[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [PI3K inhibitors](https://durgical.com/en/pharmacology/classes/pi3k-inhibitors/) › Idelalisib

# Idelalisib

## PI3K inhibitors?

PI3K inhibitors

## High alert?

An error with this medicine can cause serious harm: double checks and protocols are used.

Oral PI3Kδ inhibitor for relapsed CLL with rituximab. Boxed warnings: liver damage, severe diarrhoea or colitis, pneumonitis, infections, bowel perforation.

Updated Nov 1, 2026

## Quick facts

**Group**
[PI3K inhibitors](https://durgical.com/en/pharmacology/classes/pi3k-inhibitors/)

**Target**
PI3Kδ, catalytic subunit p110δ of phosphoinositide 3-kinase (leukocytes)

**Used for**
Relapsed chronic lymphocytic leukaemia

**Key effects**
Diarrhoea · Fever · Cough

**Monitor**
Liver tests frequently · Breathing symptoms

**ATC**
L01EM01

No doses: the clinician sets them by the current guideline.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Clinical What the labels mean

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## Mechanism of action

✂**PI3Kδ, catalytic subunit p110δ of phosphoinositide 3-kinase (leukocytes)**Idelalisib

ⓘ The crystal structure shows idelalisib bound to the p110δ subunit of mouse PI3Kδ, whose binding site closely matches the human enzyme.

**Target in 3D:** PI3Kδ, catalytic subunit p110δ of phosphoinositide 3-kinase (leukocytes). PDB structure 4XE0 (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/4XE0) · Drag to rotate · pinch to zoom

Idelalisib selectively inhibits PI3Kδ, the isoform expressed mainly in leukocytes, including normal and malignant B cells. It blocks signalling from the B-cell receptor and from the chemokine receptors CXCR4 and CXCR5, which guide B cells to the lymph nodes and bone marrow. Malignant B cells lose survival signals and protective niches, proliferate less and undergo apoptosis.

- Malignant B cells depend on PI3Kδ signalling
- Idelalisib blocks the PI3Kδ kinase site
- B-cell receptor and CXCR4/CXCR5 signals fall
- Cells leave their niches and die

## Indications

- Relapsed chronic lymphocytic leukaemia, with rituximab, when rituximab alone would be considered because of other illnesses. [Chronic lymphocytic leukaemia →](https://durgical.com/en/conditions/chronic-lymphocytic-leukaemia/)
- It has been used in relapsed follicular lymphoma and small lymphocytic lymphoma after at least two prior therapies; it is not a first-line treatment. [Non-Hodgkin lymphoma →](https://durgical.com/en/conditions/non-hodgkin-lymphoma/)

## Adverse effects

### Common

- Diarrhoea
- Fever, chills, fatigue
- Cough, pneumonia
- Nausea, rash
- Raised liver enzymes and triglycerides, hyperglycaemia

### Serious (rare, important)

- Hepatotoxicity, sometimes fatal (boxed warning)
- Severe diarrhoea or colitis (boxed warning)
- Pneumonitis (boxed warning)
- Serious infections, including cytomegalovirus (boxed warning)
- Intestinal perforation (boxed warning)
- Severe skin reactions

## Contraindications

- History of serious allergic or skin reactions to idelalisib
- Breastfeeding during therapy
- Caution in liver disease and with other hepatotoxic drugs

## Key interactions

**CYP3A substrates (e.g. midazolam)**
Idelalisib inhibits CYP3A and raises their levels.

**Strong CYP3A inhibitors**
Raise idelalisib levels and its toxicity.

**Strong CYP3A inducers (e.g. rifampicin, St John's wort)**
Lower idelalisib levels; avoided.

**Other liver-toxic drugs**
Add to the risk of hepatotoxicity; avoided.

## What is monitored

- Liver tests frequently
- Stool frequency and abdominal pain
- Breathing symptoms
- Signs of infection, including cytomegalovirus
- Complete blood count

## Administration and safety

- Oral, on a regular schedule, with or without food.
- Swallowed whole; not crushed, chewed or split unless the product instructions allow it.
- Hazardous oral chemotherapy: handled with gloves and kept away from children; caregivers who are pregnant avoid handling it.

## Pregnancy and breastfeeding

May harm the fetus; effective contraception is used during and after treatment, and breastfeeding is not done during therapy.

## Nursing care

- Review liver tests before refills; report jaundice or dark urine.
- Ask about the number of stools and abdominal pain; severe diarrhoea is reported at once.
- Ask about cough, breathlessness and fever.
- Teaching: report new or worse diarrhoea, sudden severe abdominal pain, cough or rash; ask before taking St John's wort or eating grapefruit.

## Pharmacokinetics

**Absorption**
Oral; food does not change absorption.

**Metabolism**
Aldehyde oxidase, CYP3A and UGT1A4; idelalisib itself inhibits CYP3A.

**Half-life**
About 8 hours.

## Memory aid

«iDELalisib = DELta = B cells», and its boxed list reads like a gut-and-liver alarm: «Liver, Lung, Loose stools, Leaks (perforation), Lurking infections».

## Test yourself

Think of the answer, then tap the question to see it.

## Which PI3K isoform does idelalisib inhibit?

PI3Kδ, expressed mainly in leukocytes.

## With which antibody is idelalisib given in relapsed CLL?

Rituximab.

## What are idelalisib's boxed warnings?

Hepatotoxicity, severe diarrhoea or colitis, pneumonitis, serious infections and intestinal perforation.

## Why does idelalisib raise midazolam levels?

Because idelalisib inhibits CYP3A.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/idelalisib/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## What the labels mean

**High alert**
An error with this medicine can cause serious harm: double checks and protocols are used.

## Connections

## Related drugs 3

- [Alpelisib](https://durgical.com/en/pharmacology/alpelisib/)
- [Rituximab](https://durgical.com/en/pharmacology/rituximab/)
- [Ibrutinib](https://durgical.com/en/pharmacology/ibrutinib/)

## Related conditions 2

- [Chronic lymphocytic leukaemia](https://durgical.com/en/conditions/chronic-lymphocytic-leukaemia/)
- [Non-Hodgkin lymphoma](https://durgical.com/en/conditions/non-hodgkin-lymphoma/)

[← Back to the class: PI3K inhibitors](https://durgical.com/en/pharmacology/classes/pi3k-inhibitors/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Idelalisib: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a614040.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [Idelalisib - NCI](https://www.cancer.gov/about-cancer/treatment/drugs/idelalisib) (National Cancer Institute, 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=L01EM01) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/idelalisib/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/idelalisib/