Toxicologic studies of fenfluramine

A resurging boom in new drugs for epilepsy and brain disorders

INTRODUCTION

Epilepsy is one of the most common neurological diseases affecting approximately 50 million people worldwide. Despite many advances in epilepsy research, nearly a third of patients with epilepsy have refractory or pharmacoresistant epilepsy. Despite the approval of a dozen antiepileptic drugs (AEDs) over the past decade, there are no agents that halt the development of epilepsy. Thus, newer and better AEDs that can prevent refractory seizures and modify the disease are needed for curing epilepsy. Areas covered: In this article, we highlight the recent advances and emerging trends in new and innovative drugs for epilepsy and seizure disorders. We review in detail top new drugs that are currently in clinical trials or agents that are under development and have novel mechanisms of action. Expert commentary: Among the new agents under clinical investigation, the majority were originally developed for treating other neurological diseases (everolimus, fenfluramine, nalutozan, bumetanide, and valnoctamide); several have mechanisms of action similar to those of conventional AEDs (AP, ganaxolone, and YKP3089); and some new agents represent novel mechanisms of actions (huperzine-A, cannabidiol, tonabersat, and VX-765).

Progress report on new antiepileptic drugs: A summary of the Thirteenth Eilat Conference on New Antiepileptic Drugs and Devices (EILAT XIII)

The Thirteenth Eilat Conference on New Antiepileptic Drugs and Devices (EILAT XIII) took place in Madrid, Spain, on June 26-29, 2016, and was attended by >200 delegates from 31 countries. The present Progress Report provides an update on experimental and clinical results for drugs presented at the Conference. Compounds for which summary data are presented include an AED approved in 2016 (brivaracetam), 12 drugs in phase I-III clinical development (adenosine, allopregnanolone, bumetanide, cannabidiol, cannabidivarin, 2-deoxy-d-glucose, everolimus, fenfluramine, huperzine A, minocycline, SAGE-217, and valnoctamide) and 6 compounds or classes of compounds for which only preclinical data are available (bumetanide derivatives, sec-butylpropylacetamide, FV-082, 1OP-2198, NAX 810-2, and SAGE-689). Overall, the results presented at the Conference show that considerable efforts are ongoing into discovery and development of AEDs with potentially improved therapeutic profiles compared with existing agents. Many of the drugs discussed in this report show innovative mechanisms of action and many have shown promising results in patients with pharmacoresistant epilepsies, including previously neglected rare and severe epilepsy syndromes.

Pregnancy outcomes after first trimester exposure to phentermine/fenfluramine

BACKGROUND

Fenfluramine was withdrawn from the U.S. market in 1997 because of its association with cardiac-valve abnormalities in adults. The combination of fenfluramine and phentermine had been widely used to promote weight loss, and many women were inadvertently exposed during the first trimester of pregnancy. The possible effect on the developing fetus has not been studied.

METHODS

Controlled prospective cohort study comparing 98 women who had taken phentermine/fenfluramine to 233 women who had not, all of whom contacted the California Teratogen Information Service during pregnancy.

RESULTS

The proportion of liveborn infants with major structural anomalies was similar in the two groups (3.6% vs. 1.0%, relative risk (RR) 3.59; 95% confidence interval (CI) 0.61, 21.10), as was the proportion of infants with >or=3 minor anomalies (11.7% vs. 7.6%, RR 1.53; 95% CI 0.61, 3.82). Furthermore, no pattern of malformation was identified. There were no significant differences between the groups in spontaneous pregnancy loss (6.1% vs. 8.2%, P = 0.65) or premature delivery (8.6% vs. 7.7%, P = 0.95). Birth weight and head circumference were significantly increased in the exposed group; however, these differences were not associated with anorexiant use itself. The rate of gestational diabetes was significantly increased in pregnant women who took phentermine/fenfluramine during the first trimester of pregnancy.

CONCLUSIONS

Although it is not possible from this study to rule out weak to moderate associations, the lack of an increased risk of spontaneous pregnancy loss, and major or minor anomalies in the offspring of women who took phentermine/fenfluramine at the recommended daily dose during the first trimester of pregnancy is reassuring.

