Which osteoporosis therapy is so poorly absorbed that it must be taken alone on an empty stomach?

• A. Raloxifene (Evista)
• B. Alendronate (Fosamax)
• C. Calcitonin (Miacalcin)
• D. Teriparatide (Forteo)

Answer: (B)

Extremely poor oral bioavailability is the key idea here. Alendronate, a bisphosphonate used for osteoporosis, is hardly absorbed from the gut—only a tiny fraction makes it into the bloodstream. Because of that, it must be taken with a full glass of water first thing in the morning on an empty stomach, at least about 30 minutes before any food or other meds, and you should stay upright during that time to reduce esophageal irritation. Calcium, antacids, or other minerals can bind the drug and dramatically cut absorption, so they’re avoided around dosing. The other therapies don’t require this same fasting approach: raloxifene is absorbed more predictably and isn’t driven by empty-stomach timing, calcitonin can be given intranasally or by injection with different dosing considerations, and teriparatide is a subcutaneous injection whose absorption isn’t dictated by fasting.