Kesimpta: Uses, Dosage & Side Effects
A fully human anti-CD20 monoclonal antibody for the treatment of relapsing forms of multiple sclerosis in adults
Kesimpta (ofatumumab) is a prescription medication used to treat relapsing forms of multiple sclerosis (RMS) in adults. It is a fully human monoclonal antibody that targets CD20, a protein found on the surface of B cells. By depleting these B cells, Kesimpta reduces the inflammatory immune responses that damage the protective myelin sheath around nerve fibers. Kesimpta is self-administered at home as a monthly subcutaneous injection using a pre-filled Sensoready pen, after an initial loading phase under medical supervision.
Quick Facts About Kesimpta
Key Takeaways
- Kesimpta is a targeted B-cell therapy approved for relapsing forms of multiple sclerosis, reducing annualized relapse rates by approximately 50-58% compared to teriflunomide in pivotal clinical trials (ASCLEPIOS I and II).
- It is the first self-administered anti-CD20 monoclonal antibody for MS, given as a monthly subcutaneous injection at home after an initial loading dose period.
- Common side effects include upper respiratory infections, injection-related reactions, and urinary tract infections, with reactions typically decreasing after the first injection.
- Hepatitis B screening is mandatory before starting treatment, as reactivation of the virus can occur with anti-CD20 therapies.
- Women should use effective contraception during treatment and for 6 months after the last dose, as Kesimpta may affect the immune system of an unborn child.
What Is Kesimpta and What Is It Used For?
Kesimpta contains the active substance ofatumumab, which belongs to a class of medications known as monoclonal antibodies. It is specifically designed to treat adults with relapsing forms of multiple sclerosis (RMS), a chronic autoimmune disease of the central nervous system. RMS encompasses several subtypes, including clinically isolated syndrome (CIS), relapsing-remitting multiple sclerosis (RRMS), and active secondary progressive multiple sclerosis (SPMS) with relapses.
Multiple sclerosis occurs when the immune system mistakenly attacks the myelin sheath, the protective covering around nerve fibers in the brain and spinal cord. This process, called demyelination, disrupts the transmission of nerve signals and leads to a wide range of neurological symptoms including numbness, tingling, muscle weakness, vision problems, fatigue, and cognitive difficulties. Over time, repeated attacks can cause permanent nerve damage and progressive disability.
How Does Kesimpta Work?
Kesimpta works by binding to a target protein called CD20, which is found on the surface of B lymphocytes (B cells). B cells are a type of white blood cell that plays a central role in the adaptive immune system. In multiple sclerosis, B cells are implicated in the disease process through several mechanisms: they act as antigen-presenting cells, produce pro-inflammatory cytokines, and can form ectopic lymphoid follicles in the central nervous system that perpetuate chronic inflammation.
When ofatumumab binds to CD20, it triggers the destruction of B cells through two main pathways: complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC). By depleting CD20-positive B cells from the circulation, Kesimpta reduces the inflammatory cascade that damages myelin and nerve fibers, thereby decreasing the risk of relapses, slowing symptom progression, and reducing the formation of new brain lesions visible on MRI.
Importantly, Kesimpta spares pre-B cells (which have not yet expressed CD20) and plasma cells (which have stopped expressing CD20), preserving the body's ability to regenerate its B-cell population after treatment discontinuation and maintaining some degree of pre-existing humoral immunity.
In the two pivotal Phase III trials (ASCLEPIOS I and II), Kesimpta demonstrated superior efficacy compared to teriflunomide (Aubagio) in adults with RMS. Kesimpta reduced the annualized relapse rate by approximately 50.5% in ASCLEPIOS I and 58.5% in ASCLEPIOS II. It also significantly reduced the number of gadolinium-enhancing T1 lesions on MRI (by 97.5% and 93.8%, respectively) and slowed confirmed disability worsening.
What Should You Know Before Taking Kesimpta?
