II. Indications
- Physician discretion for indication to continue
- Short term (8 to 12 weeks per year) adjunctive Obesity Management
III. Contraindications
- MAO Inhibitors within 14 days (see Drug Interactions below)
- Creatinine Clearance <15 ml/min
- Substance Use Disorder
- Hyperthyroidism
- Glaucoma
- Agitated state
- Pregnancy or Lactation
- Cardiovascular disease
IV. Precautions
- Individualize dosing to the lowest effective amount
- Tolerance to Phentermine may occur within weeks (at which point it does not suppress appetite)
- Discontinue if tolerance develops and do not exceed maximum Phentermine dose
-
DEA Controlled Substance
- Class IV (Limited dependence liability)
V. Mechanism
- Sympathomimetic amine anorectic
- Stimulates CNS adrenergic system
- Reduces food seeking behavior
VI. Medications
- Phentermine
- Capsules: 15, 30, 37.5 mg
- Tablets: 37.5 mg
- ODT Tablets: 15, 30, 37.5 mg
- Lomaira Tablets: 8 mg
- Combinations
- Qsymia (Phentermine and Topiramate)
- Phentermine is also often combined with Fluoxetine 20 mg as an alternative to Topiramate
VII. Dosing
- Not FDA approved for age <16 years
- Phentermine Tablets (18.75 or 37.5 mg)
- Start 18.75 mg orally at 1-2 hours before breakfast
- Titrate to 18.75 mg orally twice daily OR 37.5 mg orally once daily
- Phentermine Capsules (15 or 30 mg)
- Start 15 mg orally at 2 hours before breakfast
- Titrate to 30 mg orally daily
- Lomaira: 8 mg orally three times daily at 30 min before meals
- May decrease to 4 mg orally three times daily for tolerability if effective
-
Renal Dosing
- Creatinine Clearance 15 to 29 ml/min: Max Phentermine Dose 15 mg/day
- Creatinine Clearance <15 ml/min: Avoid Phentermine
VIII. Pharmacokinetics
- Phentermine hydochloride absorption is not affected by food (may taken with or without food)
- Peak concentration reached at 3 to 4.4 hours after oral dose
IX. Adverse Effects
-
Agitation
- Intolerable in 11%
-
Insomnia
- Avoid dosing late in the day
- Dose at least 10 hours before sleep
-
Substance Abuse risk
- Phentermine is related to Amphetamines
- Rare (but serious)
- Primary Pulmonary Hypertension
- Regurgitant cardiac valvular disease
X. Safety
- Pregnancy Category X
- Avoid in Lactation
XI. Drug Interactions
-
MAO Inhibitors
- Associated with Hypertensive Crisis (do not use with Phentermine within 14 days)
-
Insulin and Oral Hypoglycemics
- Monitor Glucose (dosing adjustments may be needed)
XII. Efficacy
- See Obesity Medication
- Weight Loss
- Results in 5 pound weight loss more than Placebo in one year
XIII. Resources
- Phentermine hydochloride (DailyMed)
XIV. References
- Hamilton (2020) Tarascon Pharmacopoeia
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Related Studies
| phentermine (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing) | ||
| PHENTERMINE 15 MG CAPSULE | Generic | $0.13 each |
| PHENTERMINE 30 MG CAPSULE | Generic | $0.14 each |
| PHENTERMINE 37.5 MG CAPSULE | Generic | $0.11 each |
| PHENTERMINE 37.5 MG TABLET | Generic | $0.07 each |
| lomaira (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing) | ||
| LOMAIRA 8 MG TABLET | Generic | $0.52 each |