Generic Name

Phentermine Hydrochloride

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Classification

FDA Approved Indications

• Short-term weight management in obese adults with comorbidities

Mechanism of Action

Phentermine stimulates the release of norepinephrine in the hypothalamus, decreasing appetite and increasing energy expenditure through sympathetic nervous system activation.

Dosage and Administration

Adult: Usually 15-37.5 mg once daily 1 hour before breakfast or 1-2 hours after breakfast; duration typically not exceeding 12 weeks.

Pediatric: Not approved for use in children; use not recommended.

Geriatric: Use with caution; start at lower end of dosing range due to possible increased sensitivity.

Renal Impairment: Adjust dose cautiously; consider renal function assessment.

Hepatic Impairment: Use with caution; no specific dosage adjustment established.

Pharmacokinetics

Absorption: Rapidly absorbed following oral administration.

Distribution: Widely distributed; crosses the blood-brain barrier.

Metabolism: Minimal hepatic metabolism; primarily excreted unchanged by the kidneys.

Excretion: Renal excretion; dose adjustments may be necessary in renal impairment.

Half Life: 4-7 hours.

Contraindications

• History of hypersensitivity to sympathomimetics
• History of drug abuse
• Use during or within 14 days of MAOI therapy
• History of cardiovascular disease, hypertension, hyperthyroidism, glaucoma, or agitation.

Precautions

• Use with caution in patients with hypertension, arrhythmias, or other cardiovascular conditions.
• Potential for dependence and abuse; use for the shortest duration necessary.

Adverse Reactions - Common

• Increased blood pressure (Common)
• Insomnia (Common)
• Dry mouth (Common)
• Tachycardia (Common)

Adverse Reactions - Serious

• Cardiovascular events (e.g., palpitations, hypertension, arrhythmias) (Rare)
• Psychological dependence or abuse (Rare)

Drug-Drug Interactions

• MAO inhibitors (risk of hypertensive crisis)
• Other sympathomimetics (increased cardiovascular risk)
• SSRIs (potential for serotonin syndrome)

Drug-Food Interactions

N/A

Drug-Herb Interactions

N/A

Nursing Implications

Patient/Family Teaching

• Take exactly as prescribed; do not increase dose.
• Report chest pain, severe headache, or mood changes.
• Maintain a low-calorie, low-fat diet and engage in exercise.
• Avoid use of other stimulants or weight loss products.
• Be aware of potential for dependence.

Special Considerations

Black Box Warnings:

• Potential for abuse and dependence; contraindicated in history of drug abuse.

Genetic Factors: N/A

Lab Test Interference: N/A

Overdose Management

Signs/Symptoms: Severe hypertension, hyperthermia, agitation, hallucinations, seizure,

Treatment: Supportive care; consider use of antihypertensives, cooling measures, seizure control agents, and activated charcoal if ingestion was recent.

Storage and Handling

Storage: Store at room temperature 20-25°C (68-77°F), away from light and moisture.

Stability: Stable under recommended storage conditions.