Most Common Side Effects of Kesimpta
Kesimpta (ofatumumab), an anti-CD20 monoclonal antibody for relapsing forms of multiple sclerosis (MS), commonly causes injection-related reactions and upper respiratory infections. In clinical trials, these affected over 10% of patients:
- Injection-related reactions (around 21%), including pain, redness, or swelling at the site; most occur after the first dose and decrease over time.
- Upper respiratory tract infections (39%).
- Urinary tract infections (11%).
- Headache (12%).
- Blood tests showing low immunoglobulin M (IgM) levels (up to 83%, though often asymptomatic) and low B-cell counts (nearly all patients).[1][2]
How Injection Reactions Happen and What to Expect
These reactions stem from the subcutaneous self-injection (monthly after initial doses) and typically last hours to days. Symptoms like fatigue, fever, chills, or rash appear within 24 hours. Premedication with pain relievers or antihistamines isn't routinely needed but can help; reactions drop from 20-25% after the first dose to under 5% later.[2][3]
Side Effects Patients Report Most Online
Forum discussions and patient reviews highlight injection site pain or itching as the top complaint, alongside fatigue and headaches persisting beyond the first week. Fewer mention infections unless prone to them.[4]
Serious Risks and Monitoring
Less common but serious effects include infusion-like reactions (rare with subcutaneous form), hepatitis B reactivation (screen before starting), or progressive multifocal leukoencephalopathy (PML) risk from B-cell depletion. Live vaccines are off-limits during treatment. Regular blood work tracks infections and cell counts.[1][3]
How Kesimpta Side Effects Compare to Other MS Infusions
Versus Ocrevus (ocrelizumab, IV every 6 months), Kesimpta has more local injection issues but fewer systemic infusion reactions. Both share infection and IgM risks, but Kesimpta's home dosing cuts clinic visits.[2][5]
Sources:
[1]: Kesimpta Prescribing Information (Novartis)
[2]: FDA Label for Kesimpta
[3]: MS Society on Kesimpta
[4]: Patient forums aggregated via Drugs.com reviews
[5]: ASCLEPIOS trials head-to-head data (NEJM 2020)