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Hymecromone (ATC A05AX02) is a coumarin-derived choleretic and antispasmodic used for functional and obstructive biliary tract disorders; lactation safety data are very limited, so use during breastfeeding should be individualized and cautious.medpedia.framar+6

Identity and classification

• International non-proprietary name (INN): Hymecromone (4‑methylumbelliferone).wikipedia+1
• ATC code: A05AX02 – “Other drugs for bile therapy” within A05A “Bile and liver therapy”.medpedia.framar+1
• Chemical class: Synthetic coumarin derivative lacking the anticoagulant properties of classic coumarins.drugbank+3
• Formulations: Oral tablets, typically 300–400 mg, marketed in Europe and parts of Asia for biliary indications.drugs.ncats+2

Mechanism of action and pharmacodynamics

• Hymecromone exerts a choleretic effect, increasing bile flow and improving bile composition, which helps relieve biliary stasis and functional obstruction.pubmed.ncbi.nlm.nih+4
• It has direct antispasmodic activity on smooth muscle in the biliary tract, including the sphincter of Oddi, thereby reducing ductal pressure and pain in biliary dyskinesia.drugbank+2
• Beyond classical biliary indications, hymecromone inhibits hyaluronic acid synthesis and has been investigated for anti‑inflammatory, anti‑fibrotic and anti‑tumor effects in experimental and early clinical settings.pmc.ncbi.nlm.nih+3

Approved indications and dosing

Typical adult indications (region‑dependent) include:frontiersin+4

• Biliary dyskinesia and functional disorders of the biliary tract.
• Spasm of the sphincter of Oddi.
• Adjuvant therapy in cholelithiasis and chronic cholecystitis.
• Non‑obstructive cholestasis and other conditions associated with impaired bile flow (off‑label in some jurisdictions).

Usual dosing (adults):

• Oral administration, commonly 300–400 mg three times daily with main meals for about 10–14 days, with duration adjusted to clinical response and local product information.drugs.ncats+2

Pediatric indications and dosing are not well standardized and, where used, should follow local labeling and specialist guidance due to limited evidence.ncbi.nlm.nih+1

Adverse effects and toxicology

• Common undesirable effects are gastrointestinal, especially diarrhea, sometimes with significant fluid and electrolyte loss; this may increase sensitivity to cardiac glycosides in predisposed patients.frontiersin+2
• Hypersensitivity reactions (erythema, rash, urticaria, pruritus) occur rarely but warrant discontinuation and avoidance of re‑exposure.medpedia.framar+1
• Coumarin‑like structure raises theoretical concerns about hepatotoxicity, but hymecromone lacks classic anticoagulant effects; clinically significant liver injury appears uncommon at therapeutic doses, though data are limited.drugbank+2
• Overdose data in humans are scarce; dose‑limiting toxicity in clinical studies is typically gastrointestinal, and in monitored trials doses up to 3600 mg/day have been well tolerated.pmc.ncbi.nlm.nih+1

From a toxicological perspective in lactating women:

• No specific lactation‑focused toxicity studies exist; safety assessments must extrapolate from adult pharmacokinetics (PK), protein binding, metabolism, and general tolerance.ncbi.nlm.nih+1
• Extensive first‑pass metabolism with <1% excreted unchanged in urine suggests low systemic persistence of parent drug, but active metabolites and biliary excretion patterns in human milk remain uncharacterized.frontiersin+1

Contraindications and precautions

Absolute or major contraindications:drugs.ncats+3

• Documented hypersensitivity to hymecromone or excipients.
• Acute hepatitis or acute cholangitis.
• Acute biliary colic or gallbladder empyema.
• Significant renal impairment, clinically relevant cholestasis or advanced inflammatory bowel disease (for example, Crohn disease), according to some regional product information.medpedia.framar+1

Precautions:

• Diarrhea with electrolyte depletion: monitor high‑risk patients (elderly, cardiac disease, concomitant diuretics or cardiac glycosides) and discontinue if clinically significant diarrhea develops.fpnotebook+2
• Concomitant biliary antispasmodics and analgesics are generally permissible, but global antispasmodic burden and constipation/diarrhea balance should be considered.sps+1
• Pregnancy and lactation: insufficient human data; use only after individualized risk–benefit evaluation and preferably for short courses at the lowest effective dose.ncbi.nlm.nih+1

Drug interactions

Documented or clinically relevant interactions include:drugbank+3

• Metoclopramide: mutual attenuation of therapeutic effects when co‑administered, likely due to opposing actions on biliary tract motility; concurrent use is usually discouraged or requires clear justification.drugs.ncats+1
• Cardiac glycosides (for example, digoxin): hymecromone‑induced diarrhea may lead to hypokalemia, increasing susceptibility to digoxin toxicity; monitor electrolytes and clinical status when both are used.fpnotebook+2
• Experimental and investigational combinations (for example, with anti‑fibrotic or oncologic regimens) are under study but not yet defined for routine clinical practice.synapse.patsnap+3

In lactating patients, avoidance of polypharmacy with other agents that cause diarrhea, significant dehydration or electrolyte shifts is prudent, as these effects can destabilize both maternal health and breastfeeding.mayoclinic+2

