A characterization of the acute cardiopulmonary toxicity of fenfluramine in the rat

Cardiotoxic effects of fenfluramine hydrochloride on isolated cardiac preparations and ventricular myocytes of guinea-pigs

The cardiotoxic effects of fenfluramine hydrochloride on mechanical and electrical activity were studied in papillary muscles, Purkinje fibres, left atria and ventricular myocytes of guinea-pigs. Force of contraction (f(c)) was measured isometrically, action potentials and maximum rate of rise of the action potential (V(max)) were recorded by means of the intracellular microelectrode technique and the sodium current (I(Na)) with patch-clamp technique in the cell-attached mode. For kinetic analysis (S)-DPI-201-106-modified Na(+) channels from isolated guinea-pig ventricular heart cells were used. Fenfluramine (1 - 300 microM) produced negative chronotropic and inotropic effects; additional extracellular Ca(2+) competitively antagonized the negative inotropic effect. Fenfluramine concentration-dependently reduced V(max) and showed tonic blockade of sodium channels, shortened the action potential duration in papillary muscles and Purkinje fibres. In cell-attached patches, fenfluramine decreased I(Na) concentration-dependently (10 - 100 microM), frequency-independently (0.1 - 3 Hz; 30 microM). The h(infinity) curve was shifted towards hyperpolarizing direction. At 30 microM, fenfluramine blocked the sodium channel at all test potentials to the same degree, and neither changed the threshold and reversal potentials nor the peak of the curve. No effect on single channel availability, but a significant decrease in mean open times and increase in mean closed times was observed. Mean duration of the bursts decreased and number of openings per record increased with increasing drug concentration. It is concluded that the effect on I(Na) plays an important role in the cardiotoxicity of fenfluramine in addition to primary pulmonary hypertension and valvular disorders.

Glutamatergic involvement in psychomotor stimulant action

The sympathomimetic psychomotor stimulants, including cocaine, amphetamines, and the phenylethylamine amphetamine-like derivatives, exert actions in mammalian systems that implicate involvement of the excitatory neurotransmitter, glutamate and its receptors. Despite evidence that psychomotor stimulants do not directly stimulate glutamate receptors, blockade of acute lethal, convulsive, circulatory, thermoregulatory, locomotor and stereotypical responses, as well as interference with slowly developing behavioral sensitization and brain monoaminergic neurotoxicities, can be achieved by receptor antagonists at both N-methyl-D-aspartate and AMPA/kainate glutamate receptor subtypes. Alterations in glutamatergic neurobiology, including elevations in extracellular glutamate levels, changes in glutamate receptor properties and glutamatergic neuronal degeneration, have also been attributed to psychomotor stimulant administration. Blockade of glutamate receptors offers therapeutic options in management of psychomotor stimulant toxicity.

High altitude may be synergistic with pulmonary hazards of appetite control medications fenfluramine and dexfenfluramine

Clinical observations over the past 15 years incriminated first fenfluramine and recently dexfenfluramine in the provocation of primary pulmonary hypertension. Limited animal toxicology data tend to support this inference. The basis for respiratory pathology of high-altitude pulmonary malfunction, which reaches its maximal level in high-altitude pulmonary edema, evolves from and depends upon the occurrence of pulmonary hypertension. For this reason we hypothesize that high altitude and these two anorexic medications constitute a potentially synergistic combination, of which physicians treating patients for high-altitude illness, as well as those prescribing the drugs, should be aware.

Appetite suppressants and primary pulmonary hypertension in the United Kingdom

OBJECTIVE

Amphetamine-like appetite suppressants, particularly fenfluramines, have been implicated in the aetiology of primary pulmonary hypertension. At one specialist centre in France 20% of patients with primary pulmonary hypertension had been exposed to fenfluramine. The prevalence of primary pulmonary hypertension associated with fenfluramines and other appetite suppressants in the United Kingdom is unknown. This study was performed to measure prior exposure to appetite suppressants in patients with primary pulmonary hypertension.

SETTING

Heart lung transplantation centres in England.

PATIENTS

United Kingdom residents with proven primary pulmonary hypertension referred for consideration of heart lung transplantation.

METHODS

Case surveillance study, obtaining data from the hospital and general practitioner's notes and directly from the patients or their relatives.

RESULTS

55 patients were identified. Drug histories were available from hospital records in all patients, from the general practitioner's notes in 51, and from the patients or relatives in 44. Of these, 3 female patients had been exposed to appetite suppressants (2 fenfluramine, 1 diethylpropion): 2 have since died. In each case exposure was brief and apparently predated the development of symptoms by several years.

CONCLUSIONS

Exposure of patients with severe primary pulmonary hypertension to fenfluramine and other appetite suppressants is uncommon in the United Kingdom unlike in France, where most of the cases associating primary pulmonary hypertension with fenfluramine use have originated. This may reflect more conservative prescribing of these agents in the United Kingdom.

Primary pulmonary hypertension and fenfluramine use

Not all the risk factors for primary pulmonary hypertension (PPH) are known. Appetite suppressants, including fenfluramine derivatives, are strongly suspected aetiological agents. In a 5 year retrospective study fenfluramine use was evaluated among patients referred to a medical centre specialising in the management of PPH. Fifteen (20%) of 73 patients with PPH had used fenfluramine: all of them were women and in 10 (67%) there was a close temporal relation between fenfluramine use and the development of exertional dyspnoea. Initial right heart catheterisation in the 15 women showed severe resting pulmonary hypertension (mean (SD)) with pulmonary artery pressure (PAP) 57 (9) mm Hg, cardiac index 2.1 (0.5) l/min/m2, and pulmonary vascular resistance (PVR) 29 (10) U/m2. Short-term epoprostenol infusion produced a significant vasodilator response in 10 patients (mean fall in PVR 24 (15%) compared with control values). Three fenfluramine users with PPH showed spontaneous clinical and haemodynamic improvement 3, 6 and 12 months after drug withdrawal but there was no significant difference in overall survival (transplant recipients excluded) between fenfluramine users and controls. Histological examination of lung tissue from five women who had used fenfluramine and 22 controls, with PPH showed features typical of advanced plexogenic pulmonary arteriopathy in all. These results do not accord with earlier reports that PPH associated with fenfluramine is less severe and has a better outcome. Fenfluramine may be one aetiological agent that can precipitate or hasten the development of PPH. The results of a European case-control study should give new insights into risk factors for PPH and the cause and effect relation with fenfluramine.