  A class of nonlinear models combining a pharmacokinetic compartmental model
and a pharmacodynamic Emax model is introduced. The locally D-optimal (LD)
design for a four-parameter composed model is found to be a saturated
four-point uniform LD design with the two boundary points of the design space
in the LD design support. For a five-parameter composed model, a sufficient
condition for the LD design to require the minimum number of sampling time
points is derived. Robust LD designs are also investigated for both models. It
is found that an LD design with $k$ parameters is equivalent to an LD design
with $k-1$ parameters if the linear parameter in the two composed models is a
nuisance parameter. Assorted examples of LD designs are presented.
