  The Lewis and Riesenfeld method has been investigated, by Ramos et al in
Ref.[1], for quantum systems governed by time-dependent PT symmetric
Hamiltonians and particularly where the quantum system is a particle submitted
to action of a complex time-dependent linear potential. We discuss the method
they used and propose an alternative one which leads to physically acceptable
uncertainty product and to complex x and p expectation values but describe the
classical motion. We used, for this situation, a linear pseudo hermitian
invariant operator which allow us to solve analytically the time-dependent
Schr\"odinger equation for this problem and to construct a Gaussian wave packet
solution. The normalization condition for the invariant eigenfunctions with the
Dirac delta function is correctly obtained, contrary to what is stated in
Ref.[1].
