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PI3Kδ Inhibitor — CLL / Follicular Lymphoma Pregnancy: Contraindicated — teratogenic; effective contraception required during and for 1 month after treatment

Idelalisib

Brand names: Zydelig

Adult dose

Dose: 150 mg twice daily
Route: Oral
Frequency: Twice daily (continuous)
Max: 150 mg twice daily
PI3Kδ inhibitor. Used in relapsed/refractory CLL (with rituximab — where chemotherapy is not appropriate) and relapsed follicular lymphoma (after ≥2 prior lines). Due to toxicity profile, largely superseded by ibrutinib and acalabrutinib in CLL — use restricted to patients with specific clinical scenarios.

Paediatric dose

Dose: Seek specialist opinion mg/kg
Route: Oral
Frequency: Twice daily
Max: Not established in children
Not licensed in children — specialist paediatric haematology use only

Dose adjustments

Renal

No dose adjustment required

Hepatic

Avoid in severe hepatic impairment; reduce dose and increase monitoring in moderate impairment

Paediatric weight-based calculator

Not licensed in children — specialist paediatric haematology use only

Clinical pearls

  • MHRA 2014: serious hepatotoxicity, diarrhoea/colitis, and pneumonitis — trials in untreated patients stopped early due to excess adverse events; use restricted to relapsed/refractory disease only
  • PCP prophylaxis (co-trimoxazole) and CMV monitoring are mandatory throughout treatment — immune reconstitution can paradoxically worsen at treatment initiation
  • LFT monitoring every 2 weeks for first 3 months — withhold idelalisib if ALT/AST >5× ULN; permanently discontinue if >20× ULN or any grade of bilirubin elevation with elevated LFTs
  • Immune-mediated colitis: dose-limiting in some patients; distinguish from infectious diarrhoea before treating with steroids
  • Largely replaced by BTK inhibitors (ibrutinib, acalabrutinib, zanubrutinib) in CLL practice — idelalisib reserved for specific scenarios
  • Idelalisib + rituximab (STUDY 116): significantly improved PFS in relapsed CLL patients unfit for chemotherapy

Contraindications

  • Severe hepatic impairment
  • Pregnancy
  • History of severe hypersensitivity to idelalisib

Side effects

  • Hepatotoxicity (transaminase elevation — common, may be severe)
  • Diarrhoea/colitis (immune-mediated — dose-limiting in ~15%)
  • Pneumonitis (immune-mediated)
  • Neutropenia
  • Infections (PCP, CMV, invasive fungal)
  • Rash
  • Pyrexia

Interactions

  • Strong CYP3A4 inhibitors — increase idelalisib exposure
  • Strong CYP3A4 inducers — reduce efficacy
  • CYP3A4 substrates — idelalisib is a CYP3A4 inhibitor; monitor narrow therapeutic index drugs

Monitoring

  • LFTs (every 2 weeks first 3 months, then every 4 weeks)
  • FBC
  • CMV PCR (every 4 weeks)
  • Respiratory symptoms (pneumonitis)
  • GI symptoms (colitis)

Reference: BNFc; BNF 90; MHRA Drug Safety Update (2014); STUDY 116 (Furman et al. NEJM 2014); NICE TA359; SPC Zydelig. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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