Which medication is likely responsible for Mr. Rylan's constipation?

Vincristine is known to cause constipation as a common side effect. This medication, which is part of the class of drugs known as vinca alkaloids, works by disrupting the process of cell division, specifically targeting rapidly dividing cancer cells. However, this mechanism can also affect the gastrointestinal (GI) tract and lead to decreased bowel motility.

Constipation from vincristine can occur due to its impact on the autonomic nervous system, which controls the intestines. The drug can cause paralysis of the bowel, leading to decreased peristalsis (the contractions that move contents through the intestines) and resulting in constipation. Healthcare providers often monitor patients receiving vincristine closely for this side effect and may recommend preventative measures or treatments to manage constipation.

While other medications listed may have side effects, they are not as classically linked to constipation as vincristine. Cyclophosphamide, dexamethasone, and rituximab have their own side effects but do not typically cause constipation as a prominent issue, making vincristine the most likely culprit in this scenario.