Ofatumumab

Introduction Overview

Generic Name

ofatumumab

Brand Name

Kesimpta

Dosage Form

single-dose prefilled Sensoready pen for subcutaneous use (20 mg/0.4 mL), single-dose prefilled syringe for subcutaneous use (20 mg/0.4 mL)

Drug Class

CD20 monoclonal antibodies, Selective immunosuppressants

Pharmacokinetics

Absorption:
Ofatumumab, when administered subcutaneously as Kesimpta, demonstrates predictable and efficient absorption from the injection site. Peak serum concentrations are typically observed within approximately 1 week after dosing, reflecting the drug's gradual uptake via the lymphatic system into systemic circulation. This slow absorption profile enables steady and sustained B-cell depletion with monthly administration. Subcutaneous administration avoids the infusion-related reactions seen with intravenous administration of similar monoclonal antibodies, contributing to improved tolerability. Clinical pharmacokinetic studies reveal near-linear pharmacokinetics with dose-proportional increases in systemic exposure over the therapeutic dose range.

Distribution:
Once absorbed, ofatumumab distributes primarily within the vascular and interstitial spaces, typical of large molecule monoclonal antibodies. It binds specifically to the CD20 antigen expressed on pre-B and mature B lymphocytes, resulting in targeted cellular engagement primarily within the peripheral blood and lymphoid tissues. The volume of distribution is low, estimated at approximately 3–4 liters, consistent with limited extravascular penetration due to its high molecular weight and hydrophilicity. Binding to CD20 positive cells facilitates targeted depletion without widespread tissue distribution. Ofatumumab’s Fc region may interact with neonatal Fc receptors (FcRn), prolonging its half-life by protecting the molecule from lysosomal degradation.

Metabolism:
As a fully human IgG1 kappa monoclonal antibody, ofatumumab is metabolized via proteolytic catabolism into small peptides and amino acids through the reticuloendothelial system and cellular lysosomes. This metabolic process is consistent with endogenous immunoglobulin turnover and does not involve hepatic cytochrome P450 enzymes, thereby minimizing the potential for metabolic drug-drug interactions. The metabolic rate is dependent on the target-mediated disposition as the antibody-antigen complex is internalized and processed.

Elimination:
Elimination of ofatumumab occurs predominantly through target-mediated clearance via binding to CD20-positive B-cells and subsequent cellular destruction through immune effector mechanisms including complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC). Non-specific clearance via the reticuloendothelial system also contributes to elimination. The terminal half-life varies but is approximately 15–23 days, allowing for convenient monthly dosing schedules with sustained B-cell depletion. Clearance reduces as B-cell counts decline, reflecting target saturation and reduced antigen availability. The antibody is not cleared renally or hepatically, minimizing concerns related to renal or hepatic impairment influencing elimination.

Overall, Kesimpta's pharmacokinetic profile supports effective subcutaneous monthly dosing for chronic management of relapsing multiple sclerosis, with a predictable absorption phase, limited distribution volume, proteolytic metabolism, and target-mediated elimination.

Dosage Forms

Available Dosage Forms:
- Single-dose prefilled Sensoready pen for subcutaneous use: 20 mg/0.4 mL
- Single-dose prefilled syringe for subcutaneous use: 20 mg/0.4 mL (discontinued)

Dosages for Adults and Adolescents:
- Initial dosing schedule consists of 20 mg administered subcutaneously at Weeks 0, 1, and 2.
- No injection is administered at Week 3.
- Maintenance dosing is 20 mg subcutaneously once monthly thereafter starting Week 4.

Specific Patient Populations:
- Kesimpta is indicated for adults with relapsing forms of multiple sclerosis, including clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease.
- Safety and effectiveness in pediatric populations have not been established.
- No specific dose adjustments have been recommended for elderly patients; however, clinical experience in geriatric populations is limited.
- Use in pregnancy requires careful consideration; contraception is advised during treatment and for 6 months after the last dose.
- Breastfeeding patients should weigh potential benefits and risks as data on excretion into breast milk are lacking.
- Dose administration by subcutaneous injection allows patient self-administration following proper training.
- Sites for injection include the abdomen, thigh, or outer upper arm, avoiding areas with bruising or skin abnormalities.

Comprehensive preparation instructions and disposal procedures for used devices are provided in the package insert to ensure safe and effective use.

Mechanism Of Action

Kesimpta (ofatumumab) is a fully human IgG1 kappa monoclonal antibody targeting the CD20 antigen, a transmembrane phosphoprotein expressed on the surface of pre-B and mature B lymphocytes but not on stem cells or plasma cells. Its principal mechanism involves binding specifically to a distinct epitope different from other anti-CD20 antibodies, which leads to robust and selective B-cell depletion.

