Determination and comparison of graded dose-response curves for epidural bupivacaine and ropivacaine for analgesia in laboring nulliparous women.
BACKGROUND
The potencies of bupivacaine and ropivacaine have been compared using up-and-down methodology, but their complete dose-response curves have not been compared. The authors performed a random allocation-graded dose-response study of epidural bupivacaine and ropivacaine given epidurally for labor analgesia.


METHODS
Three hundred laboring nulliparous patients were randomly given epidural bupivacaine (5, 10, 15, 20, 30, or 40 mg) or ropivacaine (7, 15, 20, 30, 45, or 60 mg) in 20 ml of saline. Visual Analog Scale pain scores were recorded for 30 min. Response was defined by the percentage decrease in pain score from baseline at 30 min, and dose-response data were analyzed by using nonlinear regression.


RESULTS
Sigmoidal Emax model dose-response curves were fitted to the datasets for bupivacaine (R = 0.53) and ropivacaine (R = 0.59). The curves had similar steepness (Hill coefficient 2.02 [95% CI, 1.55-2.50] vs. 2.25 [1.70-2.79], P = 0.55). The ED50 (dose of the drug that reduces pain score to 50% of baseline at 30 min, also known as D50) of ropivacaine was greater than that of bupivacaine (15.3 [95% CI 13.7-17.1] mg vs. 11.3 [10.0-12.7] mg, P = 0.0003), but ED90 (D90) was similar (40.6 [32.4-51.1] mg vs. 33.4 [26.2-42.7] mg, P = 0.29). The potency ratio at ED50 for ropivacaine:bupivacaine was 0.75 (95% CI, 0.65-0.88).


CONCLUSIONS
Ropivacaine is less potent than bupivacaine, but otherwise they have similar dose-response characteristics. The difference in potency is not statistically significant at ED90 doses.
Ngan Kee
Warwick D
WD
Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Hong Kong, China. warwick@cuhk.edu.hk
Ng
Floria F
FF
Khaw
Kim S
KS
Lee
Anna
A
Gin
Tony
T
D000328:Adult; D000577:Amides / Q000008:administration & dosage*; D015360:Analgesia, Epidural / Q000379:methods*; D002045:Bupivacaine / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007743:Labor, Obstetric / Q000187:drug effects* / Q000502:physiology; D010147:Pain Measurement / Q000187:drug effects* / Q000379:methods; D010298:Parity / Q000187:drug effects / Q000502:physiology; D011247:Pregnancy; D000077212:Ropivacaine; D055815:Young Adult
D000577:Amides; D000077212:Ropivacaine; D002045:Bupivacaine