Pharmacokinetics And Tissue Distribution Of (-)-Mefloquine And Its Diasteremers

Pain, as a warning sign of ongoing or impending tissue damage, is a survival mechanism. Recent studies have shown that more than one-thirds of Americans suffer from chronic pain. About 27% of European population was affected by chronic pain. More than one-fifth of patients are thought to have predominantly neuropathic pain. Neuropathic pain is caused by lesion or dysfunction of the somatosensory system. Its main clinical manifestations were spontaneous pain, hyperalgesia and allodynia. More than one half of neuropathic pain patients cannot relieve the pain.Mefloquine is a drug for the prevention and treatment of malaria. It was marketed by Roche in 1985. As a racemic mixture, Mefloquine consists of four isomers. Our previous studies have shown that (-)-Mefloquine can relieve neuropathic pain, but the pharmacokinetics and tissue distributions of (-)-Mefloquine and its two diastereomers, LV02 and LV03, are still needed to explore. This study mainly focused on the pharmacokinetics of three compounds, and the toxicity of LV02 and LV03 was also evaluated, which may provide important hints for understanding the relationship between pharmacokinetics and pharmacodynamics of Mefloquine and its isomers as possible therapeutical agents for neuropathic pain.1. Establishment of LC-MS method and method validationWe built and validated a LC-MS method for determination of three drugs (LV02, LV03 and (-)-Mefloquine) in rat plasma and tissues. We chose positive mode in mass spectrometry, and the [M+H]+m/z was 379.1. In liquid chromatography, an Agilent ZORBAXSB-C18 column was used, acetonitrile and ammonium acetate (20 mM) were used for mobile phase in the model of gradient elution. Verapmil was used as the internal standard. The method showed good selectivity, linearity, extraction recovery and stability for these three compounds.2. Pharmacokinetic and tissue distribution of (-)-Mefloquine in rats.The pharmacokinetics and tissue distribution of (-)-Mefloquine in SD rats were studied with the LC-MS method which we built previous. Blood samples were obtained at fixed time intervals after the i.p. injection of (-)-Mefloquine at a dosage of 7.5,10 and 15 mg/kg; the tissue samples were collected at fixed time intervals after the i.p. injection of (-)-Mefloquine at a dosage of 15 mg/kg. The AUC were (44.08±1.85), (137.79±45.07), (223.44±16.52) mg·min/L, respectively. The Cmax were (0.29±0.01), (0.46±0.06), (0.73±0.05) mg/L respectively and the Vd were (59.23±3.62), (37.51±5.76), (38.36±9.15) L/kg, respectively. The rat plasma concentration-time curves of the (-)-Mefloquine in three different dosages were fitted to the two-compartment open model. The tissue distribution study showed that (-)-Mefloquine was distributed widely in tissues, and it could enter into the brain through the blood brain barrier.3. Pharmacokinetic and tissue distribution of LV02 and LV03 in ratsThe pharmacokinetics and tissue distribution of LV02 and LV03 in SD rats were studied with the LC-MS method which we built previous. Blood samples were obtained at fixed time intervals after the i.p. injection of LV02 (or LV03) at a dosage of 15 mg/kg; the tissue samples were collected at a fixed time intervals after the i.p. injection of LV02 (or LV03) at a dosage of 15 mg/kg. The main pharmacokinetic parameters of LV02 and LV03 were as follows:the AUC were (978.72±17.82) and (611.81±7.61) mg·min/L, the Cmax were (2.59±0.27) and (2.02±0.12) mg/L and the Vd were (13.17±0.59) and (19.72±1.95) L/kg. The rat plasma concentration-time curves of the LV02 and LV03 were fitted to the two-compartment open model. The tissue distribution study showed that LV02 and LV03 were distributed widely in tissues, and they also could enter into brain through the blood brain barrier.4. The preliminary toxicity study of LV02 and LV03In this study, we observed the acute toxicity reaction in SD rats after the i.p. injection of LV02 or LV03. We used Up and Down method to get the LD50 of these two compounds. And some related biochemical indexes were tested. The result showed that the LD50 of two compounds was 98.11 mg/kg, the confidence interval of two drugs was 55-175 mg/kg. Meanwhile, some biochemical parameters had changes in the groups of LV02 and LV03. The experimental result suggests that the toxicity of these two compounds was less than the (-)-Mefloquine.