Is nifedipine a weak base or weak acid? I was wondering whether someone could explain me if nifedipine is a weak base or a weak acid. 
I barely can find any information about nifedipine's physicochemical properties in studies, however some suggested that it is a weak acid. If it is a weak acid, which hydrogen atom is dissociable and what would the pKa of that group be?

Thanks in advanced.

Nifedipine's structure, as shown on wikipedia:
Nifedipine is a weak acid.


$pK_b = 10.07$
$pK_a = 3.93$
$pK_a = 4.3$