What to Expect at Your First Biologic Infusion

Your first biologic infusion is almost always the longest and most watched one you will ever have, and most of that time is not the drip. Expect to be weighed, have your observations taken, answer questions about infection, have a cannula placed, wait while pharmacy prepares a dose made up for you, sit through the infusion itself (roughly 30 minutes to 2 hours depending on the drug), and often stay on for an observation period afterwards. Reactions happen, are mostly mild, and are exactly what the nurses are there to deal with.

This guide covers infused biologics used for Crohn's disease and ulcerative colitis: infliximab (Remicade and its biosimilars, such as Inflectra), vedolizumab (Entyvio), and the intravenous starting doses of ustekinumab (Stelara), risankizumab (Skyrizi), mirikizumab (Omvoh) and guselkumab (Tremfya). It describes what happens on the day and what the published evidence says about it. It does not tell you which drug to take, what dose, or whether to change anything your team has planned. Those are conversations for your IBD team, and our questions to ask about Crohn's treatment post covers what to raise before a biologic starts.

The short answer: what the day actually looks like

A first infusion follows a fairly predictable sequence wherever you have it, even though the timings vary. Here is the order the threads describe and the labels require, with what each step is for.

The "start within 3 hours" detail comes from the infliximab label, which also says the infusion must run for at least 2 hours through an in-line filter (Remicade label). That is one reason units often do not mix your dose until you are sitting in the chair: if you were late or were sent home because of an infection, the dose would be wasted.

How long does a first biologic infusion take? Drug by drug

The infusion time is set by each drug's label, and the total visit is longer. The table below uses the US labels for the infusion times. The observation column only shows what a label actually specifies, because most US labels do not name an observation period at all.

Sources: US prescribing information for Remicade, Entyvio, Stelara, Skyrizi, Omvoh and Tremfya, and the European product information for Remicade and Entyvio.

Why the same drug produces such different visit lengths

The vedolizumab row is the clearest example of something that confuses a lot of people before their first appointment. The US label says to observe patients "during infusion and until the infusion is complete" (Entyvio label). The European product information says patients should be observed for approximately 2 hours after each of the first two infusions and approximately 1 hour after every one after that (EMA Entyvio). Same molecule, same 30-minute drip, but a first visit that can run from under an hour to around three.

That matches what people report. In one r/UlcerativeColitis thread from someone frightened about their first Entyvio dose, replies describe infusions of about 30 minutes and one person being out of hospital in 2 hours. In another, a person planning a cinema trip with their sister after a first Entyvio infusion had been told to expect 1.5 to 2 hours. For infliximab, a long r/CrohnsDisease thread asking what to expect has reports ranging from 2.5 to 6 hours, with "3 to 4 hours" the most common estimate for the first one.

Local policy sits on top of the label. Units may add their own watch period, give premedication that has to take effect before the drip starts, or wait for blood results. If your unit tells you a time, that is the number to plan around.

Why the first one is the longest, and when they get shorter

First infusions are run at the full labelled duration, and the shortening, where it happens at all, comes later and only for infliximab. The European infliximab label allows subsequent infusions over not less than 1 hour in "carefully selected adult patients" who have tolerated at least three initial 2-hour infusions and are on maintenance (EMA Remicade). The US label still states at least 2 hours.

The evidence behind shortened infusions is reasonably reassuring, with one important caveat.

• A Belgian centre switched people who had tolerated at least four 2-hour maintenance infusions to 1-hour infusions. Across 9,155 maintenance infusions, mild acute reactions occurred in 0.6% of 1-hour infusions and 1.7% of 2-hour ones, and no severe reactions were documented (Breynaert 2011).
• A Canadian prospective cohort of 2,165 infusions found reactions clustered within the first eight infusions and then became sporadic, and found 1-hour maintenance infusions safe in people without a previous significant reaction (Lee 2011). The same paper notes that infliximab was "generally administered over 2h with a further 1-h postinfusion observation".
• In a specialist unit audit, people on 1-hour infusions spent a median of 1 hour 35 minutes on the unit, against a median of 3 hours 20 minutes for people given prophylactic premedication (Van Assche 2010).
• Rapid 60-minute infusions of infliximab biosimilars had no more reactions than standard infusions in one US cohort of 1,124 infusions (Rusch 2022).

