Many medications are intended only for the brain, but are taken orally. Hence <10% finds its intended target, while the remaining >90% is at best wasted, and at worst causes unwanted side-effects.
Valproate is a classic example; it is medicated as an antiepileptic, but only a small fraction crosses the brain blood barrier to make it into the brain. Because of this, a large dose is required, and unwanted side-effects are common.
However, certain (small molecule?) drugs (e.g. Ibuprofen) can be applied transdermally.
For a drug intended for brain tissue that allows transdermal application, is there any sense in applying on the (preferably shaved) scalp?
Is this a known mechanism of administration? If so, does it have a name?
Is there any way of correctly scaling the dosage? For example, if experiment shows that 50% of substance X taken transdermally reaches the bloodstream, if it is administered to the scalp is there any way of figuring out how much ends up in the brain and how much ends up in the rest of the body? Since this is a tricky and obscure question, may I also ask this: how to go about finding an answer to this? Where else can I ask?