Drug distribution in dorsal root ganglion after peripheral application of Lidocaine patch

This study investigated lidocaine distribution following patch application at peripheral position. The study included three parts. Animals in Part A (n = 12) were received 5% lidocaine patches on paravertebral (Group A1) or parasternal (Group A2) side, covering the distribution of the unilateral T3-T8 intercostal nerves. Part B (group B, n = 6) received bilateral patches along the T6-T8 intercostal nerve distribution. In Part C (n = 12), Group C1 severed the bilateral 5th-7th intercostal nerves followed by patch application approximately 0.5 cm lateral to the incisions, while Group C2 had the same patch placement without nerve cutting. All rabbits were euthanized 24 h after 5% lidocaine patch applied for 12 h. Dorsal root ganglia (DRG), fascia and spinal cord were collected. Lidocaine concentrations were determined using high-performance liquid chromatography. Lidocaine concentration in the DRGs on the treated side of A1 was significantly higher than that of A2. A1 and A2 exhibited lower lidocaine concentrations in contralateral DRGs compared to the treated side. In Group B, lidocaine concentration in DRG was higher in T6-T8 segments than in T3-T5 segments, with no significant difference in spinal cord concentration between segments. Group C showed significantly lower DRG lidocaine concentration in C1 compared to C2, with a slight decrease in spinal cord lidocaine concentration in C1. Intercostal nerves are the primary pathway for lidocaine transport from the periphery to the DRGs. Lidocaine patches should be applied as close to the spine as possible.