Analgesics and antipyretics. Pyrazolones
Código ATC: N02BB02 (Metamizole sodium)
Marcas comerciales
Metamizole sodium, Dipyrone
The exact mechanism remains under study. Active metabolites (4-methylaminoantipyrine and 4-aminoantipyrine) inhibit cyclooxygenases (COX-1, COX-2 and COX-3) with relative selectivity for the central nervous system. They also activate spinal cannabinoid and opioid receptors, distinguishing metamizole from classic NSAIDs. The antipyretic and analgesic effects exceed the anti-inflammatory effect; the drug is not classified as a classic NSAID.
Segunda línea
Metamizole is used as an analgesic for acute pain of moderate to high intensity, particularly colic (renal, biliary), postoperative pain and when NSAIDs are contraindicated due to GI or cardiovascular risk. RCTs show efficacy comparable to paracetamol and ibuprofen. Due to agranulocytosis risk, the drug was withdrawn from the US market (1977), UK (2003), Sweden (1999) and Japan. It remains available in Russia, Germany, Brazil and Spain, with prescription status varying.
Course limited to short episodes of 1–3 days. IV and IM use is appropriate in inpatient settings for severe pain.
Segunda línea
For fever refractory to standard antipyretics (paracetamol, ibuprofen), metamizole may be used as a reserve in adults. It is most often justified in inpatient settings in infectious patients. Pediatric use for fever is discouraged in most international guidelines due to agranulocytosis risk.
No recomendado
Metamizole is not used for long-term chronic pain therapy. Cumulative agranulocytosis risk, lack of anti-inflammatory effect and the availability of safer alternatives (paracetamol, ibuprofen, non-pharmacological approaches, occasionally weak opioids) make prolonged use clinically unjustified.
Advertencia destacada
No FDA boxed warning applies in the US (the drug was withdrawn in 1977). Russian labels explicitly highlight agranulocytosis risk, the need to stop the drug on fever or sore throat, and mandatory CBC monitoring for courses over 7 days.
FDA category C (not registered in the US; assessment is indicative). Not used in the first and third trimesters – risk of oligohydramnios, premature closure of the ductus arteriosus and increased childhood leukemia risk. Use in the second trimester only on strict indication and absence of alternatives. The Russian label lists pregnancy as a contraindication.
Transfers into breast milk. Breastfeeding is interrupted for at least 48 hours after the last dose.
Metamizole sodium is evaluated for the following indications with varying evidence strength: Acute pain (evidence tier B), Fever refractory to standard antipyretics (evidence tier B), Chronic musculoskeletal pain (evidence tier F). See the full indication matrix with dosing and citations above on this page.
Common side effects of Metamizole sodium (≥ 1 in 100): Hypotension, especially with rapid IV administration, Allergic skin reactions, Nausea, dyspepsia. See the Safety section for uncommon and serious reactions.
FDA category C. FDA category C (not registered in the US; assessment is indicative). Not used in the first and third trimesters – risk of oligohydramnios, premature closure of the ductus arteriosus and increased childhood leukemia risk. Use in the second trimester only on strict indication and absence of alternatives. The Russian label lists pregnancy as a contraindication.
Transfers into breast milk. Breastfeeding is interrupted for at least 48 hours after the last dose.
Metamizole sodium is contraindicated in: Hypersensitivity to pyrazolones, history of NSAID-induced asthma, urticaria or angioedema; History of agranulocytosis or neutropenia on metamizole; Acute intermittent porphyria; Glucose-6-phosphate dehydrogenase deficiency; Pregnancy (especially first and third trimesters). Full list in the Safety section.
No FDA boxed warning applies in the US (the drug was withdrawn in 1977). Russian labels explicitly highlight agranulocytosis risk, the need to stop the drug on fever or sore throat, and mandatory CBC monitoring for courses over 7 days.
withdrawn from US, UK, Swedish and Japanese markets due to agranulocytosis risk. Continued availability in Russia is a historical legacy, not safety confirmation.
daily use increases analgesic nephropathy and agranulocytosis risk. Chronic use is not appropriate.
international pediatric guidelines recommend paracetamol or ibuprofen; pediatric metamizole is used only in hospital and on strict indication.