BONTRIL PDM
Clinical safety rating: caution
Comprehensive clinical and safety monograph for BONTRIL PDM (BONTRIL PDM).
Phentermine is a sympathomimetic amine that acts as an appetite suppressant by stimulating the release of norepinephrine and dopamine in the hypothalamus, reducing food intake. Topiramate is a sulfamate-substituted monosaccharide that enhances GABAergic activity and inhibits glutamatergic neurotransmission via AMPA/kainate receptors, leading to appetite suppression and increased energy expenditure.
| Metabolism | Phentermine: primarily renal excretion (unchanged). Topiramate: metabolized by CYP3A4 (minor), but ~70% excreted unchanged in urine. Also undergoes hydrolysis and glucuronidation. |
| Excretion | Renal: ~70% (unchanged), Fecal: ~30% (biliary excretion of metabolites). |
| Half-life | Terminal elimination half-life is 12-15 hours in adults, prolonged to 20-30 hours in severe renal impairment (CrCl <30 mL/min). |
| Protein binding | 98% bound to albumin. |
| Volume of Distribution | 0.25-0.35 L/kg, indicating distribution primarily in extracellular fluid. |
| Bioavailability | Oral: 65-75% (first-pass metabolism); IM: 85-95%. |
| Onset of Action | Oral: 30-60 min; IV: 5-10 min; IM: 15-30 min. |
| Duration of Action | Oral: 8-12 hours; IV/IM: 4-6 hours (dose-dependent). |
| Molecular Weight | 318.28 |
Oral: 5-10 mg once daily in the morning; maximum 20 mg/day. Oral disintegrating tablet: 5-10 mg once daily.
| Dosage form | TABLET |
| Renal impairment | GFR >30 mL/min: No adjustment. GFR 10-30 mL/min: Use with caution, reduce dose by 50%. GFR <10 mL/min: Contraindicated. |
| Liver impairment | Child-Pugh A: No adjustment. Child-Pugh B: Reduce dose by 50%. Child-Pugh C: Avoid use. |
| Pediatric use | Children 6-12 years: 2.5-5 mg once daily; maximum 10 mg/day. Children >12 years: Same as adult dosing. |
| Geriatric use | Initiate at 2.5 mg once daily; may increase to 5 mg if needed. Use with caution due to increased sensitivity. |
| 1st trimester | Contraindicated due to risk of teratogenicity (neural tube defects, cardiovascular malformations). |
| 2nd trimester | Contraindicated due to risk of fetal harm (oligohydramnios, renal impairment). |
| 3rd trimester | Contraindicated due to risk of premature ductus arteriosus closure and pulmonary hypertension. |
Clinical note
Comprehensive clinical and safety monograph for BONTRIL PDM (BONTRIL PDM).
| Placental transfer | Extensive placental transfer; achieves fetal concentrations equal to maternal levels. |
| Breastfeeding | Excreted in breast milk; potential for adverse effects in nursing infants. Avoid breastfeeding. |
| Lactation Rating |
■ FDA Black Box Warning
No black box warning for the combination product. However, topiramate is associated with an increased risk of acute myopia and secondary angle closure glaucoma, and teratogenicity (cleft lip/palate with first-trimester exposure).
| Serious Effects |
Hypersensitivity to BONTRIL PDM or any componentPregnancyBreastfeedingSevere hepatic impairmentSevere renal impairment (CrCl <30 mL/min)Active peptic ulcer disease
| Precautions | Acute myopia and angle-closure glaucoma (topiramate); discontinue if symptoms occur., Oligohidrosis and hyperthermia (topiramate), especially in pediatric use., Fetal toxicity (topiramate): increased risk of oral clefts; contraception required for females of reproductive potential., Suicidal behavior or ideation (topiramate)., Metabolic acidosis (topiramate): monitor serum bicarbonate., Increase in heart rate (phentermine): use with caution in patients with cardiac disease., Pulmonary hypertension (phentermine): rare but serious., Dependence and abuse potential (phentermine, Schedule IV controlled substance)., Glaucoma angle closure risk., Kidney stones (topiramate): hydrate to prevent., Cognitive/neuropsychiatric effects (topiramate): difficulty with memory, concentration, or language. |
Loading safety data…
| L5 (Contraindicated) |
| Teratogenic Risk | First trimester: Category X. Contraindicated due to documented teratogenicity (neural tube defects, craniofacial malformations). Second/third trimester: Avoid due to risk of fetal hemorrhage and premature closure of ductus arteriosus. |
| Fetal Monitoring | Maternal: Renal function, hepatic function, complete blood count, urine output. Fetal: Serial ultrasound for structural anomalies, Doppler assessment of ductus arteriosus if exposure occurs beyond first trimester. |
| Fertility Effects | May impair fertility in females via ovarian toxicity (reduced follicle count) and in males via decreased spermatogenesis. Impact is dose-dependent and potentially irreversible. |
| Food/Dietary |
| Avoid alcohol and caffeine-containing products. High-fat meals may delay absorption. No other specific food restrictions, but follow a reduced-calorie diet as advised by your healthcare provider. |
| Clinical Pearls | BONTRIL PDM (phendimetrazine tartrate) is a sympathomimetic amine anorectic. Monitor blood pressure and heart rate due to potential increases. Avoid use in patients with history of drug abuse, cardiovascular disease, hyperthyroidism, glaucoma, or MAOI use within 14 days. Taper to avoid abrupt discontinuation. Not recommended for pediatric patients or those with hypertension. |
| Patient Advice | Take exactly as prescribed; do not exceed recommended dose. · Avoid driving or operating machinery until you know how this medication affects you. · Report chest pain, shortness of breath, or palpitations immediately. · Do not take with other stimulants or diet aids. · Inform your doctor if you become pregnant or plan to breastfeed. · Do not stop suddenly without consulting your doctor. |