Short-term measures of relative efficacy predict longer-term reductions in human immunodeficiency virus type 1 RNA levels following nelfinavir monotherapy

Viral load Reduction in SHIV-Positive Nonhuman Primates via Long-Acting Subcutaneous Tenofovir Alafenamide Fumarate Release from a Nanofluidic Implant

HIV-1 is a chronic disease managed by strictly adhering to daily antiretroviral therapy (ART). However, not all people living with HIV-1 have access to ART, and those with access may not adhere to treatment regimens increasing viral load and disease progression. Here, a subcutaneous nanofluidic implant was used as a long-acting (LA) drug delivery platform to address these issues. The device was loaded with tenofovir alafenamide (TAF) and implanted in treatment-naïve simian HIV (SHIV)-positive nonhuman primates (NHP) for a month. We monitored intracellular tenofovir-diphosphate (TFV-DP) concentration in the target cells, peripheral blood mononuclear cells (PBMC). The concentrations of TFV-DP were maintained at a median of 391.0 fmol/106 cells (IQR, 243.0 to 509.0 fmol/106 cells) for the duration of the study. Further, we achieved drug penetration into lymphatic tissues, known for persistent HIV-1 replication. Moreover, we observed a first-phase viral load decay of -1.14 ± 0.81 log10 copies/mL (95% CI, -0.30 to -2.23 log10 copies/mL), similar to -1.08 log10 copies/mL decay observed in humans. Thus, LA TAF delivered from our nanofluidic implant had similar effects as oral TAF dosing with a lower dose, with potential as a platform for LA ART.

Predicting virological decay in patients starting combination antiretroviral therapy

OBJECTIVE

Model trajectories of viral load measurements from time of starting combination antiretroviral therapy (cART), and use the model to predict whether patients will achieve suppressed viral load (≤200 copies/ml) within 6-months of starting cART.

DESIGN

Prospective cohort study including HIV-positive adults (UK Collaborative HIV Cohort Study).

METHODS

Eligible patients were antiretroviral naive and started cART after 1997. Random effects models were used to estimate viral load trends. Patients were randomly selected to form a validation dataset with those remaining used to fit the model. We evaluated predictions of suppression using indices of diagnostic test performance.

RESULTS

Of 9562 eligible patients 6435 were used to fit the model and 3127 for validation. Mean log10 viral load trajectories declined rapidly during the first 2 weeks post-cART, moderately between 2 weeks and 3 months, and more slowly thereafter. Higher pretreatment viral load predicted steeper declines, whereas older age, white ethnicity, and boosted protease inhibitor/non-nucleoside reverse transcriptase inhibitors based cART-regimen predicted a steeper decline from 3 months onwards. Specificity of predictions and the diagnostic odds ratio substantially improved when predictions were based on viral load measurements up to the 4-month visit compared with the 2 or 3-month visits. Diagnostic performance improved when suppression was defined by two consecutive suppressed viral loads compared with one.

CONCLUSIONS

Viral load measurements can be used to predict if a patient will be suppressed by 6-month post-cART. Graphical presentations of this information could help clinicians decide the optimum time to switch treatment regimen during the first months of cART.

Phase I/II study of the pharmacokinetics, safety and antiretroviral activity of tenofovir alafenamide, a new prodrug of the HIV reverse transcriptase inhibitor tenofovir, in HIV-infected adults

BACKGROUND

Tenofovir alafenamide (formerly GS-7340) is a new oral prodrug of tenofovir, a nucleotide analogue that inhibits HIV-1 reverse transcription. Unlike the currently marketed tenofovir prodrug, tenofovir disoproxil fumarate, tenofovir alafenamide is stable in plasma and then rapidly converted into tenofovir once inside cells.

METHODS

The pharmacokinetics, safety and antiviral activity of 40 or 120 mg of tenofovir alafenamide compared with 300 mg of tenofovir disoproxil fumarate when administered as monotherapy once daily for 14 days in HIV-1-infected, treatment-naive subjects was studied.

