OFATUMUMAB

Ofatumumab Overview

Ofatumumab (brand name Kesimpta for multiple sclerosis, Arzerra for leukemia) is a targeted prescription antibody medicine. In neurology, it is prescribed as a monthly subcutaneous (under the skin) self-injection to treat adults with relapsing forms of multiple sclerosis (RMS).

Key Facts Summary:

What Is Ofatumumab and How Does It Work?

Ofatumumab is a fully human monoclonal antibody that targets specific cells in your immune system.

Mechanism of Action

In multiple sclerosis, autoreactive immune cells, particularly CD20-positive B cells, mistakenly attack the protective myelin sheath surrounding nerve fibers in the central nervous system (brain and spinal cord).

Ofatumumab binds specifically to a distinct epitope on the CD20 cell-surface molecule expressed on pre-B and mature B lymphocytes. Binding induces antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), leading to targeted depletion of circulating CD20-positive B cells. By reducing peripheral B-cell counts while sparing stem cells and plasma cells, Ofatumumab prevents these autoreactive cells from crossing the blood-brain barrier to initiate neuroinflammation, reducing clinical relapses and MRI lesion activity.

Is Ofatumumab FDA Approved?

Yes, Ofatumumab is officially approved by the United States Food and Drug Administration. Under the brand name Kesimpta, it is approved as a disease-modifying therapy for relapsing forms of multiple sclerosis in adults.

What Is Ofatumumab Used For?

• Relapsing forms of multiple sclerosis (RMS) in adults, including clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease.
• Chronic lymphocytic leukemia (CLL) under the brand name Arzerra (administered as an intravenous infusion in oncology settings).

Before Taking Ofatumumab: Contraindications and Precautions

Because Ofatumumab depletes B cells and alters immune responses, thorough baseline screening is required prior to initiating therapy.

Who Should Not Take Ofatumumab?

• Anyone with an active Hepatitis B virus (HBV) infection (e.g., HBsAg positive).
• Anyone with a history of severe hypersensitivity or systemic allergic reactions to Ofatumumab or any of its inactive ingredients.

Ofatumumab, Pregnancy and Fertility

Discuss pregnancy plans with your doctor. Ofatumumab crosses the placenta and can cause fetal B-cell depletion and lymphopenia in newborn infants. Females of reproductive potential should use effective contraception during treatment and for at least 6 months after the final injection. It is unknown if Ofatumumab passes into human breast milk. Discuss breastfeeding risks with your provider.

Tell Your Doctor Before Taking Ofatumumab

• Disclose any active infections or a history of frequent, recurrent, or hard-to-treat infections.
• Inform your provider if you have a history of Hepatitis B or are a carrier of the virus.
• Share your complete vaccination record. Live-attenuated vaccines must be avoided during treatment.
• Provide a list of all current medications, especially drugs that weaken the immune system.

Ofatumumab Dosage and Administration

For multiple sclerosis, Ofatumumab is supplied in a prefilled Sensoready autoinjector pen or prefilled syringe for subcutaneous administration at home after proper training.

Standard Ofatumumab Dosing

• Initial Loading Doses: 20 mg injected subcutaneously at Week 0, Week 1, and Week 2.
• Skip Week: No injection is administered at Week 3.
• Maintenance Dosing: Starting at Week 4, a single 20 mg subcutaneous injection is administered once every month (every 4 weeks).

How Ofatumumab Is Administered

• Perform injections subcutaneously into the abdomen (avoiding the 2-inch area around the navel), thigh, or outer upper arm.
• Allow the autoinjector pen to reach room temperature for 15 to 30 minutes prior to injection.
• Clean the injection site with an alcohol wipe and allow it to dry completely.
• Press the pen firmly against the skin at a 90-degree angle until the green indicator fills the window and the second click is heard.

Ofatumumab Clinical Efficacy and Research

FDA approval of subcutaneous Ofatumumab for RMS was supported by two pivotal Phase 3, double-blind trials (ASCLEPIOS I and II). Monthly 20 mg subcutaneous Ofatumumab demonstrated superior efficacy compared to daily oral teriflunomide (14 mg). Results showed a significant reduction in annualized relapse rates by nearly 50%, a statistically significant reduction in 3-month and 6-month confirmed disability progression, and a near-complete suppression of gadolinium-enhancing T1 lesions and new or enlarging T2 lesions on brain MRI.

Ofatumumab Side Effects and Safety Profile

While self-administration offers convenience, peripheral B-cell depletion requires vigilance regarding infection risk and injection reactions.

