The effect of nonesterified fatty acids and progesterone on bupivacaine protein binding.

We examined the influence of elevations in levels of nonesterified fatty acids (NEFAs) and progesterone concentrations on bupivacaine protein binding. The addition of NEFAs to isolated binding proteins of bupivacaine (alpha 1-acid glycoprotein and serum albumin) resulted in an increased binding to alpha 1-acid glycoprotein and an inconsistent decrease in binding to serum albumin. The NEFA alteration in the binding of bupivacaine to isolated proteins, however, only restored the isolated protein binding to normal whole serum levels. An elevated progesterone concentration in whole serum did not alter the binding of bupivacaine. It appears from our results that increases in either NEFA or progesterone concentrations do not account for the observed decrease in bupivacaine protein binding in the term parturient.