Fig. 6. The tissue lidocaine concentration over time of the plain lidocaine (open circles ) and lidocaine with clonidine groups (closed squares ) compared with previously published data for lidocaine with epinephrine (closed triangles ) using identical sampling methodology. 8The effect of the addition of epinephrine (2.5 μg) on lidocaine clearance is much greater than the effect of adding clonidine (10 μg) within the first 60 min. The rate of decrease in plasma lidocaine concentration after 60 min is remarkably consistent for all three groups.