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NHE3 Inhibitor — Intestinal Phosphate Absorption Reducer Pregnancy: US label 8.1: tenapanor is essentially non-absorbed systemically, with plasma concentrations below the limit of quantification (less than 0.5 ng/mL), so maternal use is not expected to result in fetal exposure. Data from a small number of pregnant women have not identified any drug-associated risk for major birth defects, miscarriage, or adverse maternal or fetal outcomes. In rats and rabbits no adverse fetal effects were observed at 1 mg/kg/day in rats (about 0.2 times the maximum recommended human dose) and up to 45 mg/kg/day in rabbits (about 15 times); doses of 10 and 30 mg/kg/day were not tolerated by pregnant rats. Lactation 8.2: tenapanor and its major metabolite M1 were not detected in the breast milk of lactating women, and maternal use is not expected to result in exposure in breastfed infants; the benefits of breastfeeding should be considered with the mother's clinical need.

Tenapanor

Brand names: Xphozah

Tenapanor is an oral, minimally absorbed agent used to control hyperphosphataemia in patients with chronic kidney disease on dialysis, often when phosphate binders are inadequate or not tolerated.

Adult dose

Dose: Reduce serum phosphorus in adults with chronic kidney disease (CKD) on dialysis, as add-on therapy in patients with an inadequate response to phosphate binders or who are intolerant of any dose of phosphate binder therapy: 30 mg orally twice daily before the morning and evening meals; manage serum phosphorus levels and tolerability with dosage adjustments.
Route: Oral (tablet)
Frequency: Twice daily, just prior to the first and last meals of the day (before the morning and evening meals).
US label (XPHOZAH): the recommended dosage is 30 mg orally twice daily before the morning and evening meals. Monitor serum phosphorus and adjust the dosage as needed to manage gastrointestinal tolerability. Patients should not take it right before a hemodialysis session, and should instead take it right before the next meal following dialysis, as they may experience diarrhoea after taking it. A patient who misses a dose should skip the missed dose and take the next dose at the regular time. Tablets are available as 10 mg, 20 mg and 30 mg; the retrieved dosage text gives no stepwise titration schedule and no printed maximum dose, so none is written here. Separate administration from sodium polystyrene sulfonate by at least 3 hours. The retrieved paediatric section is cut off at the source-fetch limit. No UK SPC for tenapanor is listed on eMC — this dose is from US prescribing information (XPHOZAH 10 mg, Ardelyx, Inc.) and must be verified against UK practice.

Dose adjustments

Renal

The product is indicated in adults with CKD on dialysis, so no renal dose reduction is described. The label's dosage text says to take it right before the next meal following dialysis rather than right before a hemodialysis session. The 'Use in specific populations' text retrieved states no further renal dosing guidance (it is cut off at the source-fetch limit).

Hepatic

Not stated in the product information we used — check the full SPC.

Dose independently re-sourced from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Patients under 6 years of age, because of the risk of diarrhoea and serious dehydration
  • Known or suspected mechanical gastrointestinal obstruction

Side effects

  • Diarrhoea - the most common adverse reaction, reported in 43-53% of patients (the only adverse reaction reported in at least 5% of treated patients); reported in up to 53% in clinical trials, severe in 5%, and associated with dehydration and hyponatraemia in less than 1%
  • Most diarrhoea was mild-to-moderate and resolved over time or with dose reduction; typically reported soon after initiation but can occur at any time during treatment
  • Treatment should be discontinued in patients who develop severe diarrhoea
  • Postmarketing hypersensitivity reactions: pruritus, rash, urticaria

Interactions

  • OATP2B1 substrates - tenapanor inhibits the intestinal uptake transporter OATP2B1, so substrates (e.g. enalapril) may have reduced exposure; monitor for signs of loss of efficacy and adjust the dose of the concomitant drug as needed
  • Enalapril - with tenapanor 30 mg twice daily for five days, peak exposure (Cmax) of enalapril and enalaprilat decreased by about 70% and total exposure (AUC) by 50 to 65%; the label states a lower starting dose of enalapril is not required when coadministered
  • Sodium polystyrene sulfonate - separate administration by at least 3 hours (it binds many commonly prescribed oral medicines)

Monitoring

  • Serum phosphorus, with dosage adjusted as needed
  • Gastrointestinal tolerability, particularly diarrhoea
  • Signs of loss of efficacy of concomitant OATP2B1 substrates (e.g. enalapril)

Clinical monograph

How it works

It inhibits the gastrointestinal sodium-hydrogen exchanger NHE3, reducing intestinal phosphate absorption through the paracellular pathway.

Prescribing in practice

  • Diarrhoea is very common and can be severe, potentially causing dehydration and electrolyte disturbance, so it is contraindicated in known or suspected bowel obstruction.
  • Take as directed in relation to meals to optimise the reduction in phosphate absorption.
  • It may be used alone or with phosphate binders; review fluid and electrolyte status, particularly in those prone to volume depletion.

Monitoring

Monitor serum phosphate to guide dosing, and watch for the effects of diarrhoea on hydration and electrolytes.

Counselling the patient

  • Loose stools are common, especially at first; report severe or persistent diarrhoea.
  • Take this medicine as instructed in relation to your meals.

Evidence & guidelines

Tenapanor lowered serum phosphate in randomised controlled trials in dialysis patients, supporting its use in hyperphosphataemia.

Reference: Block et al. NEJM 2019 (AMPLIFY trial); MHRA SPC Xphozah; KDIGO CKD-MBD Guidelines 2017; 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).

Related

Curated clinical cross-links plus same-class fallbacks.

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