Which medication is most likely to have contributed to the decrease in bone density?

• A. Diphenoxylate
• B. Sulfasalazine
• C. Prednisone
• D. Propantheline

Answer: (C)

Prednisone is a classic cause of secondary osteoporosis. Chronic or high-dose glucocorticoid use disrupts bone remodeling in several ways that tip the balance toward bone loss.

First, prednisone directly suppresses bone formation by inhibiting osteoblast activity and promoting osteoblast and osteocyte death, reducing the capacity to lay down new bone. It also increases bone resorption by enhancing the activity of osteoclasts, in part through changes in RANKL signaling and decreased osteoprotegerin. Additionally, glucocorticoids reduce calcium absorption from the gut and increase calcium excretion in the urine, which lowers the available calcium for bone mineralization. Over time, these effects produce a net decrease in bone density and a higher risk of fractures, especially in weight-bearing and vertebral sites.

The other medications listed do not have the same direct, well-established impact on bone metabolism: one is an anti-diarrheal, another a drug for inflammatory bowel disease, and the last an anticholinergic—none are typically associated with causing decreased bone density in the way prednisone is.