In Reply:-We thank Drs. Donati and Plaud for pointing out the error in Figure 2in our published study.  Unfortunately, this calculation error not only escaped our attention, but also the attention of the reviewers. However, this error does not change our conclusions. The isobolographic analysis still demonstrates a synergistic interaction with respect to the neuromuscular blocking activity of the rocuronium and cisatracurium combination (Figure 1). The experimentally determined ED50(and 95% confidence interval) for the combination was 36.8 (35–38)[micro sign]g/kg for rocuronium and 8.7 (8.3–9.1)[micro sign]g/kg for cisatracurium. The theoretic additive ED50(and 95% confidence interval) was calculated to be 55.5 (53.3–57.7)[micro sign]g/kg for rocuronium and 13.1 (12.6–13.6)[micro sign]g/kg for cisatracurium. The confidence intervals of these points do not overlap, and the results of a Student t test for potency ratio were significant (P < 0.001), indicating synergism. The fractional (algebraic) analysis of this interaction still demonstrates synergism (Table 1).
Mohamed Naguib, M.B., B.Ch., M.S.C., F.F.A.R.C.S.I., M.D.
Professor of Anesthesiology; Department of Anaesthesiology; King Khalid University Hospital; Riyadh, Saudi Arabia;firstname.lastname@example.org
(Accepted for publication March 31, 1999.)