Contraindications
You must not use Kesimpta if you are allergic to ofatumumab or any of the other ingredients in this medicine (L-arginine, sodium acetate trihydrate, sodium chloride, polysorbate 80, disodium edetate dihydrate, hydrochloric acid, and water for injections). Additionally, Kesimpta is contraindicated in patients with severe immunodeficiency states, those with severe active infections, and individuals with known active malignancies.
- You are allergic to ofatumumab or any of the excipients
- You have been told you have severe problems with your immune system
- You have a severe active infection
- You have active cancer
Warnings and Precautions
Hepatitis B reactivation: Kesimpta can cause hepatitis B virus (HBV) to become active again. Your doctor will perform a blood test to check if you are at risk of hepatitis B infection before starting treatment. If you have ever had hepatitis B or are a carrier of the hepatitis B virus, your doctor will refer you to a specialist for monitoring throughout your treatment.
Infections: Because Kesimpta targets immune cells, you may become more susceptible to infections, or an existing infection may worsen. If you have an active infection, your doctor may decide to delay treatment until the infection has resolved. During treatment, inform your doctor immediately if you develop signs of infection such as fever, persistent cough, or pain during urination.
Progressive Multifocal Leukoencephalopathy (PML): Although rare, PML is a serious brain infection caused by the JC virus that has been reported with anti-CD20 antibodies. Contact your doctor immediately if you notice worsening of your MS symptoms, new or unusual neurological symptoms such as weakness, vision changes, or cognitive difficulties. Early detection of PML is critical for outcomes.
Vaccinations: Before starting Kesimpta, your doctor will check whether you need any vaccinations. Live or live-attenuated vaccines should be given at least 4 weeks before starting treatment, and inactivated vaccines should be given at least 2 weeks before. You should not receive live or live-attenuated vaccines during treatment with Kesimpta, as they may cause infection. Other types of vaccines may be less effective if given during treatment.
Injection-related reactions: These are among the most common side effects of Kesimpta and typically occur within 24 hours after injection, particularly after the first dose. Symptoms may include fever, headache, muscle pain, chills, and fatigue. Your first injection should be given under the supervision of a healthcare professional to monitor for these reactions.
Children and Adolescents
Kesimpta is not approved for use in children and adolescents under 18 years of age, as it has not been studied in this age group. The safety and efficacy of ofatumumab in pediatric patients with multiple sclerosis have not been established. Clinical studies are currently ongoing to evaluate the use of Kesimpta in pediatric MS populations.
Pregnancy and Breastfeeding
Pregnancy: You should avoid becoming pregnant while using Kesimpta and for 6 months after stopping treatment. Women of childbearing potential must use effective contraception during this period. If you become pregnant or suspect you may be pregnant during treatment or within 6 months after the last dose, contact your doctor immediately. Kesimpta may reduce the number of immune cells (B cells) in both the mother and the unborn child, which could potentially affect the baby's immune development.
Breastfeeding: Ofatumumab may pass into breast milk. Discuss the risks and benefits with your doctor before breastfeeding while using Kesimpta. If you used Kesimpta during pregnancy, consult your doctor or pharmacist before vaccinating your newborn, as the baby's immune response to vaccines may be affected.
Driving and Operating Machinery
Kesimpta is unlikely to affect your ability to drive or use machines. However, if you experience injection-related reactions such as dizziness or fatigue, you should wait until these symptoms resolve before driving or operating machinery.
Kesimpta contains less than 1 mmol (23 mg) sodium per dose, making it essentially sodium-free. It also contains 0.08 mg polysorbate 80 per dose. Polysorbates may cause allergic reactions in some individuals. Inform your doctor if you have any known allergies to polysorbates.
How Does Kesimpta Interact with Other Drugs?
Tell your doctor, pharmacist, or nurse if you are taking, have recently taken, or might take any other medicines. It is particularly important to inform your healthcare provider if you are taking or have recently taken any medications that affect the immune system, as combining these with Kesimpta may amplify immunosuppressive effects.
