[Difference in the effects of antitussive drugs on respiration and cough reflex]

In order to understand the relationship between the cough and respiratory centers in the brain stem, we investigated the effects of antitussive drugs such as codeine, dextromethorphan, eptazocine and fominoben on respiratory movement and the cough reflex. Coughs were induced using electrical stimulation of the central cut end of the right superior laryngeal nerve in lightly anesthetized dogs. The drugs were administered intraarterially into the vertebral artery. Rate (RR), amplitude (RA) and volume (RV) of the respiration and number (NC) and amplitude (AC) of the cough reflex evoked were measured as indices. Codeine produced a decrease in RR, RV and NC at 0.3 mg and, additionally, AC at 1 mg. Dextromethorphan increased RR and RV and rather enhanced NC and AC at 0.3 mg, but the agent reduced NC and AC at 3 mg even if it increased RR and RV. Eptazocine produced decreases in RA, NC and AC at 1 mg, and, additionally, RV at 10 mg. Fominoben increased RR, RA and RV dose-dependently at 0.3-3 mg, although it depressed NC and AC at 3 mg. These findings suggest that the thresholds for the cough responses and respiratory responses to antitussive drugs are different from drug to drug and that the respiratory centers and cough center in the brain stem are affected in a different manner even qualitatively.