The caveat is selection. Only people who had already tolerated several full-length infusions were moved to the faster rate, so a lower reaction rate in that group partly reflects who was chosen, not just the speed. That is also why nobody runs a first infusion fast.

One long-time infliximab user in the Crohn's thread described a six-month period when their unit shortened everyone's drip to 1.25 hours, felt markedly worse afterwards, and said roughly half the patients there did not tolerate it, after which the policy was dropped. That is one person's account of one unit and not evidence about rapid infusions in general, but it is a useful reminder that a slower rate is a reasonable thing to ask about if a shortened one does not suit you.

What they check before they start, and why your infusion can be postponed

The safety work for a biologic mostly happens weeks before your first infusion, and the day itself is a final check. Every one of these drugs carries label instructions about screening before treatment starts:

• Tuberculosis. Infliximab, ustekinumab, risankizumab, mirikizumab and guselkumab labels all require evaluation for TB before starting; the vedolizumab label says to consider it (Remicade label; Entyvio label). Our post on night sweats with Crohn's covers what the TB numbers on biologics actually look like.
• Hepatitis B. The infliximab label says to test for hepatitis B infection before starting.
• Liver tests. The risankizumab, mirikizumab and guselkumab labels ask for liver enzymes and bilirubin before starting in IBD, and the risankizumab label asks for monitoring through at least the first 12 weeks (Skyrizi label; Omvoh label; Tremfya label). That explains the Skyrizi thread in which one person described labs, a wait for results, then a one-hour infusion.
• Vaccinations. Several labels ask for vaccinations to be brought up to date before starting and say to avoid live vaccines during treatment.

On the day, the nurse will ask about fever and infection because the infliximab label is blunt: do not give it during an active infection (Remicade label). Tell them about a cold sore, a urinary infection, a chest infection or a course of antibiotics. It may make no difference, but it is their decision to make with the information in front of them.

Postponement hurts when you have been counting the days. One person in r/UlcerativeColitis had their first Entyvio loading doses cancelled days beforehand when the infusion team read a stool test as showing active C. difficile, which their GI had read differently. We cannot tell from the thread who was right, and a reply suggested the gap might be between detecting the organism and detecting its toxin. The practical lesson is to ask for any recent stool or blood results to be reviewed by your IBD team before the day, not on it.

Premedication: what it is, and what the evidence says

Premedication means drugs given before the infusion in the hope of preventing a reaction, typically paracetamol (acetaminophen), an antihistamine such as diphenhydramine (Benadryl), loratadine or cetirizine, and sometimes a steroid such as hydrocortisone. The infliximab labels allow it: the US label says patients "may be premedicated" with antihistamines, acetaminophen and/or corticosteroids (Remicade label), and the European label mentions it "especially if infusion-related reactions have occurred previously" (EMA Remicade).

Whether it prevents first-time reactions is a different question, and the evidence is not encouraging:

• A 2019 meta-analysis of ten studies (eight observational, two randomised), including 1,385 people with IBD, found corticosteroid premedication was not associated with fewer acute infliximab reactions (odds ratio 1.04 in IBD, confidence interval 0.52 to 2.07), and neither was antihistamine premedication (Fumery 2019). The combination was associated with more reactions in IBD (odds ratio 4.17), which more likely reflects who gets premedicated than harm from the premedication itself, since the studies were mostly observational and heterogeneity was high. The authors concluded these drugs "should no longer be part of standard protocols".
• In the Canadian cohort, corticosteroid premedication "had no impact on the infusion reaction rates" (Lee 2011).
• A US claims analysis of 19,637 people with IBD on infliximab found corticosteroid premedication fell from 27.4% in 2015 to 20.4% in 2020, and that 62.5% of those premedicated received it with their very first infusion, when there had been no previous reaction to prevent. The authors called it a "low-value practice" (Cohen-Mekelburg 2025).