Upon binding to CD20, ofatumumab induces immune-mediated cytolysis primarily via complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC). CDC involves the activation of the classical complement cascade, resulting in the formation of membrane attack complexes that induce lysis of the targeted B cells. ADCC recruits effector cells such as natural killer cells that recognize the Fc region of the antibody and mediates apoptosis of the bound B cells. These combined mechanisms result in rapid and sustained depletion of circulating and tissue-resident CD20-positive B cells.

B cells play a critical role in the pathogenesis of multiple sclerosis through antigen presentation, pro-inflammatory cytokine secretion, and antibody production contributing to demyelination and neurodegeneration. By depleting CD20-positive B cells, ofatumumab modulates the autoimmune response, reducing inflammatory activity within the central nervous system. This effect translates clinically to reduced relapse rates, decreased new lesion formation on MRI, and slowed disability progression.

Compared to other anti-CD20 therapies, ofatumumab's fully human structure reduces immunogenicity and hypersensitivity reactions. Its high affinity binding to the membrane-proximal small loop epitope on CD20 enhances complement activation potency. Unlike intravenous infusion of other agents, Kesimpta’s subcutaneous administration enables more consistent bioavailability and convenience, facilitating monthly self-administration. Clinical trials have demonstrated rapid onset of B-cell depletion within one week of initiation and sustained control of disease activity. Research continues to explore additional benefits such as neuroprotective properties and long-term safety with prolonged B-cell modulation.

Pharmacological Actions

Selective depletion of CD20-positive pre-B and mature B lymphocytes
Induction of complement-dependent cytotoxicity (CDC) leading to targeted B-cell lysis
Mediation of antibody-dependent cellular cytotoxicity (ADCC) causing apoptosis of B cells
Modulation of autoimmune responses involved in multiple sclerosis pathogenesis
Reduction of inflammatory cytokine production by B cells in the central nervous system
Suppression of new lesion development and demyelination in MS patients
Selective immunosuppressive effect without generalized immune ablation
Facilitation of B-cell repopulation normalization after cessation
High affinity binding to CD20 epitope enhancing complement activation
Minimal immunogenicity due to fully human monoclonal antibody design
Improved patient compliance via subcutaneous, self-administered dosing
Potential neuroprotective effects via immune modulation
Rapid depletion of B cells within days of treatment initiation
Sustained pharmacodynamic effect allowing monthly dosing schedules
Reduced relapse frequency and slowed disease progression in relapsing MS

Therapeutic Or Clinical Uses

Treatment of relapsing forms of multiple sclerosis (MS) in adults
Effective in clinically isolated syndrome with high risk of MS progression
Management of relapsing-remitting multiple sclerosis (RRMS)
Therapy for active secondary progressive multiple sclerosis (SPMS)
Reduction in annualized relapse rate and new MRI lesion formation
Slowing of neurological disability progression associated with MS
Alternative to other disease-modifying therapies in relapsing MS
Option for patients preferring subcutaneous self-administration
Treatment for patients intolerant to infusion-based anti-CD20 therapies
Used as monotherapy to modulate autoimmune B-cell activity
Adjunctive therapy in managing inflammatory and immune-mediated CNS disease
Potential to maintain long-term disease remission through B-cell depletion
Considered in patients with high disease activity and frequent relapses
Off-label exploration in other B-cell mediated conditions under investigation
Part of personalized treatment regimens for MS tailored by clinical response

Side Or Adverse Effects

Upper respiratory tract infections including sore throat, runny nose, and headache
Headache of varying severity and duration
Injection site reactions such as redness, swelling, pain, and itching
Systemic injection-related reactions including fever, chills, malaise, and rash
Serious infections including potential life-threatening bacterial, viral, or fungal infections
Hepatitis B virus reactivation leading to liver injury or failure
Progressive multifocal leukoencephalopathy (PML), a rare but fatal brain infection
Hypersensitivity reactions ranging from mild allergic symptoms to anaphylaxis
Decreased immunoglobulin levels resulting in immunosuppression
Potential fatigue and malaise related to immune modulation
Nausea and gastrointestinal discomfort reported in some patients
Increased risk of infections when combined with other immunosuppressive agents
Possible respiratory symptoms such as cough and nasal congestion
Infusion/injection-related systemic symptoms that may worsen with subsequent doses
Rare neurological symptoms including changes in coordination or cognition

Precautions

Delay treatment in patients with active infections until resolved
Screen for hepatitis B virus prior to initiating therapy to prevent reactivation
Monitor patients for signs and symptoms of infection throughout treatment
Avoid live or live-attenuated vaccines during treatment and until immune recovery
Consider vaccination at least 4 weeks before starting therapy when possible
Use caution in patients with compromised immune systems or concomitant immunosuppressants
Pregnant women should practice effective contraception during and for 6 months post-treatment
Breastfeeding patients should evaluate risks and benefits with healthcare provider
Avoid injection into bruised, red, or inflamed skin areas to reduce local reactions
Educate patients on recognizing early signs of serious infections and neurologic symptoms
Assess immunoglobulin levels periodically due to risk of hypogammaglobulinemia
Monitor liver function tests in patients at risk for hepatitis
Advise patients on proper injection technique and disposal of sharps
Consider patient's vaccination history and schedule before initiating Kesimpta
Regular neurologic assessment to detect early PML or MS worsening

