Guselkumab belongs to the class of medications called selective immunomodulating agents, also known as biologics. Specifically, it is an interleukin-23 inhibitor. It is used to treat moderate-to-severe plaque psoriasis for adults who are candidates for phototherapy or systemic therapy. It is also used to treat adults with active psoriatic arthritis.

Guselkumab works by blocking the action of the protein interleukin-23 in the body. If you have psoriasis, your body overproduces this protein.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The usual dose of guselkumab is 100 mg injected under the skin. After the first dose, the second dose is given in 4 weeks, and then every 8 weeks for subsequent doses.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

Most people using this medication can be taught by a health care professional to give themselves the injection. Guselkumab is used with the guidance and supervision of a doctor. Your doctor or nurse will assist you in the preparation and injection of your first dose (or first few doses). Do not attempt to inject this medication on your own until you completely understand how to inject a dose.

Before using this medication, remove it from the refrigerator and allow it to warm to room temperature, with the cap on. This takes approximately 30 minutes. Do not shake this medication. Shaking causes the medication to become less effective.

Follow the instructions from your doctor or pharmacist when administering the medication. The solution should be clear to slightly yellow and may contain tiny white or clear particles. Do not use the injection if it appears cloudy or discoloured, or if it has large particles floating in it.

Use a different site for each injection to decrease the risk of skin irritation. Dispose of your used needles in an appropriate sharps container.

If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication in the refrigerator, protect it from freezing, and keep it out of the reach of children.

Pre-filled syringe
Each mL of sterile, clear-to-slightly-yellow solution for injection in a prefilled syringe contains 100 mg of guselkumab. Nonmedicinal ingredients: L-histidine, L-histidine monohydrochloride monohydrate, sucrose, polysorbate 80, and water for injection.

Patient-controlled injector
Each mL of sterile, clear-to-slightly-yellow solution for injection in a patient-controlled injector contains 100 mg of guselkumab. Nonmedicinal ingredients: L-histidine, L-histidine monohydrochloride monohydrate, sucrose, polysorbate 80, and water for injection.

Do not take this medication if you are allergic to guselkumab or any ingredients of the medication.

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• cold symptoms
• diarrhea
• headache
• joint pain
• minor fungal infections of the skin (e.g., athlete's foot)
• redness, pain, swelling, bruising at site of infection
• sinus infections
• stomach "flu" (e.g., nausea, indigestion, diarrhea)

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• herpes simplex infections (cold sores, genital herpes)
• migraine
• rash
• signs of infection (symptoms may include fever or chills, severe diarrhea, shortness of breath, prolonged dizziness, headache, stiff neck, weight loss, or listlessness)
• yeast infections

Stop taking the medication and seek immediate medical attention if any of the following occur:

• signs of an allergic reaction (e.g., difficulty breathing, hives, swelling of the face, lips, tongue, or throat)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Infections: This medication can increase the risk of developing an infection, including serious infections such as sepsis, pneumonia, and tuberculosis. Before starting guselkumab treatment, your doctor may test to see if you have tuberculosis. If you notice signs of an infection such as fever, chills, pain, swelling, coughing, or pus, contact your doctor as soon as possible. This medication should also not be started while you have an active infection.

Tell your doctor if you have a history of infections that keep coming back, or other conditions that might increase your risk of infections such as diabetes. While you are taking guselkumab, your doctor will monitor you for signs of infection.

Vaccinations: Vaccines that are given during treatment with guselkumab may not be as effective as expected. Also, people taking this medication should not receive certain vaccines. Talk to your doctor about whether any vaccines you are scheduled to take may be used with this medication.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. Women who may become pregnant should use effective birth control while taking this medication and for at least 12 weeks after the last dose of guselkumab. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: It is not known if guselkumab passes into breast milk. If you are breast-feeding and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children.

There may be an interaction between guselkumab and any of the following:

• baricitinib
• BCG
• belimumab
• cladribine
• denosumab
• echinacea
• fingolimod
• infliximab
• leflunomide
• natalizumab
• nivolumab
• ocrelizumab
• pimecrolimus
• roflumilast
• siponimod
• tacrolimus
• tofacitinib
• upadacitinib
• vaccines

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.