ONA-MAST
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ONA-MAST (ONA-MAST).
ONA-MAST (onabotulinumtoxinA) is a neurotoxin that cleaves SNAP-25, a protein required for acetylcholine release at the neuromuscular junction, thereby inhibiting muscle contraction. It also inhibits release of nociceptive neurotransmitters such as substance P and glutamate from sensory neurons, contributing to analgesic effects.
| Metabolism | Metabolized via proteolytic degradation by endogenous proteases; no involvement of cytochrome P450 enzymes. |
| Excretion | Renal (approximately 60% as unchanged drug) and biliary/fecal (approximately 30% as metabolites); 10% excreted via sweat/saliva. |
| Half-life | Terminal elimination half-life 4.5 hours; clinically significant for q6h dosing to maintain therapeutic levels. |
| Protein binding | 92% bound to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Vd 1.2 L/kg; indicates extensive tissue distribution with penetration into CNS and placenta. |
| Bioavailability | Intramuscular: 85%; Oral: 40% (due to first-pass metabolism). |
| Onset of Action | Intravenous: 2-5 minutes; Intramuscular: 15-30 minutes; Oral: 45-60 minutes. |
| Duration of Action | Intravenous: 6-8 hours; Intramuscular: 8-12 hours; Oral: 6-8 hours; duration extended in hepatic impairment. |
10-30 mg subcutaneously once weekly
| Dosage form | TABLET |
| Renal impairment | GFR <30 mL/min: not recommended; GFR 30-59 mL/min: reduce dose by 50%; GFR ≥60 mL/min: no adjustment |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: not recommended |
| Pediatric use | Not established in pediatric patients <18 years |
| Geriatric use | No specific dose adjustment; monitor renal function and for increased sensitivity |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for ONA-MAST (ONA-MAST).
| Breastfeeding | Contraindicated in breastfeeding. ONA-MAST is excreted in human milk. M/P ratio unknown. Potential for severe adverse effects in nursing infants, including androgenic effects and hepatotoxicity. |
| Teratogenic Risk | FDA Pregnancy Category X. First trimester: High risk of congenital anomalies including craniofacial defects, cardiovascular malformations, and neural tube defects due to antiandrogenic effects. Second trimester: Continued risk of urogenital tract abnormalities and impaired spermatogenesis in male fetuses. Third trimester: Potential for premature closure of epiphyseal growth plates and reduced fetal growth. |
■ FDA Black Box Warning
Distant spread of toxin effect: The effects of onabotulinumtoxinA may spread from the area of injection to other areas of the body, causing symptoms consistent with botulinum toxin effects, including asthenia, generalized muscle weakness, diplopia, ptosis, dysphonia, dysarthria, urinary incontinence, and breathing difficulties. These symptoms have been reported hours to weeks after injection. Swallowing and breathing difficulties can be life-threatening. The risk is greatest in children treated for spasticity, but symptoms can occur in adults. Use with caution in patients with pre-existing neuromuscular disorders.
| Serious Effects |
["Hypersensitivity to onabotulinumtoxinA or any component of the formulation","Infection at the proposed injection site","For intradetrusor injection: patients with urinary tract infection or those unable or unwilling to catheterize if post-void residual is elevated"]
| Precautions | ["Distant spread of toxin effect (see boxed warning)","Use caution in patients with pre-existing neuromuscular disorders (e.g., myasthenia gravis, ALS, Lambert-Eaton syndrome)","Risk of anaphylaxis or allergic reactions","Caution in patients with inflammation or infection at injection site","Risk of urinary retention when used for overactive bladder","Possible increased fall risk due to muscle weakness","Use caution with concomitant aminoglycosides or other agents interfering with neuromuscular transmission"] |
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| Fetal Monitoring | Monitor for signs of maternal virilization (hirsutism, voice deepening, clitoromegaly). Fetal monitoring: serial ultrasound for congenital anomalies, amniotic fluid assessment for oligohydramnios. Maternal liver function tests and lipid profile monthly. |
| Fertility Effects | Reversible impairment of spermatogenesis in males; anovulation and menstrual irregularities in females due to hormonal suppression. Reduced fertility during treatment and for up to 3-6 months after discontinuation. |