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Phentermine (Duromine) 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 have not been established. Therefore, coadministration of drug products for weight loss is not recommended. Since the selective serotonin reuptake inhibitors (e.g., fluoxetine, sertraline, paroxetine), ergot-like drugs and clomipramine affect serotonin disposition there remains a theoretical risk that combination of these agents with phentermine may also be associated with cardiac valvular disease and is not recommended. There is no direct scientific evidence to confirm this theory.
Valvular Heart Disease: Serious regurgitate 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 fenfluramine or dexfenfluramine with phentermine for weight loss. The aetiology 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 valvular heart disease occurring with the use of phentermine alone.
Primary Pulmonary Hypertension (PPH): Cases of severe, sometime fatal primary pulmonary hypertension, have been reported in patients who have received anorectics. In a case-control epidemiological study, the duration of treatment with anorectic agents, not including phentermine, beyond three months significantly increases the risk of PPH. However, patients treated with phentermine require medical review at least every 3 months (Refer to "Dosage & Administration"). PPH has been reported in patients receiving fenfluramine/dexfenfluramine combined with phentermine. The possibility of an association between PPH and the use of phentermine alone cannot ruled out; there have been very rare cases of PPH in patients who reportedly have taken phentermine alone. The initial symptom of PPH is usually dyspnoea. Other early symptoms include: angina pectoris, syncope, lower extremity oedema or the unexplained onset or aggravation of diminished exercise tolerance. Under these circumstances, treatment should be immediately discontinued and the patient referred to a specialist unit for investigation.
Use with caution in the following circumstances: Phentermine (Duromine) should be used with caution in patients with mild hypertension. In the first days of treatment, determine that there is no loss of blood pressure control. In patients receiving Phentermine (Duromine), response to insulin and oral hypoglycaemic agents may vary due to alterations in dietary regimes. This should be kept in mind if Phentermine (Duromine) is used in diabetic patients. Phentermine (Duromine) may impair the ability to perform activities requiring mental alertness, such as driving and operating machinery, and patients therefore should be cautioned accordingly. Inappropriate use has been reported with similar drugs and the possibility of this occurrence should be considered with Phentermine (Duromine). Cardiovascular and cerebrovascular events have rarely been reported, mainly in association with rapid weight loss. Weight loss should be gradual and controlled in obese patients undergoing treatment with Phentermine (Duromine).
Phentermine (Duromine) should be used with caution in patients with established coronary artery disease. A single case of exacerbation of angina pectoris in a patient with established coronary artery disease has been reported. Phentermine (Duromine) should be used with caution in patients receiving psychotrophic drugs, including sedatives and agents with sympathomimetic activity. Phentermine (Duromine) should be used with caution in epileptic patients. Phentermine (Duromine) should be used with caution in patients receiving anti-hypertensive agents.
Effects on Laboratory Tests: There are no reports to-date to suggest that phentermine interferes with laboratory or diagnostic tests.
Carcinogenicity, Mutagenicity, Impairment of Fertility: Phentermine was not mutagenic in a bacterial gene mutation assay, however, studies to assess the potential for chromosomal damage have not been performed. No studies have been performed to determine the potential of phentermine for carcinogenesis. In rats, administration of phentermine at a dose 10 times the maximum human dose on a mg/m2 basis abolished oestrous cycling. There is no information on the potential of phentermine to impair fertility in humans.
Use in Pregnancy: Weight reduction using appetite suppression drugs is not recommended during pregnancy. In rats, administration of phentermine during late gestation at a dose 7 times the maximum human dose on a mg/m2 basis had no adverse effects on dams or offspring. There is no information on the teratological potential of phentermine. Because of inadequate evidence of safety in human pregnancy, Phentermine (Duromine) should not be used in pregnant women.
Use in Lactation: There is no data available on the safety of Phentermine (Duromine) in lactation and as such, its use in lactating women should be avoided.
