PHYSICOCHEMICAL STABILITY OF INFUSION SOLUTIONS FOR EPIDURAL ADMINISTRATION CONTAINING FENTANYL AND BUPIVACAINE OR LIDOCAINE

This study examines the physico-chemical stability of infusion solutio ns for epidural administration containing bupivacaine hydrochloride 0. 06% or 0.125% or lidocaine hydrochloride 0.25% in 0.9% sodium chloride , each with fentanyl 0.0002%. The solutions were prepared in polyvinyl chloride (PVC) infusion bags and stored without overwrap at room temp erature (25-30 degrees C) or refrigerated (4-8 degrees C). Over a peri od of 32 days stability was determined by visual inspection, pH measur ement, and HPLC assay of drug concentrations. Admixtures of bupivacain e/fentanyl and lidocaine/fentanyl proved to be chemically stable over a 32 day period, but physical incompatibility (sorption) with PVC-bags was discovered. The stability of the admixtures was influenced by pH and storage temperature. In none of the tested admixtures with an init ial pH value lower than 6, did the concentrations of fentanyl or the l ocal anesthetic decrease under 90% of the initial concentrations. A so lution of fentanyl and lidocaine with an initial pH of 6.7 exhibited a rapid decrease of drug concentrations. Supposing fentanyl loss was du e to sorption, buffered single drug fentanyl solutions of pH 5.5, 5.8, 6.3, and 6.7 were prepared in glass and PVC containers and stored und er the same conditions. All solutions in PVC bags showed relevant fent anyl loss which was more evident at higher pH, whereas fentanyl concen tration remained unchanged in glass containers at any of the tested pH values.