There is one narrower argument for steroid premedication: that it might reduce antibodies against infliximab. A French study used that as its starting assumption, then found that stopping hydrocortisone premedication in 95 people in stable remission on infliximab led to no permanent antibodies or infusion reactions over a year (Tran-Minh 2021). A Danish cross-sectional study of 57 people found steroid premedication made no difference to antibody formation or drug levels (Larsen 2019). A systematic review of infusion reaction strategies summed up the field fairly: there were no randomised trials with infusion reactions as the primary outcome, and controlled data on prevention remain scarce (Lichtenstein 2015).

None of this means you should refuse premedication or ask for it to be stopped. It is a protocol question for your team. What it does mean is that "they gave me Benadryl so I would not react" is not something the evidence clearly supports, and that the main practical effect of a sedating antihistamine may be on your afternoon and your drive home.

How common are infusion reactions, and what does one feel like?

Infusion reactions are the thing most people are frightened of, and the honest numbers are both reassuring and slightly misleading at first glance. In infliximab clinical trials, an infusion reaction was defined as any adverse event during or within 1 hour of an infusion. About 20% of people given infliximab had one, compared with 10% of people given placebo (Remicade label).

The label breaks the infliximab reactions down further: 3% of infusions came with nonspecific symptoms such as fever or chills, 1% with cardiopulmonary symptoms (mainly chest pain, blood pressure changes or breathlessness), and under 1% with itching or hives. Serious reactions occurred in under 1% of patients. Notably, infusions after the first were not associated with a higher rate of reactions (Remicade label).

Outside trials, a New York infusion centre reviewed 479 infliximab infusions in 165 people with Crohn's disease. Acute reactions were mild in 15 infusions, moderate in 6 and severe in 5, and there were 3 delayed reactions, for 29 in total: 6.1% of infusions, affecting 9.7% of patients (Cheifetz 2003). All acute reactions resolved rapidly with the centre's protocols, and everyone who had a mild or moderate reaction went on to receive further infusions. Normal tryptase levels in those tested suggested most were not true allergic (IgE-mediated) reactions.

The other infused biologics report lower rates. In the vedolizumab trials, 4% of people had an infusion-related reaction against 3% on placebo, mostly nausea, headache, itching, dizziness and fatigue, generally within 2 hours (Entyvio label); an integrated safety analysis of six trials described infusion-related reactions as low in incidence (Colombel 2017). In the mirikizumab UC induction study, infusion-related hypersensitivity was reported by 0.4% of treated people and 0.3% on placebo (Omvoh label). In the ustekinumab Crohn's trials, one person had a hypersensitivity reaction after the first IV dose, 0.08% of those given it, although the label notes that some serious reactions have happened during the first IV dose (Stelara label).

What a reaction looks like from the chair

The symptoms listed in the labels and studies are flushing, itching, hives, a rash, chills, fever, headache, nausea, dizziness, chest tightness, shortness of breath, and changes in blood pressure or heart rate. People in the threads also describe odd, hard-to-name sensations, such as an itch or a chill somewhere unexpected, during the first infusion only. Tell the nurse about anything new, even if it seems silly. The labels describe slowing or stopping the infusion and treating symptoms, then sometimes restarting at a slower rate (Remicade label). One first-time Stelara user found that asking for a slower rate settled their nausea.

What raises the risk with infliximab

Two things stand out. Antibodies to infliximab more than double the risk of acute reactions: a meta-analysis of eight studies put the risk ratio at 2.4, while noting most of the studies had a high risk of bias, and found taking an immunomodulator alongside reduced the risk (O'Meara 2014). In a Boston cohort of 287 people with Crohn's, 18% had at least one reaction, and only concomitant azathioprine or mercaptopurine remained protective after adjustment (Moss 2008). That cohort also found people who had reactions did less well over the following years, which is a reason reactions get recorded carefully, not a reason to panic during your first one.

The second is gaps in treatment. In an analysis of ACCENT I data, antibodies developed in 30% of people given a single dose followed by episodic retreatment, against 10% and 7% in the scheduled maintenance groups (Hanauer 2004). Our flying with Crohn's medication post covers why that matters when travel tempts you to move an infusion date.