Warnings

Serious and potentially fatal infections, including bacterial, viral, and fungal types
Risk of hepatitis B virus reactivation causing hepatic failure or death
Progressive Multifocal Leukoencephalopathy (PML), a rare but often fatal brain infection
Severe injection-related reactions including anaphylaxis requiring prompt medical attention
Immunosuppression leading to increased susceptibility to opportunistic infections
Use cautiously when co-administered with other immunosuppressive medications
Live attenuated vaccines are contraindicated during and for an extended period after treatment
Patients with a history of severe allergic reaction to ofatumumab should not receive Kesimpta
Potential for low immunoglobulin levels necessitating monitoring during therapy
Increased risk of infections during pregnancy and breastfeeding should be considered
Delayed hypersensitivity reactions may occur and require monitoring
Injection site reactions can be severe and recurrent
Patients should report new or worsening neurological symptoms immediately
Not interchangeable with intravenous ofatumumab formulation (Arzerra) due to different indications
Accidental overdose requires immediate medical evaluation due to B-cell depletion risks

Contraindication

Active hepatitis B virus infection
Known hypersensitivity to ofatumumab, Kesimpta, or any component of the formulation
History of life-threatening injection-related reactions to Kesimpta
Concurrent administration of live or live-attenuated vaccines
Severe active infections at the time of planned treatment initiation
Patients with a history of progressive multifocal leukoencephalopathy (PML)
Known immunodeficiency disorders contraindicating B-cell depleting therapies
Severe allergic reactions to other monoclonal antibodies requiring caution
Receipt of immunosuppressive therapy that significantly compromises immune function without clinical indication
Pregnancy when effective contraception is not used or desired
Any condition where immunosuppression poses unacceptable risk
Use in pediatric patients not established and thus contraindicated until safety proven
Concurrent participation in another investigational drug trial with overlapping immunosuppressant mechanisms
Uncontrolled systemic infections or sepsis
Severe hepatic impairment with active viral hepatitis

Drug Interactions

Increased risk of infections when combined with other immunosuppressive agents such as corticosteroids
Potential additive immune suppression with chemotherapy drugs used for cancer treatment
Possible interactions with immunomodulators increasing risk of hematologic adverse effects
Medications that impair immune function, such as calcineurin inhibitors, may enhance infection risk
Reduced efficacy of live or live-attenuated vaccines administered during or shortly before therapy
Concomitant use of other biologic immune-targeted therapies requires close monitoring
No significant cytochrome P450 metabolism-based interactions due to monoclonal antibody nature
Interactions with over-the-counter immune suppressing agents or herbal supplements not well characterized; caution advised
Potential interference with diagnostic immunoassays due to circulating monoclonal antibody
Incremental immunosuppressive effects when combined with disease-modifying therapies for multiple sclerosis
Possible alteration of immune response reducing ability to mount effective response to infections
No known interactions with typical antibiotics, but infection risk increases with immunosuppression
Monitoring recommended when combining with antiviral agents in the setting of latent infections
Potential interaction with live vaccines contraindicates their concomitant use
Close clinical monitoring advised when transitioning to or from other anti-CD20 therapies

Preparations Of The Drug

Single-dose prefilled Sensoready pen containing 20 mg of ofatumumab in 0.4 mL for subcutaneous injection
Single-dose prefilled syringe containing 20 mg of ofatumumab in 0.4 mL for subcutaneous injection (discontinued)
Inactive ingredients include arginine, disodium edetate, polysorbate 80, sodium acetate trihydrate, sodium chloride, Water for Injection, and hydrochloric acid as needed for pH adjustment
Formulated for subcutaneous administration with devices designed for patient self-injection
Provided in original carton and must be refrigerated between 2°C to 8°C (36°F to 46°F)
Stable for up to 7 days at controlled room temperature up to 30°C (86°F) with proper documentation of removal date
Should not be frozen or shaken to maintain drug stability and efficacy
Proper disposal of used Sensoready pens or syringes is necessary to prevent needlestick injuries
Packaging includes detailed instructions for use to guide patients in preparation and administration
Manufactured by Novartis Pharmaceuticals Corporation with global regulatory approvals
Packaging includes safeguards to protect from light exposure during storage
Device design enables ease of use with features to minimize injection discomfort
The drug is supplied with all necessary materials to facilitate safe home administration
Storage and handling instructions must be strictly followed to maintain product integrity
Patient support materials and counseling are provided to optimize adherence and safe use