CFTR potentiator Pregnancy: There are no or limited data (less than 300 pregnancy outcomes) from use in pregnant women; animal studies do not indicate reproductive toxicity. As a precautionary measure it is preferable to avoid use during pregnancy. Breast-feeding: it is unknown whether ivacaftor is excreted in human milk (it is excreted in rat milk) so a risk to the infant cannot be excluded - decide whether to discontinue breast-feeding or ivacaftor.

Ivacaftor

Brand names: Kalydeco

Ivacaftor is a CFTR potentiator used in the treatment of cystic fibrosis in patients with specified responsive CFTR gene mutations.

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: 150 mg every 12 hours (300 mg total daily dose) for adults and patients aged 6 years and older

Route: Oral - one 150 mg tablet taken with fat-containing food

Frequency: Every 12 hours (twice daily)

SOURCE NOTE: the adult figure above is from the US Kalydeco prescribing information (openFDA), because the UK SPC fetched is 'Kalydeco 13.4 mg granules in sachet', whose dosing table covers only patients below 25 kg and states 'greater than or equal to 25 kg: See Kalydeco tablets SmPC for further details'. The UK Kalydeco tablets SmPC was not fetched - clinician to confirm the UK adult regimen against it. Ivacaftor should only be prescribed by physicians with experience in the treatment of cystic fibrosis; if the genotype is unknown, an accurate and validated genotyping method should be performed before starting treatment to confirm an indicated CFTR mutation in at least one allele. Take with fat-containing food; avoid food or drink containing grapefruit. Missed dose (UK SPC): if 6 hours or less have passed, take as soon as possible then take the next dose at the regularly scheduled time; if more than 6 hours have passed, wait until the next scheduled dose. Patients on a combination regimen should not take more than one dose of either medicinal product at the same time. Hepatic impairment (US labelling, patients 6 years and older): no adjustment in mild (Child-Pugh A); moderate (Child-Pugh B) 150 mg orally once daily; severe (Child-Pugh C) not studied, use with caution - the UK SPC states use in severe hepatic impairment is not recommended unless benefits outweigh risks, with reduced dosing and intervals modified to clinical response. CYP3A: dosing must be reduced with moderate or strong CYP3A inhibitors (UK SPC Table 2, US labelling sections 2.4/7.1). Monotherapy is not recommended in patients homozygous for the F508del mutation (no statistically significant FEV1 difference over 16 weeks). Liver monitoring: assess ALT, AST and total bilirubin before starting, every 3 months during the first year and annually thereafter; interrupt dosing for ALT or AST greater than 5 x ULN, or greater than 3 x ULN with bilirubin greater than 2 x ULN. Paediatric dosing is by age and weight band using granule sachets (see the ivacaftor_paed draft) - no per-kg dose is stated.

Dose adjustments

Renal

No dose adjustment is necessary for mild to moderate renal impairment. Caution is recommended in severe renal impairment (creatinine clearance less than or equal to 30 mL/min) or end-stage renal disease.

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 (UK SPC section 4.3; the US labelling states 'None')

Side effects

Headache (23.9%) and dizziness - very common
Oropharyngeal pain (22.0%), upper respiratory tract infection (22.0%), nasal congestion (20.2%) - very common
Abdominal pain (15.6%) and diarrhoea (12.8%) - very common
Transaminase elevations (12.8% vs 11.5% on placebo) - very common; liver injury and total bilirubin elevations reported (frequency not known), including liver failure leading to transplantation in patients on the ivacaftor/tezacaftor/elexacaftor combination regimen
Rash (12.8%) - very common; bacteria in sputum (12.8%) - very common

Interactions

Moderate or strong CYP3A inhibitors (e.g. fluconazole, erythromycin; ketoconazole, itraconazole, posaconazole, voriconazole, telithromycin, clarithromycin) - ivacaftor is a sensitive CYP3A substrate; ketoconazole increased ivacaftor AUC 8.5-fold and fluconazole 3-fold, so the dose must be reduced in patients aged 6 months and older
Ivacaftor is not recommended in patients aged 1 month to less than 6 months taking concomitant strong or moderate CYP3A inhibitors
Food or drink containing grapefruit should be avoided during treatment

Clinical monograph

How it works

It increases the channel-open probability (gating) of CFTR protein at the cell surface, enhancing chloride ion transport and improving epithelial fluid balance.

Prescribing in practice

Monitor liver function, as elevated transaminases and hepatobiliary events have been reported with CFTR modulator therapy.
Exposure is altered by CYP3A inducers and inhibitors, so review interacting drugs and avoid potent inducers; advise avoiding grapefruit.
Cases of cataracts have been reported in paediatric patients, warranting baseline and follow-up eye examinations.

Monitoring

Monitor liver transaminases before and periodically during treatment, with ophthalmological examinations in children.

Counselling the patient

Take with fat-containing food to help absorption.
Report jaundice, dark urine or abdominal pain promptly.
Avoid grapefruit and Seville orange products.

Evidence & guidelines

Ivacaftor is supported by randomised trials and NICE access arrangements showing improved lung function and reduced sweat chloride in eligible patients.

Reference: NICE TA398; 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.

Pathways