Dextromethorphan was significantly associated with an increase in the concentration of citric acid eliciting an average of two coughs/inhalation ( C2 ) when compared with placebo , 1 h post dose by 0.49 mM ( 95 % CI 0.05 , 0.45 , geometric mean 3.09 ) compared with placebo 0.24 mM ( geometric mean 1.74 ) P < 0.05 and at 2 h 0.57 mM ( 95 % CI 0.01 , 0.43 , geometric mean 3.75 ) compared with placebo 0.34 mM ( geometric mean 2.19 ) P < 0.05 ) .
