Hanks G W, Hoskin P J, Aherne G W, Turner P, Poulain P
Royal Marsden Hospital, Sutton.
Lancet. 1987 Sep 26;2(8561):723-5. doi: 10.1016/s0140-6736(87)91083-x.
Morphine given by injection is the standard by which all other strong analgesics are measured, but when given orally in single doses it is a poor analgesic. With repeated oral administration it becomes very effective and it may be that on repeated dosage active metabolites, particularly morphine-6-glucuronide, account for much of the analgesic activity. Enterohepatic circulation may also contribute to the maintenance of blood and tissue levels of morphine and its metabolites in chronic use.
注射用吗啡是衡量所有其他强效镇痛药的标准，但单次口服时它却是一种低效镇痛药。反复口服给药后它会变得非常有效，可能是反复给药时活性代谢产物，尤其是吗啡 -6- 葡萄糖醛酸苷，发挥了大部分镇痛活性。肝肠循环也可能有助于长期使用吗啡时维持其血液和组织中的水平及其代谢产物的水平。
