Action And Clinical Pharmacology: Phentermine is a sympathomimetic amine with pharmacologic activity similar to the prototype drugs of this class used in obesity, the amphetamines. Actions include CNS 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, however, that the action of such drugs in treating obesity is primarily one of appetite suppression. Other CNS actions, or metabolic effects may be involved, for example.
Indications And Clinical Uses: As a short-term (i.e., a few weeks) adjunct to continued dietary treatment in the medical management of obesity in patients not responding to an appropriate weight reducing diet alone. Phentermine is recommended only for obese patients with an initial body mass index (BMI) ³30 kg/m or a BMI ³27 kg/min the presence of other risk factors (e.g., hypertension, diabetes, hyperlipidemia).
When prescribing anorectic agents it should be borne in mind that the role of these drugs in the management of obesity is strictly limited, since patients treated with anorectics lose only a fraction of a pound per week more than those who are on a weight-reducing diet alone. Prolonged administration of these agents must also be avoided since it can lead to drug dependence and abuse (see Warnings).
Patients with BMI values of 27 to 29 kg/mmay be candidates for phentermine therapy if they also have a concomitant risk factor (e.g., hypertension, diabetes, hyperlipidemia).
Contra-Indications: In advanced arteriosclerosis, cardiovascular disease, moderate to severe hypertension, hyperthyroidism, known hypersensitivity or idiosyncrasy to the sympathomimetic amines, glaucoma. Phentermine is also contraindicated in agitated states, patients with a history of drug abuse, and during or within 14 days following the administration of MAO inhibitors (hypertensive crisis may result).
Manufacturers’ Warnings In Clinical States: Risk of Primary Pulmonary Hypertension (PPH): Anorexigens increase the risk of developing primary pulmonary hypertension, an often fatal disorder.
Although phentermine was not identified, an epidemiological study has indicated that use of other anorexigens for longer than 3 months was associated with a 23-fold increase in the risk of developing PPH. There was no significant increase in risk for persons who had used these agents for 3 months or less.
Obesity itself (BMI ³30 kg/m was also independently associated with an increase of about 2-fold in the risk of developing PPH. In the general population, the yearly occurrence of PPH is estimated to be about 1 to 2 cases per 1 000 000 persons. Therefore, the estimated risk associated with the long-term use of anorexigen drugs is about 23 to 46 cases per million persons exposed per year. The study further suggested that the risk of PPH rises with increasing duration of use of these drugs. The effect of intermittent compared to continuous use of anorexigens on the risk of PPH has not been determined.
The onset or aggravation of exertional dyspnea, or unexplained symptoms of angina pectoris, syncope, or lower extremity edema suggest the possibility of occurrence of pulmonary hypertension. Under these circumstances, treatment should be immediately discontinued, and the patient should be evaluated for the possible presence of PPH.
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. There have been no reported cases to date of this valvular condition occurring with the use of phentermine alone.
Tolerance: 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.
Occupational Hazards: 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.
Drug Dependence: Experience with anorectic drugs with amphetamine-like properties such as phentermine has established that prolonged use of these drugs can produced tolerance, severe psychological dependence and has led to extensive abuse. This should be kept in mind when assessing the desirability of using the drug and caution should be exercised not to use the drug in individuals whose histories suggest they may increase the dosage on their own initiative. If psychological dependence occurs, gradual withdrawal of the medication is recommended. Abrupt cessation following prolonged high dosage may result in extreme fatigue and mental depression. Abuse of these drugs may lead to moderate to severe manifestations of chronic intoxication including marked insomnia, irritability, hyperactivity, personality changes and even psychosis.
Pregnancy: Phentermine should not be administered to women who are or who are likely to become pregnant unless in the opinion of the prescribing physician the potential benefits of drug therapy outweigh the possible risk to mother and fetus.
Children: Phentermine is not recommended for use in children under 12 years of age.
Adverse Reactions: The most frequently encountered side effects have been dry mouth, insomnia, constipation. Other side effects are: Cardiovascular: palpitation, tachycardia, elevation of blood pressure, primary pulmonary hypertension and/or regurgitant cardiac valvular disease (see Warnings).
CNS: overstimulation, restlessness, dizziness, euphoria, dysphoria, tremor, headache, insomnia ; rarely psychotic episodes at recommended doses.
Gastrointestinal: unpleasant taste, dryness of mouth, diarrhea, constipation, other gastrointestinal disturbances.
Endocrine: impotence, changes in libido.
Overdose: Symptoms: Manifestations of acute overdosage with phentermine include restlessness, tremor, hyperreflexia, rapid respiration, confusion, assaultiveness, hallucinations, panic states. Fatigue and depression usually follow the central stimulation. Cardiovascular effects include arrhythmias, hypertension or hypotension, and circulatory collapse. Gastrointestinal symptoms include nausea, vomiting, diarrhea, and abdominal cramps. Fatal poisoning usually terminates in convulsions and coma.
Treatment: Management of acute phentermine intoxication is largely symptomatic and includes lavage and sedation with a barbiturate. Experience with hemodialysis or peritoneal dialysis is inadequate to permit recommendations in this regard. Acidification of the urine increases phentermine excretion. I.V. phentolamine has been suggested for possible acute, severe hypertension, if this complicates phentermine overdosage.
Dosage And Administration: Exogenous Obesity: One capsule approximately 2 hours after breakfast for appetite control. Late evening medication should be avoided because of the possibility of resulting insomnia.
Administration of 1 capsule (30 mg) daily has been found to be adequate in depression of the appetite for 12 to 14 hours.
Phentermine is not recommended for use in children under 12 years of age.
Phentermine should be used for a duration of no more than a few weeks (see Warnings).
Availability And Storage: Each blue and white capsule contains: phentermine HCl 30 mg (equivalent to phentermine 24 mg). Nonmedicinal ingredients: FD&C Blue No. 1, invert sugar, methylcellulose, polyethylene glycol, starch, sucrose and titanium dioxide. The branding ink used on the gelatin capsules contains: ethyl alcohol, FD&C Blue No. 1 aluminum lake, isopropyl alcohol, n-butyl alcohol, propylene glycol and shellac. Gluten-, lactose- and tartrazine-free. Bottles of 100.
FASTIN® SmithKline Beecham Phentermine HCl Anorexiant