Noradrenergic Sympathomimetic Anorexiants,

💊 PROTOTYPE DRUG: Phentermine hydrochloride

🔍 Therapeutic Class:

• Weight management agent

• Anorexiant

🔬 Pharmacologic Class:

• CNS stimulant, sympathomimetic amine

• Structurally similar to amphetamines (Schedule IV controlled substance)

⚙ Action (Mechanism of Effect)

• Inhibits reuptake of norepinephrine and serotonin in the CNS

• Stimulates the hypothalamic satiety center → suppresses appetite

• Mimics sympathetic nervous system stimulation

💡 Indications (Use)

• Used for short-term (≤ 12 weeks) treatment of obesity

• For patients with BMI ≥ 30 or ≥ 27 with comorbidities

🧪 Pharmacokinetics

• Absorption: Well absorbed orally

• Metabolism: Liver

• Excretion: Primarily renal

• Half-life: ~20 hours

• Decreases under acidic urinary conditions

• Peak effect: 3–4.4 hours

⚠ Contraindications

Do not use in patients with:

• Moderate to severe hypertension

• Cardiovascular disease

• Hyperthyroidism

• Glaucoma

• Pregnancy or breastfeeding

• Drug abuse history

• Within 14 days of MAOI use

📛 BLACK BOX WARNING:

➡ No formal FDA Black Box Warning, but serious CV risks (e.g., pulmonary HTN, increased BP) and addiction potential demand close monitoring and caution.

🚫 Adverse Effects (ALL from the book)

• Nervousness

• Palpitations

• Tachycardia

• Primary pulmonary hypertension

• Systemic hypertension

• Hyperactivity

• Dry mouth, constipation

• Insomnia, unpleasant taste

• Impotence

• Tolerance may develop in 4–6 weeks

💉 Dosage & Route (Adults & Adolescents ≥ 16 y)

• Immediate-release: 15–37.5 mg daily or in divided doses

• Orally disintegrating tab: 15–37.5 mg once daily in the morning

• Take before breakfast or 10–14 hours before bedtime (to avoid insomnia)

👵 Age-Specific Considerations

• Adolescents ≥16 y: same dose as adults

• Not for <16 years

• Older adults: use cautiously; increased adverse risk due to comorbidities

👶 Pregnancy & Lactation

• Not safe in pregnancy

• Contraindicated in breastfeeding

❗ Drug Interactions (Box 36.4)

Increase effects:

• TCAs, linezolid

• Alcohol, CNS stimulants

• Other sympathomimetics (e.g., epinephrine)

Decrease effects:

• Urinary acidifiers, GI acidifiers, methenamine, multivitamins with minerals

👩‍⚕ Nursing Considerations

✅ Before Administering

• Take before meals

• Do not chew or crush sustained-release forms

• Ensure last dose is taken ≥6 hours before bedtime

🔎 Monitor For Therapeutic Effect

• Weight loss goal: 1–2 lbs per week

• Continued use beyond 12 weeks is not advised

⚠ Assess For Adverse Effects

• ↑ BP

• Palpitations

• CNS overstimulation (insomnia, hyperactivity, nervousness)

• GI: constipation, dry mouth

🧑‍🏫 Patient Teaching (Box 36.5)

• Take in the morning

• Monitor blood pressure regularly

• Avoid caffeine and alcohol

• Do not share medication

• May cause drowsiness—avoid driving until effects are known

• Use only as prescribed—may be habit forming

🤓 NCLEX-STYLE PRACTICE QUESTIONS FROM TEXT

Q1:
Phentermine aids weight loss by doing which of the following?
A. Decreasing appetite
B. Increasing satiety and feelings of fullness
C. Increasing metabolism
D. Decreasing absorption of dietary fat
➡ Correct Answer: A – Phentermine suppresses appetite via CNS stimulation.

Q2:
A 42-year-old patient on phentermine shows an elevated A1C level despite diet/exercise. Why?
A. Producing stimulant effects to the sympathetic nervous system
B. Decreasing the level of fat-soluble vitamins
C. Decreasing metabolism to the pancreas
D. Increasing the absorption of dietary fat
➡ Correct Answer: A – Sympathetic stimulation may interfere with glucose regulation and insulin sensitivity.

✅ SUMMARY POINTS TO KNOW

• Phentermine is the prototype anorexiant.

• Used short-term, combined with diet + exercise.

