PARACETAMOL or acetaminophen, depending on whether you are in the United States of America or the United Kingdom, chemically named N-Acetyl-p-aminophenol (APAP), is usually packaged under the trade names Cetamol, Tylenol or Panadol.

Paracetamol is a drug that is used to treat pain and fever. It has weak anti-inflammatory effects and is a Class B drug in pregnancy, which means it is safe in prescribed quantities. With the current increase in viral illnesses, paracetamol is the drug of choice to treat pain, for example headache and joint pains, brought on by the infection.

KNOW YOUR DOSES

The dose of paracetamol for children is 10-15mg/kg orally, every four hours, and for adults, one gram every eight hours. The allowable dose is 3000mg per day for adults and 2000mg per day for children younger than 12 years old.

Even if symptoms are not abated, extra doses should not be taken.

OVERDOSING

Paracetamol overdose is a very common occurence, especially in children in the USA and to a lesser extent in Jamaica. It occurs in planned as well as accidental overdose.

The toxic dose in adults is 7.5-10grams and 140mg per kilogram for children.

Paracetamol is broken down by the liver. In the recommended dose, majority of the drug is broken down by the main pathway. However, in toxic doses, a compound is formed, N-acetyl-p- benzoquinoneimine(NAPQI), that damages the liver and the

kidney cells.

Some people are more likely to be affected than others. Elderly people with liver disease, malnourished individuals and persons that take certain drugs or consume alcohol with the toxic dose, are particularly at risk.

SIGNS AND SYMPTOMS OF TOXICITY

When the toxic dose has been reached, this is usually manifested in four phases.

In phase one, which lasts for up to one day, most people have no symptoms. If symptoms are present they will experience, nausea, vomiting and weakness.

In phase 2, which lasts up to two days, pain in the abdomen, nausea and vomiting will occur. This indicates damage to the liver.

In phase three, which is between 72-96 hours, the liver injury worsens and the patient starts to have yellowing of the eyes, skin and mucous membranes, confusion, lethargy, low blood sugar, easy bleeding, and low blood pH.

In phase 4, the patient either recovers or is suffering from the late stages of liver failure. This lasts from four days to two weeks.

TREATMENT

Patients presenting to the emergency department after taking a toxic dose would normally give the history of the intake, or accompanying relatives would state that they had found the tablet bottles empty or half full. After ensuring the patient has been stabilised, they would then be examined and laboratory investigations done. These include kidney and liver function tests, as well as paracetamol (APAP) levels done after four hours of taking the toxic dose.

Treatment is aimed at removing the paracetamol from the body and giving the antidote if indicated.

If the patient presents within one hour, activated charcoal can be used to prevent absorption in the gastrointestinal tract.

For certain blood levels of APAP, no treatment is needed when plotted on a specialised graph.

If the toxic dose of paracetamol has been reached based on the graph, then n-acetyl cysteine, the antidote, will be prescribed.

Patients are usually admitted to hospital if the toxic dose has been reached. They would also need to be seen by the psychiatrist if the intake of the toxic dose was planned.

Some persons may need liver transplant if the damage is severe. Patients who are treated early usually have a good prognosis.

Dr Romayne Edwards is a consultant emergency physician at the University Hospital of the West Indies and an associate lecturer at the University of the West Indies.