Metamizole – Uses, Dosage and Side Effects

What is Metamizole?

Metamizole (also known as dipyrone, and marketed under trade names such as Novalgin) is a pyrazolone-derived analgesic belonging to the class of non-opioid pain relievers. It has potent analgesic (pain-relieving), antipyretic (fever-reducing), and antispasmodic (muscle-relaxing) properties. In many European and Latin American countries, metamizole is available by prescription and is primarily used for severe pain that does not respond adequately to other analgesics.

Mechanism of Action

Metamizole works by inhibiting the synthesis of prostaglandins – signaling molecules in the body that mediate pain, inflammation, and fever – at both the central and peripheral level. Additionally, it directly relaxes smooth muscle tissue, which accounts for its antispasmodic effect. Unlike classical non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, metamizole has only a weak anti-inflammatory effect.

Indications

• Severe acute and chronic pain, e.g., post-operative pain or cancer-related pain
• Colic pain affecting the gastrointestinal tract, gallbladder, or urinary tract
• High fever that does not respond to other antipyretic measures
• Pain associated with renal colic

Dosage and Administration

Metamizole is available in various forms including tablets, oral drops, suppositories, and injectable solutions. The standard adult dose is 500 mg to 1,000 mg per single dose, up to a maximum of 4 times daily (maximum daily dose: 4,000 mg). The exact dosage should always be determined by a healthcare professional. Dose adjustments are necessary for children, elderly patients, and those with impaired kidney or liver function.

Side Effects

Metamizole is generally well tolerated, but may cause the following side effects:

• Agranulocytosis: A rare but potentially life-threatening reduction in white blood cells (granulocytes). Warning signs include high fever, chills, and a sore throat – immediate medical attention is required if these symptoms occur.
• Drop in blood pressure (hypotension), especially with intravenous administration
• Allergic reactions, including anaphylactic shock in very rare cases
• Gastrointestinal complaints such as nausea or abdominal pain
• Skin reactions such as redness or itching

Contraindications

Metamizole must not be used in the following situations:

• Known hypersensitivity to metamizole or other pyrazolone derivatives
• Existing blood cell formation disorders (e.g., pre-existing agranulocytosis)
• Pregnancy (especially during the first and last trimester) and breastfeeding
• Infants under 3 months of age or weighing less than 5 kg
• Patients with analgesic-induced asthma or analgesic intolerance

Important Notes

Due to the risk of agranulocytosis, metamizole should only be used under medical supervision and with regular monitoring of blood counts. In some countries (e.g., the United States and the United Kingdom), metamizole has been withdrawn from the market. In Germany and other European countries, it remains available because the benefits outweigh the risks for specific indications when used appropriately.

References

1. Kötter T. et al. – Metamizole-associated risks of agranulocytosis: a systematic review and meta-analysis. PLOS ONE, 2015.
2. European Medicines Agency (EMA) – Assessment report on metamizole-containing medicinal products, 2019.
3. Jasiecka A., Maslanka T., Jarosz J. – Pharmacological characteristics of metamizole. Polish Journal of Veterinary Sciences, 2014.