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Pronunciation
(FEN ter meen)
Generic Available (U.S.)
Yes: Excludes orally disintegrating tablet
Index Terms
Controlled Substance
C-IV
Brand Names: U.S.
Pharmacologic Category
Pharmacologic Category Synonyms
Use: Labeled Indications
Short-term (few weeks) adjunct therapy in obese patients with an initial body mass index (BMI) ≥30 kg/m2 or ≥27 kg/m2 in the presence of other risk factors (eg, diabetes, hyperlipidemia, controlled hypertension); therapy should be used in conjunction with a comprehensive weight management program.
Pregnancy Risk Factor
C/X (manufacturer specific)
Pregnancy Considerations
Animal reproduction studies have not been conducted. The use of Suprenza™ is contraindicated during pregnancy. The risks of using appetite suppressing drugs in pregnant women are not known and limited information is available about the use of phentermine in pregnancy. Weight loss therapy is generally not recommended for pregnant women. Obese and overweight women should be encouraged to participate in weight reduction programs prior to attempting pregnancy; weight gain during pregnancy should be determined by their prepregnancy BMI and current guidelines.
Lactation
Excretion in breast milk unknown/not recommended
Breast-Feeding Considerations
It is unknown if phentermine is excreted in breast milk; however, other amphetamines have been detected in breast milk. Due to the potential for adverse reactions in the nursing infant, a decision should be made to discontinue nursing or discontinue the medication, depending on the importance of the drug to the mother. The use of Suprenza™ is contraindicated in breast-feeding women. Weight loss therapy is generally not recommended for lactating women. Weight loss programs which include physical activity and nutrition components should be discussed at the 6-week postpartum visit.
Contraindications
Hypersensitivity or idiosyncrasy to phentermine or other sympathomimetic amines or any component of the formulation; cardiovascular disease (current or a history of), advanced arteriosclerosis, moderate-to-severe hypertension; hyperthyroidism, glaucoma, agitated states, patients with a history of drug abuse; use during or within 14 days following MAO inhibitor therapy
Suprenza™: Additional contraindications: Pregnancy, breast-feeding
Warnings/Precautions
Special handling:
• Hazardous agent: Use appropriate precautions for handling and disposal.
Concerns related to adverse effects:
• CNS effects: Amphetamines may impair the ability to engage in potentially hazardous activities.
• Primary pulmonary hypertension (PPH): A rare, frequently fatal disease of the lungs, PPH has been reported to occur in patients receiving a combination of phentermine and fenfluramine or dexfenfluramine. The possibility of an association between PPH and the use of phentermine alone cannot be ruled out. Discontinue in patients experiencing new-onset dyspnea, chest pain, syncope, or lower extremity edema.
• Valvular heart disease: The use of some anorexigens, including phentermine, has been associated with the development of valvular heart disease. Avoid stimulants in patients with known serious structural cardiac abnormalities, cardiomyopathy, serious heart rhythm abnormalities, or other serious cardiac problems that could increase the risk of sudden death that these conditions alone carry.
Disease-related concerns:
• Diabetes: Use with caution in patients with diabetes mellitus; antidiabetic agent requirements (eg, insulin or oral hypoglycemic agents) may be decreased with anorexigens and concomitant dietary restrictions.
• Hypertension: Use with caution in patients with mild hypertension and other cardiovascular conditions that might be exacerbated by increases in blood pressure or heart rate.
• Renal impairment: Use caution in patients with renal impairment; use has not been studied; however, an increase in exposure is expected in renal impairment.
• Seizure disorders: Use with caution in patients with a history of seizure disorders.
• Tourette's syndrome: Use with caution in patients with Tourette's syndrome; stimulants may unmask tics.
Concurrent drug therapy issues:
• Anorexigens: Safety and efficacy have not been established for use with other weight loss medications, including SSRIs, over-the-counter, or herbal products.
Special populations:
• Elderly: May be inappropriate in this age group due to the risk for causing dependence, hypertension, angina, and myocardial infarction (Beers Criteria).
Other warnings/precautions:
• Abuse potential: Phentermine is pharmacologically related to the amphetamines, which have a high abuse potential; prolonged use may lead to dependency. Prescriptions should be written for the smallest quantity consistent with good patient care to minimize possibility of overdose.
