Lemtrada (alemtuzumab) for multiple sclerosis

Last updated June 12, 2025, by Margarida Maia, PhD
Fact-checked by Inês Martins, PhD

What is Lemtrada for MS?

Lemtrada (alemtuzumab) is a disease-modifying medication approved to treat adults with relapsing forms of multiple sclerosis (MS), including relapsing-remitting MS (RRMS) and active secondary progressive MS (SPMS).

Given as intravenous, or into-the-vein, infusions, it is expected to reduce the frequency of relapses, slow the development of lesions, and potentially delay disability progression.

Lemtrada is an antibody-based medication that works to lessen MS inflammation by reducing the levels and activation of key disease-driving immune cells called B-cells and T-cells. It targets the CD52 protein found at the surface of these cells.

The therapy was originally developed by Genzyme, which was later acquired by Sanofi. Sanofi now markets the therapy.

Therapy snapshot

Who can take Lemtrada?

Lemtrada is approved in the U.S. for adults with RRMS and active SPMS.

However, the medication’s prescribing information carries a boxed warning noting that it can cause serious and life-threatening health issues, including autoimmune conditions, infusion reactions, stroke, and cancer. Treatment should be administered in a setting where serious infusion reactions or anaphylaxis, a life-threatening allergic reaction, can be adequately managed, and patients should be routinely monitored for other health conditions.

Because Lemtrada can increase the risk of severe complications, it is generally recommended for patients who have failed to respond to at least two other MS treatments. To ensure safe use, the medication is available only through a restricted program that ensures that healthcare professionals, pharmacies, and infusion centers are all certified to prescribe, dispense, and infuse Lemtrada.

In the U.S., the therapy is contraindicated for patients with:

• a known history of hypersensitivity reactions (a type of exaggerated immune response), including anaphylaxis, to the active agent alemtuzumab or any other ingredient in Lemtrada
• infection with human immunodeficiency virus (HIV)
• an active infection.

It is also not recommended for people with clinically isolated syndrome — a first episode of symptoms suggestive of MS.

Lemtrada is also approved in dozens of other countries, but the exact indications may vary. In Europe, for example, the medication is approved for adults with highly active RRMS.

How is Lemtrada administered?

Lemtrada is given as intravenous infusions that are administered by a certified professional and in a setting in which equipment and personnel to appropriately manage serious side effects are available.

It is given at a recommended dose of 12 mg per day, in two treatment courses. Patients will first receive five daily infusions in the first year, followed by three daily infusions one year later. Some patients may need additional courses of treatment, always spaced at least one year apart.

Each infusion lasts about four hours, but the total appointment can take up to eight hours, including monitoring time. Before each infusion, patients will receive corticosteroids to help reduce the chance of serious reactions; antihistamines and fever reducers may also be prescribed.

To prevent herpes virus infections, antivirals are usually started on the first day of treatment and continued for at least two months after each treatment course.

Lemtrada in clinical trials

Lemtrada’s approval in the U.S. was largely supported by data from two Phase 3 clinical trials involving a total of 1,421 patients with RRMS. Both compared Lemtrada with Rebif (interferon beta-1a), an injectable medication also approved for MS, for up to two years.

• CARE-MS 1 (NCT00530348) enrolled people within five years of their diagnosis who had not received any prior MS treatment. Results showed that Lemtrada significantly reduced relapse rates by about half compared with Rebif, and also lowered the number and volume of lesions. There was a trend toward a lower risk of sustained accumulation of disability with Lemtrada, but this failed to reach statistical significance.
• CARE-MS 2 (NCT00548405) involved patients diagnosed in the past 10 years and who had experienced at least one relapse while on a prior MS therapy. Lemtrada also reduced relapse rates by about half in this trial, and it significantly reduced the risk of sustained accumulation of disability by 42%, compared with Rebif. Some MRI measures of disease activity were also lowered with the treatment.

After completing the CARE-MS trials, patients had the option to enter a long-term extension (NCT00930553) where they were treated with additional courses of Lemtrada as needed and followed for at least four more years. Over half of participants did not need additional infusions of Lemtrada or other disease-modifying therapies during this period. Most (67%-80%) remained free of confirmed disability worsening over six years, and about one-third experienced confirmed disability improvement.

Common side effects of Lemtrada

The most common side effects reported with Lemtrada in clinical trials include:

• rash
• headache
• fever
• the common cold
• nausea and vomiting
• urinary tract infection
• fatigue
• insomnia
• upper respiratory tract infection
• herpes virus infection
• urticaria (hives) and itching
• thyroid gland abnormalities
• fungal infection
• diarrhea
• sinus inflammation (sinusitis)
• burning or tingling sensations (paresthesia)
• dizziness
• flushing
• pain in the joints, extremities, back, throat, and/or abdomen.

Lemtrada also carries a boxed warning noting it can cause serious and sometimes fatal health issues for which appropriate monitoring and prompt care may be needed. These include:

• Autoimmune disorders, such as immune thrombocytopenia and anti-glomerular basement membrane disease. These conditions cause serious issues with blood cells, thyroid, liver, and kidneys, so adequate monitoring is needed monthly and for at least four years after the last dose.
• Infusion reactions, which may happen during or after treatment. These reactions can sometimes be severe and life-threatening, so treatment must be administered in a setting where serious reactions can be adequately treated.
• Stroke, which has been reported up to three days after treatment. Patients should seek immediate medical attention if they experience symptoms suggestive of stroke.
• An increased risk of cancer, namely thyroid cancer, melanoma, and blood cancers. Routine monitoring, including annual skin exams, is recommended for people receiving Lemtrada.

Other serious side effects that may occur while on treatment with Lemtrada include:

• serious infections, including progressive multifocal leukoencephalopathy, a potentially fatal brain infection
• inflammatory conditions affecting the gallbladder, lungs, intestines, and other organ systems
• serious blood-clotting issues.

Lemtrada may cause harm to a developing fetus, and women who could become pregnant should use effective contraception while taking Lemtrada and for at least four months after a treatment course. Women who are pregnant or planning to become pregnant should inform their healthcare provider before initiating the treatment.

Multiple Sclerosis News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.