Unlike bisphosphonates, or medications like Boniva, Actonel, or Fosamax, which kill the cells that degrade bone to slow bone loss, Forteo stimulates the cells that build bone to make bones larger and harder. This allows Forteo to increase bone mineral density in the spine to a much greater degree in a shorter period of time than bisphosphonates, while reducing the risk of fracture comparably. Researchers agree that bisphosphonates are adequate therapy for patients that suffer from mild to moderate osteoporosis. Once a patient suffers an osteoporotic fracture, cannot tolerate bisphosphonate therapy, or is found to have a very low T-score, Forteo becomes the drug of choice because the patient is at high risk for fracture. Even patients that have been on bisphosphonates previously can reap benefits from Forteo, but the effects may not be seen as quickly as in patients that have never taken medication for osteoporosis.
When Forteo was approved in November 2002, the FDA mandated that it carry a black-box warning because it was associated with an increased risk of osteosarcoma, or bone cancer, in rats. The particular strain of rats that were used in the studies are highly sensitive to developing cancer. Paired with the fact that the rats were exposed to more than twice the human dose for their entire lifespan indicates that developing osteosarcoma depends on the dose given and the duration of therapy. Given the limited dose of Forteo as well as length of administration (two years only), it is generally understood that this would significantly limit a patient’s risk of developing osteosarcoma. Eli Lilly, the maker of Forteo, has also given physicians guidelines to identify patients that are at increased risk of developing osteosarcoma so that they are excluded as potential drug candidates. These patients include those that have had radiation to the bones, children, and those with Paget’s disease.
It is also important to note that the background rate of osteosarcoma in the general adult population is four per one million individuals. By summer 2006, over 250,000 prescriptions of Forteo had been written in the US. Based on the background rate of osteosarcoma, Eli Lilly anticipated a case being reported in a patient that had been treated with Forteo. In July 2006, the first human case of osteosarcoma was in fact reported in a patient that had been treated with Forteo. The only information the company can disclose is that the patient was female, postmenopausal, in her second year of treatment with Forteo, and suffered from other comorbid conditions besides severe osteoporosis. Unfortunately, the patient is deceased and it is still not known whether the patient died from osteosarcoma or her other comorbid conditions.