valvular heart disease associated with the use of some anorectic agents such as fenfluramine and dexfenfluramine has been reported. possible contributing factors include use for extended periods of time, higher than recommended dose, and/or use in combination with other anorectic drugs. however, no cases of this valvulopathy have been reported when phendimetrazine tartrate has been used alone. the potential risk of possible serious adverse effects such as valvular heart disease and pulmonary hypertension should be assessed carefully against the potential benefit of weight loss. baseline cardiac evaluation should be considered to detect pre-existing valvular heart diseases or pulmonary hypertension prior to initiation of phendimetrazine treatment. phendimetrazine tartrate is not recommended in patients with known heart murmur or valvular heart disease. echocardiogram during and after treatment could be useful for detecting any valvular disorders which may occur. to limit unwarranted exposure and risks, treatment with phendimetrazine tartrate should be continued only if the patient has satisfactory weight loss within the first 4 weeks of treatment (i.e., weight loss of at least 4 pounds, or as determined by the physician and patient). tolerance to the anorectic effect of phendimetrazine develops within a few weeks. when this occurs, its use should be discontinued; the maximum recommended dose should not be exceeded. use of phendimetrazine tartrate within 14 days following the administration of monoamine oxidase inhibitors may result in a hypertensive crisis. abrupt cessation of administration following prolonged high dosage results in extreme fatigue and depression. because of the effect on the central nervous system, phendimetrazine tartrate 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. phendimetrazine tartrate is not recommended for patients who used any anorectic agents within the prior year.

tients 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 origin of the increased weight loss due to the various drug effects is 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 drug 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. the major route of elimination is via the kidneys where most of the drug and metabolites are excreted. some of the drug is metabolized to phendimetrazine and phendimetrazine-n-oxide. the average half-life of elimination when studied under controlled conditions is about 3.7 hours for both the extended-release and immediate release forms. the absorption half-life of the drug from the immediate release 35 mg phendimetrazine tablets is appreciably more rapid than the absorption rate of the drug from the extended-release formulation.