The parameters in a multiple-dose compartmental model can be estimated from plasma concentration observations after a single dose of drug. These estimates can be used to obtain confidence intervals for the multiple-dose concentrations. However, since the models are non-linear functions of the parameters, no exact confidence interval procedures are available. In this paper a conservative interval estimation procedure is applied to the one-compartment open model with rapid intravenous injection. Also, extended tables required in the estimation procedure are provided.