RESULTS

Administration of 40 mg of tenofovir alafenamide for 14 days resulted in lower tenofovir Cmax (13 versus 207 ng/mL) and lower systemic exposures (AUC0-t, 383 versus 1810 ng · h/mL) compared with subjects who received tenofovir disoproxil fumarate. There were higher intracellular tenofovir concentrations within peripheral blood mononuclear cells with both 40 mg of tenofovir alafenamide (8.2 μM) and 120 mg of tenofovir alafenamide (16.9 μM) compared with 300 mg of tenofovir disoproxil fumarate (0.9 μM). The most commonly observed adverse events were headache, nausea and flatulence, which occurred similarly across the three groups. After 14 days, the mean changes in HIV-1 RNA were -0.94 log₁₀copies/mL for the tenofovir disoproxil fumarate group, -1.57 log₁₀ copies/mL for the 40 mg of tenofovir alafenamide group and -1.71 log₁₀ copies/mL for the 120 mg of tenofovir alafenamide group. The mean first-phase HIV-1 RNA decay slopes were -0.36, -0.63 and -0.64 for the tenofovir disoproxil fumarate group, the 40 mg of tenofovir alafenamide group and the 120 mg of tenofovir alafenamide group, respectively. No resistance mutations to either tenofovir alafenamide or tenofovir disoproxil fumarate were detected.

CONCLUSIONS

Tenofovir alafenamide, a new once-daily oral prodrug of tenofovir, showed more potent anti-HIV-1 activity and higher intracellular tenofovir levels compared with tenofovir disoproxil fumarate, while maintaining lower plasma tenofovir exposure at 40 mg with good tolerability over 14 days of monotherapy.

Abacavir and tenofovir disoproxil fumarate co-administration results in a nonadditive antiviral effect in HIV-1-infected patients

OBJECTIVES

To evaluate a potential pharmacodynamic/pharmacokinetic interaction between abacavir (ABC) and tenofovir disoproxil fumarate (TDF).

DESIGN AND METHODS

This randomized trial compared 7 days of ABC or TDF monotherapy, separated by a 35-day washout, with 7 days of ABC + TDF dual-therapy in treatment-naive, HIV-1-infected patients. During each 7-day course, the slope of the phase I viral decay was estimated and steady-state intracellular concentrations of carbovir triphosphate (CBV-TP), deoxyguanosine triphosphate (dGTP), tenofovir diphosphate (TFV-DP) and deoxyadenosine triphosphate (dATP) were determined.

RESULTS

Twenty-one participants were randomized to initial monotherapy with ABC (n = 11) or TDF (n = 10). The addition of TDF did not increase the slope of viral decay compared to ABC alone (-0.15 log10 per day vs. -0.16 log10 per day, respectively). No decrease in CBV-TP or TFV-DP between monotherapy and dual-therapy was observed. However, intracellular dATP concentrations increased between monotherapy and dual-therapy [median dATP (fmol/10 cells) 3293 vs. 4638; P = 0.08], although this difference was significant only among patients randomized to TDF [median dATP (fmol/10 cells) 3238 vs. 4534; P = 0.047]. A lower TFV-DP-to-dATP ratio was associated with reduced viral decay during dual-therapy (rho = -0.529; P = 0.045).

CONCLUSION

In this study, the viral decay during ABC and TDF dual-therapy was similar to that during ABC therapy alone, suggesting a nonadditive antiviral effect. This negative pharmacodynamic interaction was not explained by changes in CBV-TP or TFV-DP concentrations. Rather, modest increases in endogenous dATP pools were associated with reduced antiviral potency of TDF during co-administration with ABC.

Plasma HIV RNA decline and emergence of drug resistance mutations among patients with multiple virologic failures receiving resistance testing-guided HAART

Early recognition of virologic failure in patients with extensive drug resistance receiving salvage-HAART is essential to avoid exposure to subinhibitory regimens. We studied plasma viral load (PVL) decline and rates of drug-resistance mutation (DRM) accumulation in such patients. A prospective, 48 week study of 38 heavily pretreated patients receiving genotypic resistance testing (GRT)-guided HAART was conducted. The rate of PVL decline was studied by weekly PVL determinations. To assess DRM accumulation, serial GRTs were performed in all nonresponders (never reaching PVL <50 or two PVLs >50 copies/ml after suppression). Over 48 weeks, 10 patients (26%) were nonresponders. Receiving less then two fully active drugs and having an elevated number of PI and NRTI mutations at baseline were strongly associated with virologic failure. There was no evidence of a difference in the change from baseline PVL to week 1 and 2 between responders and nonresponders. By contrast, PVL reductions from week 2 to week 3 and thereafter were significantly greater for responders (p < 0.01). Among nonresponders, the incidence rates per patient-month (95% CI) of emergent DRM were 0.67 (0.13-1.20), 0.40 (0.00-0.74), and 0.37 (0.00-0.75) at weeks 4, 8, and 24, respectively. Having limited baseline resistance, receiving at least two fully active drugs, and showing constant PVL reductions from week 2 to week 3 and thereafter were predictive of virologic response. In contrast, early changes in PVL levels were not. Virologic failure was associated with detection of emergent DRMs. Virologic rebound in patients on salvage-HAART should be addressed aggressively.

