title: The median effective dose of bupivacaine, levobupivacaine, and ropivacaine after intrathecal injection in lower limb surgery.
abstract: BACKGROUND
  Intrathecal anesthesia is commonly used for lower limb surgery. Bupivacaine, levobupivacaine, and ropivacaine have all been used as intrathecal drugs, but their relative potency in this context has not been fully determined. In this study, we determined the median effective dose (ED(50)) of these three local anesthetics for intrathecal anesthesia in lower limb surgery and hence their relative potencies.
  
  
  METHODS
  Seventy-five patients scheduled for lower limb surgery under combined spinal-epidural anesthesia were randomly allocated to one of three groups receiving intrathecal bupivacaine, levobupivacaine, or ropivacaine. The dose of local anesthetic was varied using up-down sequential allocation technique. The dose for the first patient in each group was 8 mg, and the dosing increment was set at 1 mg. Subsequent doses in each group were determined by the outcome in the previous patient using success or failure of the spinal anesthesia as the primary end point. A success was recorded if a bilateral T12 sensory block to cold was attained within 20 min after intrathecal injection, and the surgery proceeded successfully until at least 50 min after the intrathecal injection without supplementary epidural injection. The ED(50) was calculated using the method of Dixon and Massey.
  
  
  RESULTS
  The ED(50)s were 5.50 mg for bupivacaine (95% confidence interval [CI]: 4.90-6.10 mg), 5.68 mg for levobupivacaine (95% CI: 4.92-6.44 mg), and 8.41 mg for ropivacaine (95% CI: 7.15-9.67 mg) in intrathecal anesthesia. The relative anesthetic potency ratios are 0.97 (95% CI: 0.81-1.17) for levobupivacaine/bupivacaine, 0.65 (95% CI: 0.54-0.80) for ropivacaine/bupivacaine, and 0.68 (95% CI: 0.55-0.84) for ropivacaine/levobupivacaine.
  
  
  CONCLUSIONS
  This study suggests that in intrathecal anesthesia for lower limb surgery, ropivacaine is less potent than levobupivacaine and bupivacaine, whereas the potency is similar between levobupivacaine and bupivacaine.
authors.affiliation: Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China. yyleekwh@yahoo.com
authors.forename: Ying Y
authors.initials: YY
authors.lastname: Lee
authors.forename: Warwick D
authors.initials: WD
authors.lastname: Ngan Kee
authors.forename: Siu Y
authors.initials: SY
authors.lastname: Fong
authors.forename: John T C
authors.initials: JT
authors.lastname: Liu
authors.forename: Tony
authors.initials: T
authors.lastname: Gin
mesh_terms: D000368:Aged; D000577:Amides / Q000008:administration & dosage*; D000767:Anesthesia, Epidural; D000775:Anesthesia, Spinal; D000779:Anesthetics, Local / Q000008:administration & dosage*; D002045:Bupivacaine / Q000008:administration & dosage / Q000031:analogs & derivatives; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007278:Injections, Spinal; D000077554:Levobupivacaine; D035002:Lower Extremity / Q000294:innervation / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures; D011446:Prospective Studies; D000077212:Ropivacaine; D012677:Sensation / Q000187:drug effects
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D000077212:Ropivacaine; D000077554:Levobupivacaine; D002045:Bupivacaine