Nystatin is one of those drugs that doesn't get out of the intestine so in my understanding if you have candida in other parts of the body (likely with leaky gut) it may not help systemic candida. In this article I recently found it says that Natamycin is also a kind of drug that stays in the intestine but that Candida is not known to be resistant to it.
Pimafutsin (drug brand) has a higher efficiency compared with nystatin. No cases of resistance to natamycin in clinical practice are not met, with the repeated application of this drug minimum inhibitory concentration against C.albicans it does not change. Pimafutsin tablets is effective only in the lumen of the intestine, is practically not absorbed from the gastrointestinal tract.