Clinical trials of new antipsychotics: a critical appraisal

In recent years the efficacy of new antipsychotics has been investigated through a number of randomized controlled trials. This paper considers some methodological flaws that affect these studies and proposes possible solutions. The final goal is the implementation of a new generation of trials with the aim of demonstrating superiority of effect of the new antipsychotic over the reference one.

Antidepressant drug use in Italy since the introduction of SSRIs: national trends, regional differences and impact on suicide rates

Little is known about the use of antidepressant drugs in Italy since the introduction of selective serotonin reuptake inhibitors (SSRIs). To fill this gap, we examined antidepressant drug sales data from 1988 to 1996 for the whole country, and for the years 1995 and 1996 on the regional level. National suicide trends from 1988 to 1994 were also examined to assess whether the increasing use of SSRI antidepressants was associated with changes in suicide rates. From 1988 to 1996 an increase of antidepressant sales of 53% was recorded. This increase reflected increasing use of SSRIs, which in 1996 accounted for more than 30% of total antidepressants sold. The analysis of regional differences demonstrated heterogeneity between north, center, and south. In the south prescriptions of antidepressants and use of SSRIs were lower than in the rest of the country. In the 7-year period over which SSRI use increased, male suicide rates increased from 9.8 to 10.2 per 100,000 inhabitants, and female suicide rates declined from 3.9 to 3.2 per 100,000. These data suggest that SSRIs gave a new impetus to antidepressant sales. However, possible public health benefits related to the shift from old to new antidepressants have yet to be demonstrated.

Antidepressant agents: from tricyclics to serotonin uptake inhibitors

BACKGROUND

The number of antidepressant drugs available in the market has grown rapidly in the last few years. The present paper underlines some of the pre-clinical and clinical problems that call close attention from the regulatory authorities when approving new drugs.

METHODS

We present here a review of the literature.

RESULTS

A wide heterogeneity in the action of the various antidepressants precludes any single theory about the pathogenesis and therapy of depression. Antidepressant activity, in fact, may be achieved by acting on a number of different monoaminergic mechanisms. The variety in the neurochemical effects of antidepressants is not reflected in clinical trials, which tend to stereotypy. In many cases clinical trials aim at demonstrating equivalence rather than differences in efficacy. Regulatory authorities should, therefore, pay attention in accepting the equivalence of effects of a new drug in relation to a reference one: most clinical trials of new antidepressant drugs do not have the power to detect clinically relevant differences.

CONCLUSIONS

Unconventional new pre-clinical tests are needed to generate antidepressants with a different mechanism of action. Clinical studies are needed to promote objective comparative evaluation of the cost, benefits and toxic effects of new antidepressants.

The drug market in four European countries

Prescription drugs should be therapeutically validated products which are selected for the treatment of accurately diagnosed diseases according to the principles of evidence-based medicine. However, industrial promotion of pharmaceuticals has meant that drug prescription patterns are not always concordant with these ideals. For example, consideration of the most sold drugs in 4 European countries--Italy, France, Germany and the United Kingdom--in 1992 and 1996 shows that marked variations in the utilisation of therapeutic classes, single active principles, and even routes of administration of the same active principles exist in these countries. To some extent, these differences reflect the influence of promotion by national pharmaceutical companies, but they also arise from other factors, such as the lack of adequate pharmacological training of physicians, the paucity of reliable comparative clinical data to allow clinicians to distinguish between large numbers of more expensive 'me-too' drugs and their prototypes, and the idiosyncrasies of national drug approval and registration systems. In addition, differences in prices across countries as well as the length of time a drug has been on the market may be contributing factors. It is hoped that the creation in 1995 of the European Medicines Evaluation Agency (EMEA), which is working towards centralisation of drug marketing approval in the European Union (EU), will usher in the establishment of a common pharmaceutical culture that will combat some of the variations and inconsistencies in drug prescribing patterns evident in European countries. Adoption of such evidence-based and more rational prescribing patterns should not only reduce the number of unnecessary and perhaps undesirable prescriptions written for patients but also relieve the financial burden on national health services in EU countries.