• Appropriate use: Discontinue if satisfactory weight loss has not occurred within the first 4 weeks of treatment. Phentermine is not approved for long-term use. The limited usefulness of medications in this class should be weighed against possible risks associated with their use. Consult weight loss guidelines for current pharmacotherapy recommendations.
• Tolerance: Tolerance to the anorectic effect usually develops within a few weeks; discontinue use when tolerance develops, do not exceed recommended dosage in an attempt to overcome tolerance.
Adverse Reactions
Frequency not defined.
Cardiovascular: Hypertension, ischemic events, palpitation, primary pulmonary hypertension and/or regurgitant cardiac valvular disease, tachycardia
Central nervous system: Dizziness, dysphoria, euphoria, headache, insomnia, overstimulation, psychosis, restlessness
Dermatologic: Urticaria
Endocrine & metabolic: Changes in libido
Gastrointestinal: Constipation, diarrhea, unpleasant taste, xerostomia
Genitourinary: Impotence
Neuromuscular & skeletal: Tremor
Metabolism/Transport Effects
None known.
Drug Interactions
Alcohol (Ethyl): May enhance the adverse/toxic effect of Phentermine. Risk C: Monitor therapy
Alkalinizing Agents: May decrease the excretion of Amphetamines. Risk D: Consider therapy modification
Ammonium Chloride: May decrease the serum concentration of Amphetamines. This effect is likely due to an enhanced excretion of amphetamines in the urine. Risk C: Monitor therapy
Analgesics (Opioid): Amphetamines may enhance the analgesic effect of Analgesics (Opioid). Risk C: Monitor therapy
Antacids: May decrease the excretion of Amphetamines. Risk C: Monitor therapy
Antihistamines: Amphetamines may diminish the sedative effect of Antihistamines. Exceptions: Levocabastine (Nasal). Risk C: Monitor therapy
Antipsychotics: May diminish the stimulatory effect of Amphetamines. Risk C: Monitor therapy
Atomoxetine: May enhance the hypertensive effect of Sympathomimetics. Atomoxetine may enhance the tachycardic effect of Sympathomimetics. Risk C: Monitor therapy
Cannabinoids: May enhance the tachycardic effect of Sympathomimetics. Risk C: Monitor therapy
Carbonic Anhydrase Inhibitors: May decrease the excretion of Amphetamines. Exceptions: Brinzolamide; Dorzolamide. Risk C: Monitor therapy
Ethosuximide: Amphetamines may diminish the therapeutic effect of Ethosuximide. Amphetamines may decrease the serum concentration of Ethosuximide. Risk C: Monitor therapy
Gastrointestinal Acidifying Agents: May decrease the serum concentration of Amphetamines. Risk C: Monitor therapy
Iobenguane I 123: Sympathomimetics may diminish the therapeutic effect of Iobenguane I 123. Risk X: Avoid combination
Ioflupane I 123: Amphetamines may diminish the diagnostic effect of Ioflupane I 123. Risk C: Monitor therapy
Lithium: May diminish the stimulatory effect of Amphetamines. Risk C: Monitor therapy
MAO Inhibitors: May enhance the hypertensive effect of Amphetamines. Risk X: Avoid combination
Methenamine: May decrease the serum concentration of Amphetamines. This effect is likely due to an enhanced excretion of amphetamines in the urine. Risk C: Monitor therapy
PHENobarbital: Amphetamines may decrease the serum concentration of PHENobarbital. Risk C: Monitor therapy
Phenytoin: Amphetamines may decrease the serum concentration of Phenytoin. Risk C: Monitor therapy
Proton Pump Inhibitors: May increase the serum concentration of Amphetamines. Specifically, data indicate that Proton Pump Inhibitors may increase the rate at which Amphetamines are absorbed. Total exposure to Amphetamines is not significantly changed. Risk C: Monitor therapy
Sympathomimetics: May enhance the adverse/toxic effect of other Sympathomimetics. Risk C: Monitor therapy
Tricyclic Antidepressants: May enhance the stimulatory effect of Amphetamines. Tricyclic Antidepressants may also potentiate the cardiovascular effects of Amphetamines. Risk C: Monitor therapy
Ethanol/Nutrition/Herb Interactions
Ethanol: Concurrent use of phentermine with ethanol may result in adverse effects.
