Pharm

Phentermine

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Phentermine, Lonamin, Fastin, Lomaira

  • See Also
  1. Phentermine and Topiramate (Qsymia, Qnexa)
  2. Obesity Medication
  3. Medications Associated with Weight Gain
  4. Orlistat (Xenical)
  5. Lorcaserin (Belviq)
  6. Obesity
  7. Obesity in Children
  8. Obesity Evaluation
  9. Obesity Measurement (or Obesity Screening)
  10. Obesity Risk (or Obesity Comorbid Conditions)
  11. Obesity Management
  12. Dietary Supplements in Obesity
  13. Exercise in Obesity
  14. Obesity Resources
  • Indications
  1. Physician discretion for indication to continue
  2. Short term (8 to 12 weeks per year) adjunctive Obesity Management
    1. Morbid Obesity (BMI>30)
    2. Moderate Obesity (BMI 27) with comorbidity
  • Contraindications
  1. MAO Inhibitors within 14 days (see Drug Interactions below)
  2. Creatinine Clearance <15 ml/min
  3. Substance Use Disorder
  4. Hyperthyroidism
  5. Glaucoma
  6. Agitated state
  7. Pregnancy or Lactation
  8. Cardiovascular disease
    1. Uncontrolled Hypertension
    2. Coronary Artery Disease
    3. Arrhythmias
    4. Congestive Heart Failure
  • Precautions
  1. Individualize dosing to the lowest effective amount
  2. Tolerance to Phentermine may occur within weeks (at which point it does not suppress appetite)
    1. Discontinue if tolerance develops and do not exceed maximum Phentermine dose
  3. DEA Controlled Substance
    1. Class IV (Limited dependence liability)
  • Mechanism
  1. Sympathomimetic amine anorectic
  2. Stimulates CNS adrenergic system
  3. Reduces food seeking behavior
  • Medications
  1. Phentermine
    1. Capsules: 15, 30, 37.5 mg
    2. Tablets: 37.5 mg
    3. ODT Tablets: 15, 30, 37.5 mg
    4. Lomaira Tablets: 8 mg
  2. Combinations
    1. Qsymia (Phentermine and Topiramate)
    2. Phentermine is also often combined with Fluoxetine 20 mg as an alternative to Topiramate
  • Dosing
  1. Not FDA approved for age <16 years
  2. Phentermine Tablets (18.75 or 37.5 mg)
    1. Start 18.75 mg orally at 1-2 hours before breakfast
    2. Titrate to 18.75 mg orally twice daily OR 37.5 mg orally once daily
  3. Phentermine Capsules (15 or 30 mg)
    1. Start 15 mg orally at 2 hours before breakfast
    2. Titrate to 30 mg orally daily
  4. Lomaira: 8 mg orally three times daily at 30 min before meals
    1. May decrease to 4 mg orally three times daily for tolerability if effective
  5. Renal Dosing
    1. Creatinine Clearance 15 to 29 ml/min: Max Phentermine Dose 15 mg/day
    2. Creatinine Clearance <15 ml/min: Avoid Phentermine
  • Pharmacokinetics
  1. Phentermine hydochloride absorption is not affected by food (may taken with or without food)
  2. Peak concentration reached at 3 to 4.4 hours after oral dose
  • Adverse Effects
  1. Agitation
    1. Intolerable in 11%
  2. Insomnia
    1. Avoid dosing late in the day
    2. Dose at least 10 hours before sleep
  3. Substance Abuse risk
    1. Phentermine is related to Amphetamines
  4. Rare (but serious)
    1. Primary Pulmonary Hypertension
    2. Regurgitant cardiac valvular disease
  • Safety
  1. Pregnancy Category X
  2. Avoid in Lactation
  • Drug Interactions
  1. MAO Inhibitors
    1. Associated with Hypertensive Crisis (do not use with Phentermine within 14 days)
  2. Insulin and Oral Hypoglycemics
    1. Monitor Glucose (dosing adjustments may be needed)
  • Efficacy
  1. See Obesity Medication
  2. Weight Loss
    1. Results in 5 pound weight loss more than Placebo in one year
  • Resources
  1. Phentermine hydochloride (DailyMed)
    1. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=3b44d104-a7d0-4366-9d42-63f784f3cb22
  • References
  1. Hamilton (2020) Tarascon Pharmacopoeia