title: Minimum local analgesic doses of ropivacaine, levobupivacaine, and bupivacaine for intrathecal labor analgesia.
abstract: BACKGROUND
  Doses for intrathecal opioid-local anesthetic mixtures have been arbitrarily chosen. The aim of this study was to compare the analgesic efficacies of intrathecal ropivacaine, levobupivacaine, and bupivacaine for labor analgesia and to determine the analgesic potency ratios for these three drugs. For this purpose, the authors used the up-down sequential allocation model, which estimates the minimum local analgesic dose for intrathecal local anesthetic.
  
  
  METHODS
  Ninety-seven nulliparous term parturients in spontaneous labor, requesting combined spinal-epidural analgesia, were randomly allocated to one of three groups to receive 0.25% spinal ropivacaine, levobupivacaine, or bupivacaine. The initial dose of the local anesthetic drug was chosen to be 2.5 mg, and the testing interval was set at 0.25 mg. The subsequent doses were determined by the response of the previous parturient. Efficacy was accepted if the visual analog pain score decreased to 10 mm or less on a 100-mm scale within 30 min. The minimum local analgesic dose was calculated using the method of Dixon and Massey.
  
  
  RESULTS
  The intrathecal minimum local analgesic dose was 3.64 mg (95% confidence interval, 3.33-3.96 mg) for ropivacaine, 2.94 (2.73-3.16) mg for levobupivacaine, and 2.37 (2.17-2.58) mg for bupivacaine. The relative analgesic potency ratios were 0.65 (0.56-0.76) for ropivacaine:bupivacaine, 0.80 (0.70-0.92) for ropivacaine:levobupivacaine, and 0.81 (0.69-0.94) for levobupivacaine:bupivacaine. There were significant trends (P </= 0.021) for greater motor block with bupivacaine and levobupivacaine.
  
  
  CONCLUSIONS
  This study suggests a potency hierarchy of spinal bupivacaine > levobupivacaine > ropivacaine.
authors.affiliation: Department of Obstetric Anesthesia, Città di Roma Hospital, Italy. michela_camorcia@yahoo.it
authors.forename: Michela
authors.initials: M
authors.lastname: Camorcia
authors.forename: Giorgio
authors.initials: G
authors.lastname: Capogna
authors.forename: Malachy O
authors.initials: MO
authors.lastname: Columb
mesh_terms: D000328:Adult; D000577:Amides / Q000008:administration & dosage*; D015360:Analgesia, Epidural; D016362:Analgesia, Obstetrical; D000779:Anesthetics, Local / Q000008:administration & dosage*; D002045:Bupivacaine / Q000008:administration & dosage* / Q000031:analogs & derivatives; D005260:Female; D006801:Humans; D000077554:Levobupivacaine; D011247:Pregnancy; D000077212:Ropivacaine
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D000077212:Ropivacaine; D000077554:Levobupivacaine; D002045:Bupivacaine