Storage
Store at controlled room temperature of 20°C to 25°C (68°F to 77°F).
Mechanism of Action
Phentermine is a sympathomimetic amine with pharmacologic properties similar to the amphetamines. The mechanism of action in reducing appetite appears to be secondary to CNS effects, including stimulation of the hypothalamus to release norepinephrine.
Pharmacodynamics/Kinetics
Absorption: Well absorbed
Time to peak: Orally disintegrating tablet: 3-4.4 hours
Excretion: Primarily urine
Dosage
Note: Dosing is presented in terms of the salt, phentermine hydrochloride (not as phentermine base).
Oral: Children >16 years and Adults: Obesity:
Capsule, tablet: 15-37.5 mg/day given in 1-2 divided doses. Individualize to achieve adequate response with lowest effective dose.
Orally disintegrating tablet (ODT): One tablet (15 mg or 30 mg) every morning. Individualize to achieve adequate response with lowest effective dose.
Administration: Oral
Avoid late evening administration.
Capsules, tablets: Administer before breakfast or 1-2 hours after breakfast. Tablets may be divided in half and dose may be given in 2 divided doses.
Orally disintegrating tablets (Suprenza™): With dry hands, place tablet on the tongue and allow to dissolve, then swallow with or without water. May administer with or without food.
Monitoring Parameters
Weight, waist circumference; blood pressure
Reference Range
Adult classification of weight by BMI (kg/m2):
Underweight: <18.5
Normal: 18.5-24.9
Overweight: 25-29.9
Obese, class I: 30-34.9
Obese, class II: 35-39.9
Extreme obesity (class III): ≥40
Waist circumference: In adults with a BMI of 25-34.9 kg/m2, high-risk waist circumference is defined as:
Men >102 cm (>40 in)
Women >88 cm (>35 in)
Test Interactions
May interfere with urine detection of amphetamines/methamphetamines (false-positive).
Dietary Considerations
Capsules, tablets: Should be taken before breakfast or 1-2 hours after breakfast; avoid taking in the late evening. Most effective when combined with a low-calorie diet and behavior modification counseling.
Patient Education
Administer early in day so as not to disturb patient's sleep; can take tablet/capsule before breakfast or in two divided doses. Orally disintegrating tablets dissolve on the tongue. Follow diet and exercise plan for weight loss. Common side effects include feeling dizzy, nervous, excitable, having a dry mouth, and insomnia. Have patient call prescriber if changes in mood or behavior, very dizzy, passing out, chest pain, severe headache, or rash.
Geriatric Considerations
This medication is considered to be potentially inappropriate in this patient population (Beers Criteria severity: High).
Cardiovascular Considerations
Phentermine should be avoid in patients with cardiovascular disease. The combination with fenfluramine (Phen-Fen® - no longer available) was associated with mitral valve fibrosis and mitral regurgitation. Primary pulmonary hypertension has also been reported in patients receiving Phen-Fen®.
Dental Health: Effects on Dental Treatment
Key adverse event(s) related to dental treatment: Xerostomia (normal salivary flow resumes upon discontinuation) and unpleasant taste. Up to 10% of patients may present with hypertension. The use of local anesthetic without vasoconstrictor is recommended in these patients. See Dental Health Professional Considerations.
Dental Health: Vasoconstrictor/Local Anesthetic Precautions
Use vasoconstrictor with caution in patients taking phentermine. Amphetamines enhance the sympathomimetic response of epinephrine and norepinephrine leading to potential hypertension and cardiotoxicity.
