Neutralizing Antibodies That Reduce Effectiveness. Over time, people taking the interferons develop antibodies to the drugs, some of which can neutralize their effects. The risk for neutralizing antibodies (NAbs) increases with higher doses and greater frequency of use. Interferons injected under the skin (Betaseron, Rebif) are more likely to produce neutralizing antibodies than Avonex, which is injected into a muscle. Patients who experience this, however, often can be effectively treated with an alternative interferon or with glatiramer, which has an extremely low risk, for NAbs. In many cases, after switching drugs, NAb levels decline and the patient may be able to return to the original interferon.
Glatiramer Acetate
Glatiramer acetate (Copaxone) formerly called Cop-1 or copolymer-1, is a synthetic molecule created to resemble a basic protein found in myelin. It is being used as a decoy to trick white blood cells into attacking it instead of myelin. Studies indicate that this drug may be superior to others in reducing relapse rates, with a 2003 comparison study reporting relapse free rates of 83% during a 16-month period. The best results are in patients in early stages, but the longer patients remain on the drug, the greater the improvement. Benefits have persisted for years.
Side Effects. Side effects occur in about 15% of patients, usually right after the injection. They include pain at the injection site, chest pain, rapid heartbeat, flushing, anxiety, and shortness of breath.
Natalizumab and Other Monoclonal Antibodies
Monoclonal antibodies (MAbs) are drugs that target specific antibodies involved with the immune response. In 2004, natalizumab (Tysabri) became the only MAb approved for treatment of MS. Shortly afterwards, reports emerged of progressive multifocal leukoencephalopathy (PML) occurring among patients who took natalizumab for more than 2 years. PML is a rare neurological disease that can affect people with compromised immune systems. Based on these reports, the FDA suspended marketing of natalizumab in February 2005 and recommended that patients discontinue its use.
In June 2006, the FDA allowed natalizumab to return to the market with certain safety restrictions. Doctors can prescribe the drug only to patients who have failed to respond to or who cannot tolerate other MS treatments. Natalizumab can only be taken alone, not in combination with other immune-modifying drugs. Patients who take natalizumab must enroll in a special program called TOUCH, which is run by the drug’s manufacturer. Patients need to get magnetic resonance imaging (MRI) brain scans before they begin taking the drug, and they be evaluated regularly during drug treatment to make sure they are not at risk of developing PML.
Previous Section
