Background:  HIV/hepatitis B virus (HBV) co-infection is associated with a significant increase in liver-associated mortality and HBV treatment failure. Following treatment of HBV with nucleos(t)ide reverse transcriptase inhibitors (NRTI) there is a biphasic clearance of HBV, similar to that seen following treatment of HIV and hepatitis C virus (HCV). However, little is known about the impact of HIV infection on HBV viral kinetics following initiation of HBV-active HAART.

Methods:  HIV/HBV-co-infected patients (n = 18) were enrolled in a viral kinetics sub-study of the tenofovir (TDF) in HIV/HBV-co-infection study (TICO). TICO is a prospective, randomized (1:1:1) trial of TDF + zidovudine (AZT) vs lamivudine (3TC) + zidovudint (AZT) vs TDF+3TC within an efavirenz (EFV) -based HAART regimen initiated in ART-naïve patients with HIV/HBV co-infection in Thailand. HBV viral load was measured at days 0, 1, 2, 3, 7, 10, 14, 17, 21, 28, 42, and 56 using a combination of the bDNA assay (limit of detection 2000 copies/mL) and COBAS Taqman assay (limit of detection 200 copies/mL). HIV viral load, CD4⁺ T-cell count, and alanine aminotransferase (ALT) were also quantified regularly. To fit the viral load data, we used our model of HBV kinetics, which allows the estimation of treatment efficacy, viral clearance, and infected cell loss.

Results:  We observed a biphasic decline in HBV viral load in almost all patients (n = 17). Overall, median HBV treatment efficacy was 98%, median HBV virion half-life was 1.2 days, and median infected cell half-life was 8.1 days (range 4 days to >200 days). The viral dynamic parameters were not significantly different from previous reports from us and others following treatment of HBV mono-infected patients with HBV-active nucleoside reverse transcriptase inhibitors (NRTI) (n = 34; median virion half-life 0.9 days and median infected cell half-life 12 days). We did not observe any differences in HBV dynamic parameters between the 3TC, TDF, and TDF+3TC treatment arms (median efficacy 98%, 98%, and 99%, respectively). Moreover, there was no significant association between the HBV dynamic parameters and median (range) CD4⁺ T-cell count 26 (6 to 233) cells/µL, ALT 56 (17 to 181) U/L or log₁₀, HIV viral load 4.7 (3.5 to 5.6) copies/mL at baseline.

Conclusions:  HBV viral kinetics following initiation of HBV-active HAART is not changed by HIV co-infection. The efficacy of anti-HBV treatment (as measured by the inhibition of HBV production) in HIV/HBV co-infection, is similar to that seen following treatment of HBV mono-infection.