Tissue Distribution of Clonidine Following Intraforaminal Implantation of Biodegradable Pellets: Potential Alternative to Epidural Steroid for Radiculopathy

Abstract

Background: Epidural steroid injections have shown efficacy in short-term pain relief, but often require repeated injections in order to provide continued pain relief. It has been suggested that a continuous, locally administered dose of an anti-inflammatory compound may provide sustained pain relief at doses lower than those needed with injections. Objective: To evaluate the distribution of clonidine after transforaminal placement of a biodegradable drug delivery depot system. Study Design: A preclinical animal study. Methods: A biodegradable polymer drug depot designed to provide sustained delivery of clonidine was placed in or near a single lumbar neural foramen in 12 farm pigs. Clonidine tissue concentrations were measured at the implant site and at incremental distances from the implant over a time period of 12 weeks. Plasma clonidine levels were measured at 4 hours postimplantation on days 1, 2, 3, 5, and 7, and then weekly until the termination of the study. Results: Clonidine was detectable up to 6 cm away from the drug depot. The highest concentrations of clonidine were present within the targeted spinal nerve; the concentration decreased with increasing distance from the depot. Clonidine was undetectable in plasma from all animals at all time points. Limitations: While clonidine was detected up to 6 cm from the drug depot, it is unknown if the drug concentration has clinical relevance. Conclusions: The results indicate that a biodegradable depot designed to be placed in a specific location to provide local sustained release of an anti-inflammatory and analgesic drug may be a feasible new approach to treat radicular pain associated with intervertebral disc pathology and other spinal conditions. Key Words: clonidine, radiculopathy, pain, intraforaminal, injection, spine, sciatica