CDK4/6 inhibitor Pregnancy: Not recommended during pregnancy or in women of childbearing potential not using contraception. There are no or limited data in pregnant women and animal studies have shown reproductive toxicity. Females of childbearing potential, or their male partners, should use adequate contraception (e.g. double-barrier) during therapy and for at least 3 weeks after completing therapy for females and 14 weeks for males. Patients receiving palbociclib should not breast-feed.

Palbociclib (Specialist drug)

Brand names: Ibrance

Palbociclib is a specialist oral targeted agent used with endocrine therapy in the treatment of hormone receptor-positive, HER2-negative advanced or metastatic breast cancer.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 125 mg

Route: Oral. Tablets should be swallowed whole (not chewed, crushed or split) and may be taken with or without food; do not take with grapefruit or grapefruit juice

Frequency: Once daily for 21 consecutive days followed by 7 days off treatment (Schedule 3/1), giving a complete 28-day cycle

Treatment should be initiated and supervised by a physician experienced in the use of anticancer medicinal products, and continued as long as the patient is deriving clinical benefit or until unacceptable toxicity occurs. Take at approximately the same time each day; if a dose is missed or vomited, do not take an additional dose that day - take the next prescribed dose at the usual time. Do not ingest a tablet that is broken, cracked or otherwise not intact. DOSE REDUCTIONS: recommended dose 125 mg/day; first reduction 100 mg/day; second reduction 75 mg/day - if further reduction below 75 mg/day is required, discontinue treatment. Absolute neutrophil count of at least 1,000/mm3 and platelet count of at least 50,000/mm3 are recommended to receive treatment. Monitor full blood count before starting, at the beginning of each cycle and on Day 15 of the first 2 cycles. Permanently discontinue in patients with severe interstitial lung disease/pneumonitis. COMBINATION PARTNERS: with an aromatase inhibitor dosed per its own SPC - in pre/perimenopausal women this combination must always include an LHRH agonist; with fulvestrant 500 mg intramuscularly on Days 1, 15, 29 and once monthly thereafter, with an LHRH agonist in pre/perimenopausal women. Severe hepatic impairment (Child-Pugh C): reduce to 75 mg once daily on Schedule 3/1. No relevant use in the paediatric population for breast carcinoma; efficacy in patients under 18 years has not been demonstrated.

Dose adjustments

Renal

No dose adjustment required for mild, moderate or severe renal impairment (creatinine clearance at least 15 mL/min). Insufficient data in patients requiring haemodialysis to provide a dose adjustment recommendation.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Use of preparations containing St John's Wort

Side effects

Neutropenia and leukopenia (most common Grade 3 or above)
Infections
Fatigue
Nausea and stomatitis
Anaemia, thrombocytopenia and diarrhoea
Alopecia; raised AST and ALT; interstitial lung disease/pneumonitis

Interactions

St John's Wort: contraindicated (SPC section 4.3)
Strong CYP3A inhibitors (e.g. clarithromycin, indinavir, itraconazole, ketoconazole, lopinavir/ritonavir, nefazodone, nelfinavir, posaconazole, ritonavir, saquinavir, telaprevir, telithromycin, voriconazole): avoid concurrent use; if unavoidable, reduce the palbociclib dose (US labelling)
Grapefruit and grapefruit juice: avoid during treatment
Strong CYP3A inducers: avoid concurrent use (US labelling)
Sensitive CYP3A4 substrates with a narrow therapeutic index: their dose may need to be reduced when given with palbociclib (US labelling)

Clinical monograph

How it works

It selectively inhibits cyclin-dependent kinases 4 and 6 (CDK4/6), preventing retinoblastoma protein phosphorylation and arresting the cell cycle to slow tumour cell proliferation.

Prescribing in practice

Neutropenia is the most common and dose-limiting adverse effect, so the full blood count must be checked before starting and during treatment with dose adjustment or interruption as required.
It is metabolised by CYP3A4, so avoid concurrent strong CYP3A4 inhibitors and inducers.
Patients should be advised to report signs of infection and venous thromboembolism promptly.

Monitoring

Monitor full blood count at the start of each cycle and as clinically indicated, and watch for signs of infection.

Counselling the patient

Attend for regular blood tests and report fever, sore throat or other signs of infection straight away.
Avoid grapefruit and grapefruit juice and tell your team about any new medicines.

Evidence & guidelines

Approval was supported by the PALOMA trials and is recommended by NICE in combination with endocrine therapy for advanced breast cancer.

Reference: NICE TA495; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

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