Delayed reactions: the ones that happen days later

Some reactions happen after you have gone home, which is why you should leave with advice about what to look out for. The infliximab patient information describes delayed allergic reactions occurring 3 to 12 days after treatment, with fever, rash, headache, sore throat, muscle or joint pain, swelling of the face and hands, or difficulty swallowing (Remicade label). The prescriber section says these serum-sickness-like reactions have been seen after initial therapy, as early as the second dose, and when infliximab was restarted after a long break.

They are uncommon. In the New York series, delayed reactions followed 0.6% of infusions (Cheifetz 2003). In the Belgian maintenance cohort, they followed 0.2% of 1-hour and 0.5% of 2-hour infusions (Breynaert 2011). The risk is clearest on restarting after a gap: in a psoriasis trial of patients not on any immunosuppressant, 4% of those restarted with an induction course had serious infusion reactions, against under 1% on continuous maintenance, mostly at the second infusion (Remicade label). That is a psoriasis population, not IBD, but the label applies the warning across indications.

How you will probably feel afterwards

Most people feel fine or tired, and tiredness is so commonly reported that it is worth planning around. Across the threads we read, the recurring descriptions were: sleepy during the drip, especially after a sedating antihistamine; tired that evening; for some, wiped out the next day rather than the same day; a headache that night or for a day or two; and, much less often, a cold-like feeling or sore joints after one of the early doses. One person in r/UlcerativeColitis described being knocked out for 24 hours after each of their three Entyvio loading doses, while others in the same thread went straight back to work.

Here is the honest part: we could find no study that measured fatigue after an infusion as its own outcome, so nobody can tell you how common it is or what causes it. The labels list headache and fatigue among common adverse reactions over the whole course of treatment, which is not the same thing as how you feel on infusion day. Plausible contributors include a sedating antihistamine, an early start and a long day, the anxiety of a first appointment, and the disease itself, especially if you are anaemic or flaring. If tiredness on infusion day is severe or growing, mention it to your team; our Crohn's fatigue in remission post covers the longer-term picture.

A sensible default for the first infusion is to plan nothing demanding for the rest of the day, and to keep the next morning light if you can. After a couple, you will know your own pattern, and many people end up working through their infusions or going back to work afterwards.

Can you drive home after an infusion?

Plan a lift for the first one, and ask your unit what they require. The European labels say infliximab "may have a minor influence on the ability to drive and use machines" because dizziness may occur, and that vedolizumab has a minor influence because dizziness has been reported in a small number of patients (EMA Remicade; EMA Entyvio).

Premedication is the bigger issue. In a randomised, double-blind crossover trial in the Iowa driving simulator, 40 drivers each drove after, in turn, a single dose of the sedating antihistamine diphenhydramine, the non-sedating antihistamine fexofenadine, alcohol at about 0.1% blood alcohol, and placebo. Driving performance was poorest after diphenhydramine, worse than after alcohol, and self-rated drowsiness was not a good predictor of impairment (Weiler 2000). That trial used tablets in people with hay fever, not intravenous diphenhydramine in people with IBD, so the size of the effect will not transfer exactly. The point that does transfer is that "I feel fine" is not a reliable test. If you are given a sedating antihistamine, do not drive yourself home.

Eating, drinking and getting the cannula in

None of the six US labels we read asks you to fast for an infusion, so eat beforehand unless your unit tells you otherwise. The cannula is the part most people in the threads say they mind most, and the two tips that come up again and again are to drink plenty beforehand and to get warm.

Warmth is the tip with a trial behind it. In a randomised controlled trial in 100 neurosurgical patients, actively warming the hand and forearm for 15 minutes before cannulation cut first-attempt failures from 28% to 6% and roughly halved the time needed; a crossover study in 40 people having chemotherapy found a similar effect (Lenhardt 2002). You will not have a heated mitt, but a warm room, warm layers and warm hands are worth having, and some people in the threads walk or take the stairs before arriving to the same end.

Hydration is the most repeated tip of all, but we could find no trial testing whether drinking more water beforehand makes cannulation easier, so treat it as common sense from people who have done this many times, not proven. If you have veins that are notoriously hard to find, tell the nurse at the start; people with years of infusions sometimes end up with an implanted port, which is a conversation for your team.

