The present invention features solid compositions comprising Compound I A , I B , I C or I D , or a pharmaceutically acceptable salt thereof, in an amorphous form. Such compositions are useful for treating HCV infection. In one embodiment, Compound I A , I B , I C or I D , or a pharmaceutically acceptable salt thereof, is formulated in an amorphous solid dispersion which comprises a pharmaceutically acceptable hydrophilic polymer and preferably a pharmaceutically acceptable surfactant.