the paracetamol dose was requested. Her kidney function returned to normal, but her suspected sepsis did not resolve. She was moved to a respiratory ward where her blood tests showed signs of liver failure. On day 29, after consulting a senior colleague, the junior doctor was advised to stop her paracetamol and arrange further tests to assess her liver function. She suffered pain, confusion and jaundice, with a distended painful stomach. Blood tests indicated a significant paracetamol overdose. She was prescribed intravenous antidoting treatment for paracetamol overdose but this was only started nearly 10 hours later. She died the next day. At the inquest, the coroner concluded that her “prescription of paracetamol was higher than it should have been and this played a part in her death”.

HSIB’s findings

HSIB highlighted that safe prescription of paracetamol depends on establishing a patient’s weight, recording it on their medication chart and using the documented weight to determine the correct dose. However, their investigation found no evidence that the patient was weighed until 12 days after her admission. Staff interviews suggested that they believed weighing a patient was a low priority task (compared with measuring heart rate, blood pressure etc). Whilst aspects of the task, equipment availability and workload were raised as possible barriers to weighing patients generally,  HSIB felt that in this case staff had simply not recognised that it was an outstanding task. Some staff believed they could accurately judge visually whether a patient weighed less than 50kg. In this case they described the patient as frail and slight in build, but did not seem to realise the potential significance of her low bodyweight in relation to her prescribed medications.  

The NHS trust’s medicines policy included a requirement to record a patient’s weight on a dedicated box on their medication chart, but staff did not consistently record the patient’s weight as it was not seen as priority information. Even if weight was recorded on the medication chart, staff might not notice it or pay attention to it when prescribing paracetamol. After this patient died, the trust’s medicines policy was amended to require patients to be weighed within 24 hours of admission and then weekly. However, six frontline clinical staff told HSIB that they couldn’t recall ever checking the trust’s medicine policy, and mostly used national prescribing guidance and online tools.  

The patient’s weight was not recorded on the medication chart until 28 days after admission, and even then it did not inform the dose of paracetamol prescribed. The pharmacist reduced her heparin to reflect her weight loss, but her paracetamol dose was not altered until she was diagnosed with liver toxicity 29 days after her admission. HSIB found that even once the paracetamol overdose had been identified, there was a delay in starting the antidote treatment.

HSIB identified that whilst oral paracetamol toxicity is a known patient safety issue in the NHS, it can be under recognised and more evidence is needed to fully understand its relationship with low bodyweight. There is also limited literature on the wider system factors that hinder safe prescribing of paracetamol to adults with low bodyweight, to help NHS learn at a national level.

Their national investigation highlighted that accurate assessment and recording of weight is a crucial factor in reducing the patient’s risk of severe harm from liver toxicity from paracetamol. However, information and advice from the two independent bodies that provide oral paracetamol prescribing guidance for clinicians is not consistent, and other factors create challenges to the timely weighing of patients on a ward.

HSIB’s safety observations

HSIB’s safety observations included that it might be beneficial:

  • for electronic prescribing and medication administration systems to include an alert for oral paracetamol that prompts the prescribing doctor to document a patient’s weight and consider the risk of liver toxicity when their weight is less than 50kg;
  • for national bodies to review the evidence on oral paracetamol and low bodyweight and provide agreed prescribing guidance;
  • for available technological solutions, such as beds with built-in scales, to be used to weigh patients. HSIB recognised that this might be challenging for the NHS given the cost of such equipment.

Making a claim

HSIB’s investigation, and the patient’s experience, highlights the tragic, avoidable harm that is caused when a healthcare system, and the individuals working within it, habitually ignore fundamental aspects of patient care.  Inconsistent guidance and lack of research may indeed hinder clinical judgment, but there is no valid justification for guessing a patient’s weight, ignoring medicine safety policies, or deeming the safety risks associated with prescribed medication as insignificant or acceptable to ignore.

Boyes Turner’s medical negligence team welcome HSIB’s investigation, safety observations and the insight that it has provided into negligent prescribing practises and the gaps in guidance for prescribers. We remain committed to securing compensation for patients who have suffered severe injury, and the families of those who have died, as a result of negligent hospital care

If you have suffered severe injury or the death of a parent or partner as a result of negligent NHS care, you can talk to one of our solicitors, free and confidentially, to find out more about making a claim by contacting us here.