There's NY GI DR who developed daily supplement to relieve constip. I ordered online & there was immediate help. Name is VISCERA so you can google for more info. Seems oriental mint is key. Good news did not create diarrhea when I ingested one.
Hope this is helpful to hubby! Swig46

I had a similar experience during my 4 recent cycles of chemo, particularly during the first week of each cycle. I was prescribed Movacol by my oncology team and that made all the difference, gentle rather than harsh, but still uncomfortable at times. Since ending chemo, no further constipation thankfully.

I was getting scared not being able to pass stool. I was told to take miralax at least twice a day. I take three doses a day and doing well. You can take more if you need to. The miralax draws liquid to the bowels and makes for much needed fluid to soften stools. Three doses makes it very soft and easy to pass. You will have to try and find what dose works for you.