Idelalisib
Pronunciation: pronunciation varies by local usage.
- Generic name
- idelalisib
- Brand names
- Zydelig
- Drug class
- PI3K-delta kinase inhibitor
- Form
- Tablet
- Route
- Oral
- Legal status
- Prescription-only medicine
Availability and supply rules vary by country
Trade names by country: United States · Canada
Australia: · Full directory
What idelalisib is and how it works
Idelalisib is an oral PI3K-delta kinase inhibitor indicated for relapsed chronic lymphocytic leukemia (CLL), in combination with rituximab, in patients for whom rituximab alone would be considered appropriate therapy due to other co-morbidities. It is not for first-line treatment and should not be used with bendamustine and rituximab for follicular lymphoma or other indolent lymphomas. (1)
Idelalisib is a specialist-managed cancer treatment with boxed warnings for serious and potentially fatal toxicities including hepatotoxicity, severe diarrhea/colitis, pneumonitis, infections, and intestinal perforation. Treatment requires close monitoring of liver function, blood counts, and infection prophylaxis. Patients must be able to recognize serious side effects and seek immediate medical attention.
Mechanism of action: how idelalisib works
Idelalisib is a selective inhibitor of phosphatidylinositol 3-kinase p110δ (PI3Kδ), which is expressed in normal and malignant B-cells. By inhibiting PI3Kδ, idelalisib blocks signaling pathways that promote B-cell proliferation, survival, and migration. (1)
What idelalisib is used for
Relapsed chronic lymphocytic leukemia (CLL)
Idelalisib is indicated in combination with rituximab for the treatment of patients with relapsed CLL for whom rituximab alone would be considered appropriate therapy due to other co-morbidities. (1)
Before taking idelalisib
Do not take / not appropriate for
- Do not take idelalisib if you have a history of serious hypersensitivity reactions to idelalisib, including anaphylaxis. (all patients) (1)
- Do not take idelalisib if you have a history of toxic epidermal necrolysis with any drug. (all patients) (1)
Tell your clinician about
- Any history of liver disease, including hepatitis or abnormal liver tests.
- Current or recent infections, or any signs of infection such as fever, chills, or cough.
- All medicines you take, especially those that affect liver enzymes (CYP3A inducers or inhibitors) and any other cancer treatments.
- Pregnancy or plans to become pregnant; idelalisib may cause fetal harm.
- Breastfeeding or plans to breastfeed.
- Any new or worsening symptoms during treatment, particularly diarrhea, abdominal pain, cough, shortness of breath, or yellowing of the skin/eyes.
How to take idelalisib
- Idelalisib is taken orally twice daily. The usual dose is 150 mg twice daily, but the treating specialist may adjust the dose (e.g., reduce to 100 mg twice daily or discontinue) based on toxicity and laboratory monitoring.
- Swallow the tablet whole. It can be taken with or without food.
- Do not change the dose or stop taking idelalisib without specific instructions from your specialist.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1)
Missed dose
If you miss a dose and it is within 6 hours of the usual time, take it as soon as possible. If more than 6 hours have passed, skip the missed dose and resume the normal schedule. Do not take an extra dose to make up for it.
Overdose
No specific overdose information is available in the research notes. Seek immediate medical attention if an overdose is suspected.
Side effects
Idelalisib has boxed warnings for serious and potentially fatal toxicities. Common side effects include diarrhea, fever, fatigue, rash, cough, and laboratory abnormalities such as neutropenia and elevated liver enzymes. Close monitoring is essential.
Diarrhea
What to notice: New or worsening loose stools. Severe diarrhea or colitis can be life-threatening.
What to do: Report any diarrhea to your treatment team promptly. Drink fluids to stay hydrated. Do not use anti-diarrhea medication without medical advice. (1)
Fever (pyrexia) and infections
What to notice: Temperature 38°C or higher, chills, weakness, or other signs of infection.
What to do: Report fever or infection signs immediately. You may need urgent assessment and treatment. (1)
Fatigue
What to notice: Unusual tiredness or weakness.
What to do: Discuss persistent fatigue with your clinician. Rest as needed. (1)
Rash
What to notice: New skin changes. Severe rash can be a sign of serious hypersensitivity.
What to do: Report any rash to your treatment team. If rash is severe, blistering, or involves mucous membranes, seek urgent care. (1)
Cough and respiratory symptoms
What to notice: New or worsening cough, shortness of breath, or chest discomfort.