What to bring

The threads are remarkably consistent, and nearly all of it is about comfort over a long sit:

• Layers or a blanket. Infusion rooms and the fluid itself can feel cold; many people mention getting chilly.
• A short-sleeved top or a front-opening layer, so the nurse can reach your arm and take blood pressure without you undressing.
• Something to do one-handed: a phone, a tablet with shows already downloaded (hospital wifi is often poor), a book, headphones, and a long charging cable.
• Snacks and a drink. Some units provide them and some run out.
• Easy clothing for the toilet. You will usually be connected to a pump on a pole; ask how bathroom trips work before the drip starts, and go just before it does.
• A list of your medicines and allergies, and any questions you want to ask the nurse.
• Someone to take you home, at least for the first one.

Will you feel better after the first infusion?

Some people do within days, many do not, and the timescale depends heavily on the drug. These are the trial results for how many people responded after the starting doses, set against placebo, because the placebo response in IBD trials is large enough to matter.

The infliximab figure comes from a small 1997 trial of a single infusion, using the 5 mg/kg group; the higher-dose groups responded less often (50% and 64%). The vedolizumab and ustekinumab trials were funded by their manufacturers, as their abstracts state. The vedolizumab Crohn's trial did show more remission at week 6 (14.5% against 6.8%), and more people who responded to induction stayed in remission at a year, but the early response gap was small (Sandborn 2013). That is the evidence behind the common advice in the threads not to judge a slower drug by how you feel in the first week or two.

These are trial averages measured with research scores, not a prediction for you. What they do suggest is to agree with your team in advance when and how they will judge whether the drug is working, so a slow start is not mistaken for failure, and a real failure is not left too long.

Scoring your symptoms the day before your first infusion gives you a baseline to compare against later. The Harvey-Bradshaw Index above is a Crohn's score built from the previous day's symptoms; for ulcerative colitis, the PRO-2 calculator does the same job. Our IBD symptom diary post covers what else is worth recording, including the treatment record of reactions, premedication and infusion dates that will matter years from now.

Home infusion, and moving from infusions to injections

Not every biologic stays an infusion. Vedolizumab can move to injections after the two starting infusions, and ustekinumab, risankizumab, mirikizumab and guselkumab use intravenous doses only to start (or, for guselkumab, injections throughout as an alternative) before switching to injections under the skin (Entyvio label; Tremfya label). For several of these drugs, the infusion chair is a few-visit experience.

Some people get maintenance infusions at home. The evidence on that is thin and not reassuring. A matched retrospective study at one New York IBD centre compared 69 people who moved to home infusion of infliximab or vedolizumab with 69 matched people who stayed at the hospital infusion centre. The home group had more adverse outcomes, a composite of stopping therapy, IBD-related emergency visits or hospitalisation (43.5% against 21.7%), more emergency visits, and fewer clinic visits and blood tests (Fenster 2020). The authors suggested reduced monitoring might explain it. It is one small, single-centre, non-randomised study, so it cannot show that home infusion itself causes worse outcomes, but it is worth knowing if home infusion is offered.

Many people prefer the infusion chair. In telephone interviews with 405 people on IV biologics across six conditions, 82% preferred their IV medicine to self-injection, most often because they did not want to inject themselves, liked less frequent dosing, or valued having a health professional give it (Bolge 2017). That study was carried out by employees of Janssen, which makes the infused biologics Remicade and Stelara, as its disclosure states. Weigh it accordingly, though it fits what many people say in the threads about their infusion nurses.

A worked example: two first infusions in the same week

Two hypothetical people, both newly starting a biologic, show how different "your first infusion" can be. They are illustrations built from the label rules and the patterns in the threads, not real patients.

Sam, starting infliximab for Crohn's at a US hospital unit. Arrives at 8:30. Weighed, observations taken, asked about infection and recent antibiotics. Bloods drawn through the new cannula. Given paracetamol and an oral antihistamine under the unit's protocol, which takes half an hour to settle before the drip can start, and pharmacy prepares the weight-based dose once Sam has been checked. The drip runs from about 9:45 to 11:45, with observations at intervals. The unit keeps Sam for a further half hour. Cannula out at 12:20. Sam's partner drives, because of the antihistamine. Sam naps in the afternoon and has a mild headache that evening. Total: almost 4 hours.