As a monoclonal antibody, ofatumumab is degraded by proteolytic enzymes (catabolism) rather than by the cytochrome P450 (CYP) enzyme system in the liver. This means that conventional drug-drug interactions mediated through CYP enzymes are not expected. No formal drug interaction studies have been conducted with Kesimpta. However, there are important clinical considerations when using Kesimpta alongside other treatments.
Significant Interactions
| Interacting Drug/Class | Type | Clinical Significance | Recommendation |
|---|---|---|---|
| Live or live-attenuated vaccines | Contraindicated | Risk of vaccine-induced infection due to immunosuppression | Administer at least 4 weeks before starting Kesimpta. Do not give during treatment. |
| Inactivated vaccines | Reduced efficacy | Immune response to vaccines may be diminished | Administer at least 2 weeks before starting Kesimpta. Monitor antibody response if given during treatment. |
| Other immunosuppressants (e.g., azathioprine, methotrexate, cyclosporine) | Additive immunosuppression | Increased risk of infection and prolonged immunosuppression | Use with caution. Consider the duration of action and mode of action of previous MS therapies when switching. |
| Other anti-CD20 therapies (e.g., ocrelizumab, rituximab) | Overlapping mechanism | Prolonged and compounded B-cell depletion | Allow adequate washout period. Monitor B-cell counts and immunoglobulin levels before switching. |
| Fingolimod, siponimod (S1P modulators) | Additive immunosuppression | Lymphocyte sequestration combined with B-cell depletion | Allow adequate washout (typically 1-2 months for fingolimod) before starting Kesimpta. Monitor lymphocyte counts. |
| Natalizumab | Additive immunosuppression | Combined immune modulation may increase PML risk | Allow adequate washout (typically 6-8 weeks). Screen for PML risk factors including JCV antibody status. |
| Corticosteroids (short-term for relapses) | Generally compatible | Short-term use for MS relapse management is acceptable | Can be used concurrently for relapse treatment. Monitor for increased infection risk with prolonged use. |
Switching from Other MS Therapies
When switching to Kesimpta from another disease-modifying therapy (DMT), your doctor will consider the pharmacokinetic and pharmacodynamic properties of the prior treatment. For example, if you are switching from fingolimod, a washout period is necessary to allow lymphocyte counts to recover before starting Kesimpta. If switching from natalizumab, your doctor will wait an appropriate period and may perform JC virus antibody testing before initiating Kesimpta to mitigate PML risk.
For patients switching from other anti-CD20 therapies such as ocrelizumab or rituximab, your doctor will assess B-cell recovery and immunoglobulin levels. The timing of the switch will depend on the duration since the last infusion and the extent of ongoing B-cell depletion.
What Is the Correct Dosage of Kesimpta?
Always use Kesimpta exactly as your doctor has told you. Check with your doctor, pharmacist, or nurse if you are not sure. Kesimpta is given as a subcutaneous injection (an injection under the skin) using the pre-filled Sensoready pen. The pen is designed for single use only and should be disposed of after each injection.
Standard Dosing Schedule
| Timing | Dose | Notes |
|---|---|---|
| Week 0 (Day 1) | 20 mg subcutaneous | First injection under medical supervision |
| Week 1 | 20 mg subcutaneous | Loading dose |
| Week 2 | 20 mg subcutaneous | Loading dose |
| Week 3 | No injection | Treatment break |
| Week 4 | 20 mg subcutaneous | First monthly maintenance dose |
| Every month thereafter | 20 mg subcutaneous | Ongoing monthly maintenance |
Administration and Injection Sites
Kesimpta can be injected at any time of day (morning, afternoon, or evening). The recommended injection sites are the front of the thighs (most common), the lower abdomen (but not within 5 cm of the navel), or the outer upper arm (only if administered by a caregiver or healthcare professional). You should rotate injection sites with each dose and avoid injecting into areas that are bruised, tender, red, scaly, hard, or have scars or stretch marks.
