Anti-CD20 monoclonal antibody Pregnancy: US label §8.1: there are no adequate data on the developmental risk associated with use in pregnant women. Ofatumumab may cross the placenta and cause fetal B-cell depletion based on animal findings; no teratogenicity was seen after intravenous administration to pregnant monkeys during organogenesis, but increased mortality, depletion of B-cell populations and impaired immune function were observed in offspring in the absence of maternal toxicity at plasma levels higher than those in humans. Monoclonal antibodies can be actively transported across the placenta and ofatumumab may cause immunosuppression in the in utero-exposed infant. A pregnancy exposure registry (MotherToBaby Pregnancy Study in Multiple Sclerosis) monitors outcomes in women exposed during pregnancy. UK SPC §4.6 wording was not captured - clinician to check the SPC.

Ofatumumab

Brand names: Kesimpta, Arzerra

Ofatumumab is a fully human anti-CD20 monoclonal antibody given by subcutaneous injection as a disease-modifying therapy for relapsing multiple sclerosis.

Adult dose

Dose: 20 mg

Route: Subcutaneous injection only - into the abdomen, thigh or outer upper arm. Do not inject into moles, scars, stretch marks, or areas where the skin is tender, bruised, red, scaly or hard.

Frequency: Initial dosing: 20 mg at Weeks 0, 1 and 2. Subsequent dosing: 20 mg once monthly starting at Week 4.

SOURCE CAVEAT: no UK SPC (eMC) record was captured in this bundle - the dose above is taken from the US prescribing information for KESIMPTA (Novartis Pharmaceuticals Corporation, label date 2026-04-01), a subcutaneous 20 mg/0.4 mL presentation used in relapsing forms of multiple sclerosis. Ofatumumab is also marketed in other presentations for other indications, so the clinician must confirm that this product and indication match the page before use, and verify the regimen against the current UK SPC. ASSESSMENTS BEFORE THE FIRST DOSE (US §2.1): screen for hepatitis B virus (contraindicated in active HBV); obtain quantitative serum immunoglobulins (consult immunology experts first if low); obtain serum aminotransferases (ALT and AST), alkaline phosphatase and bilirubin. Because live-attenuated or live vaccines are not recommended during treatment and after discontinuation until B-cell repletion, give all immunisations at least 4 weeks before initiation for live or live-attenuated vaccines and, whenever possible, at least 2 weeks before initiation for inactivated vaccines. ADMINISTRATION (US §2.3-2.4): intended for patient self-administration, but the first injection should be performed under the guidance of a healthcare professional. Sensoready pens and prefilled syringes are single-use only. Remove from the refrigerator and allow to reach room temperature for about 15 to 30 minutes before administration - do not remove the needle cover from a prefilled syringe while it warms. Do not use if the liquid contains visible particles or is cloudy. MISSED DOSE: administer as soon as possible without waiting until the next scheduled dose; subsequent doses are then given at the recommended intervals. PAEDIATRIC: safety and effectiveness in paediatric patients have not been established (US §8.4) - verify any under-18 use against a children's formulary. ELDERLY: clinical studies did not include sufficient numbers of geriatric patients to determine whether they respond differently from younger subjects (US §8.5).

Dose independently re-sourced from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Active hepatitis B virus infection (US label §4)
History of hypersensitivity to ofatumumab, or a life-threatening injection-related reaction to this product - hypersensitivity reactions have included anaphylaxis and angioedema (US label §4)

Side effects

Upper respiratory tract infection - most common (incidence greater than 10%)
Headache - most common (incidence greater than 10%)
Injection-related reactions - most common (incidence greater than 10%)
Local injection site reactions - most common (incidence greater than 10%)
Serious, including life-threatening and fatal, infections have occurred with anti-CD20 therapies; also reduction in immunoglobulins, hypersensitivity reactions including anaphylaxis and angioedema, and clinically significant liver injury (US label §5)

Interactions

Immunosuppressant drugs, including systemic corticosteroids - concomitant use may increase the risk of infection; consider the risk of additive immune system effects (US label §7.1)
Switching from other therapies with immune effects - the duration and mechanism of action of the prior therapy should be taken into account because of potential additive immunosuppressive effects when initiating ofatumumab (US label §7.1)
Live-attenuated or live vaccines are not recommended during treatment and after discontinuation until B-cell repletion (US label §2.1/§5.1)

Clinical monograph

How it works

It binds CD20 on B lymphocytes, leading to their depletion and a reduction in the B-cell-driven inflammation responsible for relapses and central nervous system lesions.

Prescribing in practice

Screen for hepatitis B before starting, as B-cell depletion can cause viral reactivation, and avoid initiating in active infection.
It is suitable for home self-administration after appropriate training, with the first dose often given under supervision for injection reactions.
Update vaccinations beforehand, as live vaccines are not recommended during treatment, and monitor for infections.

Monitoring

Monitor for infections and injection-related reactions, with hepatitis B screening and immunoglobulin levels checked as indicated.

Counselling the patient

Learn correct subcutaneous injection technique and rotate sites.
Report any signs of infection between doses.
Ensure required vaccinations are completed before starting therapy.

Evidence & guidelines

Ofatumumab reduced relapse rate compared with an active comparator in pivotal trials and is recommended by NICE for relapsing multiple sclerosis.

Reference: NICE TA699; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

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