Stability of a Baclofen and Clonidine Hydrochloride Admixture for Intrathecal Administration

Abstract

Implantable infusion pumps for the intrathecal administration of analgesics are commonly used in the treatment of severe or intractable chronic pain. Drugs used in these pumps include morphine, baclofen, clonidine, hydromorphone, meperidine, fentanyl, and bupiva-caine. This study investigates the chemical and physical stability of baclofen (1000 mcg/mL) and clonidine hydrochloride (200 mcg/mL) at 37°C for 10 weeks using a stability-indicating HPLC assay. The formulations included baclofen alone, clonidine hydrochloride alone, and a mixture of the two drugs. At each time point, the amount of drug remaining was greater than 90% of original. Week 10 percentages were 99.7% for baclofen alone, 100.7% for clonidine alone, and 103.2% and 101.1% for baclofen and clonidine hydrochloride, respectively in the drug mixture. These results demonstrate the stability of this admixture for long-term intrathecal administration.