Priya, starting vedolizumab for ulcerative colitis at a UK hospital. Arrives at 13:00. Observations, infection questions, cannula. No premedication. The 30-minute infusion finishes at 13:55, and in line with the European label she is observed for about 2 hours afterwards, because it is one of her first two infusions. Discharged at 16:00. She feels fine and gets the bus home, but is tired the next morning. Her third and later infusions are scheduled with a 1-hour watch period, and she has been told she can discuss switching to injections.

Same week, both "first biologic infusions", and one took twice as long as the other for reasons that had nothing to do with how either person was doing.

What to note on the day

A few minutes of notes on the day save a lot of guesswork later. Record the drug and brand (biosimilars count, since switching between them is common), the date, anything given as premedication, the start and end times, any reaction and how it was treated, and how you felt that evening and over the next few days. If you have a reaction, write down what happened in your own words while you remember it, because "I had a reaction to the second one" is much less useful to a future clinician than the symptoms and timing. Our post on tracking symptoms during a flare covers keeping notes when you feel rough.

If you would rather do this in an app, Clairop lets you log symptoms and medications alongside each other and turns them into a one-page summary for appointments; you can see how it works on the how it works page.

Myths about first infusions

"The first infusion is the most dangerous one." It is the most closely watched one, which is not the same thing. The infliximab label reports that infusions after the first were not associated with more reactions (Remicade label). Reactions do cluster in the early months, within roughly the first eight infusions in one cohort (Lee 2011), and the clearest risk pattern is restarting after a long gap.

"Premedication stops you reacting." The best available summary found steroids and antihistamines did not reduce acute infliximab reactions (Fumery 2019). Your unit may still use them; it is not a guarantee either way.

"A reaction means the drug is finished for you." Not necessarily. In the New York series, everyone who had a mild or moderate acute reaction was able to continue with further infusions using a prevention protocol (Cheifetz 2003). Whether to continue after a reaction is a decision for your team.

"If I feel nothing after the first one, it is not working." For vedolizumab in Crohn's disease, the week 6 response gap over placebo was small and not statistically significant, yet the drug still showed benefit in maintenance (Sandborn 2013). Ask your team when they expect to judge it.

"Entyvio is a 30-minute appointment." The drip is about 30 minutes. Whether the visit is 45 minutes or 3 hours depends on the observation rule your unit follows.

When to get help promptly

During the infusion, tell the nurse at once about anything new: itching, flushing, a rash, chest tightness, breathlessness, dizziness, a racing heart, swelling of the lips or tongue, or feeling faint. Do not wait to see if it settles.

After you get home, contact your IBD team or out-of-hours service promptly if you develop fever, a widespread rash, joint or muscle pains with a temperature, swelling of the face or hands, a sore throat, or difficulty swallowing in the days or weeks afterwards, since these are the delayed-reaction symptoms the infliximab label lists. Also report signs of infection, such as fever, a productive cough, burning when you pass urine, or a hot, painful area of skin, because these drugs can make infections more serious.

Call emergency services for breathing difficulty, swelling of the face, lips or throat, chest pain, or collapse.

And separately from the infusion, see a doctor promptly for heavy or increasing blood in your stool, severe abdominal pain, persistent vomiting, a high fever, signs of dehydration, or unexplained weight loss. A first biologic dose often comes during a flare, and the flare can still get worse before the drug has had time to work. Our Crohn's flare guide covers what to watch for.

The honest bottom line

A first biologic infusion is mostly a long, slightly boring, closely supervised sit in a reclining chair. Budget half a day, bring layers and something to do, eat beforehand, get warm, and arrange a lift if there is any chance you will be given a sedating antihistamine. Expect to be asked about infection, and do not be surprised if bloods or pharmacy add a wait. Reactions happen, mostly mild, mostly during the drip or within a couple of hours, and the people watching you are trained for them. Tiredness afterwards is common and unstudied, so plan an easy evening. And give the drug the time its own trials say it needs before you decide what the first one did or did not do.