Idelalisib (Zydelig®)

Author: Christina Bach, MBE, LCSW, OSW-C
Last Reviewed: July 21, 2026

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Pronounce: I-Dela-Lisib

Classification: Kinase Inhibitor

About Idelalisib (Zydelig®)

A kinase is an enzyme that helps a cell grow. There are different types of kinases. Each type affects a different phase of cell growth. Kinase inhibitors slow down the growth of cancer cells. 

This medication works by targeting a protein called phosphoinositide 3-kinase (PI3K) delta, which is important in the activation and proliferation of B cells. PI3K is seen in higher than normal levels in many B-cell cancers (including CLL, follicular B-cell lymphoma and small lymphocytic lymphoma).

How to Take This Medication

This medication comes in a tablet form and is taken twice a day, with or without food. The tablet should be swallowed whole, and not broken, crushed, or chewed. If you miss a dose, and it is less than 6 hours since your dose was due, take the dose right away. If you miss a dose and it is more than 6 hours since the last dose, then skip that dose and take your regular dose at the next scheduled time. Do not take 2 doses at once to make up for a missed dose.

It is important to make sure you are taking the correct amount of medication every time. Before every dose, check that what you are taking matches what you have been prescribed.

The blood levels of this medication can be affected by certain foods and medications, so they should be avoided. These include: grapefruit, grapefruit juice, dexamethasone, ketoconazole, rifampin, phenytoin, St. John’s wort, cimetidine, paroxetine and many others. Be sure to tell your provider about all medications (prescription and over-the-counter) and supplements you take.

Storage and Handling

Store your medication in the original container with the label. If you want to use a pillbox, talk to your pharmacist. Keep it in a dry place at room temperature unless your provider or pharmacist tells you otherwise. Keep containers out of reach of children and pets.

If a caregiver prepares your dose for you, they should consider wearing gloves or pour the pills directly from their container into the cap, a small cup, or directly into your hand. They should avoid touching the pills. They should always wash their hands before and after giving you the medication. Pregnant or nursing people should not prepare the dose for you. Ask your provider where to return any unused medication for disposal. Do not flush down the toilet or throw in the trash. 

Where Do I Get This Medication?

Some cancer medications are only available through specialty pharmacies. Your provider or pharmacist will start this process. Your insurance plan may also affect where you can get your medication.  Call your prescription plan provider to find out which specialty pharmacies are in-network.

Insurance Information

This medication may be covered by your prescription plan. If you qualify, you may be able to get financial help through patient assistance programs (PAP). Co-pay cards may also be available to lower your out-of-pocket cost if you have commercial (not Medicare/Medicaid/Tricare) insurance. Your pharmacist, social worker, or navigator can help find resources for financial support.

Possible Side Effects

These are some of the most common or most serious side effects of this medication. Talk with your provider about the side effects you are having and how they can be managed.

Infection and Low White Blood Cell Count (Leukopenia or Neutropenia)

This medication can cause serious infections, with or without a decrease in white blood cell counts.

White blood cells (WBC) help your body fight infection. While you are having cancer treatment, your WBC count can drop, putting you at a higher risk of an infection. Tell your provider right away if you have a fever (a temperature greater than 100.4°F or 38°C), sore throat or cold, shortness of breath, cough, burning with urination, or a sore that doesn't heal.

Tips for preventing infection:

  • Hand washing,  both yours and your visitors, is the best way to prevent the spread of infection.
  • Avoid large crowds and people who are sick (those who have a cold, fever, or cough, or if someone you live with has these symptoms).
  • When working outside, wear clothes that protect you, like long pants and gloves.
  • Do not handle pet waste.
  • Keep all cuts and scratches clean.
  • Shower or bathe daily.
  • Brush your teeth at least twice a day.
  • Do not cut cuticles or ingrown nails. You may wear nail polish, but not fake nails.
  • Ask your providers before scheduling dental appointments or procedures.