Common Ofatumumab Side Effects

• Systemic injection-related reactions (fever, headache, myalgia, chills, and fatigue, occurring predominantly with the first injection).
• Local injection site reactions (erythema, pain, pruritus, or swelling).
• Upper respiratory tract infections (nasopharyngitis, sinusitis).
• Urinary tract infections.
• Decreased serum immunoglobulin levels (IgG, IgM).

Serious Ofatumumab Adverse Events

• Serious Infections: Severe viral, bacterial, or fungal infections due to B-cell depletion.
• Hepatitis B Reactivation: Reactivation of latent HBV infection resulting in fulminant hepatitis, hepatic failure, or death.
• Progressive Multifocal Leukoencephalopathy (PML): Opportunistic John Cunningham (JC) virus brain infection leading to severe neurological disability or death.
• Severe systemic hypersensitivity or anaphylactic reactions.

Managing Ofatumumab Side Effects

Systemic injection-related reactions (mild fever or body aches) occur mostly during the initial loading phase and diminish with subsequent doses. Over-the-counter antipyretics (acetaminophen) or antihistamines may be taken prior to initial doses to mitigate symptoms. Promptly evaluate signs of serious infection, such as high fever, persistent cough, dysuria, or spreading skin erythema.

Ofatumumab Drug Interactions and What to Avoid

Co-administration with other immunomodulatory agents or administration of live vaccines requires precise clinical timing.

Ofatumumab Drug-Drug Interactions

• Immunosuppressive Agents (Corticosteroids, DMARDs, biological therapies): Concomitant use or sequential therapy without adequate wash-out increases the risk of additive immunosuppression and severe infections.
• Live Vaccines (e.g., MMR, Varicella, Yellow Fever, Nasal Flu): Live-attenuated vaccines are contraindicated during treatment and until B-cell repletion occurs due to the risk of vaccine-derived infection. Non-live vaccines should be administered at least 2 weeks prior to initiating therapy.

Ofatumumab, Food and Alcohol

• Food intake does not affect subcutaneous absorption.
• Maintain adequate oral hydration; avoid excessive alcohol intake to support immune function.

Ofatumumab Missed Dose, Overdose and Storage

Adherence to the monthly schedule maintains continuous targeted B-cell depletion and prevents neuroinflammatory disease activity.

Missed Dose of Ofatumumab

If an injection is missed, administer the dose as soon as possible without waiting for the next scheduled date. Subsequent doses should be scheduled 4 weeks apart from the date of the newly administered dose.

Overdose and Emergency

In the event of an accidental overdose, monitor the patient for exaggerated B-cell depletion, prolonged lymphopenia, and systemic infection. Provide supportive medical care as indicated.

How to Store Ofatumumab

• Store prefilled pens or syringes refrigerated between 36°F and 46°F (2°C and 8°C) in the original carton to protect from light.
• Do not freeze or shake.
• Unopened pens may be stored at room temperature (up to 86°F/30°C) for a single period of up to 7 days. If unused after 7 days at room temperature, discard the pen.

Ofatumumab Patient Management and Monitoring

Pre-treatment screening and ongoing laboratory evaluation ensure patient safety during long-term B-cell depletion.

Tests Before Starting Ofatumumab

• Hepatitis B virus screening (HBsAg and total anti-HBc testing).
• Baseline serum quantitative immunoglobulin testing (IgG, IgA, IgM).
• Screening for active infections and completion of necessary non-live vaccines at least 2 weeks prior.

Monitoring During Ofatumumab Treatment

• Periodic quantitative serum immunoglobulin testing (IgG, IgM).
• Routine clinical monitoring for signs and symptoms of bacterial, viral, or fungal infections.
• Periodic neurological assessments and MRI imaging to evaluate MS disease activity.

Ofatumumab Do’s and Don’ts

• DO store autoinjector pens in the refrigerator in their original box to protect from light.
• DO inspect the solution through the viewing window; it should be clear to slightly opalescent.
• DON’T inject into skin that is tender, bruised, red, scaly, or hardened.
• DON’T receive live-attenuated vaccines during therapy or prior to B-cell recovery.

Frequently Asked Questions

References

• U.S. FDA prescribing information for Kesimpta (Ofatumumab) injection
• U.S. FDA Drugs@FDA drug approval overview (Application No. 125326)
• ASCLEPIOS I and ASCLEPIOS II Phase 3 Clinical Trial Results in Relapsing Multiple Sclerosis

Legal Disclaimer

The information provided is for educational and informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider at any hospital or any local clinic before starting or stopping any medication.