toxylact
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Budesonide (ATC A07EA06): Toxicological-Lactological Monograph
ATC class and general pharmacology
A07EA06 designates budesonide, classified as an alimentary-tract anti-inflammatory agent under “corticosteroids acting locally”; the WHO ATC/DDD Index lists oral and local-use defined daily doses of 9 mg and 1.5 mg, respectively.atcddd.fhi
Budesonide is a synthetic glucocorticoid with high topical anti-inflammatory activity and weak mineralocorticoid activity. It acts through glucocorticoid receptors, modulating transcription of inflammatory mediators and suppressing cytokine-driven intestinal inflammation; its receptor affinity is approximately 200-fold that of cortisol and 15-fold that of prednisolone.accessdata.fda
Intestinal formulations are designed to deliver the drug to affected bowel segments while limiting systemic exposure through extensive presystemic hepatic metabolism. Extended-release budesonide tablets may release at intestinal pH ≥7\geq 7≥7, while other oral formulations target the ileum and/or right colon; the therapeutic principle is local mucosal action with relatively low systemic bioavailability.accessdata.fda
After absorption, approximately 80–90% undergoes first-pass metabolism, mainly via CYP3A4. Budesonide is 85–90% protein bound, has a steady-state distribution volume of 2.2–3.9 L/kg, and has an intravenous elimination half-life of approximately 2–3.6 hours.accessdata.fda
The principal metabolites, 6β-hydroxybudesonide and 16α-hydroxyprednisolone, have less than 1/100 of the glucocorticoid activity of the parent compound. Excretion is predominantly as metabolites in urine and feces, with no unchanged budesonide detected in urine.accessdata.fda
Toxicological profile
Despite its intended local action, budesonide can produce systemic corticosteroid toxicity, particularly with prolonged treatment, hepatic dysfunction, high systemic exposure, or concomitant CYP3A4 inhibition. Relevant manifestations include hypercorticism, hypothalamic-pituitary-adrenal axis suppression, impaired stress response, metabolic effects, mood or sleep changes, acne, fluid retention, hypertension, reduced bone density, glaucoma, cataract progression, and increased susceptibility to infection.accessdata.fda
In clinical trials of oral extended-release budesonide for ulcerative colitis, commonly reported adverse reactions included headache, nausea, decreased blood cortisol, upper abdominal pain, fatigue, flatulence, abdominal distension, acne, urinary tract infection, arthralgia, and constipation. An abnormal ACTH-stimulation response occurred in 47% of patients after 4 weeks and 79% after 8 weeks of 9 mg daily treatment, demonstrating that clinically meaningful adrenal-axis effects may occur even with locally targeted therapy.accessdata.fda
CYP3A4 inhibitors substantially increase systemic exposure; ketoconazole increased exposure to oral budesonide approximately eightfold, while grapefruit juice approximately doubled it. Ritonavir, azole antifungals, macrolides, and other potent CYP3A4 inhibitors require careful review, and grapefruit products should be avoided during treatment.accessdata.fda
Reduced hepatic function is a major toxicological modifier because oral budesonide systemic availability was approximately 2.5-fold higher in patients with cirrhosis. Patients with moderate-to-severe liver disease should therefore be monitored for systemic corticosteroid adverse effects and may require treatment reassessment.accessdata.fda
Lactation pharmacology and infant exposure
Budesonide’s lactation profile is favorable because maternal systemic exposure is limited by extensive first-pass metabolism, milk concentrations are very low, and the drug ingested by the infant has low oral bioavailability. LactMed considers inhaled, oral, and rectal budesonide acceptable during breastfeeding.ncbi.nlm.nih
In a study involving eight women with Crohn disease receiving oral budesonide 3 mg once daily, budesonide was undetectable in all milk samples collected over eight hours after dosing, using an assay limit below 0.02 micrograms/L. The estimated maximum exposure for a fully breastfed infant was 0.007% of the maternal dose, equivalent to approximately 0.3% of the maternal weight-adjusted dose.ncbi.nlm.nih
No infant serum budesonide concentrations were reported in the available oral-use study, but no adverse effects were observed and infant growth and development were normal during exposure through breast milk. Direct milk-concentration studies for rectal budesonide are unavailable, although systemic exposure from local rectal formulations is generally expected to remain limited.ncbi.nlm.nih
The available direct oral lactation study used 3 mg/day, whereas intestinal inflammatory disease regimens may use 9 mg/day. Nevertheless, the combination of extremely low measured milk transfer, low infant oral bioavailability, extensive first-pass metabolism, and short maternal plasma half-life supports a very low expected systemic infant exposure (LactMed: Budesonide; FDA UCERIS prescribing information).ncbi.nlm.nih+1
Lactological safety assessment and clinical recommendations
Budesonide is considered compatible with breastfeeding when clinically indicated, including oral and rectal intestinal formulations. No interruption of breastfeeding, routine milk discarding, or dose-timing strategy is generally required.ncbi.nlm.nih
The maternal disease should be adequately controlled, since active inflammatory bowel disease can adversely affect maternal health, nutrition, caregiving capacity, and pregnancy-related outcomes. Choosing an effective locally acting treatment may reduce the need for systemic corticosteroids and support continuation of breastfeeding.accessdata.fda
Clinical caution is appropriate when maternal exposure is expected to be unusually high, including severe hepatic impairment, prolonged high-dose therapy, or co-administration of potent CYP3A4 inhibitors. In such circumstances, clinicians should assess the mother for systemic corticosteroid effects and consider prudent infant observation for poor feeding, inadequate weight gain, unusual irritability, or signs of adrenal suppression, although these effects are not expected from usual therapeutic exposure via milk (FDA UCERIS prescribing information; LactMed: Budesonide).ncbi.nlm.nih+1
For preterm, medically fragile, or exclusively breastfed infants, individualized assessment remains appropriate. However, the available evidence does not support withholding breastfeeding solely because the mother requires budesonide therapy.ncbi.nlm.nih
