Metamizole

Metamizole sodium is an analgesic and antipyretic belonging to the group of non-opioid analgesics. Due to a rare but serious side effect (agranulocytosis), metamizole is no longer approved for use in many countries. In German-speaking countries, however, its use is still widespread. It is usually administered in the form of tablets.

Pharmacodynamics

The exact mechanism of action has not yet been deciphered. What is certain is the inhibition of the enzyme cyclooxygenase, which is essential for the development of pain. However, researchers suspect that opioid and 5-HT receptors are additional targets of the drug, which may also influence pain perception to a certain extent.

Pharmacokinetics

Metamizole is used exclusively as the sodium salt metamizole sodium. This makes it possible to administer the substance as a tablet. The half-life of metamizole is very short. It is metabolized in the liver and the bioavailability is about 90%. The plasma half-life is about 2.5 hours. Excretion occurs through the kidneys.

Drug Interactions

Concomitant administration with chlorpromazine should be avoided as dangerous hypothermia may result.

In combination with methotrexate, liver damage may occur.

Side effects

Due to the rare and life-threatening side effect agranulocytosis, Metamizole is no longer used in many countries. The incidence here is 1 treated per 1 000 000 patients.

Other side effects that may occasionally occur

• Hypotension
• Drug exanthema
• Reddening of the urine
• Leukopenia
• Skin reactions

Toxicological data

LD50 (rat, oral): 4351 mg.kg-1