Short answer: Both are bisphosphonates for osteoporosis and Paget's disease of bone.12 Reclast (zoledronic acid) is a 5 mg infusion into a vein, once a year for treatment or every 2 years for prevention. Fosamax (alendronate) is a 70 mg tablet once a week, taken with plain water on rising and staying upright for 30 minutes. Neither has a boxed warning or reports a trial against the other.
| Reclast | Fosamax | |
|---|---|---|
| Drug | Zoledronic acid1 | Alendronate2 |
| Approved for | Treating and preventing postmenopausal osteoporosis, bone mass in men, treating and preventing steroid-induced osteoporosis, Paget's disease1 | Treating and preventing postmenopausal osteoporosis, bone mass in men, treating steroid-induced osteoporosis, Paget's disease2 |
| How given | 5 mg infusion into a vein over at least 15 minutes, by a nurse or doctor1 | Tablet on rising with 6 to 8 ounces of plain water, at least 30 minutes before food, drink or other medicine, then upright for 30 minutes2 |
| Osteoporosis treatment | Once a year1 | 70 mg once weekly or 10 mg once daily2 |
| Osteoporosis prevention | Once every 2 years1 | 35 mg once weekly or 5 mg once daily2 |
| Kidney limits | Not given with creatinine clearance under 35 mL/min or acute kidney impairment1 | Not recommended with creatinine clearance under 35 mL/min2 |
| Side effects in label trials | Postmenopausal women over 3 years: fever 17.9% vs 4.6% on placebo, muscle pain 11.7% vs 3.7%, mostly within 3 days of the infusion1 | 3-year trials: abdominal pain 6.6% on 10 mg daily vs 4.8% on placebo; with 70 mg weekly, abdominal pain 3.7%2 |
| Boxed warning | None1 | None2 |
Both labels warn about low blood calcium, corrected before starting, jaw bone death (osteonecrosis), unusual thigh bone fractures and severe bone, joint or muscle pain. Both say the best length of use has not been set and that people at low fracture risk may be considered for stopping after 3 to 5 years.12 Reclast adds acute kidney failure, even after one dose, so people are well hydrated and kidney function is checked before each dose; flu-like symptoms in the first days after the infusion; and a note that people on Zometa, the same drug, are not given Reclast.1 Fosamax adds irritation of the esophagus and stomach, and is not for people who cannot sit or stand upright for 30 minutes or who have certain esophagus problems.2 These numbers come from separate trials with different people, lengths and methods, so they are not a head-to-head comparison.
Which, if either, fits is for your prescriber. More detail: Reclast side effects, Fosamax side effects, the Reclast and Fosamax dosing schedules, the Fosamax missed-dose page, and Reclast vs Prolia: how do the yearly infusion and the 6-month shot differ?.