Niacinamide for cystic acne

I have cystic acne and I have tried everything for it. I have niacinamide deficiency and have a condition called pellegra due to it. But I'm not currently taking any medicine for it. I was thinking of taking niacinamide supplements as it is also good for acne . Is there any specific dosage or anything I have to consider while taking it? Any other suggestions for healing cystic acne and Whiteheads will also help a lot <3