Pharmacokinetics relevant to lactation

Key PK characteristics (mostly from non‑lactating adults) informing lactation risk assessment:pmc.ncbi.nlm.nih+4

• Absorption: Rapid oral absorption with onset of biliary effect within a few hours.
• Distribution: Limited published quantitative data; coumarin derivatives are often moderately protein‑bound, which tends to reduce free fraction transfer into milk, but hymecromone‑specific binding is not well defined.
• Metabolism: Extensively metabolized in the liver (phase II conjugation predominates); less than 1% of an administered dose is excreted unchanged in urine.frontiersin
• Excretion: Primarily via urine as metabolites; biliary excretion of conjugates is likely but not quantified.frontiersin
• Elimination half‑life: Not well characterized in public summaries; clinical dosing three to four times daily suggests a relatively short functional half‑life.pmc.ncbi.nlm.nih+2

Implications for breastfeeding:

• Short half‑life and extensive metabolism favor lower and more transient milk levels, particularly if doses are timed after feeds; however, lack of direct milk measurements means this remains theoretical.mayoclinic+3
• Potential conjugated metabolites in bile and gut could theoretically reach milk, but their pharmacological activity for the breastfed infant is unknown.ncbi.nlm.nih+1

Lactation safety assessment

Evidence base:

• No controlled studies, case series or milk–plasma (M/P) ratio measurements for hymecromone in breastfeeding women could be identified in standard references searched.ncbi.nlm.nih+1
• Major lactation safety resources (for example, LactMed and specialist breastfeeding factsheets) do not list hymecromone explicitly as a characterized substance as of current updates.breastfeedingnetwork+1
• Consequently, formal classification in systems such as Hale’s Lactation Risk Categories has not been clearly documented in public‑access summaries.womenscare+1

Reasoned toxicological‑lactological appraisal (for single‑agent hymecromone):

Factors that tend to reduce theoretical risk to the breastfed infant:

• Short treatment courses in biliary indications (commonly 10–14 days).medpedia.framar+2
• Expected short half‑life and extensive hepatic metabolism with minimal unchanged renal excretion.frontiersin
• Absence of sedative, central nervous system depressant or strong cardiovascular actions at therapeutic doses, thus low expectation of acute pharmacodynamic effects in an infant from trace exposures.drugbank+2

Factors that increase uncertainty or potential risk:

• Complete absence of measured concentrations in breast milk, infant serum or clinical follow‑up data in breastfeeding dyads.ncbi.nlm.nih+1
• Biliary excretion and localized intestinal effects, raising theoretical concerns for infant gut motility or diarrhea if appreciable amounts were ingested via milk.fpnotebook+2
• Very young, preterm or medically fragile infants have greater susceptibility to fluid–electrolyte imbalance and to drugs lacking robust lactation safety data.mayoclinic+2

Pragmatic clinical positioning for breastfeeding:

• In healthy term infants, short‑term maternal use of hymecromone at standard oral doses is likely to result in low infant exposure, but due to missing data the drug should be considered of unknown risk rather than definitively safe.fpnotebook+3
• For preterm, low‑birth‑weight, jaundiced, or otherwise high‑risk infants, or when prolonged courses are anticipated, alternative choleretic or antispasmodic agents with established lactation safety are preferable where clinically adequate.sps+3
• If hymecromone is considered essential, strategies such as:
• Using the lowest effective dose for the shortest feasible duration.
• Administering doses immediately after breastfeeding or before the infant’s longest sleep interval.
• Monitoring the infant for changes in stool frequency/consistency, feeding behavior, sedation or unusual irritability.
  are reasonable risk‑mitigation approaches.mayoclinic+2

Provisional lactation risk wording (for professional use):

• “Hymecromone: No data on excretion into breast milk or effects on the breastfed infant. Based on pharmacokinetics and clinical use, clinically significant transfer is unlikely with short‑term standard dosing, but uncertainty remains. Prefer alternatives with established lactation safety, especially in newborn or preterm infants; if used, monitor the infant and maternal biliary disease carefully.”fpnotebook+3

Monitoring of the breastfed infant

When a breastfeeding woman receives hymecromone, recommended monitoring parameters for the infant include:mayoclinic+2

• Gastrointestinal: Onset of diarrhea, vomiting, changes in stool pattern or signs of dehydration (reduced wet diapers, dry mucosa, weight concerns).
• General: Excessive sleepiness or, conversely, marked irritability or feeding difficulties.
• Dermatologic: New rash or urticaria possibly reflecting hypersensitivity.

Any concerning signs should prompt reassessment of maternal therapy, including possible discontinuation of hymecromone or temporary interruption of breastfeeding, guided by clinical urgency and availability of safer alternatives.fpnotebook+2

Key counseling points for breastfeeding patients

For healthcare professionals advising lactating women:mayoclinic+2

• Explain that hymecromone is used to treat biliary tract spasm and dyskinesia and is usually prescribed for relatively short periods.
• Emphasize that there are no direct breastfeeding studies; decisions are therefore based on general pharmacology and experience rather than robust lactation data.
• Discuss alternative therapies with better characterized breastfeeding safety when disease severity and local availability allow.
• If hymecromone is chosen:
• Use the minimal effective dose and shortest course.
• Optimize dosing schedule around feeds.
• Provide clear instructions on infant monitoring and when to seek medical review.