Figure 6: Baso-apical concentration gradient for different species
Since the longitudinal distribution of substances is determined essentially by diffusion and clearance, the concentration gradients depend on the length of the diffusion pathway, i.e. the length of the cochlear scalae. It can therefore be assumed that concentration gradients in larger cochlea are more extreme. This fact must be considered if the results from animal experiments involving different species are to be applied to the human situation. It is entirely conceivable that a substance applied to the round window membrane of the murine inner ear experiences no problems in gaining access to the apicocochlear area, while with the same application protocol in man effective medication levels may only be found in the basocochlear region.