Before injection, remove the pre-filled pen from the refrigerator 15 to 30 minutes beforehand to allow it to reach room temperature. Inspect the solution through the viewing window: it should be clear to slightly opalescent and colorless to slightly brownish-yellow. Do not use the pen if the solution contains visible particles or is cloudy. Do not shake the pen.
Missed Dose
If you miss a scheduled dose of Kesimpta, inject the missed dose as soon as possible. Do not wait until your next scheduled injection. The timing of subsequent injections should then be recalculated from the date of the missed dose injection, not from the original schedule. It is important to receive each injection on time to maintain the full therapeutic benefit of Kesimpta.
Overdose
If you have injected too much Kesimpta, contact your doctor immediately. In clinical studies, single doses up to 100 mg have been administered subcutaneously without dose-limiting toxicities. However, exceeding the prescribed dose may increase the risk of immunosuppression-related adverse effects. There is no specific antidote for ofatumumab overdose; treatment is supportive.
Stopping Treatment
Do not stop using Kesimpta or change your dose without talking to your doctor. If you and your doctor decide to discontinue Kesimpta, be aware that some side effects related to low B-cell levels may persist for some time after your last injection. Your B-cell levels will gradually return to normal over several months. During this recovery period, some side effects described in this article may still occur. Your doctor will monitor your immune status during this transition.
Clean the injection site with an alcohol swab using a circular motion and allow it to dry. Hold the pen at a 90-degree angle against the skin and press firmly to start the injection. You will hear a first click when the injection begins. Keep the pen pressed against the skin until you hear a second click, which indicates the injection is nearly complete. Verify that the green indicator fills the window before removing the pen. If bleeding occurs, press a cotton ball or gauze against the injection site for 10 seconds without rubbing.
What Are the Side Effects of Kesimpta?
Like all medicines, Kesimpta can cause side effects, although not everybody gets them. The side effects seen with Kesimpta are primarily related to its mechanism of action on the immune system. Because Kesimpta depletes B cells, which play a role in fighting infections, patients may be more susceptible to certain infections during treatment. Most side effects are mild to moderate in severity and manageable with appropriate medical care.
Injection-related reactions are among the most frequently reported adverse events. These systemic reactions typically occur within 24 hours after a Kesimpta injection, particularly after the first dose. Pre-treatment with acetaminophen (paracetamol), antihistamines, or corticosteroids may be considered at your doctor's discretion. The frequency and severity of injection-related reactions generally decrease with subsequent injections.
Very Common
May affect more than 1 in 10 people
- Upper respiratory tract infections (sore throat, runny nose, sinusitis)
- Injection-related systemic reactions (fever, headache, muscle pain, chills, fatigue) — most common after the first injection
- Urinary tract infections
- Local injection site reactions (redness, pain, itching, swelling at the injection site)
Common
May affect up to 1 in 10 people
- Decreased blood levels of immunoglobulin M (IgM), a protein that helps protect against infections
- Oral herpes (cold sores) or herpes infection around the mouth
- Nausea, vomiting (reported in connection with injection-related reactions)
Not Known
Frequency cannot be estimated from the available data
- Allergic reactions (skin rash, hives, breathing difficulties, swelling of face, eyelids, lips, mouth, tongue, or throat, chest tightness, feeling faint)
- Signs of a serious allergic reaction: skin rash, hives, difficulty breathing, swelling of face, lips, tongue, or throat, chest tightness, or feeling faint
- Signs of PML: worsening of MS symptoms, new weakness, vision changes, or any new or unusual neurological symptoms
- Signs of a serious infection: high fever, persistent cough, pain during urination, or symptoms that do not improve with standard treatment
Long-Term Safety Considerations
With prolonged treatment, immunoglobulin levels (particularly IgM) may gradually decrease. Your doctor will monitor your immunoglobulin levels periodically. A significant decrease in immunoglobulin levels may increase your susceptibility to infections. In such cases, your doctor may decide to pause or discontinue treatment. Post-marketing surveillance and long-term extension studies continue to monitor the safety profile of Kesimpta over extended treatment periods.
