Drug Interactions between benzphetamine and dextromethorphan / phenylpropanolamine

CONTRAINDICATED: The efficacy of centrally-acting appetite suppressants in combination with other anorectic agents has not been studied, but available data suggest that combined use may have the potential for serious cardiac problems. In a case-control epidemiological study, the use of anorectic agents was associated with an increased risk of pulmonary hypertension, a rare but often fatal disorder, and use for longer than three months was associated with a 23-fold increase in risk. Increased risk of pulmonary hypertension with repeated courses of therapy cannot be excluded. The use of some anorectic agents such as fenfluramine and dexfenfluramine has been associated with valvular heart disease. Possible contributing factors include use for extended periods of time, higher than recommended dosages, and/or use in combination with other anorectic drugs.

MANAGEMENT: Centrally--acting appetite suppressants should not be used in combination with other anorectic agents, including prescription, over-the-counter, and herbal preparations. In addition, they are not recommended for patients who have used any anorectic agents within the prior year. The potential risk of possible serious adverse effects such as valvular heart disease and pulmonary hypertension should be assessed carefully against the benefit of weight loss, and baseline cardiac evaluation should be considered to detect preexisting valvular heart diseases or pulmonary hypertension prior to initiating treatment. These agents are not recommended for use in patients with known heart murmur or valvular heart disease, severe hypertension, or symptomatic cardiovascular disease including arrhythmias. Patients should be advised to immediately discontinue the medication and contact their physician if they experience potential signs and symptoms of pulmonary hypertension such as new onset or aggravation of exertional dyspnea, chest pain or tightness, syncope, and lower extremity edema.

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MONITOR: Coadministration of amphetamines and amphetamine-like drugs with other agents that also increase serotonin levels or effects, may increase the risk of serotonin syndrome. The exact mechanism by which serotonin levels are increased differs depending on the specific medication(s) involved. Serotonin syndrome is believed to result from the hyperstimulation of postsynaptic 5-HT receptors and while postsynaptic 5-HT1A and 5-HT2A receptors are usually implicated, it is more likely that no single receptor is solely responsible. Clinical data are limited. Serotonin syndrome involving amphetamines has most frequently been reported with the use of MDMA, or ecstasy, an amphetamine derivative with enhanced serotonergic activity over classical amphetamines, which tend to be more dopaminergic. However, case reports of serotonin syndrome involving amphetamines and amphetamine-like drugs have been documented with concomitant use of other serotonergic substances (e.g., selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, monoamine oxidase inhibitors). Abuse and/or overdose may increase the risk of experiencing this adverse effect.

MANAGEMENT: Caution is recommended when amphetamines and amphetamine-like drugs are used with other agents that also increase serotonin levels or effects. Initiating patients with lower doses and ensuring close clinical monitoring for signs and symptoms of serotonin syndrome (e.g., altered mental status, hypertension, restlessness, myoclonus, hyperthermia, hyperreflexia, diaphoresis, shivering, tremor) is advised. Particular caution is recommended when increasing the dosages of these agents. If serotonin syndrome develops or is suspected during the course of therapy, all serotonergic agents should be discontinued immediately, and treatment rendered as indicated.

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