OBESTIN-30
Clinical safety rating: caution
Comprehensive clinical and safety monograph for OBESTIN-30 (OBESTIN-30).
ObesTin-30 is a selective serotonin reuptake inhibitor (SSRI) that blocks serotonin reuptake, increasing serotonin levels in the synaptic cleft, which modulates appetite and mood.
| Metabolism | Hepatic via CYP2D6 and CYP3A4; metabolite N-desmethylobestin active. |
| Excretion | Renal excretion of unchanged drug accounts for approximately 60% of the administered dose; fecal elimination via biliary excretion accounts for approximately 30%, with the remainder as metabolites. |
| Half-life | Terminal elimination half-life is approximately 12 hours (range 10–14 hours) in patients with normal renal function; half-life may be prolonged to >24 hours in severe renal impairment (CrCl <30 mL/min). |
| Protein binding | Approximately 98% bound to serum albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Volume of distribution is 4.5 L/kg, indicating extensive extravascular distribution and tissue binding. |
| Bioavailability | Oral bioavailability is 45% due to first-pass metabolism; bioavailability is unaffected by food. |
| Onset of Action | Oral: 30–60 minutes; peak effect at 1–2 hours. |
| Duration of Action | Duration of action is 8–12 hours after a single oral dose, with sustained effect over 24 hours with once-daily dosing due to prolonged receptor binding. |
30 mg subcutaneously once daily.
| Dosage form | CAPSULE |
| Renal impairment | If CrCl <30 mL/min, reduce dose to 15 mg subcutaneously once daily. No adjustment for CrCl ≥30 mL/min. |
| Liver impairment | Child-Pugh A or B: no adjustment necessary. Child-Pugh C: reduce dose to 15 mg subcutaneously once daily. |
| Pediatric use | 0.5 mg/kg (max 30 mg) subcutaneously once daily for patients ≥12 years. Not recommended under 12 years. |
| Geriatric use | No specific dose adjustment required based on age; monitor renal function and adjust per renal criteria. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for OBESTIN-30 (OBESTIN-30).
| Breastfeeding | Excretion into human breast milk is unknown; M/P ratio not established. Risk of infant exposure with potential CNS stimulation and growth impairment. Breastfeeding is contraindicated due to potential for serious adverse effects. |
| Teratogenic Risk | OBESTIN-30 (phentermine) is FDA Pregnancy Category X. First trimester: risk of fetal malformations (e.g., oral clefts, heart defects) based on animal studies and limited human data. Second and third trimesters: risk of fetal growth restriction, preterm birth, and neonatal withdrawal symptoms (hyperirritability, poor feeding). |
■ FDA Black Box Warning
Increased risk of suicidal thoughts and behavior in children, adolescents, and young adults taking antidepressants.
| Serious Effects |
Concomitant use with MAOIs, pimozide, or thioridazine; hypersensitivity to ObesTin-30.
| Precautions | Serotonin syndrome, bleeding risk, hyponatremia, activation of mania/hypomania, seizures, angle-closure glaucoma. |
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| Fetal Monitoring |
| Maternal: blood pressure, heart rate, weight gain, signs of abuse/dependence. Fetal: ultrasound for growth and anatomy in second trimester; fetal heart rate monitoring if signs of distress or maternal toxicity. Neonatal: monitoring for withdrawal symptoms after delivery. |
| Fertility Effects | May impair fertility in women due to metabolic effects (e.g., altered menstrual cycles, reduced ovulation). In men, may affect spermatogenesis based on animal studies. Use is not recommended in women attempting conception. |