The risk of infections should be weighed against the benefit of reducing MS disease activity. In clinical trials, the overall rate of infections was similar between Kesimpta and the comparator (teriflunomide), and serious infections were uncommon. There was no increased risk of malignancies observed in clinical trials, although long-term data collection is ongoing.
How Should You Store Kesimpta?
Keep Kesimpta out of the sight and reach of children. Do not use this medicine after the expiry date stated on the carton and label after EXP. The expiry date refers to the last day of that month.
Store the pre-filled pen(s) in the outer carton to protect from light. Store in a refrigerator at 2°C to 8°C (36°F to 46°F). Do not freeze the product. If the pen has been accidentally frozen, do not use it.
If necessary, Kesimpta can be stored at room temperature (not above 30°C / 86°F) for a single period of up to 7 days. If not used during this period, the pen can be returned to the refrigerator for a maximum of an additional 7 days. This room temperature storage should only occur once per pen.
Do not use this medicine if the solution contains visible particles or is cloudy. The solution should be clear to slightly opalescent and colorless to slightly brownish-yellow.
Do not dispose of medicines via wastewater or household waste. Ask your pharmacist how to dispose of medicines you no longer use. These measures will help protect the environment.
What Does Kesimpta Contain?
Active Ingredient
The active substance is ofatumumab. Each pre-filled Sensoready pen contains 20 mg of ofatumumab in 0.4 mL of solution. Ofatumumab is a fully human monoclonal antibody of the IgG1 subclass, produced by recombinant DNA technology. It targets the CD20 antigen on the surface of B lymphocytes.
Inactive Ingredients (Excipients)
| Ingredient | Role | Notes |
|---|---|---|
| L-arginine | Stabilizer | Amino acid that helps maintain protein stability |
| Sodium acetate trihydrate | Buffer | Maintains pH of the solution |
| Sodium chloride | Tonicity agent | Adjusts osmolality of the solution |
| Polysorbate 80 (E433) | Surfactant | Prevents protein aggregation. May cause allergic reactions in some individuals. |
| Disodium edetate dihydrate | Chelating agent | Binds metal ions to prevent degradation |
| Hydrochloric acid | pH adjuster | Used to adjust pH to optimal range |
| Water for injections | Solvent | Vehicle for the active substance |
Appearance and Pack Sizes
Kesimpta solution for injection is clear to slightly opalescent and colorless to slightly brownish-yellow. It is available in single packs containing 1 pre-filled Sensoready pen and multipacks consisting of 3 cartons, each containing 1 pre-filled Sensoready pen. Not all pack sizes may be marketed in all countries.
The marketing authorization holder is Novartis Europharm Limited, based in Dublin, Ireland. Manufacturing is carried out by Novartis Farmaceutica S.A. in Barcelona, Spain, and Novartis Pharma GmbH in Nuremberg, Germany.
Frequently Asked Questions About Kesimpta
Kesimpta (ofatumumab) is approved for the treatment of relapsing forms of multiple sclerosis (RMS) in adults. This includes clinically isolated syndrome, relapsing-remitting MS, and active secondary progressive MS. It works by targeting and depleting CD20-positive B cells that are involved in the inflammatory process that damages the myelin sheath around nerves. In clinical trials (ASCLEPIOS I and II), Kesimpta reduced annualized relapse rates by approximately 50-58% compared to teriflunomide.