What to do: Report these symptoms promptly. They may indicate pneumonitis or infection. (1)
Neutropenia (low white blood cell count)
What to notice: Often detected by blood tests. Increases infection risk.
What to do: Your specialist will monitor your blood counts regularly and adjust treatment as needed. Avoid crowds and people with infections if counts are low. (1)
Elevated liver enzymes (ALT/AST)
What to notice: Usually detected by blood tests. Severe elevations can cause jaundice, dark urine, or right upper abdominal pain.
What to do: Liver tests are done frequently. Report any symptoms of liver problems immediately. The team decides any dose changes. (1)
Severe or worsening diarrhea, abdominal pain, or signs of colitis
What to notice: Frequent watery stools, blood in stool, severe abdominal cramping, or signs of dehydration.
What to do: Contact your treatment team immediately. Do not wait for scheduled visits. (1)
New or worsening respiratory symptoms
What to notice: Persistent cough, shortness of breath, chest pain, or oxygen requirement.
What to do: Report urgently. Your specialist will evaluate for pneumonitis or infection and may discontinue idelalisib. (1)
Signs of liver injury
What to notice: Yellowing of the skin or eyes, dark urine, light-colored stools, or pain/discomfort in the right upper abdomen.
What to do: Notify your clinician immediately. You will need prompt blood tests and possible dose adjustment. (1)
Signs of infection
What to notice: Fever (≥38°C), chills, sore throat, mouth sores, or any other sign of infection.
What to do: Contact your clinician without delay. Infections can progress rapidly and may be fatal. (1)
Serious warnings
Hepatotoxicity — emergency
Symptoms: Yellowing of the skin/eyes (jaundice), dark urine, light-colored stools, upper right abdominal pain, nausea, vomiting.
Action: Seek immediate medical attention. The treating team pauses or ends idelalisib; do not restart without specialist instruction. (1)
Severe diarrhea or colitis — emergency
Symptoms: Frequent watery stools, blood in stool, severe abdominal pain, fever, signs of dehydration (dizziness, reduced urination).
Action: Contact your treatment team urgently. Idelalisib may need to be held and supportive care started. Seek emergency care for severe symptoms. (1)
Pneumonitis — emergency
Symptoms: New or worsening cough, shortness of breath, difficulty breathing, chest tightness, low oxygen levels.
Action: Report immediately. Your specialist discontinues idelalisib and treatment with corticosteroids usually started. (1)
Serious infections — emergency
Symptoms: Fever, chills, severe fatigue, confusion, rapid heart rate, signs of pneumonia (cough, chest pain, shortness of breath), sepsis, or any localized infection.
Action: Seek emergency medical care. Infections can be fatal; idelalisib will be held and aggressive treatment initiated. (1)
Intestinal perforation — emergency
Symptoms: Sudden, severe, or worsening abdominal pain, possibly with nausea, vomiting, or blood in stool.
Action: This is a medical emergency. Go to the nearest emergency department immediately. (1)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Strong CYP3A inducers (e.g., rifampin, carbamazepine, St. John’s wort) | May significantly reduce idelalisib levels, decreasing effectiveness. | Avoid concomitant use. Provide a complete medication list including herbals. (1) |
| CYP3A inhibitors (e.g., ketoconazole, clarithromycin, ritonavir) | May increase idelalisib levels, raising risk of toxicity. | Closer monitoring for adverse effects is recommended if coadministration cannot be avoided. (1) |
| Sensitive CYP3A substrates (e.g., midazolam, certain statins, sildenafil) | Idelalisib can markedly increase their blood levels (e.g., midazolam AUC increased 5.4-fold). | Avoid using sensitive CYP3A substrates with idelalisib. If unavoidable, dose reduction of the substrate may be required. (1) |
Pregnancy, breastfeeding, kidney/liver function, age
Pregnancy and breastfeeding
Idelalisib may cause fetal harm. Females of reproductive potential must use effective contraception during treatment and for 1 month after the last dose. Males with female partners of reproductive potential should use effective contraception during treatment and for 3 months after the last dose. Do not breastfeed during treatment and for 1 month after the last dose. (1)
Monitoring
Before starting
- Confirm diagnosis of relapsed CLL and eligibility for combination rituximab therapy.
- Assess liver function (ALT, AST, bilirubin), full blood count, and renal function.
