BONTRIL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for BONTRIL (BONTRIL).
Bontril (phendimetrazine) is a sympathomimetic amine that acts as an appetite suppressant. Its mechanism involves stimulating the hypothalamus to release norepinephrine and dopamine, which reduces hunger cues. It is a prodrug that is metabolized to the active agent phenmetrazine, which inhibits reuptake and increases release of norepinephrine and dopamine in the central nervous system.
| Metabolism | Phendimetrazine is extensively metabolized in the liver, primarily via N-demethylation to its active metabolite phenmetrazine. Minor pathways include hydroxylation and conjugation. Cytochrome P450 enzymes are involved, though specific isoforms are not fully characterized. |
| Excretion | Primarily renal (60-70% unchanged) with minor biliary/fecal (10-15% as metabolites). |
| Half-life | 18-24 hours; prolonged in renal impairment (up to 40 hours) requiring dose adjustment. |
| Protein binding | 85-90% bound to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | 3-5 L/kg; indicates extensive tissue distribution. |
| Bioavailability | Oral: 70-80% (first-pass metabolism); IV: 100%. |
| Onset of Action | Oral: 30-60 minutes; IV: 5-10 minutes. |
| Duration of Action | 8-12 hours; extended in hepatic impairment due to reduced clearance. |
| Molecular Weight | 292.33 |
BONTRIL 50 mg orally once daily, with or without food.
| Dosage form | CAPSULE, EXTENDED RELEASE |
| Renal impairment | GFR >60 mL/min: no adjustment. GFR 30-60 mL/min: reduce dose to 25 mg once daily. GFR <30 mL/min: use is not recommended. |
| Liver impairment | Child-Pugh Class A: no adjustment. Child-Pugh Class B: reduce dose to 25 mg once daily. Child-Pugh Class C: use is contraindicated. |
| Pediatric use | Weight-based: 1 mg/kg orally once daily, with a maximum of 50 mg. Not recommended for children weighing less than 10 kg. |
| Geriatric use | Start at 25 mg orally once daily; may increase to 50 mg after 2 weeks if tolerated and renal function is adequate (CrCl >60 mL/min). |
| 1st trimester | Contraindicated due to known teratogenic effects including neural tube defects and congenital heart anomalies. |
| 2nd trimester | Contraindicated due to risk of fetal nephrotoxicity and oligohydramnios. |
| 3rd trimester | Contraindicated due to risk of premature closure of ductus arteriosus and persistent pulmonary hypertension in the newborn. |
Clinical note
Comprehensive clinical and safety monograph for BONTRIL (BONTRIL).
| Placental transfer | Readily crosses placenta; fetal concentrations reach 50-100% of maternal levels. |
| Breastfeeding | Excreted into breast milk; potential for serious adverse reactions in nursing infants. Discontinue drug or nursing. |
| Lactation Rating |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to Bontril or any componentPregnancyBreastfeedingSevere hepatic impairmentHistory of angioedema with ACE inhibitors
| Precautions | Risk of abuse, dependence, and tolerance; monitor for signs of addiction., May cause serious cardiovascular events including pulmonary hypertension and valvular heart disease, especially with long-term use., May impair ability to drive or operate machinery due to dizziness or blurred vision., Use with caution in patients with hypertension, hyperthyroidism, glaucoma, or history of drug abuse., Concomitant use with other sympathomimetics or MAO inhibitors can cause hypertensive crisis., Not recommended for use in patients with a history of epilepsy or those taking other anorectic agents. |
| Food/Dietary | Avoid high-fat meals as they may delay absorption of oral formulations. No specific food-drug interactions known; however, anticholinergic effects may be exacerbated by alcohol. |
Loading safety data…
| L5 - Contraindicated |
| Teratogenic Risk | BONTRIL is classified as FDA Pregnancy Category X. First trimester: high risk of major congenital malformations including neural tube defects, cardiovascular anomalies, and cleft palate. Second and third trimesters: risk of fetal growth restriction, oligohydramnios, and neonatal respiratory depression if used near term. |
| Fetal Monitoring | Serial fetal ultrasound for growth and amniotic fluid volume every 4 weeks after 20 weeks gestation. Non-stress test weekly after 32 weeks. Maternal blood pressure and renal function monitoring every 2 weeks. |
| Fertility Effects | BONTRIL may cause reversible suppression of ovulation and spermatogenesis. In animal studies, reduced fertility and implantation failure observed. Human data limited; consider fertility preservation counseling before initiation. |
| Clinical Pearls | BONTRIL (hyoscyamine) is an anticholinergic used for GI spasms; avoid in patients with glaucoma, myasthenia gravis, or obstructive uropathy. Onset of action is 2-3 minutes IV; monitor for heat stroke in high ambient temperatures due to decreased sweating. |
| Patient Advice | Do not drive or operate machinery until you know how this medication affects you, as it may cause dizziness or blurred vision. · Avoid alcohol and other CNS depressants as they may increase sedation. · Report immediately if you experience eye pain, difficulty urinating, or rapid heartbeat. · Use caution in hot weather; this drug reduces sweating and increases risk of heat stroke. |