Part A: Drug Interaction Study of Sofosbuvir and Antiretroviral Therapy (ART) Combinations in HIV and Hepatitis C Virus (HCV) Co-infected Patients. Part B: Efficacy and Safety of Sofosbuvir for 12 Weeks in HIV/HCV Co-infected Patients.

Sofosbuvir (SOF) 400 mg (1 × 400 mg tablet or 2 × 200 mg tablets) administered orally once daily

Efavirenz (EFV) 600 mg/emtricitabine (FTC) 200 mg/tenofovir disoproxil fumarate (TDF) 300 mg fixed-dose combination (FDC) tablet administered orally once daily

Efavirenz (EFV) 600 mg tablet administered orally once daily

Zidovudine (ZDV) 300 mg/lamivudine (3TC) 150 mg FDC tablet administered orally twice daily

Atazanavir (ATV) 400 mg tablet administered orally once daily

Ritonavir (RTV) 100 mg tablet administered orally once daily

FTC/TDF (200/300 mg) FDC tablet administered orally once daily

Darunavir (DRV) 800 mg (2 × 400 mg tablets) administered orally once daily

Raltegravir (RAL) 400 mg administered administered orally twice daily

Pegylated interferon alfa (PEG) 180 μg administered once weekly by subcutaneous injection

Ribavirin (RBV) tablets administered orally in a divided daily dose according to package insert weight-based dosing recommendations (\< 75kg = 1000 mg and ≥ 75 kg = 1200 mg)