Ive been taking miralax twice a day for the past 10 years but would like to wean since im prone to low serum sodium . when i cut back even a bit, i have no bm despite fiber and fluids. could i switch to citrucel in am and miralax in evening?

You can try but I do not see the difference in the overall adverse effects because both laxatives are of the same category, i.e. osmotic laxative. I am not sure how low you sodium is but it could be due to high free water intake which you have been used to for combating constipation. If you cut down free water intake 10-20% sodium level will be up and I hope it won't worsen the constipation.

You may have more success with a simple wean if you increase your pattern of voluntary emptying. The large bowel just removes moisture from feces, MiraLAX binds water preventing removal, keeping stool soft. If you move stuff along quicker any ballooning of the large bowel can shrink and less drying will occur. I am leery of adding another medication when simple measures may do the trick.