Are me-too drugs justified?

The successful progress of pharmacology in the treatment of several diseases has led to the development of a powerful pharmaceutical industry with an estimated market of over $250 billion. It is therefore understandable that as drug development and marketing has become a major business it has adopted the rules common to other commercial fields. This is a potentially dangerous trend because it undermines what should be the main goal of drug development, i.e. to make active medicinal agents available to the patient with precise and reliable information, at the lowest possible cost, particularly when a national health system has to supply the drugs to patients who have too low an income to pay for them. The huge drug market has also set in motion a competition among pharmaceutical firms. This has meant that as soon as a prototype drug becomes available several other similarly active compounds immediately follow. These followers are usually called "me-too drugs". Me-too drugs can be broadly defined as chemically related to the prototype, or other chemical compounds which have an identical mechanism of action. This increasing marketing of me-too drugs has been questioned, so pharmaceutical firms are justifying the development of not-so-innovative drugs. The most common arguments can be summarized as follows: me-too drugs offer an improvement on the efficacy of the prototype; they show a different profile of adverse effects; they are effective in patients resistant to the prototype; they improve compliance in long-term treatment; they are less expensive than the prototype. It is the purpose of this paper to review the evidence substantiating these statements, giving some figures regarding me-too drugs and presenting a few examples.

Neuropharmacological effects of low and high doses of repeated oral dexfenfluramine in rats: a comparison with fluoxetine

The neuropharmacological effects of repeated oral doses of dexfenfluramine (DF; 1.25-10 mg/kg, twice daily for 21 days) were examined in rats and related to the drug brain levels. Results were compared with fluoxetine (FL) given at similar doses relative to its anorectic ED50. Both drugs dose-dependently slowed body weight gain and reduced brain serotonin (5-HT). However, at 1.25 mg/kg DF caused only a slight and transient decrease in cortical 5-HT. Comparable doses of FL (6.25-12.5 mg/kg) lowered 5-HT more than DF, besides slightly reducing striatal dopamine. At higher doses DF markedly reduced 5-HT in all regions, and to a lesser extent noradrenaline in hippocampus. There was a negative relationship between 5-HT and log total active drug levels and the indole was approximately halved at drug levels about 50 times lower with DF than FL. However, the ratio between drug levels causing marked 5-HT reductions and those considered anorectic was similar for DF and FL because brain levels at the anorectic ED50 were higher with FL than DF. Long-lasting reductions of 5-HT were also observed but recovery was only consistently slow beginning from 5 mg/ kg DF. Comparable doses of FL could not be used because its general toxicity leads to the death of rats after only 2-4 multiples of its anorectic ED50.

Pharmacology of amineptine, an antidepressant agent acting on the dopaminergic system: a review

Amineptine is a tricyclic antidepressant agent with a unique capacity to reduce dopamine uptake selectively in vitro: this effect is also obtained in vivo. In vivo, amineptine increases striatal homovanillic acid without affecting the levels of other metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and 3-methoxytyramine. However, relatively high doses of amineptine preferentially lower the extracellular DOPAC level, assessed by pulse voltammetry, in the nucleus accumbens but not in the striatum. Microdialysis techniques confirm an increase in extracellular dopamine in various brain areas (striatum, nucleus accumbens and frontal cortex) and an increase in extracellular noradrenaline in the frontal cortex and dorsal hippocampus. Chronic treatment with amineptine induces downregulation of dopamine D2, beta- and alpha 2-adrenergic receptors. Amineptine enters the brain and its pharmacological effects are probably induced by the unchanged drug, rather than its two main metabolites.

