Leukemia patients now have more options

When imatinib (Gleevec, Novartis) became available several years ago, it brought new hope for people with chronic myeloid leukemia (CML).

In clinical studies, dasatinib and nilotinib were effective in patients who had already tried imatinib. According to the National Cancer Institute, drug efficacy in CML is usually measured by hematologic or cytogenetic response, or both. A hematologic response is a reduction or elimination of abnormal white blood cells. A cytogenetic response is a reduction or elimination of the Philadelphia (Ph) chromosome of stem cells in the bone marrow.

Whether the two newer drugs will eventually be approved as primary therapy for CML is hard to say. Some clinicians are now using dasatinib as initial treatment, said Susannah Koontz, Pharm.D., a clinical practice specialist in pediatric hematology/oncology at the M. D. Anderson Cancer Center in Houston. Nilotinib is still too new for data on the drug as primary treatment to be in yet. In five years, things could change if evidence supports the newer drugs as initial therapy for CML, especially if resistance to imatinib increases. Under such circumstances, said Koontz, "Sometimes a newer drug will overtake an older one."

Adverse reactions

Adverse reactions with nilotinib were usually relatively mild (e.g., rash, itching, headache, nausea, vomiting, fatigue, and constipation). More serious reactions included thrombocytopenia and neutropenia. Nilotinib can also prolong the QT interval, which is a potentially life-threatening effect. Prolonged QT can trigger torsades de pointes, an arrhythmia that may then progress to atrial fibrillation and, potentially, to sudden death. Sudden deaths have occurred in patients taking nilotinib.

On the positive side, some of the more common adverse reactions to imatinib and dasatinib were rarely observed with nilotinib in clinical studies. Edema in legs, ankles, and feet and fluid in the lungs have been associated with both imatinib and dasatinib, but rarely with nilotinib. The cramps and weight gain often seen with imatinib were also uncommon with nilotinib. It should be noted that dasatinib also may prolong QT and has warnings to this effect in the prescribing information. Imatinib does not.

Although some adverse effects of nilotinib, imatinib, and dasatinib can be serious, most of them can be prevented or corrected through dose adjustments and proper monitoring. Experts believe it is remarkable that two effective and fairly well-tolerated drugs-imatinib and dasatinib-have become available for CML. With the recent approval of nilotinib, the arsenal for treating CML patients is even better. Nilotinib "represents an important advance for the small number of patients resistant or intolerant to prior therapy," said David Epstein, president and CEO of Novartis Oncology.

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THE AUTHOR is a writer based in the Seattle area.