6 Markenson JA. Mechanisms of chronic pain[J].Am J Med,1996,101(Suppl 1A)∶S6
7 Raffa RB. A novel approach to the pharmacology of analgesia[J].Am JMed,1996,101(Suppl 1A)∶S40
8 Lewis KS,Han NH. Tramadol∶a new centrally acting analgesic[J].Am J HealthSyst Pharm,1997,54(6)∶643～652
9 Viegas OA,Khaw B,Ratnam SS. Tramadol in labour pain in primiparous patients.Aprospective comparative clinical trial[J].Eur J Obstet Gynecol Reprod Biol,1993,49(3)∶131～135
10 Bredow V. Use of tramadol versus pethidine versus denaverine suppositories inlabor，a contribution to noninvasive therapy of labor pain[J]. Zentralbl Gynakol,1992,114(11)∶551～554
