Only a few data have thus far been published on the pharmacokinetics
of amikacin in neonates. To gain further information
on this issue, we studied a series of 32 neonates who were
treated with amikacin for suspected or documented bacterial
infection. Nineteen neonates were preterm (mean gestational
age = 32.0 ± 3.6 weeks, mean body weight = 1.74 ± 0.81 kg)
while the remaining 13 were full-term (mean body weight =
3.19 ± 0.82 kg). The 32 neonates were given amikacin by
intramuscular route. A total of 121 concentrations were measured
(average number of concentrations per patient = 3.8;
range 3-6). To estimate amikacin pharmacokinetic parameters,
the serum concentration values of the drug were fitted to
the one-compartment pharmacokinetic model. The calculated
pharmacokinetic parameters were the following (mean ± SD):
clearance = 64.6 ± 30.8 ml/h/kg; volume of distribution =
0.655 ± 0.414 liters/kg; half-life = 7.6 ± 4.4 h. These results
are similar to the values reported previously, with the important
exception of the volume of distribution, which was considerably
higher in our study. The intraindividual variability
of amikacin pharmacokinetics was evaluated by the standard
two-stage method yielding an intraindividual variability coefficient
of 28.9%. No previous estimate of this parameter has as
yet been published. The population parameters of amikacin in
neonates, derived from the present study (i.e. coefficient for
intraindividual variability and means ± SD for clearance and
volume of distribution), can be applied to a further series of
neonates to facilitate the prospective use of the bayesian method
for individualizing amikacin dosage.