Effect of morphine and tramadol on serum levels of lidocaine after epidural administration in dogs
The objective of this study was to evaluate whether the addition of morphine or tramadol to lidocaine influences serum lidocaine concentrations in dogs administered these drugs epidurally prior to elective orchiectomy or ovariohysterectomy. Thirty dogs were divided into three groups of 10 each, with equal numbers of females and males. One group received epidurally 2% lidocaine combined with 0.9% NaCl, another received 2% lidocaine combined with morphine, and a third group received 2% lidocaine combined with tramadol. Blood samples for the determination of serum lidocaine concentrations were taken 10, 30, 60 and 90 min after epidural administration. Serum lidocaine concentrations were measured by gas chromatography-mass spectrometry (GC-MS). There was a total of 120 serum samples obtained. In most animals a peak serum lidocaine concentration was detected ten minutes after epidural administration. There were no significant differences in the detected serum lidocaine concentrations within observed groups of animals, or between males and females. Therefore, results suggest that morphine and tramadol can be used as additives to epidural lidocaine in dogs at the investigated doses, without significantly influencing lidocaine absorption from the epidural space and its serum concentration.