药物的皮肤吸收常受到皮肤角质层的限制。口服给药时,胃肠道的吸收差异和肝脏的“首次通过”机制也会影响药物的生物有效性。注射给药,尤其是静脉注射,可使药物全部地输送到血液中,并很快到达作用部位,其缺点是血药浓度下降较快,致使疗效不能持久。理想的给药系统应在整个治疗期间保持恒定的有效血药浓度,静脉滴注可以达到此目的,但需住院和周密的医疗照顾。 Skin absorption of the drug is often limited by the cuticle of the skin. Oral administration, gastrointestinal absorption differences and the liver’s “first pass” mechanism also affects the bioavailability of the drug. Injectable drugs, especially intravenous injection, can make the drug fully delivered to the blood, and soon reach the site of action, the disadvantage is the rapid decline in plasma concentration, resulting in curative effect can not be sustained. The ideal drug delivery system should maintain a constant effective plasma concentration throughout treatment, which is achieved by intravenous drip but requires hospitalization and thorough medical attention.