• Stimulates norepinephrine + serotonin → appetite suppression.

• Many adverse effects: CV, CNS, GI.

• Not for use in pregnancy, breastfeeding, or CVD patients.

• Watch for tolerance after 4–6 weeks.

• Controlled substance: Schedule IV – abuse potential.

💊 OTHER DRUGS IN THE CLASS

These drugs are all FDA-approved for short-term use (≤12 weeks) for weight management. Like phentermine, they are controlled substances due to their abuse potential.

1. Benzphetamine

• Schedule: III (higher abuse potential than phentermine)

• Mechanism: Similar to phentermine — stimulates CNS to release norepinephrine → appetite suppression

• Dosage:

  • Start: 25 mg once daily

  • Titrate up: 25–50 mg 1–3 times daily

  • Max dose: 50 mg three times daily

• Adverse Effects:

  • CNS: nervousness, insomnia, hyperactivity

  • CV: ↑ BP, palpitations

  • GI: dry mouth, constipation

• Use in Pregnancy: Animal studies show fetal harm → Avoid in pregnancy

• Key Notes: Often less commonly prescribed due to stronger stimulant effects and increased side effects

2. Diethylpropion

• Schedule: IV (like phentermine)

• Structure: Chemically similar to bupropion

• Mechanism: Stimulates norepinephrine release in CNS → suppresses appetite

• Dosage:

  • Immediate-release (IR): 25 mg three times daily (before meals)

  • Controlled-release (CR): 75 mg every morning

• Adverse Effects:

  • Same CNS and CV stimulant side effects as phentermine

  • Can cause insomnia, increased BP, dry mouth, constipation

• Special Note: Structurally similar to bupropion, which may help reduce cravings

• Caution: May counteract antihypertensives

3. Phendimetrazine (Bontril PDM)

• Schedule: III

• Mechanism: Similar CNS stimulant, promotes norepinephrine release → suppresses appetite

• Dosage:

  • Immediate-release: 17.5–35 mg 2–3 times daily, 1 hour before meals
    → Max: 70 mg three times daily

  • Sustained-release: 105 mg once daily in the morning

• Adverse Effects:

  • CV: palpitations, tachycardia, ↑ BP

  • CNS: insomnia, anxiety, restlessness

  • GI: dry mouth, constipation

• Caution in Hypertension: Can raise BP significantly

4. Phentermine–Topiramate (Qsymia)

• Schedule: IV

  • Contains phentermine (anorexiant) + topiramate (anti-seizure drug)

• Mechanism:

  • Phentermine: appetite suppression via norepinephrine release

  • Topiramate: enhances satiety (feeling full) and reduces cravings

• Dosage: (Titrated based on response)

  • Start: 3.75 mg phentermine/23 mg topiramate once daily x 14 days

  • Then: 7.5 mg/46 mg once daily for 12 weeks

  • Max: 15 mg/92 mg daily

• Adverse Effects:

  • All the CV/CNS effects of phentermine

  • Topiramate-related: paresthesia, dizziness, altered taste, insomnia, constipation

• Pregnancy Warning:

  • Risk of cleft lip/palate if used during 1st trimester

  • Must discontinue before pregnancy

• Breastfeeding: Contraindicated

• Use: For longer-term weight management vs. short-term only

⚠ SHARED RISKS ACROSS THIS CLASS

All noradrenergic sympathomimetic anorexiants can cause:

• CV side effects: ↑ HR, ↑ BP, palpitations

• CNS effects: insomnia, nervousness, euphoria, restlessness

• GI effects: dry mouth, constipation

• Dependence: Habit-forming (controlled substances)

🚫 USE WITH CAUTION IN:

• Cardiovascular disease

• Hypertension

• Glaucoma

• Hyperthyroidism

• Patients with history of substance abuse

• Pregnancy & lactation (ALL are contraindicated)

✅ NURSING POINTS FOR ALL OF THEM

• Give early in the day to avoid insomnia

• Avoid caffeine and other stimulants

• Monitor BP and HR regularly

• Do NOT crush or chew extended/sustained-release forms

• Monitor for tolerance (losing effect over time)

🧠 QUICK MEMORY TIP

All these drugs:

• Suppress appetite through norepinephrine release

• Cause stimulating side effects (↑ BP, insomnia, dry mouth)

• Are short-term, controlled, and not safe during pregnancy