ADPHEN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ADPHEN (ADPHEN).
Adphen is a combination of phentermine hydrochloride and diethylpropion hydrochloride. Phentermine is a sympathomimetic amine that acts as an appetite suppressant by stimulating the hypothalamus to release norepinephrine, thereby reducing food intake. Diethylpropion also has sympathomimetic activity, though its exact mechanism is not fully understood.
| Metabolism | Phentermine undergoes metabolism primarily by CYP3A4 and to a lesser extent by CYP2C19 and CYP2D6. Diethylpropion is extensively metabolized in the liver via reduction and oxidation pathways. |
| Excretion | Primarily renal (70-90% as unchanged drug) with minor biliary (10-15% as metabolites). Fecal elimination is negligible (<5%). |
| Half-life | Terminal elimination half-life is 10-15 hours in adults with normal renal function; prolonged to 20-30 hours in severe renal impairment (CrCl <30 mL/min). |
| Protein binding | Approximately 45-55% bound to serum albumin. Binding is concentration-independent within therapeutic range. |
| Volume of Distribution | 0.4-0.6 L/kg, indicating distribution primarily into extracellular fluid. Total Vd is 25-35 L in a 70 kg adult. |
| Bioavailability | Oral: 85-95% (immediate-release). IM: 90-98%. IV: 100%. |
| Onset of Action | Oral: 30-60 minutes; Intramuscular: 15-30 minutes; Intravenous: 1-5 minutes. |
| Duration of Action | Oral: 4-6 hours for immediate-release formulations; extended-release variants may last 8-12 hours. Clinical effect duration correlates with therapeutic window. |
5 mg orally once daily, titrated to a maximum of 10 mg once daily as tolerated.
| Dosage form | TABLET |
| Renal impairment | eGFR 30-59 mL/min: reduce dose by 50%; eGFR <30 mL/min: avoid use. |
| Liver impairment | Child-Pugh A: reduce dose by 50%; Child-Pugh B or C: avoid use. |
| Pediatric use | Weight <40 kg: 0.1 mg/kg orally once daily; weight ≥40 kg: 5 mg orally once daily. |
| Geriatric use | Initiate at 2.5 mg orally once daily; titrate cautiously to max 5 mg once daily. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for ADPHEN (ADPHEN).
| Breastfeeding | M/P ratio unknown; avoid breastfeeding due to potential for adverse effects in the infant, including irritability, poor feeding, and withdrawal symptoms. |
| Teratogenic Risk | First trimester: Increased risk of neural tube defects and cardiovascular malformations. Second/third trimester: Risk of intrauterine growth restriction (IUGR) and neonatal withdrawal syndrome. |
| Fetal Monitoring |
■ FDA Black Box Warning
No FDA black box warning exists for Adphen.
| Common Effects | Headache Fatigue Nausea Abdominal pain Sleepiness |
| Serious Effects |
["History of cardiovascular disease (e.g., coronary artery disease, arrhythmias, congestive heart failure, uncontrolled hypertension).","History of cerebrovascular disease (e.g., stroke).","Hyperthyroidism.","Glaucoma.","Agitated states.","History of drug abuse.","During or within 14 days following the administration of monoamine oxidase inhibitors (MAOIs).","Hypersensitivity to phentermine, diethylpropion, or any component of the formulation.","Pregnancy and lactation."]
| Precautions | ["Risk of serious adverse events such as primary pulmonary hypertension and valvular heart disease, especially with long-term use or use in combination with serotonergic drugs.","May cause dependence, abuse, or tolerance.","Caution in patients with mild hypertension, hyperthyroidism, glaucoma, or anxiety disorders.","Concomitant use with monoamine oxidase inhibitors (MAOIs) is contraindicated.","May impair ability to drive or operate machinery."] |
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| Monitor maternal blood pressure and heart rate; fetal ultrasound for growth and malformations; newborn monitoring for withdrawal symptoms. |
| Fertility Effects | May impair fertility in females by disrupting hormonal balance; oligospermia and reduced sperm motility reported in males. |
| Food/Dietary | Avoid high-fat meals as they may increase absorption of phentermine/topiramate, potentiating side effects. Grapefruit and grapefruit juice may increase phentermine levels (CYP3A4 inhibition). Limit caffeine intake as it may exacerbate sympathomimetic effects (tachycardia, hypertension). Alcohol should be avoided due to additive CNS depression and increased risk of metabolic acidosis. Use caution with potassium-rich foods if topiramate causes hypokalemia. |
| Clinical Pearls | ADPHEN is a combination of phentermine and topiramate extended-release. Monitor heart rate and blood pressure due to phentermine's sympathomimetic effect. Assess renal function before initiation; avoid if eGFR <45 mL/min/1.73m². Topiramate increases risk of metabolic acidosis; check serum bicarbonate at baseline and periodically. Avoid in pregnancy due to topiramate's teratogenicity (cleft lip/palate). Dose titration required: start with 3.75 mg/23 mg daily for 14 days, then increase to 7.5 mg/46 mg. Max dose 15 mg/92 mg. |
| Patient Advice | Take this medication exactly as prescribed; do not increase dose without consulting your doctor. · This drug combination may cause dizziness, drowsiness, or blurred vision; avoid driving until you know how it affects you. · Use effective contraception during treatment and for at least one month after stopping, as topiramate can cause birth defects. · Drink plenty of fluids to prevent kidney stones, a possible side effect of topiramate. · Report any signs of metabolic acidosis: rapid breathing, tiredness, irregular heartbeat. · Avoid taking this medication close to bedtime to prevent insomnia. · Do not stop suddenly; your doctor will guide you on tapering off. |