Impact of antenatal exposure of mice to fenfluramine on cardiac development and long-term growth of the offspring

The objective of this investigation was to determine, in a placebo-controlled manner, whether antenatal exposure to formulations of fenfluramine and dexfenfluramine impacted cardiac development and long-term growth of exposed mice offspring. One hundred forty-four CD-1 mice were randomized to six treatment groups (n=23 or 25) to obtain, per group, 5 gravids for killing on gestational day (GD) 15 and < or =10 deliveries for assessing growth of the offspring. Either fenfluramine preparation was administered in feed bars in two doses: 1 and 3.2 times the equivalent human daily dosage according to body surface area. The drugs were given from 2 weeks before mating until GD 15. The mice ingested each drug at target values, averaging 10.5+/-0.3 and 31.8+/-1.9 mg/kg/d for fenfluramine and 5.0+/-0.2 and 16.2+/-0.4 mg/kg/d for dexfenfluramine. The drug concentration was about 36% in the fetal brain compared with the adult brain. The maternal and the offspring hearts, including mitral and aortic valves, of fenfluramine-exposed mice were indistinguishable from the placebo-exposed mice. The duration of gestation and the litter size were the same between the treatment groups. The mean body weights, body lengths, and head circumferences and early functional testing did not differ significantly between the fenfluramine or dexfenfluramine-exposed offspring and the placebo-exposed offspring. There were no significant treatment differences in growth measured as body weights to PND 120. Neither fenfluramine formulation, given before conception and during gestation, impacted cardiac development and long-term growth of the mice offspring.

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.

A study of the neurotoxic effect of MDMA ('ecstasy') on 5-HT neurones in the brains of mothers and neonates following administration of the drug during pregnancy

1. It is well established that 3,4-methylenedioxymethamphetamine (MDMA or 'ecstasy') is neurotoxic and produces long term degeneration of cerebral 5-hydroxytryptamine (5-HT) nerve terminals in many species. Since MDMA is used extensively as a recreational drug by young people, it is being ingested by many women of child bearing age. We have therefore examined the effect of administering high doses of MDMA to rats during pregnancy on the cerebral content of both the dams and the neonates. 2. MDMA (20 mg kg-1, s.c.) was injected twice daily on days 14-17 of the gestation period. The initial dose produced a marked hyperthermic response in the dam which was progressively attenuated in both peak height and area under the curve following further doses of the drug. The body weight of the dams decreased during the period of treatment. 3. There was a modest decrease in litter size (-20%) of the MDMA-treated dams. 4. The concentration of 5-HT and its metabolite 5-HIAA was decreased by over 65% in the hippocampus and striatum and 40% in the cortex of the dams 1 week after parturition. In contrast, the content of 5-HT and 5-HIAA in the dorsal telencephalon of the pups of the MDMA-treated dams was the same as that seen in tissue from pups born to control animals. 5. Administration of MDMA (40 mg kg-1, s.c.) to adult rats increased thiobarbituric acid reacting substances (TBARS) in cortical tissue 3 h and 6 h later, indicating increased lipid peroxidation. No increase in TBARS was seen in the cortical tissue of 7-10 day neonates injected with this dose of MDMA 3 h or 6 h earlier. 6. The data suggest that exposure to MDMA in utero during the maturation phase does not produce damage to 5-HT nerve terminals in the foetal rat brain, in contrast to the damage seen in the brains of the mothers. This may be due to MDMA being metabolized to free radical producing entities in the adult brain but not in the immature brain or, alternatively, to more effective or more active free radical scavenging mechanisms being present in the immature brain.

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

Fenfluramine (FN) is a potent serotonin-releasing drug used primarily as an anorectic agent. The symptomatology of its acute lethality has been well documented in animal models such as the rat. A very prominent feature of this lethality profile is hypoxia, as demonstrated by the onset of severe cyanosis just prior to death. It is not clear in the literature whether this hypoxia is the result of a direct pulmonary effect or is secondary to cardiac injury. To further characterize this aspect of FN's toxicity, respiratory and electrocardiographic measurements were taken in anaesthetized rats subjected to high doses of FN (129.6 mg/kg, i.p.). Death occurred in these animals within 15 min of drug administration, apparently as the result of abrupt respiratory cessation, followed by cardiac ischaemia. No significant gross or histopathological lesions were evident in these animals. In other trials, prior treatment with diethylcarbamazine (DEC) was found to potentiate the lethality of FN, while cyproheptadine (CHP) pretreatment attenuated FN's toxic effects. Necropsies, conducted 24 h after FN administration, revealed widespread alveolar and pulmonary interstitial haemorrhage in the CHP-pretreated animals. The data suggest that high doses of FN directly result in pulmonary hypertension, which secondarily induces ischaemic cardiac injury.

