The numerical simulation of nanowires in the optical regime (400-790 THz) requires the accurate incorporation of appropriate electromagnetic constitutive material parameters. In this paper we utilize phenomenological models based on a Lorentz-Drude damped oscillator for describing the optical properties of an arbitrary solid . A computationally efficient method of including these constitutive parameters in a full-wave electromagnetic solver is presented through the use of equivalent circuit models and integral equations. These models can be represented as equivalent electric circuits which can be simulated with both frequency-domain  and time-domain  EFIE formulations. Integral equation solvers using these models are very efficient in terms of memory and time in comparison with other full-wave solvers such as the FDTD method. It is demonstrated that nanowires at near infrared and the lower part of the visible spectrum can be accurately simulated with integral equations .