Some attention should also be given to the
osmotic effects of a topical application. Although
marked deviation from isotonicity has an irritant
effect, the intact horny layer is relatively tolerant
to osmotic changes. However, some customers can
be less tolerant and a broken surface is also susceptible.
In these circumstances, SLN and NLC
show suitable isotonicity with the appropriate
body fluids. Although the need for an isotonic
preparation has no profound therapeutic implications,
a markedly hypertonic preparation causes
an unpleasant sting and tends to discourage the
customer for its use.
Formulation aspects