Phentermine (Resin Complex)
Action And Clinical Pharmacology: Phentermine is a sympathomimetic amine with pharmacologic activity similar to the prototype drug of this class used in obesity, amphetamine (d- and dl-amphetamine). 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.
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 clinical trials.
The magnitude of increased weight loss of drug-treated patients over placebo-treated patients is only a fraction of a pound a week (less than 500 g). 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 nondrug factors on weight loss. The natural history of obesity is measured in years; whereas, the studies cited are restricted to a few weeks or months duration. Thus, the total impact of drug-induced weight loss over that of diet alone must be considered clinically limited. The bioavailability of phentermine has been studied in humans in which blood levels of phentermine were measured by a gas-chromatography method. Blood levels obtained with the 15 and 30 mg resin-complex formulations indicated slower absorption with a reduced but prolonged peak concentration and without a significant difference in prolongation of blood levels when compared with the same doses of phentermine hydrochloride. The clinical significance of these differences is not known. In clinical trials establishing the efficacy of phentermine, a single daily dose produced an effect comparable to that produced by other regimens of anorectic drug therapy.
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 who have not responded to an appropriate weight reducing diet alone. Phentermine is recommended only for obese patients with an initial body mass index Â³30 kg/m or Â³27 kg/min the presence of other risk factors (e.g., hypertension, diabetes, hyperlipidemia).
The limited usefulness of agents of this class (see Pharmacology) should be measured against possible risk factors inherent in their use such as those described below. See Table I.
Contra-Indications: Advanced arteriosclerosis, symptomatic 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 MAO inhibitors (hypertensive crises may result).
Tricyclic Antidepressant (hypertensive crises may result or cardiac arrhythmia).
Manufacturers’ Warnings In Clinical States: Primary Pulmonary Hypertension: 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 Primary Pulmonary Hypertension (PPH). There was no significant increase in risk for persons who had used these agents for 3 months or less. Obesity itself (body mass index Â³30 kg/m was also independently associated with an increase of about two-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 of 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.
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.
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.
When using CNS active agents, consideration must always be given to the possibility of adverse interactions with alcohol.
Drug Dependence: Phentermine 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 phentermine 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 intoxication is psychosis, often clinically indistinguishable from schizophrenia.
Pregnancy: Safe use in pregnancy has not been established. Use of phentermine by women who are or may become pregnant requires that the potential benefit be weighed against the possible hazard to mother and infant.
Children: Phentermine is not recommended for use in children under 12 years of age.
Precautions: Caution is to be exercised in prescribing phentermine for patients with even mild hypertension. Insulin requirements in diabetes mellitus may be altered in association with the use of phentermine and the concomitant dietary regimen.
Phentermine 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.
Adverse Reactions: Cardiovascular: palpitation, tachycardia, elevation of blood pressure, primary pulmonary hypertension (see Warnings).
CNS: overstimulation, restlessness, dizziness, insomnia, euphoria, dysphoria, tremor, headache; rarely psychotic episodes at recommended doses with some drugs in this class.
Gastrointestinal: dryness of the mouth, unpleasant taste, diarrhea, constipation, other gastrointestinal disturbances.
Endocrine: impotence, changes in libido.
Symptoms And Treatment Of Overdose: Symptoms and Treatment: Manifestations of acute overdosage may 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. Overdosage of pharmacologically similar compounds has resulted in fatal poisoning, usually terminating in convulsions and coma.
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 recommendation in this regard. I.V. phentolamine has been suggested on pharmacologic grounds for possible acute, severe hypertension, if this complicates overdosage.
Dosage And Administration: 1 capsule daily, before breakfast or 10 to 14 hours before retiring. For individuals exhibiting greater drug responsiveness, Ionamin 15 will usually suffice. Ionamin 30 is recommended for less responsive patients. 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: 15 mg: Each yellow and gray capsule, printed with “IONAMIN”, “15”, and “E” in black, contains: phentermine 15 mg as the cationic exchange resin complex. Nonmedicinal ingredients: calcium phosphate, D&C Yellow No. 10, FD&C Yellow No. 6, gelatin, iron oxide, lactose, magnesium stearate and titanium dioxide. Energy: 1.5 kJ (0.22 kcal). Bottles of 100.
30 mg: Each yellow capsule, printed with “IONAMIN”, “30”, and “E” in black, contains: phentermine 30 mg as the cationic exchange resin complex. Nonmedicinal ingredients: calcium phosphate, D&C Yellow No. 10, FD&C Yellow No. 6, gelatin, lactose, magnesium stearate, polacrilin potassium and titanium dioxide. Energy: 0.9 kJ (0.013 kcal). Bottles of 100 and 400. (Shown in Product Recognition Section)
IONAMINÂ® RhÃ´ne-Poulenc Rorer Phentermine (Resin Complex) Anorexiant
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