Short answer: Forteo (teriparatide) is a 20 mcg injection under the skin once a day; Reclast (zoledronic acid) is a 5 mg infusion into a vein, once a year for most uses.12 Forteo is a parathyroid hormone analog; Reclast is a bisphosphonate. Neither has a boxed warning, and neither label reports a trial of one against the other.
| Forteo | Reclast | |
|---|---|---|
| Drug type | Parathyroid hormone analog (PTH 1-34)1 | Bisphosphonate2 |
| Approved for | Postmenopausal women, men and steroid-induced osteoporosis, each at high fracture risk or after other treatments failed1 | Treat and prevent postmenopausal osteoporosis; men; steroid-induced osteoporosis; Paget's disease2 |
| How given | 20 mcg under the skin of the thigh or abdomen, self-injected1 | 5 mg into a vein over at least 15 minutes, by a nurse or doctor2 |
| How often | Once a day1 | Once a year; every 2 years for prevention; once for Paget's disease2 |
| How long | Over 2 years in a lifetime only if fracture risk stays or becomes high1 | Best length not set; stopping may be considered after 3 to 5 years at low risk2 |
| Kidney | Not studied with active kidney stones1 | Not used with creatinine clearance under 35 mL/min2 |
| Side effects in label trials | Pain 21.3% vs 20.5% on placebo; joint pain 10.1% vs 8.4%; dizziness 8.0% vs 5.4%1 | Fever 17.9% vs 4.6% on placebo; headache 12.4% vs 8.1%; muscle pain 11.7% vs 3.7%2 |
| Missed dose | No rule; no more than 1 injection a day1 | Call your provider to schedule the next dose2 |
| Boxed warning | None1 | None2 |
Forteo's warnings include osteosarcoma, seen in rats and reported rarely in people; it is avoided in people at higher bone cancer risk, such as those with Paget's disease or past radiation to the skeleton. It can briefly raise blood calcium and cause dizziness on standing, so the first doses are given where you can sit or lie down.1 Reclast's warnings include acute kidney failure, low calcium, jaw bone death, unusual thigh fractures and severe bone, joint or muscle pain; a flu-like reaction in the first 3 days after the infusion is common.2
Forteo's label compares it with a daily oral bisphosphonate in steroid-induced osteoporosis, and Reclast's compares it with a weekly oral bisphosphonate in men; neither comparator is the other drug.12 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: Forteo side effects, Reclast side effects, the Forteo and Reclast dosing schedules, the Forteo and Reclast missed-dose pages, the teriparatide and zoledronic acid guides, and Forteo vs Tymlos: how do teriparatide and abaloparatide compare?.