Role of the appendageal pathway in the percutaneous absorption of pyridostigmine bromide in various vehicles.

We studied the percutaneous absorption of [14C]-labelled pyridostigmine bromide mixed into various vehicles through normal and appendage-free scar rat skin, in vitro during 72 h. At the end of the experiment, the percentages of the drug absorbed were higher for nerol 8% in ethanol (respectively 78.4 +/- 3.6% and 72.8 +/- 4.5% on normal and scar skin) and azone 5% in ethanol-propylene glycol (90:10) (respectively 76.4 +/- 4.4% and 57.2 +/- 7.1% on normal and scar skin). Propylene glycol 10% in ethanol inhibits pyridostigmine absorption: 9.9 +/- 2.6% and 2.2 +/- 1.2% vs 14.7 +/- 3.8% and 5.5 +/- 5.1% with ethanol on control and scar skin. The transappendageal pathway seems to be less important for nerol (55% to 82% of the absorption routes between 4 h and 32 h) and azone (60% to 79% of the absorption routes until 32 h) than for propylene glycol (63% to 96% of the absorption pathways during the whole experiment), dimethylsulfoxide (about 78% during the first 32 h) and ethanol (more than 50% during most of the time). These results show that it is possible to increase or decrease the percutaneous absorption, as well as to modulate the relative importance of the transepidermal route and the transfollicular pathway.