Epidural Block for Abdominal Surgery: Aspects of Clinical Pharmacology of Etidocaine

Abstract

A randomized, prospective, controlled study has compared 1% etidocaine (E) in nineteen patients and 0.5% bupivacaine (B) in 22 patients when used with 1/200,000 adrenaline for epidural blockade. There were unexpected similarities in onset profiles for the two agents, however etidocaine produced a superior intensity of sensory and motor blockade without increased toxicity. Onset times for sympathetic blockade (E = 6.9 ± 1.2, B = 6.8 ±1.2 minutes) were similar for both agents as were times to maximum change in blood pressure (E = 19.4 ± 9.7, B = 18.9 ± 3.7 minutes). Initial onset time for sensory loss to pin prick (partial sensory block) was surprisingly similar for the two drugs (E = 5.6 ± 0.6, B = 6.4 ± 0.7 minutes). However, onset of loss of touch sensation (complete sensory block) was much more rapid for etidocaine (E = 17.7 ± 1.7 minutes, B = 36.8 ± 3.5 minutes). Readiness for surgery, as assessed by spread of complete sensory block into four segments above and below the injection site, was rapid for etidocaine (23.1 ± 2.3 minutes) but this degree of blockade was only achieved in two patients following bupivacaine. Complete blockade on both sides of the body was achieved for two segments on either side of the infection site in 100% of patients following etidocaine, compared to only 30–50% following bupivacaine. A similar example of superior neural penetration was seen in onset of blockade of the large S1 root (E = 8.3 ± 1.4, B = 16.2 ± 4.6 minutes) Complete spread of motor blockade was much more rapid for etidocaine (14.7 ± 2.8, B = 28.9 ± 2.8 minutes). Degree of motor blockade was also significantly greater for etidocaine from ten minutes post blockade onwards (P < 0.001). Peak plasma concentrations were in keeping with ctox/cmax ratios of 1.9 for bupivacaine and 2.7 for etidocaine. Etidocaine was shown to be extensively and rapidly metabolized and to have a high degree of plasma protein binding.