THE ROLE OF HYALURONIDASE ON LIDOCAINE AND BUPIVACAINE PHARMACOKINETICS AFTER PERIBULBAR BLOCKADE

Orbital regional anesthesia is the only circumstance where hyaluronida se is routinely added to local anesthetics to accelerate the onset of the block. The aim of this study was to compare the pharmacokinetics o f lidocaine and bupivacaine with or without hyaluronidase for peribulb ar blockade. Twenty-one patients scheduled for cataract surgery with l ens implantation were included in this prospective randomized study. P eribulbar blocks were achieved with plain bupivacaine 0.5% (5.5 mL), l idocaine 2% (5.5 mL), and hyaluronidase (100 IU = 2 mL) (n = 10) or st erile water (2 mL) (n = 11). Plasma bupivacaine and lidocaine concentr ations were measured by high-performance liquid chromatography at regu lar intervals from the end of the local anesthetic injection until the 360th minute. Maximum plasma concentration (C-max) and time to reach C-max (T-max) were obtained for all the patients except one who needed a supplementary injection and was excluded from the study. The time t o onset and duration of the analgesia and akinesia were monitored at t he times of sampling. Motor blockade was incomplete in two patients in each group without affecting surgery. The T-max and absorption half-l ife (t(1/2a)) of lidocaine and bupivacaine were not different within e ach group (P > 0.05). The T-max of lidocaine was shorter in the presen ce of hyaluronidase (17.1 +/- 2.6 min vs 32.7 +/- 6.0 min) as well as the T-max of bupivacaine (16.8 +/- 3.9 min vs 26.5 +/- 4.4 min). The C -max of lidocaine and bupivacaine were not modified by the addition of hyaluronidase. The clearance, terminal half-life, and volume of distr ibution were not different between groups. The absorption of lidocaine and bupivacaine from the peribulbar space are hastened by the additio n of hyaluronidase. The T-max of lidocaine is not different from that of bupivacaine within each group suggesting that the absorption of loc al anesthetics is minimally influenced by the liposolubility of the dr ugs. Moreover, hyaluronidase influences the absorption kinetics of bot h lidocaine and bupivacaine in the same manner.