There is always a risk for side effects,interactions or allergic reactions, so please make sure both meds are suitable for you by asking a physician.
As fas as I know, nexium (esomeprazole) only interferes with biaxin (clarithromycin). It heightens the amount of esomeprazole by inhibiting the degradation of esomeprazole. Macrobid is nitrofurantoin, not clarithromycin. You may also look here: http://www.ehealthme.com/drug_interactions_side_effects/Nexium-2792078.
Went to drug.com and it stated:
No results found - however, this does not necessarily mean no interactions exist. ALWAYS consult with your doctor or pharmacist.