Tenapanor

The dosage of tenapanor is strictly dependent on the condition being treated and should be individualized by a healthcare professional.

• For Irritable Bowel Syndrome with Constipation (IBS-C): The standard recommended dosage is 50 mg taken orally twice daily. This is typically administered immediately before breakfast (or the first meal of the day) and immediately before dinner (or the last meal of the day).
• For Hyperphosphatemia in CKD on Dialysis: The starting dose is generally 30 mg taken orally twice daily. Based on the patient's serum phosphorus levels and gastrointestinal tolerance (specifically the occurrence of diarrhea), a physician may adjust the dose. The dosage range for this indication typically spans from 20 mg to 30 mg twice daily.

Tenapanor is NOT approved for use in pediatric patients. There is a specific safety concern regarding the risk of severe dehydration in children.

• Contraindication: Tenapanor is strictly contraindicated in patients less than 6 years of age.
• Avoidance: Use should be avoided in patients aged 6 years to less than 18 years, as the safety and efficacy have not been established in this population. In young animal studies, tenapanor caused death due to dehydration shortly after weaning.

Renal Impairment

Since tenapanor acts locally in the gastrointestinal tract and has negligible systemic absorption, dosage adjustments are generally not required for patients with renal impairment. In fact, one of its primary indications is for patients with end-stage renal disease (ESRD) on dialysis.

Hepatic Impairment

No dosage adjustments are typically necessary for patients with hepatic impairment (liver disease). Because the drug does not rely on hepatic metabolism or systemic circulation, liver function does not significantly impact the drug's efficacy or safety profile.

Elderly Patients

Clinical trials have included patients aged 65 and older, and no overall differences in safety or effectiveness were observed between these patients and younger patients. No specific age-based dose adjustments are required, though providers should monitor for dehydration and diarrhea more closely in the frail elderly.

To ensure the best results and minimize side effects, follow these instructions:

1. 1Timing: Take tenapanor immediately before your morning and evening meals. Taking it with food helps the drug interact correctly with the sodium in your diet.
2. 2Administration: Swallow the tablets whole. Do not crush, chew, or break the tablets, as this may alter the drug's release profile in the gut.
3. 3Consistency: Take the medication at the same time every day to maintain a consistent effect on bowel movements or phosphorus levels.
4. 4Storage: Store the medication in its original container at room temperature (68°F to 77°F or 20°C to 25°C). Keep the container tightly closed and protect it from moisture. The original bottle often contains a desiccant (a small packet to keep the pills dry); do not remove or eat this packet.

If you miss a dose of tenapanor, skip the missed dose and take your next dose at the regular time before your next meal. Do not take two doses at the same time to make up for a missed one. Taking an extra dose may significantly increase the risk of severe diarrhea.

Symptoms of an overdose are likely to manifest as an exaggerated pharmacological effect, primarily severe and persistent diarrhea. This can lead to significant fluid loss and electrolyte imbalances (such as low potassium or sodium). In the event of a suspected overdose, contact your local poison control center or seek emergency medical attention immediately. Treatment is generally supportive, focusing on rehydration and electrolyte replacement.

> Important: Follow your healthcare provider's dosing instructions. Do not adjust your dose without medical guidance. If you experience severe diarrhea that does not stop, contact your doctor immediately.

The most frequently reported side effect of tenapanor across all clinical trials is diarrhea. Because tenapanor works by increasing fluid in the intestines, diarrhea is a direct extension of its mechanism of action.

• Diarrhea: This typically occurs within the first two weeks of starting treatment. It can range from mild to severe. Patients may experience loose, watery stools or an increased urgency to have a bowel movement. In most cases, the diarrhea is manageable and may resolve as the body adjusts, but in some patients, it may require dose reduction or discontinuation.
• Abdominal Distension: Some patients report a feeling of fullness or bloating in the abdominal area.
• Flatulence: Increased gas production is common as the gut microbiome and fluid levels shift.

These effects occur in a smaller percentage of patients but are still notable:

• Dizziness: This may be secondary to fluid shifts or mild dehydration.
• Abdominal Pain: While the drug is intended to treat pain in IBS-C, some patients may experience new or different cramping as intestinal motility increases.
• Nausea: A general feeling of stomach upset, often occurring shortly after taking the dose.
• Rectal Hemorrhage: Rare instances of minor bleeding, often associated with the increased frequency of bowel movements or irritation of the rectal lining.

