Azelaic acid is not water-soluble, so you can only find it in creams or gels.
There's a kinda new AA derivative (potassium azeloyl diglycinate) that is water-soluble and conveys many of the same benefits as 'normal' azelaic acid.
There have been some studies that show AA works (PAD has only been tested on skin), but all in cases with alopecia areata or totalis which both are autoimmune diseases and require a different sort of treatment than male pattern baldness. AA works very well against facial redness/inflammation caused by acne or rosacea, so that's probably why it helps those with inflammation due to autoimmune diseases as well. Male pattern baldness is just caused by a hair susceptibility to DHT. Yes, AA is a potent 5a-r inhibitor, but topicals don't get much in your blood system at all to have a noticeable impact on DHT. Just take finasteride (and add topical minoxidil), or just don't bother.
Or better use AA on your skin. You may go bald, but at least you'll have bright skin.