Effect of pH on absorption of sufentanil citrate in a portable pump reservoir during storage and administration under simulated epidural conditions.

Sufentanil (5 micrograms/ml as citrate) was investigated for its stability when diluted with sodium chloride 0.9%, in 100 ml polyvinyl chloride portable pump reservoirs during administration under simulated epidural conditions at 32 degrees C for 48 h. Sufentanil was absorbed into the polyvinyl chloride, resulting in a reduction of 10.9% of the concentration after 48 h. The absorption of sufentanil (5 micrograms/ml as citrate), alone and in combination with bupivacaine hydrochloride (2 mg/ml), was investigated when diluted with sodium chloride 0.9% in combination with a citrate buffer (pH 4.6), in the same reservoirs under similar conditions. There was no loss of sufentanil after 48 h in both experiments. The effect of the pH on the absorption of sufentanil in polyvinyl chloride was investigated at different pH values. After storage for 21 days at 32 degrees C there was 5.1% loss of sufentanil at pH 4 and 80.6% loss at pH 6. The citrate buffer at the optimum pH (4.6) has a low, acceptable buffer capacity for epidural administration.