ModerateAntiplatelet agents (low dose) / NSAIDs (analgesic dose)×Analgesics and antipyretics. Pyrazolones
Updated · Methodology
Mechanism
The metamizole label states it literally: it can reduce the antiplatelet effect of acetylsalicylic acid when given concomitantly, so caution is needed in patients on low-dose aspirin for cardioprotection. The mechanism mirrors the one described for ibuprofen, competition for access to platelet cyclooxygenase, and it hits the very indication that tolerates no loss of efficacy.
Symptoms
Loss of antiplatelet effect gives no warning symptom. What shows up is the event the aspirin was meant to prevent, and only in patients with coronary disease or previous stroke. Metamizole keeps its own haematological warning signs.
Management
For a patient on 100 mg aspirin for cardioprotection, paracetamol is the analgesic of choice, as it does not compete for platelet cyclooxygenase. If metamizole is necessary, use short courses and avoid giving it right before the aspirin dose.
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Sources
- AEMPS: Ficha técnica Metamizol Cinfa 575 mg cápsulas duras EFG (2024)– AEMPS, CIMA, nº registro 68116, sección 4.5
- AEMPS: Ficha técnica Ácido acetilsalicílico Cinfa 100 mg comprimidos gastrorresistentes EFG (2024)– AEMPS, CIMA, nº registro 74266, sección 4.5