• Severe Dehydration: Resulting from prolonged, untreated diarrhea.
• Hypokalemia: Low blood potassium levels, which can occur if electrolytes are lost through excessive diarrhea.
• Hyponatremia: Low blood sodium levels, though rare due to the local nature of the drug.

> Warning: Stop taking Tenapanor and call your doctor immediately if you experience any of these.

• Severe Diarrhea: Diarrhea that is persistent, prevents you from performing daily activities, or is accompanied by signs of dehydration.
• Signs of Dehydration: These include extreme thirst, very dark urine, decreased urination, dry mouth, sunken eyes, or feeling lightheaded/fainting.
• Severe Abdominal Pain: Sharp or worsening pain that does not feel like typical gas or cramping.
• Allergic Reaction: Symptoms include hives, difficulty breathing, or swelling of the face, lips, tongue, or throat.

Because tenapanor is a relatively new medication (approved in 2019/2023), long-term data over decades is still being collected. However, current clinical evidence suggests that the primary long-term risk is the potential for chronic electrolyte imbalances if diarrhea is not properly managed. There is no evidence currently suggesting that tenapanor causes structural changes to the gut or increases the risk of cancer.

Tenapanor carries a FDA Boxed Warning regarding its use in pediatric patients.

• Risk of Serious Dehydration: Tenapanor is contraindicated in children less than 6 years of age. In nonclinical studies, tenapanor administration to young rats resulted in deaths, likely due to severe dehydration. The safety and effectiveness of tenapanor have not been established in patients less than 18 years of age. Healthcare providers should avoid the use of tenapanor in patients aged 6 years to less than 18 years. If diarrhea occurs in any patient, but especially those at higher risk, prompt medical intervention for rehydration is necessary.

Report any unusual symptoms to your healthcare provider. Your doctor may monitor your electrolytes and fluid status periodically while you are on this medication.

Tenapanor is a potent modulator of intestinal fluid and electrolyte transport. While its local action minimizes systemic risks, it poses specific challenges related to gastrointestinal health and fluid balance. Patients must be aware that the primary risk is diarrhea, which can lead to complications if not monitored.

WARNING: RISK OF SERIOUS DEHYDRATION IN PEDIATRIC PATIENTS

• Tenapanor is contraindicated in patients less than 6 years of age; in nonclinical studies in rats, tenapanor caused death that was presumed to be due to dehydration.
• Avoid use of tenapanor in patients 6 years to less than 18 years of age.
• The safety and effectiveness of tenapanor have not been established in patients less than 18 years of age.

• Gastrointestinal Obstruction: Tenapanor should not be used in patients with known or suspected mechanical gastrointestinal obstruction (a physical blockage in the intestines). Increasing fluid and motility against a blockage can lead to serious complications, including bowel perforation.
• Severe Diarrhea Management: Diarrhea is the most common adverse reaction. If severe diarrhea occurs, the medication should be suspended, and the patient should be rehydrated. Once resolved, the drug may be restarted at a lower dose or discontinued permanently depending on medical advice.
• Electrolyte Imbalances: Patients, especially those with CKD or those taking diuretics, should be monitored for changes in serum electrolytes. Excessive loss of fluid in the stool can deplete potassium, sodium, and bicarbonate.
• Allergic Reactions: Although rare, hypersensitivity reactions can occur. Patients with a known allergy to tenapanor hydrochloride or any of the inactive ingredients (such as microcrystalline cellulose or magnesium stearate) should avoid this medication.

For patients taking tenapanor for hyperphosphatemia (Xphozah), regular monitoring of serum phosphorus levels is required to assess efficacy and adjust the dose. For all patients, healthcare providers may periodically check:

• Blood Pressure: To ensure dehydration isn't causing hypotension (low blood pressure).
• Electrolyte Panel: To check levels of potassium, sodium, and chloride.
• Renal Function: While the drug is used in renal patients, monitoring overall stability is standard practice.

Tenapanor is not known to cause drowsiness or impair cognitive function. However, if a patient experiences dizziness due to dehydration or low blood pressure, they should avoid driving or operating heavy machinery until they feel stable.

There are no known direct chemical interactions between tenapanor and alcohol. However, alcohol can irritate the gastrointestinal tract and may worsen diarrhea or dehydration. It is generally advised to limit alcohol consumption while managing IBS-C or CKD.

