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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
MAOIs can cause hypertensive crisis High potential for abuse and dependence.
| Breastfeeding | Phentermine is excreted into human milk. M/P ratio is unknown. Potential for serious adverse reactions in nursing infants, including irritability, sleep disturbance, and cardiovascular effects. Breastfeeding is not recommended during therapy and for 1-2 weeks after last dose. |
| 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. |
■ FDA Black Box Warning
None
| Common Effects | Insomnia |
| Serious Effects |
["Concurrent or MAOI use within 14 days","Hyperthyroidism","Glaucoma","Agitated states","History of drug abuse","Cardiovascular disease (e.g., CAD, arrhythmias)","Hypertension (moderate/severe)","Pregnancy/lactation"]
| 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"] |
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| 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. |