I have read the Known substance-interactions and their effects page as it stated MAOI and Corticosteroids are a bad idea but does this pertain to Nasal Corticosteroid sprays also?

The average half life of standard corticosteroids are somewhere between 10-50 hours while the half life for a corticosteroid nasal spray such as mematasone furoate is 5.8 hours and other sprays being 3 hours or even less.

Given the relatively short half life of the sprays compared to standard corticosteroids how much time should one give between taking the two substances?

For anyone wondering why it is harmful, Harmala alkaloids inhibit CYP3a4 which has a role in metabolising prednisone, so the combination can magnify the effects of the steroid including adverse effects on glucose tolerance and lipid profiles.

Anyone?

Mometasone furoate via nasal spray is a low dose (typically 100-400mcg/day, usually around 200mcg in adults) and systemic absorption is low which makes it less likely to cause problematic interactions. Using mometasone as a cream, especially over large areas of the body (for example in inflammatory skin conditions like eczema) is potentially more problematic as this results in greater degrees of absorption, requiring metabolism by CYP3A4. This also depends on how long the cream is used for.