Dental Comment
Many diet physicians have prescribed fenfluramine (“fen”) and phentermine (“phen”). When taken together the combination is known as “fen-phen”. The diet drug dexfenfluramine (Redux®) is chemically similar to fenfluramine (Pondimin®) and was also used in combination with phentermine called “Redux-phen”. While each of the three drugs alone had approval from the FDA for sale in the treatment of obesity, neither combination had an official approval. The use of the combinations in the treatment of obesity was considered an “off-label” use. Reports in medical literature have been accumulating for some years about significant side effects associated with fenfluramine and dexfenfluramine. In 1997, the manufacturers, at the urging of the FDA, agreed to voluntarily withdraw the drugs from the market. The action was based on findings from physicians who evaluated patients taking fenfluramine and dexfenfluramine with echocardiograms. The findings indicated that approximately 30% of patients had abnormal echocardiograms, even though they had no symptoms. This was a much higher than expected percentage of abnormal test results. This conclusion was based on a sample of 291 patients examined by five different physicians. Under normal conditions, fewer than 1% of patients would be expected to show signs of heart valve disease. The findings suggested that fenfluramine and dexfenfluramine were the likely cause of heart valve problems of the type that promoted FDA's earlier warnings concerning “fen-phen”. The earlier warning included the following: The mitral valve and other valves in the heart are damaged by a strange white coating and allow blood to flow back, causing heart muscle damage. In several cases, valve replacement surgery has been done. As a rule, the person must, thereafter for life, be on a blood thinner to prevent clots from the mechanical valve. This type of valve damage had only been seen before in persons who were exposed to large amounts of serotonin. The fenfluramine increases the availability of serotonin.
Nursing: Physical Assessment/Monitoring
Avoid use in patients with heart disease (including structural heart disease, cardiomyopathy, arrhythmias). Use for a short period of time; as tolerance develops discontinue use.
Dosage Forms
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Capsule, oral, as hydrochloride: 15 mg, 30 mg, 37.5 mg
Adipex-P®: 37.5 mg
Tablet, oral, as hydrochloride: 37.5 mg
Adipex-P®: 37.5 mg [scored]
Tablet, orally disintegrating, oral, as hydrochloride:
Suprenza™: 15 mg, 30 mg [contains tartrazine; peppermint flavor]
Pricing: U.S. (www.drugstore.com)
Capsules (Phentermine HCl)
15 mg (10): $24.99
30 mg (10): $19.99
37.5 mg (10): $17.99
Tablets (Adipex-P)
37.5 mg (10): $32.99
Tablets (Phentermine HCl)
37.5 mg (10): $14.99
References
Abenhaim L, Moride Y, Brenot F, et al, “Appetite-Suppressant Drugs and the Risk of Primary Pulmonary Hypertension. International Primary Pulmonary Hypertension Study Group,” N Engl J Med, 1996, 335(9):609-16.
“Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: Executive Summary. Expert Panel on the Identification, Evaluation, and Treatment of Overweight in Adults,” Am J Clin Nutr, 1998, 68(4):899-917.
Devan GS, “Phentermine and Psychosis,” Br J Psychiatry, 1990, 156:442-3.
Hamer R and Phelps D, “Inadvertent Intra-arterial Injection of Phentermine: A Complication of Drug Abuse,” Ann Emerg Med, 1981, 10:148-50.
Kokkinos J and Levine SR, “Possible Association of Ischemic Stroke With Phentermine,” Stroke, 1993, 24(2):310-3.
Levine B, Caplan YH, and Dixon AM, “A Fatality Involving Phentermine,” J Forensic Sci, 1984, 29(4):1242-5.
Mokhlesi B, Leikin JB, Murray P, et al, “Adult Toxicology in Critical Care: Part II: Specific Poisonings,” Chest, 2003, 123(3):897-922.
Snow V, Barry P, Fitterman N, et al, “Pharmacologic and Surgical Management of Obesity in Primary Care: A Clinical Practice Guideline from the American College of Physicians,” Ann Intern Med, 2005, 142(7):525-31.
Thurman EM, Pedersen MJ, Stout RL, et al, “Distinguishing Sympathomimetic Amines from Amphetamine and Methamphetamine in Urine by Gas Chromatography/Mass Spectrometry,” J Anal Toxicol, 1992, 16(1):19-27.
“U.S. Preventative Services Task Force. Screening for Obesity in Adults: Recommendations and Rationale,” Ann Intern Med, 2003, 139(11):933-49
International Brand Names
Lexi-Comp.com
Last full review/revision March 2012
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