| 毒性の概要 | IDENTIFICATION AND USE: Mefloquine is a white or slightly yellow crystalline powder that is formulated into tablets. Mefloquine is an antimalarial agent which acts as a blood schizonticide. It is used for the prevention and treatment of malaria caused by strains of Plasmodium falciparum or P. vivax. HUMAN EXPOSURE AND TOXICITY: Overdosage of mefloquine produces manifestations that are similar to the adverse reactions reported with the drug. Vertigo, hallucinations, dizziness, nausea, hypotension, tachycardia, and seizures occurred in 2 patients who ingested an overdosage of mefloquine (up to 5250 mg over 5 days). Since seizures may also occur at therapeutic doses, mefloquine is contraindicated in patients with a history of seizures. Mefloquine has also been associated with neuropsychiatric manifestations: anxiety, paranoia, depression, hallucinations and psychotic behavior. These manifestations may continue long after mefloquine has been discontinued. These neuropsychiatric effects have been reported both after overdose and at therapeutic doses. To minimize the chance of these adverse effects, use of mefloquine for prophylaxis is contraindicated in patients with active depression, a recent history of depression, generalized anxiety disorder, psychosis, schizophrenia or other major psychiatric disorders. There is also evidence that the use of halofantrine during mefloqune therapy and within 15 weeks of the last dose of mefloquine increases the risk of a potential fatal prolongation of the corrected QT interval (QTc). This risk may also be increased following co-administration with ketoconazole. Clinically significant QTc interval prolongation has not been reported with mefloquine monotherapy. Several studies in pregnant women have shown no increase in the risk of teratogenic effects or adverse pregnancy outcomes following mefloquine treatment or prophylaxis during pregnancy. The WHO concluded however, that treatment with mefloquine should be undertaken cautiously during the first 12-14 weeks of gestation. ANIMAL STUDIES: While two year studies in mice and rats failed to show an increase in tumors, mefloquine did produce toxic effects. In one such study, rats were administered mefloquine in the diet at 0, 5, 12.5 or 30 mg/kg/day for 2 years. In the high dose group the weight gain of both sexes was significantly depressed and the incidence of spontaneous death was increased. Males had decreased testicle size and paralysis of hind limbs, while females showed increased vaginal hemorrhage, cystic ovaries and distended uteri filled with fluid. Elevated liver enzymes and blood urea nitrogen levels occurred for both sexes. At study completion, both sexes showed lesions in eye, lung, kidney, reproductive organs, skeletal muscle, spleen and lymph node. Retinal degeneration, opacity of the lens and/or retinal edema occurred at both the mid and high dose group. (Severity was greater in females). Mild lesions of reproductive organs and bile duct hyperplasia were seen in the mid dose group. Males had lesions in the epididymis and prostateepithelial vacuolization of epididymis, foamy macrophages in lungs and skeletal muscle degeneration were observed in both sexes of the low dose group. The potential for mefloquine to cause neurological effects were investigated in 7-week-old female rats given a single oral dose of the drug. Potential mefloquine-induced neurological effects were monitored using a standard functional observational battery, automated open field tests, automated spontaneous activity monitoring, a beam traverse task, and histopathology. Mefloquine induced dose-related changes in endpoints associated with spontaneous activity and impairment of motor function and caused degeneration of specific brain stem nuclei (nucleus gracilis). Increased spontaneous motor activity was observed only during the rats' normal sleeping phase, suggesting a correlate to mefloquine-induced sleep disorders. Mefloquine was also shown to be teratogenic in mice, rats and rabbits. In one study, rats were administered mefloquine at doses up to 100 mg/kg/day by intragastric intubation. In the high dose group, rats grew slower and consumed less feed than controls. Fetuses had reduced body weight, reduced crown-rump length, increased incidence of externally visible soft tissue and skeletal defectsdomes craniums occurred at a high rate, high incidence of hydrocephalusmalformed interparietals, incompletely ossified supra occipitals, and incompletely ossified skull bones were also observed. In a similar study in the mouse, mefloquine at doses of 100 and 200 mg/kg/day resulted in decreased body weight and a high incidence of cleft palate in fetuses. Mefloquine was also shown to impair fertility in both male and female rats. Mefloquine was not found to be mutagenic in the following tests: Ames Test, Fluctuation Test, Host (Mouse) Mediated Assay, Micronucleus Test, Induction of Point Mutations, Yeast Treat and Plate Test. |
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