Background: Dipyrone is an analgesic and antipyretic agent with a distinctive spasmolytic effect on smooth muscles. We recently showed that dipyrone significantly relaxed precontracted tracheal smooth muscle in guinea pig.

Objective: To investigate whether this in vitro observation could be observed in vivo in the respiratory function parameters of asthma patients.

Method: Twenty-two patients, aged 18 to 75 years and diagnosed with asthma according to the American Thoracic Society criteria were enrolled at the time they had any indication for dipyrone use. Pulmonary function tests were performed before and 30, 60, 90, and 120 minutes after oral intake of 1 g of dipyrone. The tests were repeated without dipyrone intake in a situation of spontaneous recovery after a minimum washout period of 2 days.

Results: Patients were classifi ed according to their baseline forced expiratory volume in 1 second (FEV1) as having mild obstruction (FEV1 ≥ 80% predicted) or moderate obstruction (FEV1 60%-80% predicted). Signifi cant improvement with dipyrone was seen in FEV1 and peak expiratory fl ow rates at 25%, 50% and 75% of forced vital capacity and in maximum midexpiratory fl ow rate only in patients with moderate asthma. No significant change was observed on the spontaneous recovery day except in FEV1.

Conclusion: Dipyrone had a significant effect leading to an improved small airway function in asthmatic patients with moderate airway obstruction, confirming our recent in vitro findings.

Key Words: Asthma. Bronchodilation. Dipyrone (Metamizole sodium). Spirometry.