Before you begin using a medication, be sure to inform your doctor of any medical conditions or Allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use Tysabri (Natalizumab).

Chronic progressive multiple sclerosis (MS): The safety and effectiveness of using Tysabri (Natalizumab) by people with chronic progressive MS have not been established. Currently, Tysabri (Natalizumab) is only recommended for people with the relapsing-remitting form of MS.

Infections: Tysabri (Natalizumab) may increase the risk of infections. If you notice any signs of an infection such as fever or chills, severe diarrhea, shortness of breath, prolonged dizziness, headache, stiff neck, weight loss, or listlessness, contact your doctor immediately.

Infusion-related reactions: Some people may experience an infusion-related reaction, including headache, dizziness, fatigue, hives, itching, and chills, up to 2 hours after the start of an infusion. If you notice these symptoms, let your doctor know right away.

Kidney function: If you have Kidney Disease or decreased kidney function, discuss with your doctor how Tysabri (Natalizumab) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Tysabri (Natalizumab), and whether any special monitoring is needed.

Liver function: Tysabri (Natalizumab) may cause damage to the liver. If you have liver disease or decreased liver function, discuss with your doctor how Tysabri (Natalizumab) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Tysabri (Natalizumab), and whether any special monitoring is needed.

If you experience symptoms of liver problems (e.g., abdominal pain, persistent vomiting, feeling unwell, fever, itching, yellowing of the skin and eyes, dark urine), contact your doctor immediately.

Progressive multifocal leukoencephalopathy (PML): Tysabri (Natalizumab) has been associated with an increased risk of a rare brain infection called progressive multifocal leukoencephalopathy (PML), which can lead to disability or death. The risk of developing this infection increases with the length of time Tysabri (Natalizumab) is used.

Signs and symptoms of PML include progressive weakness on one side of the body; clumsiness of limbs; vision disturbances; changes in thinking, memory, and orientation; confusion; and personality changes. Some of the symptoms are similar to MS, so if you develop any of these symptoms or any other unusual symptoms, or if your MS gets worse, contact your doctor immediately. Your doctor should do an MRI scan before you start Tysabri (Natalizumab) to help distinguish a subsequent MS relapse from PML.

Pregnancy: Tysabri (Natalizumab) should not be used during pregnancy unless the benefits outweigh the risks. There have been reports of blood abnormalities in newborns born to women who were treated with Tysabri (Natalizumab) during pregnancy. If you become pregnant while taking Tysabri (Natalizumab), contact your doctor immediately.

Breast-feeding: Tysabri (Natalizumab) passes into breast milk. If you are a breast-feeding mother and are taking Tysabri (Natalizumab), it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using Tysabri (Natalizumab) have not been established for children and adolescents less than18 years of age.

Seniors: Safe and effective dosing has not been established for seniors. As they are at a higher risk of developing severe adverse reactions to Tysabri (Natalizumab), seniors should be closely monitored by their physician.