Mechanism of inhibition of tumor necrosis factor production by chlorpromazine and its derivatives in mice

In previous work, we reported that chlorpromazine inhibits tumor necrosis factor (TNF) production in endotoxin lipopolysaccharide-treated mice, and protects against lipopolysaccharide toxicity. Chlorpromazine is used as an antipsychotic and has several effects on the central nervous system. It acts on different neurotransmitter receptors and has other biochemical activities some of which, like inhibition of phospholipase A2, might be responsible for the inhibitory effect on TNF production. To investigate the role of these actions in the inhibition of TNF production by chlorpromazine, we have synthesized some chlorpromazine derivatives that do not have central activities. Some of these analogs have lost their affinity for various receptors and their phospholipase A2 inhibitory activity, but still inhibit TNF production. No correlation was found between TNF inhibition and the ability to inhibit nitric oxide (NO) synthase, whereas a good correlation was evident between TNF inhibition and antioxidant activity.

In vitro and in vivo effects of the anorectic agent dexfenfluramine on the central serotoninergic neuronal systems of non-human primates. A comparison with the rat

The effects of repeated subcutaneous (s.c) injections of dexfenfluramine (d-F; 10 mg/kg, twice daily, for 4 days) on the contents of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the brain were assessed in primates (cynomolgus and rhesus monkeys) and compared with the regional brain concentrations of unchanged drug and its active metabolite, dexnorfenfluramine (d-NF). This four-day, high-dose, regimen caused a large depletion of 5-HT (more than 95%) and of 5-HIAA (80-90%) in all brain areas studied (cortex, hippocampus, putamen, caudate nucleus and hypothalamus) 2 h after the last injection of d-F. Analysis of the plasma and brain contents of d-F and d-NF confirmed that both compounds were concentrated as in other species, in regions of the primate brain. However, d-NF was concentrated to a greater extent than d-F, and there were differences between the two primate species. Unlike in the rat brain, concentrations of d-NF greatly exceeded those of d-F in the primate brain suggesting that in these primates the d-NF may play a major role in the overall neurochemical response. The effects of d-F and d-NF on different in vitro parameters of serotoninergic neuronal function did not show appreciable differences between cynomolgus or rhesus monkeys when compared to rats, the ability of the two compounds to inhibit 5-HT reuptake, to enhance its release, and to affect the binding of [3H] -d-F or of [3H] -mesulergine (a ligand for 5-HT2C receptors) being similar. Kinetic differences in the disposition of d-F appear to have more relevance than biochemical effects in providing an explanation for the more marked brain depletion induced by d-F in primates than in rodents.

Pharmacology of ingestive behaviour

We have attempted to provide a progress report on current research on the role of catecholamines and serotonin receptor subtypes in feeding control. Recent evidence suggests that only some of the several catecholamine receptor subtypes are specifically involved in feeding control. They include the beta 1/2-adrenoceptors, the alpha 1-adrenoceptors and the D1 dopamine receptors: stimulation of these receptors reduces feeding in rats. Stimulation of serotonergic 5-HT1B and 5-HT2C receptors reduces feeding and perhaps enhances the satiating effect of food. Recently, an interesting reciprocal relation between serotonin and cholecystokinin has been discovered in relation to feeding control. The serotonergic 5-HT2A receptors are involved in stress-induced anorexia and regulate the hyperphagia induced by neuropeptide Y in the nucleus paraventricularis of the hypothalamus. Both effects may involve changes in the secretion of corticotropin-releasing factor. These findings may help elaborate neuronal models of feeding control and perhaps facilitate progress in the pharmacotherapy of human obesity and eating disorders.

