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由于围产期的生理学特性,药物的应用不可避免的要通过胎盘转移到胎儿发生作用,甚至危及其安全。影响药物胎盘转移的因素,涉及药物理化特性,母体-胎盘-胎儿单位的生理学改变,以及药物在胎儿体内归转、分布及排泄等问题。一、药物的理化特性 (一)药物的脂溶性与离子化度:血-胎盘屏障对药物的转移,有很大的选择性。凡药物的分子为脂溶性,且在生理学pH的范围下呈非离子状态时,则能迅速弥散通过胎盘至胎儿血循环内,如硫贲妥钠、安基比林。相较之下,高pKa(分解常数)的碱基与低pKa的酸基弥散得较慢。水溶性、高离子化的药物如管箭毒,肝素弥散速率
Because of the perinatal physiological characteristics, the application of the drug inevitably has the effect of transferring to the fetus through the placenta, even endangering its safety. The factors that affect the transfer of drug placenta involve the physical and chemical characteristics of the drug, the physiological changes of maternal-placenta-fetal unit, and the problem of drug transfer, distribution and excretion in the fetus. First, the physical and chemical properties of drugs (a) the fat-soluble drugs and ionization degree: blood - placental barrier on the transfer of drugs, there is a great selectivity. Where the drug molecule is lipid-soluble and non-ionic at physiological pH range, it rapidly diffuses through the placenta into the fetal blood circulation such as thiopental and ampicillin. In contrast, bases with a high pKa (decomposition constant) diffuse more slowly than those with a low pKa. Water-soluble, highly ionized drugs such as tube poison, heparin diffusion rate