Cough is produced by the same neuronal pool implicated in respiratory rhythm generation and antitussive drugs acting at the central level, such as the opioids, may depress ventilation. Levodropropizine is classified as a non-opioid, peripherally-acting antitussive drug acting at the level of airway sensory nerves. However, the lack of a central action by Levodropropizine remains to be fully established. We set out to compare the effects of Levodropropizine and the opioid antitussive agent Dihydrocodeine on the respiratory responses to a conventional CO2 re-breathing test in patients with chronic cough of any origin.
Twenty-four outpatients (aged 39-70 years) with chronic cough were studied. On separate runs, each patient was randomly administered 60 mg Levodropropizine, or 15 mg Dihydrocodeine or matching placebo. Subsequently, patients breathed, for 5 min, a mixture of 93% oxygen and 7% CO2. Fractional end-tidal CO2 (FETCO2) and inspiratory minute ventilation (VI) were continuously monitored. Changes in breathing pattern variables were also assessed.
At variance with Dihydrocodeine, Levodropropizine and placebo did not affect respiratory responses to hypercapnia (P<0.01). The ventilatory increases by hypercapnia were mainly accounted for by a rise in the volume components of the breathing pattern.
The results are consistent with a peripheral action by Levodropropizine; the assessment of ventilatory responses to CO2 may represent a useful tool to investigate the central respiratory effects of antitussives.