Ask your providers before you or someone you live with has any vaccines

Diarrhea

Diarrhea can be a very serious side effect of this medication. Notify your provider if the number of bowel movements you have in a day increases by 6 or more. Talk with your provider about which over the counter medications you can take and how to take them, as this will often differ from the instructions on the box.

Diarrhea is when you pass three or more stools in a day. Your providers can suggest medications to relieve diarrhea. Do not take any medications to manage your diarrhea without talking to your provider first, as your stool may need to be tested. To manage it, try eating foods that are low in fiber and bland, like white rice and boiled or baked chicken. Try not to eat raw fruits, vegetables, whole grain breads, cereals, and seeds. Soluble fiber is a type of fiber found in some foods that helps absorb (soak up) fluid. Foods high in soluble fiber are applesauce, bananas (ripe), canned fruit, oranges, boiled potatoes, white rice, foods made with white flour, oatmeal, cream of rice, cream of wheat, and farina. Stay hydrated by drinking 8 to 10 glasses of non-alcoholic, non-caffeinated fluid each day.

Liver Toxicity

This medication can cause liver toxicity, or liver problems, which your provider may monitor for with blood tests called liver function tests. Symptoms may be:

  • Yellowing of your skin or eyes.
  • Dark or brown urine.
  • Pain in your abdomen (belly).

Tell your provider if you have any of these symptoms.

Pneumonitis

Pneumonitis is inflammation of the lungs. Tell your provider right away if you get any new or worsening symptoms, like:

  • Shortness of breath.
  • Trouble breathing.
  • A cough.
  • Fever.

Gastrointestinal (GI) Tear

This medication can cause gastrointestinal (GI) perforation, or a tear, in the wall of your intestines. Signs of this can be:

  • New or worsening pain in the abdomen (belly).
  • New abdominal swelling.
  • Chills.
  • Fever.
  • Constipation.
  • Nausea or vomiting.

If you have any of these symptoms, call your provider.

Fatigue

Fatigue can cause exhaustion, feeling worn out and that your body is "heavy" and hard to move, or being unable to focus. It is common when you have cancer, and it is not the same as feeling tired. You may need to adjust your schedule to manage fatigue. Plan times to rest during the day and save your energy for more important activities. Exercise can help lessen fatigue. Talk to your providers about ways to deal with this side effect.

Nausea and/or Vomiting

Talk to your providers if you have nausea and/or vomiting. They can prescribe medications to help you. Making changes to your diet can also help. Avoid things that make your symptoms worse, like heavy or greasy/fatty foods and spicy or acidic foods, like tomatoes, lemons, and oranges. Try saltines or ginger ale to help your symptoms.  

Call your providers if you cannot keep fluids down for more than 12 hours or if you feel lightheaded or dizzy.

Reproductive Concerns

There is a higher risk of health problems for your baby if you are pregnant, become pregnant, or get someone pregnant while on this medication. To lower the risk of birth defects, you should use birth control (contraception) to avoid pregnancy. Talk with your provider about what kind of birth control is safest for you and your partner.

If you can become pregnant, you will need to use effective birth control during treatment and for 1 month after the last dose of this medication, even if your menstrual cycle has stopped or changed. If you can get someone pregnant, you will need to use effective birth control during treatment and for 3 months after the last dose of this medication, even if you believe you are not producing sperm. You should not breastfeed during treatment and for 1 month after the last dose of this medication.

Important but Less Common Side Effects

Allergic Reactions

In some cases, patients can have an allergic reaction to this medication. Signs of a reaction can include: shortness of breath or difficulty breathing, swelling of the lips or throat or difficulty swallowing. Seek medical help right away or call 911 if these symptoms develop. Depending on the severity of your reaction, you may still be able to receive the medication with a pre-medication to prevent a reaction.

Severe Skin Reactions

A serious allergic reaction to this medication can cause skin and mucous membrane (inside of your mouth, nose, throat, and other body parts) problems that can also affect other organs in your body. These reactions are called severe cutaneous adverse reactions (SCARs).

Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN) are types of serious skin reactions that need treatment right away. If you have a new rash or blisters, flu-like symptoms, or lesions (sores) on mucous membranes, call your provider right away.