Phentermine hydrochloride USP has the chemical name of
alpha, alpha-Dimethylphenethylamine hydrochloride. The structural formula is as
phentermine (Phentermine) chemical structure
Phentermine hydrochloride is a white, odorless,
hygroscopic, crystalline powder which is soluble in water and lower alcohols,
slightly soluble in chloroform and insoluble in ether.
Phentermine®, an anorectic agent for oral administration, is
available as a capsule or tablet containing 37.5 mg of phentermine
hydrochloride (equivalent to 30 mg of phentermine base).
Phentermine® Capsules contain the inactive ingredients Corn
Starch, Gelatin, Lactose Monohydrate, Magnesium Stearate, Titanium Dioxide,
Black Iron Oxide, FD&C Blue #1, FD&C Red #40 and D&C Red #33.
Phentermine® Tablets contain the inactive ingredients Corn
Starch, Lactose (Anhydrous), Magnesium Stearate, Microcrystalline Cellulose,
Pregelatinized Starch, Sucrose, and FD&C Blue #1. Phentermine weight loss
Advanced arteriosclerosis, cardiovascular disease, moderate
to severe hypertension, hyperthyroidism, known hypersensitivity or idiosyncrasy
to the sympathomimetic amines, glaucoma.
Patients with a history of drug abuse.
During or within 14 days following the administration of
monoamine oxidase inhibitors (hypertensive crises may result). Phentermine weight loss.
Phentermine® is a sympathomimetic amine with pharmacologic
activity similar to the prototype drugs of this class used in obesity, the
amphetamines. Actions include central nervous system stimulation and elevation
of blood pressure. Tachyphylaxis and tolerance have been demonstrated with all
drugs of this class in which these phenomena have been looked for.
Drugs of this class used in obesity are commonly known as
"anorectics" or "anorexigenics". It has not been
established that the action of such drugs in treating obesity is primarily one
of appetite suppression. Other central nervous system actions, or metabolic
effects, may be involved, for example.
Adult obese subjects instructed in dietary management and
treated with "anorectic" drugs lose more weight on the average than
those treated with placebo and diet, as determined in relatively short-term
The magnitude of increased weight loss of drug-treated patients
over placebo-treated patients is only a fraction of a pound a week. The rate of
weight loss is greatest in the first weeks of therapy for both drug and placebo
subjects and tends to decrease in succeeding weeks. The possible origins of the
increased weight loss due to the various drug effects are not established. The
amount of weight loss associated with the use of an "anorectic" drug
varies from trial to trial, and the increased weight loss appears to be related
in part to variables other than the drugs prescribed, such as the
physician-investigator, the population treated and the diet prescribed. Studies
do not permit conclusions as to the relative importance of the drug and
non-drug factors on weight loss.
The natural history of obesity is measured in years,
whereas the studies cited are restricted to a few weeks duration; thus, the
total impact of drug-induced weight loss over that of diet alone must be
considered clinically limited. Phentermine weight loss.
Phentermine® is 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,
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; there have been rare cases of PPH in patients who
reportedly have taken phentermine alone. 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. The possibility
of an association between valvular heart disease and the use of phentermine
alone cannot be ruled out; there have been rare cases of valvular heart disease
in patients who reportedly have taken phentermine alone.
Tolerance to the anorectic effect usually develops within a
few weeks. When this occurs, the recommended dose should not be exceeded in an
attempt to increase the effect; rather, the drug should be discontinued.
Phentermine® 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. Phentermine weight loss.
Indications and Usage
Phentermine® (phentermine hydrochloride) is indicated as a
shortterm (a few weeks) adjunct in a regimen of weight reduction based on
exercise, behavioral modification and caloric restriction in the management of
exogenous obesity for patients with an initial body mass index >=30 kg/m2,
or >=27 kg/m2 in the presence of other risk factors (e.g., hypertension,
Below is a chart of Body Mass Index (BMI) based on various
heights and weights.
BMI is calculated by taking the patient's weight, in
kilograms (kg), divided by the patient's height, in meters (m), squared. Metric
conversions are as follows: pounds ÷ 2.2 = kg; inches x 0.0254 = meters.
BODY MASS INDEX (BMI), kg/m2
Height (feet, inches)
phentermine (Phentermine) chart of body mass index (BMI)
The limited usefulness of agents of this class (see
Clinical Pharmacology) should be measured against possible risk factors
inherent in their use such as those described below. Phentermine weight loss.