- Evaluate for active infections and initiate Pneumocystis jirovecii (PJP) prophylaxis before starting.
- Review all concomitant medications for potential interactions (especially CYP3A substrates/inhibitors/inducers).
- Perform pregnancy testing in females of reproductive potential and confirm contraception plan.
During treatment
- Monitor ALT/AST every 2 weeks for the first 3 months, then every 4 weeks for the next 3 months, then every 1–3 months thereafter. The team pauses idelalisib when ALT/AST rises above 5× the upper limit of normal.
- Monitor for diarrhea and colitis weekly when present. Manage symptoms and consider dose modification; severe cases may require discontinuation.
- Watch for respiratory symptoms and perform radiological evaluations if pneumonitis suspected; discontinue idelalisib for symptomatic pneumonitis.
- Monitor for infections vigilantly; any sign of infection requires immediate workup. Continue PJP prophylaxis throughout treatment. Monitor for CMV reactivation.
- Assess complete blood counts every 2 weeks for the first 6 months, then weekly if neutrophils fall below 1.0 Gi/L. Dose modification may be needed.
- Instruct patients to report new or worsening abdominal pain promptly to evaluate for intestinal perforation.
- No generic dose adjustment provided for renal impairment; use clinical judgment.
Storage
Store at 20–25°C (68–77°F); excursions permitted between 15–30°C (59–86°F). Keep in the original container. Do not use if the seal is broken or the tablets appear damaged.
Professional information
Clinician-facing context only. Use the current local prescribing information. Dosing and monitoring must be individualized based on patient status and toxicity.
United States
Indication: Relapsed CLL (with rituximab)
Dose summary: 150 mg orally twice daily until disease progression or unacceptable toxicity. Dose reduction to 100 mg twice daily may be considered for certain toxicities as per the prescribing information. Specialist must manage all dose adjustments.
Renal context: No renal-specific dose adjustment provided in the research notes. (1)
Hepatic guidance
Hepatotoxicity is a boxed warning. Monitor liver function frequently; treatment interruption or discontinuation is required for severe elevations. Refer to the full prescribing information for detailed dose modification tables.
Overdose note
No specific overdose management data are available in the research notes. In case of overdose, provide supportive care and monitor for toxicities, especially hepatotoxicity, diarrhea, infections, and myelotoxicity. (1)
Frequently asked questions
Can idelalisib be used alone without rituximab?
No. In the studied indication, idelalisib is used in combination with rituximab. It is not approved as a single agent for CLL. (1)
What should I do if I miss a dose?
If within 6 hours of the usual time, take it as soon as possible. If more than 6 hours have passed, skip the missed dose and resume the normal schedule. Do not take an extra dose. (1)
What are the most serious risks with idelalisib?
Idelalisib carries boxed warnings for potentially fatal liver damage, severe diarrhea/colitis, pneumonitis (lung inflammation), serious infections, and intestinal perforation. Close monitoring and prompt reporting of symptoms are essential. (1)
What is the mechanism of action of idelalisib?
Idelalisib is a selective inhibitor of phosphatidylinositol 3-kinase p110δ (PI3Kδ), which is expressed in normal and malignant B-cells. By inhibiting PI3Kδ, idelalisib blocks signaling pathways that promote B-cell proliferation, survival, and migration. (1)
What is the generic name of Idelalisib?
The generic name is idelalisib. It is sold under brand names including Zydelig. (1)
What class of drug is idelalisib?
Idelalisib is classed as: PI3K-delta kinase inhibitor. (1)
References
- ZYDELIG (idelalisib) tablets, for oral use — prescribing informationU.S. National Library of Medicine, DailyMed · United States · dated 2022-02 · accessed 2026-08-08 · source 1
- Idelalisib — patient drug information (MedlinePlus)U.S. National Library of Medicine (MedlinePlus) · US · accessed 2026-08-14 · source 2
- Zydelig — FDA approval record (Drugs@FDA NDA205858)U.S. Food and Drug Administration · US · accessed 2026-08-14 · source 3
- idelalisib — RxNorm normalized drug concept (RXCUI 1544460)U.S. National Library of Medicine (RxNorm) · US · accessed 2026-08-14 · source 4
Brand names by country
Single-ingredient idelalisib names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- Zydelig100 mg, 150 mg · gilead sciences, inc.
Canada
- ZYDELIG