Adjunct to exercise, behavioral modification, and caloric restriction in the short-term management (a few weeks) of exogenous obesity.
May use in patients with no underlying risk factor but a pretreatment body mass index (BMI) of ≥30 kg/m2 and in those with an underlying risk factor (e.g., hypertension, diabetes mellitus, hyperlipidemia) and a pretreatment BMI of ≥27 kg/m2.
Teach patient to curtail overeating and consume a suitable diet to help induce and maintain weight loss.
Administration
Oral Administration
Administer phentermine resin complex capsule before breakfast or 10–14 hours before retiring; swallow capsule whole.
Administer phentermine hydrochloride 37.5-mg capsule or tablet (Adipex-P®) before or 1–2 hours after breakfast; avoid late evening administration because of possible insomnia.
Dosage
Available as phentermine resin complex; dosage expressed in terms of phentermine. Also available as phentermine hydrochloride; dosage expressed in terms of phentermine hydrochloride.
Adjust dosage according to individual response and tolerance; use the smallest dosage required to produce the desired response.
Adults
Exogenous Obesity
Oral
Phentermine (as resin complex): Usual dosage is 15 or 30 mg once daily.
Phentermine hydrochloride: Usual dosage is 8 mg 3 times daily (given 30 minutes before meals) or 15–37.5 mg once daily (in the morning). Alternatively, 18.75 mg twice daily.
Special Populations
Geriatric Patients
Select dosage with caution, starting at lower end of dosage range. \
Known hypersensitivity or idiosyncrasy to sympathomimetic amines.
Warnings/Precautions
Warnings
Concomitant Drug Therapy for Weight Loss
Avoid concomitant use with other drugs for weight loss, including anorexigenic agents (e.g., phendimetrazine), SSRI antidepressants (e.g., fluoxetine, fluvoxamine, paroxetine, sertraline), and MAO inhibitors, since severe adverse reactions may occur. (See Specific Drugs under Interactions.)
Primary Pulmonary Hypertension
Risk of primary pulmonary hypertension (frequently fatal) when used in combination with at least one other anorexigenic agent, including dexfenfluramine or fenfluramine (both no longer commercially available in the US) or phendimetrazine or in those with a history of receiving at least one other anorexigenic agent.
Risk with use of phentermine alone cannot be ruled out; primary pulmonary hypertension reported rarely in patients receiving phentermine alone.
Discontinue if new, unexplained symptoms of dyspnea, angina, syncope, or edema of the lower extremities occur, and evaluate for possible pulmonary hypertension.
Valvular Heart Disease
Risk of serious regurgitant valvular (principally mitral, aortic, and/or tricuspid; usually multivalvular) heart disease when used in combination with phendimetrazine or with dexfenfluramine or fenfluramine (both no longer commercially available in the US).
Risk with use of phentermine alone cannot be ruled out; valvular heart disease reported rarely in patients receiving phentermine alone.
Medical history and cardiovascular examination are recommended for patients who received dexfenfluramine or fenfluramine alone or in combination with other anorexigenic drugs (e.g., phentermine). Perform echocardiogram in those with signs/symptoms suggestive of valvular heart disease and base subsequent testing and/or treatment on the specific valve lesions. Strongly consider performing echocardiographic evaluation in all patients exposed to these anorexigenic agents who are about to undergo invasive procedures for which anti-infectiveprophylaxis for bacterial endocarditis is indicated. In case of emergency procedures when cardiac evaluation cannot be performed, administer preventive anti-infective therapy.
Tolerance to Anorexigenic Effect
Tolerance to anorexigenic effect usually develops within a few weeks. When it does, discontinue therapy; do not attempt to increase effect by exceeding recommended dosage.
CNS Effects
Performance of activities requiring mental alertness or physical coordination may be impaired.
Abuse Potential
Potential for abuse; habituation or addiction reported with similar drugs (e.g., amphetamines).
Manifestations of chronic intoxication may include psychosis resembling schizophrenia, severe dermatoses, marked insomnia, irritability, hyperactivity, and personality changes.
Abrupt discontinuance following prolonged high dosage may result in extreme fatigue, depression, and sleep EEG changes.
General Precautions
Prescribe and dispense in the smallest feasible quantity to minimize possibility of overdosage.
Hypertension
Use with caution in patients with mild hypertension; monitor BP closely. Contraindicated in those with moderate or severe hypertension.
Diabetes Mellitus
Use with caution in patients with diabetes mellitus; insulin requirements may decrease in association with phentermine use and the concomitant dietary regimen and weight loss.
Specific Populations
Pregnancy
Category C.
Whether potential benefits outweigh risks is questionable; use during pregnancy (especially during the first trimester) probably should be considered a contraindication.
Lactation
Not known whether phentermine is distributed into milk. Discontinue nursing or the drug.
Pediatric Use
Safety and efficacy not established; use not recommended in children <16 years of age.
Geriatric Use
Insufficient experience in patients ≥65 years of age to determine whether geriatric patients respond differently than younger adults; select dosage with caution, starting at lower end of dosage range, due to greater frequency of decreased hepatic, renal, and/or cardiac function and of concomitant disease and drug therapy observed in the elderly. Monitoring of renal function may be useful.
Renal Impairment
Use with caution; clearance may be decreased and risk of toxicity increased.
Common Adverse Effects
Palpitation, tachycardia, increased BP, overstimulation, restlessness, insomnia, tremor, dizziness, headache, euphoria, dysphoria, dryness of the mouth, unpleasant taste, diarrhea, constipation, vomiting, other GI disturbances, urticaria, impotence, changes in libido.
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