The effect of previous d-amphetamine treatment on the disposition and lethality of fenfluramine in the rat

In an earlier study, it was found that a 15-day ip postfeeding session d-amphetamine treatment rendered an apparent "tolerance" to the feed intake suppressant effects of fenfluramine. The purpose of the present study was to determine if such d-amphetamine treatment altered the disposition of fenfluramine in a way which might account for this decrement in the feed intake suppressant effect of fenfluramine. In addition, the effect of d-amphetamine on fenfluramine toxicity was also examined in an attempt to further characterize and correlate fenfluramine dispositional changes. It was found that plasma and, to some extent, brain concentrations of fenfluramine were elevated in the d-amphetamine-treated rats as compared to a saline control group. The acute, ip LD50 for fenfluramine in d-amphetamine-treated rats was 68 mg/kg (95% CI = 64.8 to 71.4), a value significantly lower than that observed in the saline-treated animals (97 mg/kg; 95% CI = 93.3 to 100.9). The overall results of this study suggest that the anorectic tolerance conferred toward fenfluramine by previous subchronic treatment with d-amphetamine does not result from decreased plasma or brain concentrations of fenfluramine. In fact, such concentrations are increased by prior d-amphetamine treatment, and this increase may in part account for the increased lethality of fenfluramine observed in these animals.

Psychotropic drugs as behavioral teratogens

Three psychotropic drugs were administered to pregnant rats and were then evaluated for their behavioral and reproductive effects in the offspring. Control rats received either saline or vitamin A. Prochlorperazine had the most disruptive effects on reproduction and growth, but had the least effect on behavior. Propoxyphene had no apparent effects on reproduction or growth, but produced a variety of behavioral changes. Fenfluramine was intermediate in its effects on reproduction and growth and had behavioral effects that were revealed in tests of preweaning development. The data suggest that systematic tests of behavior add important information to evaluations of reproductive toxicity that cannot, at present, be obtained by other means.

Fenfluramine poisoning

In a series of 53 fenfluramine intoxications (15 taken from the literature), 10 were lethal after doses of 28.7--70 mg/kg of body weight. Cardiac arrest occurred 1--4 hr after ingestion in 9 cases; all these 9 patients died. Two out of 3 patients with more than 15 mg/kg had coma and convulsions. Other frequent signs were mydriasis, tachycardia, and rubor of the face. The additional signs of nystagmus, hypertonia, trismus, hyperreflexia, clonus, excitation, hyperthermia, and sweating define the clinical syndrome of fenfluramine intoxication. Symptoms begin 30--60 min after ingestion and can persist during several days. Early gastric lavage, instillation of activated charcoal, diazepam in case of seizures, chlorpromazine for malignant hyperthermia, propranolol for extreme tachycardia, and lidocaine in the event of ventricular extrasystoles are recommended. If trismus is a prominent sign, muscle relaxants must be given before gastric lavage can be done. The relatively benign course after survival of the first 4 hr suggests supportive therapy only in the later phase of intoxication.

Tolerance and cross-tolerance to the effects of amphetamine, methamphetamine and fenfluramine on milk consumption in the rat

It has been reported that rats develop tolerance to the milk intake suppressant effects of d-amphetamine, d-methamphetamine, and d, l-fenfluramine. However, it has been hypothesized that the mechanism of action of fenfluramine is different from that of the other two drugs. In the present experiment, rats were given one of these 3 phenylethylamine derivatives each day until tolerance developed to the suppression of milk intake. A second of these drug s was then substituted and milk intake measured. There was cross-tolerance to the drug-induced suppression between d-amphetamine and d-methamphetamine, but not between d-amphetamine and d,l-fenfluramine. The lack of cross tolerance suggests a different mechanism of action for these drugs.