While both Kesimpta (ofatumumab) and Ocrevus (ocrelizumab) target CD20 on B cells, they differ in important ways. Kesimpta is a fully human monoclonal antibody administered as a monthly subcutaneous self-injection at home using a pre-filled pen. Ocrevus is a humanized antibody that requires intravenous infusion every 6 months at a healthcare facility. The convenience of self-administration at home is a key advantage of Kesimpta. Both have shown significant efficacy in reducing MS relapses, and both are generally well tolerated.
Kesimpta begins depleting B cells rapidly after the first injection. The loading dose regimen (injections at weeks 0, 1, and 2) is designed to achieve rapid and near-complete B-cell depletion within the first few weeks. In clinical trials, significant reductions in MRI lesion activity were observed as early as the first month. Clinical benefits, including reduction in relapse rates, were evident within the first 3 months of treatment. Your doctor will typically assess the effectiveness of treatment over 6 to 12 months.
Yes, you can travel with Kesimpta, but you need to maintain proper storage. The pre-filled pen should be kept refrigerated at 2-8°C during transport using a cooler bag with ice packs. If refrigeration is not available, Kesimpta can be stored at room temperature (up to 30°C) for a single period of up to 7 days. You may need a letter from your doctor confirming that you require the medication for air travel. Plan your travel around your injection schedule to ensure you don't miss a dose.
Injection-related reactions are common, especially after the first injection. Symptoms may include fever, headache, muscle pain, chills, and fatigue, typically appearing within 24 hours. These reactions usually decrease with subsequent injections. Your doctor may recommend taking acetaminophen (paracetamol) or an antihistamine before your injection to reduce symptoms. If you experience severe symptoms such as difficulty breathing, swelling of the face or throat, or chest tightness, seek emergency medical attention immediately as these could indicate a serious allergic reaction.
All information is based on international medical guidelines and peer-reviewed research: EMA Summary of Product Characteristics (SmPC) for Kesimpta, FDA Prescribing Information, the ASCLEPIOS I and II Phase III clinical trials published in the New England Journal of Medicine (2020), AAN Practice Guidelines for MS Disease-Modifying Therapies (2024), and ECTRIMS/EAN Treatment Guidelines. All medical claims are based on evidence level 1A, the highest quality of evidence from systematic reviews and randomized controlled trials.
References
- European Medicines Agency (EMA). Kesimpta (ofatumumab) – Summary of Product Characteristics. Last updated 2025. Available at: ema.europa.eu
- U.S. Food and Drug Administration (FDA). Kesimpta (ofatumumab) – Prescribing Information. Revised 2024. Available at: fda.gov
- Hauser SL, Bar-Or A, Cohen JA, et al. Ofatumumab versus Teriflunomide in Multiple Sclerosis. New England Journal of Medicine. 2020;383(6):546-557. doi:10.1056/NEJMoa1917246
- American Academy of Neurology (AAN). Practice Guideline: Disease-Modifying Therapies for Adults with Multiple Sclerosis. 2024.
- Montalban X, Gold R, Thompson AJ, et al. ECTRIMS/EAN Guideline on the Pharmacological Treatment of People with Multiple Sclerosis. Multiple Sclerosis Journal. 2024;30(2):135-168.
- Bar-Or A, Grove RA, Austin DJ, et al. Subcutaneous ofatumumab in patients with relapsing-remitting multiple sclerosis: The MIRROR study. Neurology. 2018;90(20):e1805-e1814.
- World Health Organization (WHO). Atlas of MS. 3rd edition. 2020. Available at: who.int
- British National Formulary (BNF). Ofatumumab. National Institute for Health and Care Excellence (NICE). 2025. Available at: bnf.nice.org.uk
- Gartner J, et al. Efficacy and safety of ofatumumab in recently diagnosed, treatment-naive patients with multiple sclerosis: Results from ASCLEPIOS I and II. Multiple Sclerosis Journal. 2022;28(10):1562-1575.
- National Multiple Sclerosis Society. Disease-Modifying Therapies for MS. 2025. Available at: nationalmssociety.org
Editorial Team
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