Metamizole and paracetamol — similar but not the same drugs

Abstract

Both metamizole and paracetamol (acetaminophen) are popular non-opioid analgesics and antipyretic drugs. The mechanism of action of paracetamol and metamizol is complex and has been under debate for long time. The most probably mechanism responsible for the analgesic effect of metamizole is achieved through both action of COX-1/-2 and the impact on the opioidergic and cannabinoid system. Beside the analgesic and antipyretic effect, it produces also a significant spasmolytic effect. The results of recent studies reveal that paracetamol is a preferential inhibitor of COX-2 isoenzyme, however, its effect depends to a great extent on the state of environmental oxidation/reduction. The analgesic effect of paracetamol is also due to the activation of canabinoid CB1 receptors and the 5-HT3 subtype of serotonin receptors.

Metamizole is predominantly applied in the therapy of acute pain, especially visceral pain, and of fever refractory to other treatments. Metamizole is a relatively safe drug. It seems that in the past the risk of metamizole-induced agranulocytosis was overdrew. Metamizole is contraindicated in pregnancy and breastfeeding women. Paracetamol overdose can lead to acute hepatic and renal failure. Paracetamol monotherapy, on condition that the drug is administered at therapeutic doses, is well tolerated by the majority of patients. On another hand, according to the previous study, a long-term application of paracetamol may increase the risk of adverse reactions typical for COX-2 inhibitors such as hypertension, heart infarction or renal failure. However, up to now paracetamol remains still the drug of choice for treating minor to moderate pain in pregnant women and in patients with coagulation, renal or cardiovascular disorders.