Tenapanor does not typically require a tapering schedule. If the medication is stopped, the symptoms of IBS-C (constipation) or hyperphosphatemia (high phosphorus) are likely to return to baseline levels within a few days. Always consult your doctor before stopping the medication.

> Important: Discuss all your medical conditions with your healthcare provider before starting Tenapanor, especially if you have a history of bowel blockages or are prone to dehydration.

There are currently no medications that are strictly contraindicated for use with tenapanor based on systemic chemical interactions. However, tenapanor is contraindicated in patients with known mechanical gastrointestinal obstruction. Using tenapanor alongside other potent osmotic laxatives (like high-dose lactulose or polyethylene glycol) is generally discouraged unless directed by a specialist, as the cumulative effect can lead to profound fluid loss.

• Entecavir: Some studies suggest that tenapanor may reduce the absorption of entecavir (used for Hepatitis B). If taken together, the effectiveness of the antiviral may be diminished. Monitor the viral load closely.
• Other Minimally Absorbed Drugs: Because tenapanor alters the fluid and pH environment of the gut, it may theoretically affect the solubility and absorption of other drugs that remain in the GI tract.

• Phosphate Binders: When used for CKD, tenapanor is often used with phosphate binders (like sevelamer or calcium acetate). While this is a therapeutic combination, the timing may be important. However, no specific physical incompatibility has been identified that requires staggered dosing beyond the standard 'take before meals' instruction.
• Diuretics (Water Pills): Medications like furosemide or hydrochlorothiazide increase fluid loss through the kidneys. Taking these with tenapanor (which increases fluid loss through the gut) increases the risk of dehydration and electrolyte depletion.

• High-Fat Meals: In clinical trials, taking tenapanor with a high-fat meal was associated with an increased frequency of bowel movements compared to taking it in a fasted state. This is why the drug is specifically labeled to be taken immediately before meals to standardize its effect.
• Grapefruit/Caffeine: There are no known interactions with grapefruit or caffeine, though caffeine may worsen the laxative effect in sensitive individuals.

• St. John's Wort: While tenapanor is not systemically absorbed, St. John's Wort can affect gut motility and might interfere with the predictable action of tenapanor.
• Magnesium Supplements: Magnesium itself has a laxative effect. Combining tenapanor with magnesium-based supplements may lead to severe diarrhea.

Tenapanor does not typically interfere with common laboratory tests (like urine screens or liver function tests). However, it will directly affect serum phosphorus and stool consistency tests, which are the intended clinical outcomes.

Interaction Mechanism Summary

• Mechanism: Primarily pharmacodynamic (additive effects on the gut) rather than pharmacokinetic (CYP enzyme inhibition).
• Consequence: Increased risk of diarrhea or reduced absorption of specific co-administered drugs.
• Management: Monitor fluid status and ensure other medications are taken as prescribed, potentially monitoring for reduced efficacy of drugs like entecavir.

> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, including over-the-counter laxatives or antacids.

Tenapanor must NEVER be used in the following circumstances:

1. 1Pediatric Patients Under 6 Years of Age: Due to the high risk of fatal dehydration. This is based on nonclinical data where young animals experienced rapid, severe fluid loss.
2. 2Mechanical Gastrointestinal Obstruction: If there is a physical blockage in the small or large intestine (caused by tumors, adhesions, or severe impaction), tenapanor could cause a dangerous buildup of fluid and pressure behind the obstruction, leading to bowel rupture or perforation.

Conditions requiring a careful risk-benefit analysis by a physician include:

• Severe Active Inflammatory Bowel Disease (IBD): Patients with active Crohn's disease or Ulcerative Colitis may have a compromised intestinal lining. The use of an NHE3 inhibitor could potentially exacerbate inflammation or cause excessive fluid shifts in an already sensitive gut.
• Aged 6 to 18 Years: Use is generally avoided because the safety profile in this age group has not been fully characterized, and the risk of dehydration remains a concern.
• Severe Autonomic Neuropathy: Patients with severe nerve damage affecting the gut may have unpredictable responses to medications that alter intestinal motility.

There are currently no other NHE3 inhibitors on the market, so cross-sensitivity within the class is not a known issue. However, patients who have had severe hypersensitivity reactions to other intestinal secretagogues (like linaclotide or plecanatide) should be monitored closely, even though the chemical structures are unrelated.