Week-12 response to therapy as a predictor of week 24, 48, and 96 outcome in patients receiving the HIV fusion inhibitor enfuvirtide in the T-20 versus Optimized Regimen Only (TORO) trials

BACKGROUND

Early virological response to antiretroviral therapy is predictive of long-term treatment outcome in therapy-naive patients. In treatment-experienced patients, such correlations are less well defined, because initial responses may be less pronounced and transient because of accumulated cross-resistance to prior therapies. Our objectives were to explore how the virological and immunological status of treatment-experienced patients at an early time point (week 12) during enfuvirtide-based therapy predicted their responses at weeks 24, 48, and 96 in the T-20 versus Optimized Regimen Only (TORO) trials.

METHODS

Post hoc, modified, on-treatment and intent-to-treat analyses were performed to determine whether the relationship between virological and immunological outcomes at weeks 24, 48, and 96 were predicted by the patients' week-12 responses to therapy.

RESULTS

Using a modified on-treatment analysis for patients who, by week 12, achieved a decrease in their HIV-1 RNA load of > or =1 log10 copies/mL, 39.2% (95% CI, 33.6%-44.8%) and 59.5% (95% CI, 53.8%-65.1%) achieved a viral load of <50 copies/mL or <400 copies/mL at week 96, respectively, compared with 1.3% (95% CI, 0%-3.8%) and 2.6% (95% CI, 0%-6.1%) of patients, respectively, who did not achieve an early virological response. Using the same modified on-treatment analysis method for patients who, at week 12, achieved a CD4 cell count increase of > or =50 cells/mm3, 87.2% (95% CI, 82.6-91.8) maintained or improved this response through week 96, compared with 56.6% (95% CI, 47.5-65.8) of patients who did not achieve this early categorical immunological response.

CONCLUSION

Enfuvirtide-based treatment regimens are associated with a rapid and durable response. Week-12 virological and immunological responses to treatment with enfuvirtide are predictive of subsequent outcomes in triple-class treatment-experienced patients.

Increased Antiretroviral Potency by the Addition of Enfuvirtide to a Four-Drug Regimen in Antiretroviral-Naive, HIV-Infected Patients

Objective

To assess if enfuvirtide (ENF) increases antiviral activity of a highly active four-drug antiretroviral (ARV) regimen containing lopinavir/ritonavir, efavirenz, lamivudine and tenofovir in ARV-naive, HIV-infected patients.

Methods

Pilot study in ARV-naive, HIV-infected patients with viral load (VL) >10,000 copies/ml and no documented resistance to any of the study drugs. Patients were randomized to receive ENF (ENF Group) or not (Control Group) in combination with lopinavir/ritonavir, efavirenz, lamivudine and tenofovir as a backbone. The primary endpoint was to assess differences in the HIV-1 RNA decay rate during the first phase of viral decay. VL and treatment adherence were measured at baseline, every 6 h during the first 3 days, and once daily from day 3 to 6. Individual HIV-1 RNA decay rates were obtained using a non-linear least squares regression model.

Results

Eight subjects were included in each study group. Mean (sd) baseline VL was 4.98 (0.38) log10 copies/ml in the ENF Group and 5.10 (0.49) log10 copies/ml in the Control Group ( P=0.607). Baseline CD4+ cell count was 463 (306) and 362 (225) cells/mm3 in the ENF and the Control Group, respectively ( P=0.484). First phase HIV-1 RNA decay rate was 0.802 (0.127) d-1 in the ENF Group and 0.624 (0.182) d-1 in the Control Group ( P=0.045). By day 6, VL was 3.55 (0.40) and 3.92 (0.36) log10 copies/ml in the ENF and the Control Group, respectively ( P=0.079).

Conclusion

The addition of ENF increased the antiviral potency of a highly active four-drug ARV regimen by 28.5% in ARV-naive, HIV-infected patients. The clinical impact of this finding should be assessed.

