Ciliotoxicity of intranasal formulations: Menthol enantiomers

It is shown, using in vitro measurements of beat frequency of rat tracheal cilia, that (+)‐(1S, 2R, 5S)‐menthol and (−)−(1R, 2S, 5R)−menthol have equipotent ciliotoxicities despite the fact that inhalation of menthol vapours from the crystals of the pure enantiomers show clearly that the (−)−(1R, 2S, 5R)‐menthol produces a more potent cooling sensation. Differential scanning calorimetry demonstrates the formation of a racemic compound when equimolar amounts of the two enantiomers are admixed. © 1993 Wiley‐Liss, Inc.