Ocrevus (ocrelizumab) is given as an intravenous infusion at a medical facility, with each session lasting roughly 2.5 to 3.5 hours depending on the dose. A newer subcutaneous option, Ocrevus Zunovo, can deliver the medication in about 10 minutes. Both require administration by a healthcare professional and a monitoring period afterward.
How the First Dose Works
Your first round of Ocrevus is split into two smaller infusions of 300 mg each, given two weeks apart. Each of these initial infusions takes about 2.5 hours. Splitting the dose this way reduces the chance of a reaction, since your body is encountering the medication for the first time.
Before you can start treatment, your medical team will run several screening tests. These include hepatitis B testing, liver function tests, and a review of your vaccination history. Any live or live-attenuated vaccines need to be given at least four weeks before your first dose, and non-live vaccines should ideally be completed at least two weeks prior. This matters because Ocrevus works by depleting a specific type of immune cell, which can reduce your response to vaccines once treatment begins.
Ongoing Infusions Every Six Months
After the initial two-dose sequence, you’ll receive a single 600 mg infusion every six months. The standard infusion time for these maintenance doses is about 3.5 hours. Some infusion centers offer a shorter protocol that delivers the same 600 mg dose in roughly 2 hours, which your doctor may recommend if you tolerated previous infusions well.
Each appointment is longer than the infusion itself. You’ll receive premedication beforehand (typically a corticosteroid and an antihistamine) to lower the risk of a reaction, and you’ll be monitored for at least one hour after the infusion finishes. All told, plan for a half-day commitment at the infusion center for each visit.
The Subcutaneous Option: Ocrevus Zunovo
In 2024, the FDA approved Ocrevus Zunovo, a subcutaneous formulation that’s injected under the skin of the abdomen rather than infused into a vein. A healthcare professional delivers 920 mg of ocrelizumab in a 23 mL injection over approximately 10 minutes, repeated every six months.
There’s an important catch: Ocrevus Zunovo is not used for the very first doses. You still need to complete your initial IV infusions before switching to the subcutaneous version. The injection contains an enzyme called hyaluronidase that helps the medication absorb through tissue under the skin, which is why the volume can be delivered so quickly. For people who find the hours-long IV infusions burdensome, this option significantly shortens treatment visits.
What Happens in Your Body During Treatment
Ocrevus targets a protein called CD20, which sits on the surface of certain immune cells called B cells. Once the medication enters your bloodstream (or absorbs from the injection site), it attaches to CD20 and triggers the destruction of those cells. This is relevant to multiple sclerosis because B cells play a role in driving the immune attacks that damage nerve fibers.
The depletion is thorough in the bloodstream but not uniform everywhere. B cells in lymph nodes and inflamed areas of the central nervous system aren’t eliminated to the same degree. Importantly, the cells responsible for producing long-term antibodies (plasma cells in bone marrow) don’t carry CD20, so they survive treatment. This is why you generally retain immunity from past infections and vaccines you received before starting Ocrevus, even as the drug reshapes your active immune response.
Infusion Reactions: What to Expect
Infusion-related reactions are the most common side effect, and they’re most likely during your first infusions. Symptoms can include throat irritation, flushing, headache, and itching. In clinical studies, virtually all reactions were mild or moderate, with no severe (grade 4 or 5) reactions reported. About 5% of patients who had no throat irritation during their initial doses experienced it later, while those who had throat symptoms early on were more likely to see them recur.
If a reaction occurs, the infusion team can slow or pause the drip, which usually resolves symptoms quickly. Your premedication regimen may also be adjusted for future visits, though studies have found that tweaking the timing or type of premedication doesn’t dramatically change reaction rates. Most people find that reactions become less frequent and less noticeable with subsequent infusions, which is part of why the shorter infusion protocol becomes an option after the first few doses.
Practical Tips for Infusion Day
Wear comfortable clothing with sleeves that roll up easily, since the IV goes into your arm. Bring entertainment: a book, laptop, or headphones, because even the shorter protocol means at least a few hours in the chair once you factor in premedication and post-infusion monitoring. Eating a light meal beforehand is generally a good idea, and staying well hydrated can make it easier for the nurse to place your IV line.
Some people feel fatigued for a day or two after their infusion. This isn’t universal, but it’s common enough that scheduling your appointment before a rest day (rather than a busy workday) can make the experience more manageable. If you’re receiving the subcutaneous injection instead, the visit is much shorter, but you’ll still need to stay for observation afterward.