Modeling long-term HIV dynamics and antiretroviral response: effects of drug potency, pharmacokinetics, adherence, and drug resistance

We propose a long-term HIV-1 dynamic model by considering drug potency, drug exposure, and drug susceptibility. Using a Bayesian approach, HIV-1 dynamic parameters were estimated by fitting the model to viral load data from a phase 1/2 randomized clinical study of 2 indinavir (IDV)/ritonavir (RTV)-containing highly active antiretroviral (ARV) therapy regimens in HIV-infected subjects who had previously failed protease inhibitor-containing ARV therapies. A large between-subject variation in estimated viral dynamic parameters was observed, even after accounting for variations in drug exposure and drug susceptibility, suggesting that characteristics of HIV-1 dynamics are host dependent. Significant correlations of baseline factors such as HIV-1 RNA levels and CD4 cell counts with viral dynamic parameters were found. These correlations coincide with biologic interaction mechanisms between HIV and the host immune system and also provide an explanation for the correlations between the baseline viral load and phase 1 viral decay rate, for which inconsistent results have been reported in the literature. The relations between viral dynamic parameters and virologic response were established, and these results suggest that viral dynamic parameters may play an important role in determining treatment success or failure. In particular, we estimated a drug efficacy threshold for each patient that can be used to assess whether an ARV regimen is potent enough to suppress HIV viruses in the individual patient. Our findings indicate that it is necessary to individualize the ARV regimen to treat HIV-1-infected patients. The proposed mathematic models and statistical techniques may provide a framework to simulate and predict antiviral response for individual patients.

[Therapeutic strategies for HIV infection: early response to antiretroviral treatment, predictive factor for the longer term response]

Despite the wide armamentarium available against the human immunodeficiency virus, the efficacy of therapeutic molecules is reduced by the selection of resistant viral strains. Several data argue in favour of an early control of viral replication ever since the first treatment: the intensity of the initial viral replication, as well as results of studies on antiretroviral drugs given as first line treatment and on the early inhibitory response of viral replication. Although an early control is essential for long-term antiviral success, the optimal time limit for the virologic response still needs to be established early knowledge of the virologic response could prove useful in the evaluation of new and more successful therapeutic combinations. Nevertheless, the impact of an earlier control of viral replication on long-term treatment efficacy and on the prevention of resistance emergence deserves further investigation.

Pharmacokinetics, pharmacodynamics and drug interaction potential of enfuvirtide

Enfuvirtide, the first fusion inhibitor approved for the treatment of HIV-1 infection, is a synthetic peptide that binds to HIV-1 glycoprotein 41, blocking the fusion of viral and cellular membranes. When administered subcutaneously at the recommended dose of 90 mg twice daily with optimised background antiretroviral therapy, enfuvirtide significantly reduces plasma HIV-1 RNA levels up to 48 weeks compared with optimised background therapy alone. Enfuvirtide exhibits a small volume of distribution (5.48 L), low systemic clearance (1.4 L/h) and high plasma protein binding (92%). Less than 17% of enfuvirtide is converted to a minimally active deaminated form of the parent drug. Both enfuvirtide and its metabolite are primarily eliminated via catabolism to amino acid residues. Following subcutaneous administration, enfuvirtide is almost completely absorbed, and exposure increases almost linearly with dose over the range 45-180 mg. When administered at the recommended dose in adults, subcutaneous absorption is slow and protracted, resulting in relatively flat steady-state plasma concentration-time profiles. Bioavailability is high (84.3%) and the elimination half-life (3.8 hours) supports twice-daily administration. Comparable absorption was observed from three different anatomical injection sites. The pharmacokinetic-pharmacodynamic relationship indicates that the recommended dose, in combination with other active antiretrovirals, is optimal. Enfuvirtide clearance is influenced to a small extent by sex and bodyweight but this does not necessitate dosage adjustment. In vitro and in vivo studies indicate that enfuvirtide has a low potential to interact with concomitantly administered drugs. Enfuvirtide did not influence concentrations of drugs metabolised by cytochrome P450 (CYP) 3A4, CYP2D6 or N-acetyltransferase, and had only minimal effects on those metabolised by CYP1A2, CYP2E1 or CYP2C19. Coadministration of ritonavir, ritonavir-boosted saquinavir or rifampicin (rifampin) did not result in clinically significant changes in enfuvirtide pharmacokinetics. In HIV-1-infected paediatric patients, subcutaneous dosages based on bodyweight (2 mg/kg twice daily) produce pharmacokinetics broadly similar to those observed in adults administered 90 mg twice daily.

