METRETON
Clinical safety rating: caution
Comprehensive clinical and safety monograph for METRETON (METRETON).
Antihistamine and mast cell stabilizer. Competitively inhibits histamine at H1 receptors and prevents release of histamine and other mediators from mast cells.
| Metabolism | Not extensively metabolized; primarily excreted unchanged in urine. |
| Excretion | Renal (80-90% as unchanged drug and metabolites), biliary/fecal (10-20%) |
| Half-life | Terminal elimination half-life is 24-36 hours; increased in renal impairment (up to 60 hours in anuria) |
| Protein binding | 75-85% bound to albumin and alpha-1-acid glycoprotein |
| Volume of Distribution | 0.5-1.0 L/kg; indicates moderate tissue distribution |
| Bioavailability | Oral: 50-70% (first-pass metabolism); Intramuscular: 80-100% |
| Onset of Action | Oral: 30-60 minutes; Intramuscular: 15-30 minutes; Intravenous: immediate |
| Duration of Action | Oral: 8-12 hours; Intramuscular: 6-8 hours; Intravenous: 4-6 hours; duration prolonged in hepatic impairment |
1-2 mg/kg intramuscularly or intravenously every 6-8 hours as needed; maximum 100 mg per dose.
| Dosage form | SOLUTION/DROPS |
| Renal impairment | CrCl 10-50 mL/min: administer every 12 hours; CrCl <10 mL/min: administer every 12-18 hours or consider dose reduction by 50%. |
| Liver impairment | Child-Pugh Class A: no adjustment; Class B: reduce dose by 50%; Class C: avoid use or reduce dose by 75%. |
| Pediatric use | 0.5-1 mg/kg intramuscularly or intravenously every 6-8 hours; maximum 25 mg per dose for children <40 kg. |
| Geriatric use | Start at lower end of dosing range (e.g., 0.5-1 mg/kg) with extended intervals (every 8-12 hours) due to decreased 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 METRETON (METRETON).
| Breastfeeding | Prednisolone and chlorpheniramine (components of METRETON) are excreted into breast milk. M/P ratio for prednisolone is approximately 0.5-0.7. Low risk at maternal doses <20 mg/day; higher doses may cause infant adrenal suppression or growth delay. Consider alternative antihistamine with lower excretion. |
| Teratogenic Risk | Pregnancy Category C: Fetal risk cannot be ruled out. First trimester: Increased risk of cleft palate and cardiac malformations due to corticosteroid component (prednisolone). Second and third trimesters: Potential for intrauterine growth restriction, adrenal suppression in neonate. Avoid use unless benefit outweighs risk. |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to any component of the formulation"]
| Precautions | ["Do not inject; for ophthalmic use only.","May cause transient burning or stinging.","Use with caution in patients with narrow-angle glaucoma."] |
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| Fetal Monitoring | Maternal: Blood pressure, blood glucose, signs of infection, weight gain. Fetal: Ultrasound for growth restriction if used long-term in second/third trimester; neonatal assessment for adrenal suppression if used near term. |
| Fertility Effects | No known direct effect on fertility. Corticosteroids may cause menstrual irregularities or ovulatory dysfunction at high doses, potentially impacting conception. Antihistamines are not associated with fertility impairment. |