THURSDAY, April 30 (HealthDay News) -- The risk of developing leukemia from a drug used to treat rapidly-progressing multiple sclerosis is three times higher than previously reported, new research shows.
Italian researchers found that for every 1,000 people given mitoxantrone (Novantrone), an estimated 7.4 people will develop acute leukemia, compared with fewer than 2.5 people in prior estimates. Mitoxantrone is an immunosuppressant approved by the U.S. Food and Drug Administration for treatment of secondary progressive MS.
In the study, about 0.74 percent of people taking the drug developed leukemia. Previous research had put the risk of leukemia at .07 to .25 percent.
This rate is significantly higher than what has been previously reported, said study author Dr. Vittorio Martinelli of University Vita-Salute in Milan.
The potential risk of leukemia should be carefully considered against the potential benefits of mitoxantrone treatment on every single patient, Martinelli urged in a summary of his research, which is to be presented Thursday at the American Academy of Neurology's annual meeting, in Seattle.
Mitoxantrone is one of the only drugs that has been shown to benefit people with a secondary progressive MS who are having attacks of symptoms that include numbness, loss of balance, difficulty walking, fatigue, vision problems and impaired thinking.
In Martinelli's study of 2,854 people with multiple sclerosis, 21 have developed acute leukemia, and eight have died.
About 85 percent of people diagnosed with MS begin with a relapsing-remitting course, in which attacks are followed by partial or total recovery, according to the National Multiple Sclerosis Society.
More than 60 of those go on to develop secondary progressive MS, in which symptoms worsen over time, and there are fewer, shorter periods without symptoms. Eventually the disease can lead to loss of vision and paralysis.
Because research has shown that the drug can cause heart failure at high cumulative dosages as well as acute leukemia, doctors exercise caution when giving it to patients, said Patricia O'Looney, vice president of biomedical research for the National Multiple Sclerosis Society.
But the difficulty, she said, is that there are few other options for people with secondary progressive MS, and quality of life has to be balanced with risk of heart damage and leukemia.
"That's the frustrating part," O'Looney said. "When someone is reaching a very progressive form of the disease, and other drugs aren't working, we desperately need something in the clinical care of patients to try to help them. But there's no question about it. Novantrone is a strong drug, and with strong drugs, there are side effects."
Mitoxantrone is given in an IV infusion, usually in doses of 10 to 20 milligrams spaced about thee months apart.
Current U.S. guidelines call for people to receive a total lifetime dose of no more than 140 mg, O'Looney said.
People in the Italian study had received substantially less. Those who developed leukemia were given an average of 82 mg, compared with 63 mg for those who did not develop leukemia.
The leukemia occurred an average of three years after the first use of the drug and an average of 18 months after treatment had ended, according to the study.
"It is vital that all MS patients treated with mitoxantrone undergo prolonged and careful hematological follow-up to check for acute leukemia," Martinelli said.