Interaction of the novel antipsychotic drug amperozide and its metabolite FG5620 with central nervous system receptors and monoamine uptake sites: relation to behavioral and clinical effects

SEEING THROUGH THE MIST: ABUNDANCE VERSUS PERCENTAGE. COMMENTARY ON METABOLITES IN SAFETY TESTING

Recent attention has been given to the potential roles that metabolites could play in safety evaluations of new drugs. In 2002, a proposal was published on "metabolites in safety testing" ("MIST"), which suggested some guidelines regarding when it is necessary to provide greater assessment of the safety of metabolites. However, this proposal was based on relative abundance values, i.e., the percentage that a metabolite comprises of total exposure to drug-related material. In the present commentary, we propose that absolute abundance criteria be used rather than relative abundance. The absolute abundance of a metabolite in circulation or excreta in humans should be combined with other information regarding the chemical structure of the metabolite (e.g., similarity to the parent drug, presence of chemically reactive substituents) and potential mechanisms of toxicity (e.g., suprapharmacological effects, secondary pharmacological effects, nonspecific effects). Decision trees are described that can be used to address human metabolites in safety testing.

A history of antipsychotic drug development

The history of antipsychotic drug development has had a long and torturous course, often based on chance findings that bear little relationship to the intellectual background driving observations. In 1891, Paul Ehrlich observed the antimalarial effects of methylene blue, a phenothiazine derivative. Later, the phenothiazines were developed for their antihistaminergic properties. In 1951, Laborit and Huguenard administered the aliphatic phenothiazine, chlorpromazine, to patients for its potential anesthetic effects during surgery. Shortly thereafter, Hamon et al. and Delay et al. extended the use of this treatment in psychiatric patients and serendipitously uncovered its antipsychotic activity. Between 1954 and 1975, about 15 antipsychotic drugs were introduced in the United States and about 40 throughout the world. Thereafter, there was a hiatus in the development of antipsychotics until the introduction of clozapine treatment in the United States in 1990 opened the era of "atypical" antipsychotic drugs, which show a reduced potential to induce extrapyramidal symptoms (EPS), an increased efficacy for the negative symptoms of schizophrenia, no elevation of prolactin after chronic use (except risperidone), and, at least for clozapine, effectiveness in some patients previously regarded as treatment-refractory. This review describes the available atypical antipsychotic drugs and their characteristics, and concludes by highlighting those in the pharmaceutical "pipeline."

The effects of amperozide on cocaine-induced social withdrawal in rats

Cocaine decreases social interactions in both humans and animals, but it is not known whether the drugged animal withdraws from an undrugged conspecific, the undrugged conspecific avoids the drugged animal, or a combination of these two factors occurs. In the first experiment, the source of cocaine-induced social withdrawal was determined using a tether paradigm, in which the movement of one of the rats was restricted to one half of the observation chamber, such that the freely moving rat had the option of escaping social interactions. There were decreases in social interactions in the condition in which both rats were freely moving, and in the condition in which the undrugged rat was tethered, but not when the drugged rat was tethered and could not escape social contact. A second experiment was conducted to test the efficacy of the potent serotonin receptor antagonist, amperozide, in attenuating cocaine-induced social withdrawal using the condition in which the drugged rat was freely moving. Either amperozide (1.0, 3.0, and 5.0 mg/kg) or saline vehicle was injected into rats 1 h before receiving a 30.0 mg/kg cocaine dose. Cocaine decreased social interactions. Amperozide restored social interactions to near control levels and elevated social interactions in the animals treated with saline vehicle.