Using a nonprogrammed calculator to solve lengthy pharmacokinetic equa
tions is time consuming and carries the potential for entry error. Sho
rter equations reduce both the time and the risk. The aminoglycosides
and vancomycin are usually administered as short infusions. The pharma
cokinetic equation describing multiple-dose administration of short in
fusions is much longer than the corresponding equation for bolus dosin
g. This study examined the percentage errors that would occur using th
e bolus equation instead of the infusion equation at various drug half
-lives. When the half-life is 5 or more times the duration of infusion
, the error in predicting concentration is 6.8% or less. Although clin
icians should make their own decisions on how much error is acceptable
and whether introducing guaranteed error is appropriate to save time
and reduce risk of potential error, it appears that the simpler bolus
equation may be used safely when the half-life is at least 5 times the
duration of the infusion.