Metamizol Sf (Metamizole Sodium Monohydrate)

Metamizole sodium is indicated for conditions where rapid analgesic, antipyretic, or antispasmodic control is required.

• Pain: provides rapid relief of moderate to severe acute pain, including postoperative and trauma‑related pain.
• Fever: reduces high fever when other antipyretics are insufficient or contraindicated.
• Spasm: alleviates smooth‑muscle spasm associated with gastrointestinal or biliary colic.

• Metamizole sodium acts by non‑selectively inhibiting cyclooxygenase enzymes, which decreases the synthesis of prostaglandins involved in pain, fever, and inflammation. The reduction of prostaglandin E2 and other mediators leads to diminished peripheral nociceptor sensitisation and central fever regulation, while additional effects on calcium channels contribute to its antispasmodic activity.

Metamizole sodium may be associated with a range of adverse reactions, varying from mild to potentially life‑threatening.

Common Side Effects

• Nausea: mild to moderate nausea reported after injection.
• Vomiting: occasional episodes of vomiting.
• Dizziness: transient light‑headedness or vertigo.
• Hypotension: transient drop in blood pressure, especially with rapid IV administration.
• Rash: mild skin erythema or urticaria.

Serious or Rare Side Effects

• Agranulocytosis: severe reduction in neutrophil count, potentially fatal if not detected.
• Anaphylaxis: rare severe allergic reaction with respiratory compromise.
• Severe hypotension: profound blood pressure fall requiring intervention.
• Hepatotoxicity: rare liver enzyme elevations.
• Stevens‑Johnson syndrome: extremely rare severe skin reaction.

When prescribing Metamizole sodium, clinicians should consider several safety measures to minimise risk.

• Monitor blood counts: regular complete blood count monitoring is advised to detect agranulocytosis early.
• Use caution in renal impairment: adjust dosing or monitor renal function in patients with reduced kidney function.
• Avoid rapid IV bolus: administer intravenously over several minutes to reduce hypotension risk.
• Contraindicated in known hypersensitivity: do not use in patients with previous allergic reactions to pyrazolones.
• Caution in patients with cardiovascular disease: monitor blood pressure due to possible hypotensive effects.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Metamizole sodium can interact with other medicines, altering efficacy or safety.

Major Interactions (Avoid)

• Myelosuppressive agents: concurrent use may increase risk of severe neutropenia or agranulocytosis.
• Other pyrazolones or NSAIDs: additive risk of blood dyscrasias and gastrointestinal irritation.
• ACE inhibitors: may potentiate hypotensive effects when combined with rapid IV administration.

Moderate Interactions (Monitor Closely)

• Anticoagulants (e.g., warfarin): may enhance anticoagulant effect, requiring INR monitoring.
• Diuretics: potential for enhanced hypotension, monitor blood pressure.
• Antihypertensives: may require dose adjustment due to additive blood pressure lowering.
• Lithium: possible increase in lithium levels, monitor serum concentrations.