MYTELASE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MYTELASE (MYTELASE).
Mytelase (ambenonium chloride) is a reversible acetylcholinesterase inhibitor that increases acetylcholine concentration at cholinergic synapses by inhibiting its hydrolysis. This enhances neuromuscular transmission and improves muscle strength.
| Metabolism | Primarily metabolized by the liver via microsomal enzymes, with uncertain specific CYP involvement. Excreted renally as metabolites and unchanged drug. |
| Excretion | Primarily renal (80-90% as unchanged drug via glomerular filtration and tubular secretion); minor biliary/fecal excretion (<5%). |
| Half-life | 3-4 hours (short; requires frequent dosing every 3-4 hours for myasthenia gravis management). |
| Protein binding | <10% (negligible binding to serum proteins). |
| Volume of Distribution | 0.7-1.4 L/kg (large Vd suggests extensive tissue distribution, including into skeletal muscle). |
| Bioavailability | Oral: 20-30% (high first-pass metabolism; variable absorption). |
| Onset of Action | Oral: 30-90 minutes; Intramuscular: 15-30 minutes; Intravenous: 1-15 minutes. |
| Duration of Action | Oral: 2-4 hours; Parenteral: 1-2 hours (clinical effect duration; shorter for IV/IM due to rapid redistribution). |
Oral: 5–25 mg three times daily; maximum 100 mg/day. IV: 2–5 mg every 2–4 hours as needed for myasthenic crisis.
| Dosage form | TABLET |
| Renal impairment | CrCl <50 mL/min: reduce dose by 50% and increase interval. CrCl <10 mL/min: avoid use. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B: reduce dose by 50%. Child-Pugh C: avoid use. |
| Pediatric use | Oral: 1–2 mg/kg/day in 3–5 divided doses; IV: 0.04–0.15 mg/kg/dose every 4–6 hours. |
| Geriatric use | Start at low end of dosing range (5 mg three times daily); titrate slowly due to renal clearance decline and increased fall risk. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MYTELASE (MYTELASE).
| Breastfeeding | Excretion into human milk is unknown. M/P ratio not established. Use caution; potential for infant muscle weakness and cholinergic effects. |
| Teratogenic Risk | Pregnancy Category C. First trimester: Limited human data, animal studies show increased fetal resorptions and malformations at high doses. Second/Third trimesters: May cause premature labor due to inhibition of acetylcholinesterase at the neuromuscular junction; fetal bradycardia and muscle weakness reported. |
| Fetal Monitoring |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to ambenonium or any component.","Mechanical intestinal or urinary obstruction.","Concurrent use with depolarizing neuromuscular blockers (e.g., succinylcholine) due to prolonged paralysis."]
| Precautions | ["Cholinergic crisis: Overdosage can cause severe muscarinic and nicotinic effects (e.g., bradycardia, hypotension, respiratory paralysis).","Myasthenic crisis: Distinguish from cholinergic overdose; both may present with weakness.","Bronchial asthma or cardiac arrhythmias: Use with caution due to potential exacerbation.","Pregnancy: Use only if clearly needed (Category C)."] |
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| Monitor fetal heart rate and uterine activity during labor and delivery. Assess newborn for signs of cholinergic excess (e.g., muscle weakness, bradycardia, increased secretions). |
| Fertility Effects | No specific human studies. Animal studies indicate no significant adverse effects on fertility at therapeutic doses. |