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IONAMIN (phentermine resin complex) Capsules are indicated only as short-term monotherapy for the management of exogenous obesity. The safety and efficacy of combination therapy with phentermine and any other drug products for weight loss, including selective serotonin reuptake inhibitors (e.g., fluoxetine, sertraline, fluvoxamine, paroxetine), have not been established. Therefore, the coadministration of these drug products for weight loss is not recommended.

Primary Pulmonary Hypertension (PPH) – a rare, frequently fatal disease of the lungs – has been reported to occur in patients receiving a combination of phentermine with fenfluramine or dexfenfluramine. The possibility of an association between PPH and the use of phentermine alone cannot be ruled out. The initial symptom of PPH is usually dyspnea. Other initial symptoms include: angina pectoris, syncope, or lower extremity edema. Patients should be advised to report immediately any deterioration in exercise tolerance. Treatment should be discontinued in patients who develop new, unexplained symptoms of dyspnea, angina pectoris, syncope, or lower extremity edema.

Valvular Heart Disease

Serious regurgitant cardiac valvular disease, primarily affecting the mitral, aortic and/or tricuspid valves, has been reported in otherwise healthy persons who had taken a combination of phentermine with fenfluramine or dexfenfluramine for weight loss. The etiology of these valvulopathies has not been established and their course in individuals after the drugs are stopped is not known.

If tolerance to the “anorectic” effect develops, the recommended dose should not be exceeded in an attempt to increase the effect: rather, the drug should be discontinued.

IONAMIN (phentermine resin complex) may impair the ability of the patient to engage in potentially hazardous activities such as operating machinery or driving a motor vehicle; the patient should therefore be cautioned accordingly.

When using CNS active agents, consideration must always be given to the possibility of adverse interactions with alcohol.

Drug Dependence

IONAMIN (phentermine resin complex) is related chemically and pharmacologically to amphetamine (d- and dl-amphetamine) and other stimulant drugs that have been extensively abused. The possibility of abuse of IONAMIN (phentermine resin complex) should be kept in mind when evaluating the desirability of including a drug as part of a weight reduction program. Abuse of amphetamine (d- and dl-amphetamine) and related drugs may be associated with intense psychological dependence and severe social dysfunction. There are reports of patients who have increased the dosage of some of these drugs to many times that recommended. Abrupt cessation following prolonged high dosage administration results in extreme fatigue and mental depression; changes are also noted on the sleep EEG. Manifestations of chronic intoxication with anorectic drugs include severe dermatoses, marked insomnia, irritability, hyperactivity, and personality changes. The most severe manifestation of chronic intoxications is psychosis, often clinically indistinguishable from schizophrenia.

Usage in Pregnancy

Safe use in pregnancy has not been established. Use of IONAMIN (phentermine resin complex) by women who are or may become pregnant requires that the potential benefit be weighed against the possible hazard to mother and infant.

Pediatric Use

IONAMIN Capsules (phentermine resin) are not recommended for use in pediatric patients under 16 years of age.

Caution is to be exercised in prescribing IONAMIN (phentermine resin complex) for patients with even mild hypertension. Insulin requirements in diabetes mellitus may be altered in association with the use of IONAMIN (phentermine resin complex) and the concomitant dietary regimen.

IONAMIN (phentermine resin complex) may decrease the hypotensive effect of adrenergic neuron blocking drugs.

The least amount feasible should be prescribed or dispensed at one time in order to minimize the possibility of overdosage.

Geriatric Use

Clinical studies of IONAMIN (phentermine resin complex) did not include sufficient numbers of subjects aged 65 or over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

This drug is known to be substantially excreted by the kidney, and the risk of toxic reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, and it may be useful to monitor renal function.

Last reviewed on RxList: 4/8/2009
This monograph has been modified to include the generic and brand name in many instances.