PHENDIMETRAZINE TARTRATE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PHENDIMETRAZINE TARTRATE (PHENDIMETRAZINE TARTRATE).
Phendimetrazine is a sympathomimetic amine that acts as an appetite suppressant by stimulating the hypothalamus to release norepinephrine, leading to decreased food intake and increased energy expenditure. It is a prodrug that is metabolized to phenmetrazine, which is a potent central nervous system stimulant with amphetamine-like effects.
| Metabolism | Primarily metabolized in the liver via N-demethylation to its active metabolite, phenmetrazine. Other metabolites include phendimetrazine N-oxide and norphenmetrazine. CYP450 enzymes are involved, though specific isoforms not well characterized. |
| Excretion | Primarily renal (≥70% unchanged) with minor biliary/fecal elimination (<10%) |
| Half-life | Terminal half-life 3-4 hours; clinical context: requires multiple daily dosing |
| Protein binding | 10-15% bound to albumin |
| Volume of Distribution | 2-3 L/kg; indicates extensive tissue distribution |
| Bioavailability | Oral: approximately 80-90% |
| Onset of Action | Oral: 30-60 minutes |
| Duration of Action | 4-6 hours; note: tolerance may develop with prolonged use |
| Molecular Weight | 236.31 |
Oral: 35 mg twice daily or three times daily, 1 hour before meals; extended-release: 105 mg once daily in the morning.
| Dosage form | TABLET |
| Renal impairment | Contraindicated in severe renal impairment (GFR < 30 mL/min). No specific dose adjustments for mild-moderate impairment; use with caution. |
| Liver impairment | Not recommended in Child-Pugh class B or C. Use with caution in mild impairment. |
| Pediatric use | Not recommended for children under 12 years; safety and efficacy not established. |
| Geriatric use | Start at lower end of dosing range; monitor for increased sensitivity and cardiovascular effects. |
| 1st trimester | Avoid due to potential teratogenic effects and association with fetal abnormalities (e.g., oral clefts, cardiac defects). |
| 2nd trimester | Avoid; use only if benefit outweighs risk as it may cause fetal growth restriction and neonatal withdrawal. |
| 3rd trimester | Avoid; risk of neonatal withdrawal syndrome (hyperactivity, irritability, poor feeding) and premature delivery. |
Clinical note
Comprehensive clinical and safety monograph for PHENDIMETRAZINE TARTRATE (PHENDIMETRAZINE TARTRATE).
| Placental transfer | Phendimetrazine crosses the placenta; evidence from animal studies and human case reports indicates transfer. |
| Breastfeeding | Phendimetrazine is excreted into breast milk in small amounts; however, due to its stimulant effects, it may cause irritability, poor feeding, and sleep disturbances in the infant. Avoid breastfeeding or discontinue the drug. |
■ FDA Black Box Warning
Phendimetrazine is not approved for use in patients with a history of drug abuse or dependence. It has a high potential for abuse and may lead to dependence. Use caution in patients with cardiovascular disease or hypertension.
| Serious Effects |
Hypersensitivity to phendimetrazine or any component of the formulationAdvanced arteriosclerosisCardiovascular disease (e.g., symptomatic coronary artery disease, uncontrolled hypertension)HyperthyroidismGlaucomaAgitated statesHistory of drug abuseConcurrent use or within 14 days of MAO inhibitors (risk of hypertensive crisis)Pregnancy
| Precautions | Increased risk of pulmonary hypertension and valvular heart disease; monitor for dyspnea, chest pain, or edema. Tolerance may develop; discontinue if tolerance occurs. May impair ability to perform hazardous tasks. Use with caution in patients with hypertension, diabetes, or glaucoma. Do not use with MAOIs or within 14 days of discontinuation. |
| Food/Dietary | Avoid alcohol and excessive caffeine (coffee, tea, energy drinks) as they may increase CNS stimulation and risk of side effects. Take with or without food; high-fat meals may delay absorption of extended-release formulations. Maintain a calorie-reduced diet as part of a comprehensive weight loss plan. |
Loading safety data…
| Lactation Rating | L5 (Contraindicated) |
| Teratogenic Risk | First trimester: Limited data; potential for increased risk of oral clefts. Second/third trimester: Anorexiant effects may cause fetal growth restriction; avoid use due to maternal hypertension risk. |
| Fetal Monitoring | Monitor maternal blood pressure and heart rate; fetal growth ultrasound if used during pregnancy. Discontinue if maternal hypertension or fetal distress. |
| Fertility Effects | No known adverse effects on fertility; weight loss may improve ovulatory function in obese women. |
| Clinical Pearls | Phendimetrazine tartrate is a schedule III controlled substance with high abuse potential. It is approved only for short-term (up to 12 weeks) monotherapy for exogenous obesity. Contraindicated in patients with glaucoma, hyperthyroidism, agitated states, history of drug abuse, or cardiovascular disease. Taper dose to avoid withdrawal. Monitor blood pressure and heart rate; may cause pulmonary hypertension. Avoid use with MAOIs (risk of hypertensive crisis) and within 14 days of discontinuation. |
| Patient Advice | Take exactly as prescribed; do not increase dose or duration. · Take last dose of the day 4-6 hours before bedtime to prevent insomnia. · Do not crush or chew extended-release tablets; swallow whole. · Avoid driving or operating heavy machinery until you know how this medication affects you. · Report chest pain, shortness of breath, fainting, or leg swelling immediately. · Do not stop abruptly; follow your doctor's tapering plan. · Store securely; keep out of reach of others as this medication can be habit-forming. · Do not take with alcohol or other CNS stimulants. · Use with caution if you have high blood pressure, diabetes, or a history of depression. |