> Important: Your healthcare provider will evaluate your complete medical history, including any history of abdominal surgeries or chronic bowel conditions, before prescribing Tenapanor.

Tenapanor is minimally absorbed systemically following oral administration, which means maternal exposure is negligible. Consequently, fetal exposure is expected to be minimal.

• Risk Summary: Available data are insufficient to identify a drug-associated risk of major birth defects or miscarriage. However, because the drug is not absorbed into the bloodstream, it is generally considered to have a low risk for developmental toxicity.
• Clinical Considerations: Pregnant women with IBS-C or CKD should still consult their OB/GYN. Maintaining electrolyte balance is crucial during pregnancy, and severe diarrhea should be avoided.

It is not known if tenapanor is excreted in human milk. However, because systemic absorption in the mother is negligible, it is highly unlikely that clinically significant amounts of the drug would reach the breast milk or the nursing infant.

• Recommendation: The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for tenapanor. Monitor the infant for signs of diarrhea if the mother is taking the medication.

As noted in the Black Box Warning, tenapanor is contraindicated in children under 6. Its use is avoided in all patients under 18. The primary concern is that the immature gut of a child may be hypersensitive to NHE3 inhibition, leading to rapid and life-threatening dehydration.

In clinical trials, approximately 10-15% of patients were 65 years of age or older. No overall differences in safety or effectiveness were observed between these patients and younger subjects.

• Considerations: Older adults are at a higher risk for complications from diarrhea, such as falls due to dizziness or acute kidney injury from dehydration. Providers should ensure geriatric patients have adequate access to fluids.

Tenapanor is specifically indicated for patients with end-stage renal disease (ESRD) on dialysis. No dose adjustment is required for any level of renal impairment. The drug's action is entirely independent of kidney filtration.

No dosage adjustment is required for patients with mild to severe hepatic impairment (Child-Pugh Class A, B, or C). Since the drug is not systemically absorbed and does not undergo significant hepatic metabolism, liver function does not affect the pharmacokinetics of the drug.

> Important: Special populations require individualized medical assessment. Always inform your specialist if you are planning to become pregnant or are currently nursing.

Tenapanor is a potent, selective inhibitor of the Sodium-Hydrogen Exchanger 3 (NHE3). NHE3 is an antiporter protein found on the apical surface of epithelial cells in the small intestine and colon. Its normal function is to exchange one intracellular hydrogen ion (H+) for one luminal sodium ion (Na+).

• By blocking this exchange, tenapanor keeps sodium within the intestinal lumen.
• The resulting osmotic gradient draws water into the gut, increasing stool volume and softening consistency.
• For phosphate control, the inhibition of NHE3 leads to an increase in intracellular protons, which triggers a signaling pathway that tightens the junctions between cells, specifically blocking the paracellular absorption of phosphate.

• Onset of Action: For IBS-C, patients may notice an increase in bowel movement frequency within 24 to 48 hours. For phosphorus reduction, the effect is typically seen within 1 to 2 weeks of consistent dosing.
• Duration: The effect lasts as long as the drug is present in the gut. Once discontinued, NHE3 activity returns to normal within approximately 48-72 hours.
• Tolerance: There is no evidence of pharmacological tolerance; the drug remains effective with long-term use.

| Parameter | Value |

|---|---|

| Bioavailability | < 1% (Negligible) |

| Protein Binding | Not Applicable (Systemic levels < 0.5 ng/mL) |

| Half-life | Not Applicable (Local action) |

| Tmax | Not Applicable |

| Metabolism | Negligible (Minor CYP3A4/5 if absorbed) |

| Excretion | Fecal (> 99%) |

• Molecular Formula: C44H60Cl2N8O4S2 · 2HCl
• Molecular Weight: 914.9 g/mol (as HCl salt)
• Solubility: Soluble in water and gastrointestinal fluids.
• Structure: A complex sulfonamide derivative designed for high potency at the NHE3 receptor and extremely low permeability across the intestinal wall.

Tenapanor is classified as a Gastrointestinal Agent, Miscellaneous or more specifically as an NHE3 Inhibitor. It is currently the only drug in this class approved for human use, distinguishing it from secretagogues like Linaclotide (a guanylate cyclase-C agonist).