title: Epidural pain relief in labour: potencies of levobupivacaine and racemic bupivacaine.
abstract: We have compared the minimum local analgesic concentrations (MLAC) of levobupivacaine relative to racemic bupivacaine in a prospective, randomized, double-blind, sequential allocation study. Women in labour were given a 20-ml bolus of epidural levobupivacaine or bupivacaine diluted to a concentration determined by up-down sequential allocation. The initial concentration was 0.07% w/v for both drugs. Efficacy was defined using a visual analogue pain score (VAPS) at 10 mm or less within 30 min. The MLAC of levobupivacaine was 0.083% w/v (95% CI 0.065-0.101) and the MLAC of bupivacaine 0.081% w/v (95% CI 0.055-0.108). In molar terms, the MLAC of levobupivacaine was 2.87 mmol litre-1 (95% CI 2.25-3.49) and the MLAC of bupivacaine 2.49 mmol litre-1 (95% CI 1.69-3.32). With regard to the commercial preparations, the potency ratio levobupivacaine: bupivacaine was 0.98 (95% CI 0.67-1.41), and this is unlikely to be of clinical relevance. In molar terms, the ratio was 0.87 (95% CI 0.60-1.25). With regard to toxicity, the evidence should be evaluated in the light of a possible 13% potency difference in molar concentration in favour of racemic bupivacaine.
authors.affiliation: St James' University Hospital, Leeds.
authors.forename: G
authors.initials: G
authors.lastname: Lyons
authors.forename: M
authors.initials: M
authors.lastname: Columb
authors.forename: R C
authors.initials: RC
authors.lastname: Wilson
authors.forename: R V
authors.initials: RV
authors.lastname: Johnson
mesh_terms: D000328:Adult; D015360:Analgesia, Epidural / Q000379:methods*; D016362:Analgesia, Obstetrical / Q000379:methods*; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000737:chemistry; D002045:Bupivacaine / Q000008:administration & dosage* / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D010147:Pain Measurement; D011247:Pregnancy; D011446:Prospective Studies; D013237:Stereoisomerism
chemical_list: D000779:Anesthetics, Local; D002045:Bupivacaine