What Causes Swelling In The Penis While On Linzess For Constipation?

My husband -- age 72 --- has been taking Linzess for four days for constipation. The first two days, he took one capsule (145 mg) each night. It had no affect. The next two nights, he increased the dosage to two capsules (2 x145 mg.) (His gastroenterologist told him he could increase it if it didn t work.) Linzess worked well for him, using 290 mg. But this morning, literally overnight, his penis is swollen is swollen. Is this a side effect of Linzess. He says it itches a little bit. No trouble urinating, he says, but not as much stream. He says it developed during the night. But could Linzess cause the swelling? Thank you. Submitted by his spouse.##