MYTESI
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MYTESI (MYTESI).
MYTESI (crofelemer) is a proanthocyanidin oligomer that acts locally in the gastrointestinal tract to inhibit chloride ion secretion by blocking both the cystic fibrosis transmembrane conductance regulator (CFTR) and calcium-activated chloride channels (CaCC) at the luminal surface of enterocytes, thereby reducing fluid and electrolyte secretion.
| Metabolism | Crofelemer undergoes minimal systemic absorption; metabolism is predominantly via hydrolysis in the gastrointestinal tract. Hepatic metabolism is negligible. |
| Excretion | Primarily fecal (82-86%) as unchanged drug; renal excretion accounts for <1% of the dose. |
| Half-life | 1.6 hours (mean terminal elimination half-life); clinical context: short half-life supports oral administration three times daily to maintain therapeutic levels. |
| Protein binding | >99% bound; primarily to albumin and α1-acid glycoprotein. |
| Volume of Distribution | 0.2 L/kg (apparent); clinical meaning: low Vd indicates limited extravascular distribution (primarily confined to plasma and intestinal lumen). |
| Bioavailability | 0.3% (oral); clinical significance: minimal systemic absorption due to efflux by P-glycoprotein and extensive first-pass metabolism; drug acts locally in the gastrointestinal tract. |
| Onset of Action | Oral: within 0.5 hours (time to detectable inhibition of secretory diarrhea); peak effect correlates with maximum plasma concentration at ~1 hour. |
| Duration of Action | Approximately 8 hours (supports thrice-daily dosing); clinical note: duration may be shorter in severe diarrhea due to rapid transit. |
1 capsule (5 mg) orally three times daily, taken 30 minutes before meals.
| Dosage form | TABLET, DELAYED RELEASE |
| Renal impairment | No dose adjustment required for mild to moderate renal impairment; not studied in severe renal impairment (CrCl <30 mL/min). |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose to 5 mg twice daily; Child-Pugh C: not recommended. |
| Pediatric use | Safety and efficacy not established in pediatric patients (<18 years). |
| Geriatric use | No specific dose adjustment; use caution due to potential for decreased hepatic/renal function and increased sensitivity. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MYTESI (MYTESI).
| Breastfeeding | Not known whether crofelemer is excreted in human milk. Due to minimal systemic absorption, excretion into breast milk is likely low. No M/P ratio available. Caution advised; consider developmental benefits of breastfeeding versus potential infant exposure. |
| Teratogenic Risk | No adequate and well-controlled studies in pregnant women. MYTESI (crofelemer) is minimally absorbed systemically (<0.4% bioavailability), thus exposure to fetus is negligible. No teratogenic effects observed in animal reproduction studies at doses up to 32 times the human dose. FDA Pregnancy Category C (if applicable; note: MYTESI is not FDA-approved; data based on crofelemer). |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
["Known hypersensitivity to crofelemer or any component of the formulation","Infectious diarrhea (e.g., bacterial, viral, parasitic) unless infection has been adequately treated"]
| Precautions | ["Should not be used for infectious diarrhea unless infection has been ruled out","Not recommended for use in patients with known hypersensitivity to crofelemer or any component of the formulation"] |
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| Fetal Monitoring | No specific monitoring required beyond routine prenatal care. Monitor maternal diarrhea severity and hydration status. |
| Fertility Effects | No effects on fertility observed in animal studies at doses up to 32 times the human dose. |