PHENTERMINE RESIN 30
Clinical safety rating: avoid
Contraindicated (not allowed)
Sympathomimetic amine that stimulates release of norepinephrine from presynaptic terminals, suppressing appetite via hypothalamic action.
| Metabolism | Primarily hepatic via CYP450 (minor); major metabolites: p-hydroxy-phentermine, N-hydroxyphentermine (inactive); renal excretion of unchanged drug and metabolites |
| Excretion | Phentermine is primarily excreted renally as unchanged drug (70-80%) and metabolites (20-30%). Biliary/fecal excretion is negligible (<5%). |
| Half-life | Terminal elimination half-life is approximately 19-24 hours in adults, supporting once-daily dosing; may be prolonged in renal impairment. |
| Protein binding | Approximately 20-30% bound to plasma proteins (primarily albumin). |
| Volume of Distribution | Volume of distribution is about 3-4 L/kg, indicating extensive tissue distribution. |
| Bioavailability | Oral bioavailability is approximately 70-90% for the resin formulation; food may reduce absorption slightly. |
| Onset of Action | Oral resin formulation: Anorectic effect begins within 1-2 hours after ingestion. |
| Duration of Action | Duration of anorectic effect is 12-14 hours for the resin formulation, allowing once-daily dosing; clinical effect wanes with continued use beyond a few weeks due to tolerance. |
| Molecular Weight | 149.23 |
30 mg orally once daily in the morning.
| Dosage form | CAPSULE, EXTENDED RELEASE |
| Renal impairment | Contraindicated in severe renal impairment (eGFR <30 mL/min). No specific dose adjustment for mild-moderate impairment. |
| Liver impairment | Contraindicated in hepatic impairment. Avoid use. |
| Pediatric use | Not recommended for patients under 16 years of age. |
| Geriatric use | Use with caution; lower initial dose may be considered due to potential increased sensitivity and renal function decline. However, no specific dose adjustment recommended. |
| 1st trimester | Use is contraindicated due to teratogenic risk; associated with increased incidence of congenital malformations (e.g., oral clefts, neural tube defects). |
| 2nd trimester | Avoid use; maternal hypertension and reduced placental perfusion may lead to fetal growth restriction. |
| 3rd trimester | Avoid use; risk of neonatal withdrawal symptoms (e.g., hyperactivity, irritability) and maternal cardiovascular complications. |
Clinical note
MAOIs can cause hypertensive crisis High potential for abuse and dependence.
| Placental transfer | Crosses placenta; based on molecular weight and lipophilicity, transfer is expected. Animal studies show fetal concentrations similar to maternal. |
| Breastfeeding | Excreted into breast milk in small amounts; due to potential for infant stimulation and cardiovascular effects, breastfeeding is generally not recommended. Consider alternative agents with established safety. |
■ FDA Black Box Warning
None
| Common Effects | Insomnia |
| Serious Effects |
Hypersensitivity to phentermine or any componentConcurrent use or within 14 days of MAO inhibitorsHistory of cardiovascular disease (e.g., coronary artery disease, arrhythmias, uncontrolled hypertension)HyperthyroidismGlaucomaAgitated statesHistory of drug abusePregnancy
| Precautions | Risk of pulmonary hypertension and valvular heart disease (especially with serotonergic drugs), Potential for abuse and dependence (Schedule IV controlled substance), Hypertension, palpitations, tachyphylaxis, primary pulmonary hypertension |
| Food/Dietary | Avoid alcohol as it may enhance CNS depressant effects when combined with phentermine. Caffeine and other stimulants may increase cardiovascular side effects and should be limited. High-fat meals may delay absorption but do not require specific restriction. Maintain a calorie-controlled diet as part of weight loss program. Grapefruit juice may theoretically increase drug levels; avoid excessive consumption. |
Loading safety data…
| Lactation Rating | L5 (Contraindicated) |
| Teratogenic Risk | Phentermine is pregnancy category X. Use is contraindicated in all trimesters due to potential for fetal harm. Animal studies have shown teratogenic effects, including increased incidence of fetal malformations. There is no indication for use in pregnancy; weight loss offers no benefit to the pregnant patient and may cause fetal harm. |
| Fetal Monitoring | Maternal: Blood pressure, heart rate, CNS stimulation (insomnia, anxiety, tremor), and potential for abuse/dependence. Fetal: None recommended because use is contraindicated; if inadvertent exposure, assess for growth parameters and congenital anomalies. |
| Fertility Effects | Phentermine may impair fertility in females due to anorectic effects and potential alteration of hormonal balance. No specific human data; based on animal studies, fertility may be reduced. Patients planning pregnancy should discontinue use. |
| Clinical Pearls | Phentermine resin is a sympathomimetic amine anorectic used short-term for obesity. It is contraindicated in patients with cardiovascular disease, hyperthyroidism, glaucoma, or history of drug abuse. Avoid concomitant use with MAOIs or within 14 days. Monitor blood pressure and heart rate due to stimulant effects. Tolerance may develop; discontinue if no weight loss within 4 weeks. Abuse potential exists; schedule IV controlled substance. |
| Patient Advice | Take this medication exactly as prescribed, usually once daily in the morning to prevent insomnia. · Do not crush or chew the resin capsules; swallow whole to ensure proper release. · Avoid taking this medication late in the day to reduce risk of sleep problems. · Report any chest pain, shortness of breath, palpitations, or leg swelling immediately. · This medication is for short-term use only (typically up to 12 weeks) and should be combined with diet and exercise. · Do not use if you are pregnant, planning to become pregnant, or breastfeeding. · Avoid alcohol or other CNS stimulants while taking this medication. · Notify your doctor if you experience restlessness, tremor, or mood changes. |