I've taken this from an interview with Brotzu, and I've added my 2 cents to it as a Med student.
Minoxidil works by stimulating pericytes to secrete vasodilating stimuli. Pericytes are special types of cells which are found along blood vessels.
PGE1 (and by extension, DGLA) acts directly on endothelial cells as well as pericytes (which are the inner lining of blood vessels) and promotes vasodilation on a cell to cell basis. This could be a more direct and potent method of stimulating vasodilation in microvasculature of the scalp which is great. It would result in increased scalp blood flow, and sustain hair follicles.
So it terms of using minoxidil - my broscience is that it would be fine to keep taking it. If the Brotzu lotion is released and if it works as it is reported too, then it would be a replacement for minoxidil. It would function physiologically in the same way to dilate blood vessels, but do it in a more potent way - therefore improving upon any affects you had from using minoxidil previously.
The link explaining the physiological background to this:
http://bellicapelliforum.com/en/interview/exclusive-interview-with-dr-brotzu-for-bellicapelli/