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P2X3 receptor antagonist Pregnancy: There are no data from the use of gefapixant in pregnant women. Animal studies do not indicate direct or indirect harmful effects with respect to reproductive toxicity. As a precautionary measure, it is preferable to avoid the use of Lyfnua during pregnancy and in women of childbearing potential not using contraception. Lactation: available pharmacodynamic/toxicological data in animals have shown excretion of gefapixant in milk and a risk to newborns/infants cannot be excluded — a decision must be made whether to discontinue breast-feeding or to discontinue/abstain from therapy, taking into account the benefit of breast-feeding for the child and the benefit of therapy for the woman. Fertility: no human data are available; in rats there was no effect on mating or fertility. (§4.6)

Gefapixant

Brand names: Lyfnua

Gefapixant is an orally administered selective P2X3 receptor antagonist used for the treatment of refractory or unexplained chronic cough.

Adult dose

Dose: Refractory or unexplained chronic cough (RCC/UCC) in adults: one 45 mg tablet taken orally twice daily, with or without food
Route: Oral use. Tablets should be swallowed whole and may be taken with or without food; patients should be instructed not to break, crush or chew the tablets
Frequency: Twice daily
Max: 45 mg twice daily. The SPC states a single recommended dose and no higher dose anywhere in §4.2; §4.2 verbatim on missed doses: 'Patients should not double their next dose or take more than the prescribed one.'
Indication: this is the licensed UK product for the page's own indication — §4.2 refers explicitly to 'the indication of refractory or unexplained chronic cough', and §4.4 to 'the use of 45 mg gefapixant twice daily in patients with refractory chronic cough (RCC) or unexplained chronic cough (UCC)'. Missed dose: skip the missed dose and go back to the regular schedule. Elderly (≥ 65 years): no dose adjustment is required, but gefapixant is known to be substantially excreted by the kidney and elderly patients are more likely to have decreased renal function, so the risk of adverse reactions may be greater — care should be taken with initial dosing frequency. Renal impairment: dose reduction is required in severe renal impairment (see renalAdjustment). Hepatic impairment: not studied, but no dose adjustment is recommended as hepatic metabolism is a minor route of elimination. Paediatric: §4.2 verbatim — 'There is no relevant use of Lyfnua in the paediatric population (under 18 years of age) for the indication of refractory or unexplained chronic cough.' Obstructive sleep apnoea: for patients with OSA, appropriate treatment for OSA should be considered prior to initiating treatment with gefapixant. Sulphonamides: gefapixant contains a sulphonamide moiety but is considered to be a non-sulphonylarylamine; it has not been studied in patients with a history of hypersensitivity to sulphonamide, cross-hypersensitivity cannot be excluded, and it should be used with caution in patients with known hypersensitivity to sulphonamides. Acute lower respiratory tract infection: treatment with gefapixant should be evaluated and individualised in patients who develop one. Each tablet contains less than 1 mmol sodium (23 mg), that is to say essentially 'sodium free'.

Paediatric dose

Dose: Not applicable — there is no relevant use in the paediatric population (under 18 years of age) for the indication of refractory or unexplained chronic cough
Route: N/A — no paediatric use is described in this SPC
Frequency: N/A
Max: Not established
§4.2 Paediatric population, verbatim: 'There is no relevant use of Lyfnua in the paediatric population (under 18 years of age) for the indication of refractory or unexplained chronic cough.' §4.5 adds that interaction studies have only been performed in adults. No paediatric figure is published here and the adult regimen has NOT been carried across or scaled. Verify any under-18 use against a children's formulary and specialist advice.

Dose adjustments

Renal

Dose adjustment is required in patients with severe renal impairment (eGFR < 30 mL/minute/1.73 m²) not requiring dialysis: reduce to one 45 mg tablet taken once daily. No dose adjustment is required in mild or moderate renal impairment (eGFR ≥ 30 mL/minute/1.73 m²). Insufficient data are available in patients with end-stage renal disease requiring dialysis to make dosing recommendations.

Hepatic

Patients with hepatic impairment have not been studied. However, given that hepatic metabolism is a minor route of elimination of gefapixant, no dose adjustment is recommended.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance or to any of the excipients listed in section 6.1 (§4.3 — this is the only contraindication stated in this SPC)

Side effects

  • Dysgeusia — very common; reported in 41% of patients, commonly as taste bitter, taste metallic or taste salty (§4.8)
  • Ageusia — very common; reported in 15% of patients (§4.8)
  • Hypogeusia — very common; reported in 11% of patients (§4.8)
  • Taste disorder — common (§4.8)
  • Dizziness — common (§4.8)
  • Headache — common (reported in a phase 3b study in female patients with cough-induced stress urinary incontinence) (§4.8)
  • Upper respiratory tract infection — common (§4.8)
  • Decreased appetite — common (§4.8)
  • Cough, including reports of worsening, exacerbation, increase or increased cough — common (§4.8)
  • Oropharyngeal pain — common (§4.8)
  • Nausea, diarrhoea, dry mouth, salivary hypersecretion, upper abdominal pain, dyspepsia, oral hypoaesthesia, oral paraesthesia — all common (§4.8)
  • Insomnia — common (§4.8)
  • Urinary calculus, nephrolithiasis, bladder calculus — uncommon (§4.8)
  • Taste-related reactions usually begin within 9 days of starting treatment and are mostly mild (65%) to moderate (32%); they resolved in 96% of patients but persisted for more than a year after discontinuation in 1.6% (§4.8)
  • Adverse reactions led to discontinuation in 22% of patients receiving gefapixant, most often dysgeusia (9%) and ageusia (4%) (§4.8)

Monitoring

  • Obstructive sleep apnoea — consider appropriate treatment for OSA before initiating gefapixant (§4.4)
  • Taste-related adverse reactions — very commonly reported and the principal cause of discontinuation; in most patients these resolve soon after stopping (median 5 days), but in a few they persist for more than a year (§4.4, §4.8)
  • Acute lower respiratory tract infection — treatment should be evaluated and individualised in patients who develop one (§4.4)
  • Renal function — dose reduction is required if eGFR falls below 30 mL/minute/1.73 m²; take care with initial dosing frequency in elderly patients, who are more likely to have decreased renal function (§4.2)

Clinical monograph

How it works

It blocks P2X3 receptors on airway sensory nerve fibres, attenuating ATP-mediated activation of the cough reflex arc and thereby reducing cough hypersensitivity.

Prescribing in practice

  • Taste disturbance, including reduced or altered taste, is a very common and characteristic adverse effect that can lead to discontinuation.
  • It is reserved for chronic cough that persists despite assessment and treatment of underlying causes.
  • Dose considerations apply in renal impairment as elimination is predominantly renal.

Monitoring

Monitor cough response and tolerability, particularly taste-related adverse effects.

Counselling the patient

  • An altered or reduced sense of taste is common and is usually reversible if the medicine is stopped.
  • It is used when cough continues despite treating other possible causes.
  • Discuss with your prescriber if taste changes become troublesome.

Evidence & guidelines

Gefapixant has been evaluated in randomised trials in refractory and unexplained chronic cough demonstrating reductions in cough frequency.

Reference: SmPC; Confirm identity and dosing against the manufacturer SPC (eMC) and NICE. 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).

Related

Curated clinical cross-links plus same-class fallbacks.

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