Depletion and time-course of recovery of brain serotonin after repeated subcutaneous dexfenfluramine in the mouse. A comparison with the rat

The indole-depleting effects of repeated subcutaneous doses of dexfenfluramine (D-F) (2.5, 5, 10, 20 and 40 mg/kg/day, for four days) in mice were examined with regard to the initial response and time-course of recovery and related to the pharmacokinetics of D-F and its active metabolite dexnorfenfluramine (D-NF). Steady-state plasma and brain concentrations of D-F rose dose-dependently with a metabolite-to-drug ratio averaging 0.4 in brain. This confirmed that in mice D-NF contributes less than in other species to the effects of D-F. Regional serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) contents were decreased dose-dependently 4 hr after the last injection of D-F. However, two weeks after D-F (2.5-10 mg/kg/day) brain indoles had almost totally recovered, and the long-term effects of the 20 mg/kg/day dose were completely reversed by six weeks, when significant effects are still observable in rats. Although substantial recovery was evident even at 40 mg/kg/day, 5-HT but not 5-HIAA was still slightly reduced nine weeks later. Comparative studies in rats given 2.5-20 mg/kg/day D-F indicated much more severe initial indole depletions than in mice. Brain levels of D-F and D-NF were much higher in rats than in mice. The total active drug brain concentration (D-F + D-NF) was significantly correlated with 5-HT content in both species, with approx 20 nmol/g of total drug causing 50% reduction. These findings point to species differences in D-F kinetics as a main reason for differences in the neurochemical response, supporting the view that the recovery of indoles over time is related to the extent of initial depletion, which in turn depends on critical drug brain concentrations. In view of the qualitative and quantitative species differences in the pharmacodynamics and pharmacokinetics of D-F neither of these rodent species is a suitable model for predicting potential drug toxicity in humans.

Biological actions of drugs affecting serotonin and eating

The present status of knowledge on drugs affecting food intake and presumably acting via a serotoninergic mechanism is reviewed. The mechanism of action of these drugs is analyzed at the neurochemical level. All the drugs, to various extents, inhibit the uptake of serotonin (5HT), increase the release of 5HT and decrease brain levels of 5HT and 5HIAA. However, the underlying mechanisms are not identical as exemplified by comparisons made with d-fenfluramine, d-norfenfluramine, fluoxetine, sertraline and paroxetine. An analysis of the role of 5HT in the inhibition of food intake reveals that only d-fenfluramine is inhibited by antiserotonin agents. The role of the different 5HT receptor-subtypes in this antagonism is discussed. More selective 5HT antagonists are needed to establish which 5HT receptor(s) controls food intake.

Oral kinetics of dexfenfluramine and dexnorfenfluramine in non-human primates

1. Large doses of dexfenfluramine in animals cause a decrease of serotoninergic markers but none of the species so far investigated shows sufficient kinetic and metabolic similarity with man to be a valid model for safety studies. The plasma kinetics of dexfenfluramine and its active metabolite dexnorfenfluramine were therefore studied in baboon, rhesus and cynomolgus monkeys given dexfenfluramine hydrochloride orally (2 mg/kg) in order to investigate whether any of these primates have a biodisposition particularly similar to man. 2. The drug was rapidly N-deethylated to dexnorfenfluramine achieving comparatively low mean maximum plasma levels (Cmax) of 12-14 ng/ml in all primates, and rapidly disappeared thereafter with half-lives (t1/2) ranging from 2 to 3 h in the baboon and rhesus monkey to 6 h in the cynomolgus monkey. Its normetabolite reached higher mean Cmax (52-97 ng/ml) and the t1/2's were longer, varying from about 11 h in the rhesus monkey to 22 h in the cynomolgus monkey. The metabolite-to-parent drug ratio (14-37), in terms of plasma area under curve (AUC), greatly exceeded that in man (< 1), being higher than in all species investigated so far. 3. Comparative repeat dose simulation in monkey and man indicated that the dosage in primates would need to be increased 10-fold to achieve comparable dexfenfluramine steady-state plasma Cmax, producing nor-metabolite levels several times those in man, whilst for comparable metabolite Cmax, those of the parent drug would be correspondingly too low. 4. In view of the different mechanism of action of dexfenfluramine and dexnorfenfluramine within the serotoninergic system none of these primates is therefore a suitable model for safety assessment in terms of exposure of the active moieties in comparison with man.