Lidocaine serum concentration after epidural administration in combination with morphine and fentanyl in rabbit--a preliminary study.

Morphine and fentanyl are often used as adjuvants in epidural anesthesia to prolong analgesia. The aim of this study was to evaluate the impact of addition of morphine or fentanyl to lidocaine on serum lidocaine concentrations in rabbits after epidural administration. During general anesthesia, rabbits of the group L received epidurally 2% lidocaine, rabbits of the group LM 2% lidocaine and morphine, and rabbits of the group LF 2% lidocaine and fentanyl. Blood for determination of serum lidocaine concentration was taken before anesthesia and in first 90 min after epidural administration. After 5, 10, and 25 min in the group L the lidocaine serum concentrations were the lowest, while in the group LM the lidocaine serum concentrations were the highest. Morphine and fentanyl did not cause significant changes of serum lidocaine concentration in rabbits and may be used as adjuvant in epidural anesthesia without significant increase in lidocaine absorption from epidural space.