Metafen

Metafen is available in tablet form, with each tablet containing 500 mg of paracetamol.

The package contains 20 tablets, and the product is intended for oral administration, being indicated only for adults and adolescents over 12 years of age.

Metafen is indicated for the symptomatic treatment of:

• Headaches and migraines;
• Toothache, including post-extraction pain;
• Sore throats and muscle pain;
• Joint and bone pain;
• Menstrual pain;
• General discomfort associated with colds and flu-like symptoms;
• Fever of various aetiologies.

The usual dose for adults and adolescents weighing over 50 kg is 1–2 tablets (500–1000 mg) administered at intervals of 4–6 hours, not to exceed 8 tablets (4000 mg) in 24 hours.

For adolescents over 12 years of age, 1 tablet every 4–6 hours is recommended, not exceeding 4 tablets per day.

The tablets should be swallowed whole with sufficient liquid (approximately 200 ml of water). It is recommended to administer as needed, observing the intervals mentioned, to avoid overdose.

If the pain persists for more than 5 days or the fever lasts for more than 3 days, the treatment should be re-evaluated by a doctor.

Metafen is contraindicated in the following situations:

• Known hypersensitivity to paracetamol or any of the excipients;
• Severe liver damage or active liver disease;
• Children under 12 years of age;
• Chronic alcohol consumption;
• Concomitant administration with other medicines containing paracetamol (due to the increased risk of overdose).

Caution is advised in patients with:

• Liver or kidney failure;
• Gilbert's syndrome (mild jaundice);
• Glucose-6-phosphate dehydrogenase deficiency;
• Haemolytic anaemia;
• Severe malnutrition, anorexia or low body mass index;
• Chronic alcoholism;
• Sepsis or other conditions that reduce glutathione levels.

Concomitant alcohol consumption should be avoided as it significantly increases the risk of liver damage. 

Metafen is generally well tolerated when used as recommended. However, rare or very rare side effects may occur:

• Haematological disorders: changes in platelets, coagulation disorders;
• Neurological disorders: dizziness, tremors, confusion, hallucinations;
• Gastrointestinal disorders: nausea, abdominal pain, diarrhoea, vomiting;
• Hepatic disorders: increased liver enzymes, jaundice, liver failure;
• Skin reactions: pruritus, urticaria, transient rash, excessive sweating.
• Thrombocytopenia, leukopenia, haemolytic anaemia;

• Angioedema, severe anaphylactic reactions;
• Stevens-Johnson syndrome or toxic epidermal necrolysis.

In case of severe allergic reactions (swelling of the face, lips, difficulty breathing), treatment should be discontinued immediately and emergency medical assistance should be sought.

Paracetamol may interact with a number of medicines such as:

• Hepatic enzyme inducers (phenobarbital, phenytoin, carbamazepine, rifampicin): increase the risk of liver toxicity;
• Oral anticoagulants (warfarin, coumarin derivatives): may enhance the anticoagulant effect;
• Zidovudine: increases the risk of neutropenia;
• Probenecid: reduces paracetamol clearance, requiring dose adjustment;

Concomitant administration with alcohol should be avoided, and the medicine should be taken with sufficient water.

Paracetamol overdose is a medical emergency. Ingestion of a dose higher than the recommended dose can lead to severe, even fatal, liver failure. Early symptoms include nausea, vomiting, abdominal pain and pallor, followed by apparent improvement, after which signs of liver necrosis may appear.

Treatment consists of administering N-acetylcysteine as quickly as possible, preferably within the first 8 hours after ingestion.

Metafen should be stored at temperatures below 25°C, in its original packaging, protected from moisture and light. Keep out of the reach of children. Do not use the medicine after the expiry date stated on the packaging. 

• WebMD, Paracetamol
• NIH, Acetaminophen
• PubMed, Paracetamol: mechanism of action, applications and safety issues
• MDPI, Paracetamol: a review of guideline recommendations