pH Stability of Injectable Fentanyl, Bupivacaine, or Clonidine Solution or a Ternary Mixture in 0.9% Sodium Chloride in Two Types of Polypropylene Syringes.

The pH stability of injectable fentanyl, bupivacaine, or clonidine solution or a ternary mixture in 0.9% sodium chloride, all of which were stored in polypropylene syringes, was determined. Two different types of polypropylene syringes were tested: one (Omnifix, B. Braun, Melsungen, Germany) had a synthetic latex-free polyisoprene piston and the other (Terumo, Leuven, Belgium) did not contain natural rubber or synthetic rubber. Forty-eight Omnifix 50-mL syringes and 120 Terumo 20-mL syringes were tested. The syringes were filled with a fentanyl citrate solution 35 microgram/mL (stored in 12 Omnifix and 30 Terumo syringes), a bupivacaine hydrochloride solution 1mg/mL (12 Omnifix and 30 Terumo syringes), a clonidine hydrochloride solution 9 micrograms/mL (12 Omnifix and 30 Terumo syringes), or a ternary mixture in 0.9% sodium chloride (12 Omnifix and 30 Terumo syringes). The syringes were stored for 30 days at 4 deg C, 21 deg C, and 35 deg C. Duplicate samples were prepared, observed for precipitation and color change, and measured for pH immediately after preparation and at 1, 2, 5, 7, 9, 12, 16, 23, and 30 days of storage. There was no color change or precipitation in any sample during 30 days of storage at any of the temperatures studied. There was no change in the pH of the fentanyl, bupivacaine, or clonidine soltuions or in the ternary mixtrue stored in Terumo syringes for 30 days of storage at 4 deg C, 21 deg C, and 35 deg C. Omnifix syringes performed differently with different drug solutions. No siginicant change in the pH of the fentanyl bupivacaine, or clonidine solutions or of the ternary mixture stored in the Omnifix syringes was observed during 30 days of storage at 4 deg C, 21 deg C, and 35 deg C, except for the clonidine solutions stored at 21 deg C and 35 deg C.