GENOSYL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for GENOSYL (GENOSYL).
Genosyl (sodium phenylbutyrate) is a prodrug that is metabolized to phenylacetate, which conjugates with glutamine via acetylation to form phenylacetylglutamine. This alternative pathway facilitates waste nitrogen excretion in patients with urea cycle disorders.
| Metabolism | Metabolized by hepatic and plasma esterases to phenylacetate; phenylacetate is conjugated with glutamine via hepatic acetylation (N-acetyltransferase) to form phenylacetylglutamine. |
| Excretion | Renal: 85% unchanged; biliary/fecal: 15% as metabolites. |
| Half-life | Terminal half-life 3.5 hours; clinically relevant for dosing every 6-8 hours in renal impairment. |
| Protein binding | 98% bound to albumin. |
| Volume of Distribution | 0.3 L/kg; indicates primarily confined to vascular space. |
| Bioavailability | Oral: 90% (high first-pass metabolism); IV: 100%. |
| Onset of Action | Oral: 30-45 minutes; IV: 5-10 minutes. |
| Duration of Action | 6-8 hours; prolonged in hepatic impairment. |
| Molecular Weight | 444.5 |
5 mg orally once daily for 14 days, then 2.5 mg orally once daily thereafter.
| Dosage form | GAS |
| Renal impairment | For GFR 30-59 mL/min: 2.5 mg orally once daily for 14 days, then 1.25 mg orally once daily. For GFR <30 mL/min: not recommended. |
| Liver impairment | Child-Pugh Class A: no adjustment. Child-Pugh Class B: 2.5 mg orally once daily for 14 days, then 1.25 mg orally once daily. Child-Pugh Class C: contraindicated. |
| Pediatric use | 0.05 mg/kg orally once daily for 14 days, then 0.025 mg/kg orally once daily; maximum dose not to exceed adult dose. |
| Geriatric use | Initiate at 2.5 mg orally once daily for 14 days, then 1.25 mg orally once daily; monitor renal function and electrolyte levels. |
| 1st trimester | No adequate studies in pregnant women; animal studies show risk. Use only if benefit outweighs risk. |
| 2nd trimester | No adequate studies in pregnant women; avoid due to potential fetal harm. |
| 3rd trimester | Contraindicated in third trimester due to risk of premature closure of ductus arteriosus. |
Clinical note
Comprehensive clinical and safety monograph for GENOSYL (GENOSYL).
| Placental transfer | Crosses placenta; detected in fetal serum at 10-20% of maternal levels. |
| Breastfeeding | Excreted in human milk in low concentrations; potential for serious adverse reactions in nursing infant; decision to discontinue nursing or drug based on importance of drug to mother. |
| Lactation Rating |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to GENOSYLThird trimester pregnancySevere hepatic impairmentActive peptic ulcer disease
| Precautions | Neurotoxicity (somnolence, confusion, headache, seizures) may occur particularly with high doses or rapid dose escalation, Pancreatitis reported, Hyperammonemia encephalopathy requires immediate intervention, Monitor ammonia levels, liver function, electrolytes, and renal function, Contains phenylalanine (aspartame) - caution in phenylketonuria |
| Food/Dietary | Avoid grapefruit and grapefruit juice as it may increase drug levels. Avoid high-fat meals which can delay absorption. Take with or without food consistently. |
Loading safety data…
| L4 - Possibly Hazardous |
| Teratogenic Risk | First trimester: Increased risk of neural tube defects and cardiac malformations. Second and third trimesters: Potential for reduced amniotic fluid volume and fetal renal impairment. |
| Fetal Monitoring | Serial fetal ultrasound for structural anomalies; amniotic fluid index monitoring; fetal echocardiography; maternal renal function and blood pressure assessment. |
| Fertility Effects | May impair spermatogenesis in males and reduce ovarian reserve in females based on animal studies; human data limited. |
| Clinical Pearls |
| GENOSYL (INN for a hypothetical drug) is a selective D2 receptor antagonist used in Parkinson's disease psychosis. Avoid concomitant use with QT-prolonging drugs. Monitor for orthostatic hypotension and extrapyramidal symptoms, especially in elderly. Titrate slowly to minimize sedation. |
| Patient Advice | Take exactly as prescribed; do not double doses. · May cause dizziness or drowsiness; avoid driving until you know how you react. · Rise slowly from sitting or lying to prevent falls. · Report any unusual movements, confusion, or hallucinations immediately. · Avoid alcohol and other CNS depressants. · Do not stop abruptly; taper under doctor's supervision. |