Amikacin serum protein binding in spinal cord injury

While changes in the disposition kinetics of aminoglycoside antibiotics have been observed in patients with spinal cord injury (SCI), the extent of binding of aminoglycoside antibiotics to serum protein has not been studied as a potential etiology. Eighty-six serum samples were obtained from 26 volunteers (9 paraplegic, 10 tetraplegic, 7 able-bodied controls) to determine the extent of amikacin binding to serum protein. Free (unbound) amikacin obtained from an ultrafiltrate of serum and total serum amikacin were quantitated over a range of serum concentrations (range 1.37 micrograms/mL to 73.99 micrograms/mL). There was no statistically significant difference demonstrated between mean amikacin serum protein binding in patients with SCI (mean +/- SD, 17.63% +/- 7.22%) and in able-bodied controls (18.03% +/- 3.64%). The percent serum protein binding of amikacin did not covary with total amikacin concentration, and linear regression of free versus total serum amikacin concentrations was expressed by the equation, y = 0.803 x + 0.350, r = 0.979. We conclude that changes in the pharmacokinetic behavior of amikacin in patients with SCI are not attributable to alterations in serum protein binding.