A study aimed at clarifying the mechanism of action of metamizole suggested that the clinically proven effect of this analgesic on colicky pain originating from the biliary tract could be due to agonism on β2-adrenergic receptors in the smooth muscle of the bile ducts.
Metamizole belongs to the group of non-opioid analgesics. It has clinically documented analgesic, antipyretic, and spasmolytic effects. However, the precise mechanism of its action is not fully clarified. The authors of a recently published study thoroughly summarized the pharmacological effects of metamizole on gastrointestinal motility, spasms, and the gastric mucosa, using studies published up to the end of 2017.
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The primary analgesic mechanism of action of non-opioid analgesics with antipyretic effects and weak anti-inflammatory action, such as metamizole, is likely the inhibition of cyclooxygenase 3 (COX-3). However, various neurotransmitter systems such as cannabinoid, vanilloid, serotonergic, and adrenergic are probably also involved. Metamizole is a prodrug that acts through its main metabolites – 4-methylaminoantipyrine and 4-aminoantipyrine.
According to experimental studies in rats, intravenous application of metamizole slows down the emptying of liquid stomach contents with the involvement of capsaicin-sensitive afferent nerves. This effect is likely due to the activation of β1 - or β2-adrenergic receptors via the sympathetic nervous system. Unlike many nonsteroidal anti-inflammatory drugs, metamizole does not lead to gastric mucosal damage and does not increase the risk of gastric ulcers.
Clinically, the efficacy of metamizole has been proven for colicky abdominal pain originating from the biliary and intestinal tracts. Studies in humans have demonstrated the presence of β2-receptors in the smooth muscle of the bile duct walls. Given the involvement of these receptors in the effect of metamizole on the slowing of gastric emptying, it is likely that this type of receptor also plays a role in its spasmolytic effect on the sphincter of Oddi. Conversely, there is no evidence that metamizole affects the motility of the small and large intestines. Therefore, its clinically proven effect in intestinal colic is likely due to its analgesic action.
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Source: Collares E. F., Troncon L. E. A. Effects of dipyrone on the digestive tract. Braz J Med Biol Res 2019; 52(2): e8103, doi: 10.1590/1414-431X20188103.
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