4. Female subjects of childbearing potential with a negative serum pregnancy test prior to entry into the study and who are practicing an adequate method of birth control (eg oral or parenteral contraceptives, intrauterine device, barrier, abstinence) and who do not plan to become pregnant during the course of the study. Female subjects may be included without a negative serum pregnancy test if they are surgically sterile or at least 2 years post-menopausal.