Stability of clonidine in clonidine-hydromorphone mixture from implanted intrathecal infusion pumps in chronic pain patients

Clonidine is frequently added to opioids in implantable intrathecal pumps for the management of chronic pain. In such devices, a small non-retrievable volume is always present in the reservoir, and its effect on drug stability is unknown. Furthermore, stability of clonidine, when mixed with hydromorphone, has not been previously determined. This study examined the stability of clonidine when co-administered with hydromorphone in implanted intrathecal pumps. Samples of hydromorphone-clonidine before pump refill and from residual solution at subsequent refill were obtained from chronic pain patients. Clonidine concentration was measured using HPLC. Twenty paired samples from 3 patients were analyzed. All 3 patients had a SynchroMed pump implanted for 3-5 years. We found no loss in clonidine concentration during the time between refills (35 ± 13 days), and no correlation between clonidine concentration and time interval between refills. In conclusion, clonidine, mixed with hydromorphone, is stable when delivered by implantable intrathecal pump for long-term use.