Hs. Feldman et al., ANTINOCICEPTIVE AND MOTOR-BLOCKING EFFICACY OF ROPIVACAINE AND BUPIVACAINE AFTER EPIDURAL ADMINISTRATION IN THE DOG, Regional anesthesia, 21(4), 1996, pp. 318-326
Background and Objectives. This study was initiated to evaluate the an
tinociceptive and motor blocking capabilities of epidurally administer
ed 0.5% and 0.75% ropivacaine and bupivacaine using a blinded, random
crossover design in the dog. Additionally, serum drug concentrations a
nd serum protein binding were determined. Methods. Twelve male beagles
were prepared with chronic epidural and arterial catheters under ster
ile conditions. The epidural space was identified by a loss-of resista
nce technique using an 18-gauge thin-wall Crawford needle via the midl
ine approach. The catheter was attached to a Schraeder-type Teflon val
ve sutured subcutaneously. local anesthetic drugs were administered in
to the lumbar epidural space in a constant volume of 3.0 mL. Evaluatio
n of antinociceptive and motor blocking qualities were evaluated at re
gular intervals. Arterial blood samples were drawn during the 15 minut
es following local anesthetic injection for drug concentration and pha
rmacokinetic analysis. Results. Onset time of motor block in the ropiv
acaine 0.5% group was longer than in other groups but not significantl
y different. Duration of motor and sensory block demonstrated a dose-d
ependent relationship of both drugs. Bupivacaine 0.5% and 0.75% produc
ed motor block (81 +/- 42 minutes and 198 +/- 44 minutes [mean +/- SD]
, respectively) of significantly longer duration than corresponding co
ncentrations of ropivacaine (69 +/- 35 minutes and 133 +/- 32 minutes,
respectively). The onset times for sensory block of the vertebral der
matomes were not different between groups. No difference was found in
duration of dermatomal sensory block between the 0.5% solutions. Howev
er, the duration of dermatomal sensory block was significantly longer
in the bupivacaine 0.75% group than in any other group. Peak arterial
serum drug concentrations were not different between drugs at equal co
ncentrations and were reached between 2 and 6 minutes in all animals.
Both drugs wee highly bound in serum proteins (>98%). No severe advers
e effects or sequelae were observed. Conclusions. The 0.5% solutions p
roduced similar sensory block of the vertebral dermatomes. Duration of
dermatomal block with 0.75% bupivacaine was longer than with the corr
esponding ropivacaine concentration. Ropivacaine produced motor block
of shorter duration as compared with bupivacaine. Serum concentrations
of the two drugs were similar after injection of the same doses. In t
his animal model, ropivacaine produced shorter durations of sensory an
d motor block than corresponding concentrations of bupivacaine. These
data are consistent with previously published data in animals and huma
ns.