TMC125 exerts similar initial antiviral potency as a five-drug, triple class antiretroviral regimen

OBJECTIVE

TMC125, a next generation, non-nucleoside reverse transcriptase inhibitor (NNRTI), demonstrated a remarkable decline of plasma HIV-1 RNA during a phase IIa study. We compared the initial rate of decline of plasma HIV-1 RNA achieved by TMC125 monotherapy with that of a triple class, five-drug regimen, containing drugs from all three currently licensed classes (zidovudine, lamivudine, abacavir, indinavir and nevirapine).

METHODS

The decline in plasma HIV-1 RNA of 12 HIV-1 infected, antiretroviral (ART) naive patients treated for 1 week with TMC125 monotherapy was compared with that observed in the ERA study (n = 11). The plasma HIV-1 RNA elimination rate constant was calculated based on at least four plasma HIV-1 RNA measurements during the first week of treatment (first-order elimination) and compared using the Student's t test.

RESULTS

Median ages were 23 and 38 years for TMC125 and ERA patients, respectively (P = 0.001), median baseline plasma HIV-1 RNA levels were 4.2 and 4.8 log10 copies/ml (P = 0.001) and median baseline CD4 T-cell counts were 458 x 10(6) and 360 x 10(6) cells/l (P = 0.08). The median plasma HIV-1 RNA elimination rate constant was 0.68/day in TMC125 treated patients, and 0.56/day in ERA participants (P = 0.24). The median decline in plasma HIV-1 RNA after 7 days was 1.92 and 1.76 log10 copies (P = 0.77) and the median increase of CD4 T cells was 119 x 10(6) and 60 x 10(6) cells/l, respectively (P = 0.29).

CONCLUSION

Monotherapy with TMC125 in ART-naive, HIV-1-infected individuals resulted in a similar rate of decline of plasma HIV-1 RNA during 1 week of therapy as therapy with a five-drug regimen.

A randomized, double-blind, placebo-controlled trial of TMC125 as 7-day monotherapy in antiretroviral naive, HIV-1 infected subjects

OBJECTIVE

To evaluate antiviral activity, tolerability, safety and pharmacokinetics of treatment with TMC125 (a non-nucleoside reverse transcriptase inhibitor), 900 mg twice daily for 7 days.

DESIGN

Randomized, double-blind, placebo-controlled, phase IIA clinical trial.

SETTING

Two hospital clinics in Moscow and St Petersburg, Russian Federation.

PARTICIPANTS

Nineteen antiretroviral-naive, HIV-1-infected subjects.

INTERVENTIONS

Randomization (2:1) was to twice daily treatment with either 900 mg TMC125 or matched placebo as monotherapy for 7 days.

MAIN OUTCOME MEASURES

Change in plasma HIV-1 RNA from baseline values (primary); change in CD4 cell counts from baseline, and evaluation of safety, tolerability and pharmacokinetics of TMC125 treatment (secondary).

RESULTS

A mean decrease from baseline in plasma HIV-1 RNA of 1.99 log10 copies/ml and 0.06 log10 copies/ml was achieved after 7 days in the TMC125 and placebo groups, respectively (P < 0.001). Plasma viral daily decay rates of 0.33 log10 copies/ml and 0.02 log10 copies/ml were observed in the TMC125 and placebo groups, respectively (P < 0.001). A steady-state plasma concentration of TMC125 was attained within 5 days of treatment with a mean minimum concentration of 246 ng/ml and a mean maximum concentration of 419 ng/ml. The majority of subjects did not report any adverse events. No abnormalities consistent with changes in blood chemistry, haematology, urinalysis, electrocardiograph or vital signs were observed.

CONCLUSIONS

TMC125 administered as monotherapy for 7 days yielded a 1.99 log10 copies/ml reduction in HIV-1 RNA in antiretroviral-naive, HIV-1-infected subjects. TMC125 was well tolerated and represents a promising and highly potent, next generation non-nucleoside reverse transcriptase inhibitor candidate.

Viral dynamics and their relations to baseline factors and longer term virologic responses in treatment-naive HIV-1-infected patients receiving abacavir in combination with HIV-1 protease inhibitors

From a study of 71 HIV-1-infected patients receiving abacavir in combination with 1 of 5 different HIV-1 protease inhibitors (indinavir, ritonavir, saquinavir, nelfinavir, or amprenavir), we found that the baseline HIV-1 RNA levels were highly predictive of the viral decay rates. The baseline HIV-1 RNA levels were negatively correlated with the first phase viral decay rates (r = -0.77, P < 0.001) and positively correlated with the second phase viral decay rates (r = 0.68, P < 0.001). In addition, the first phase viral decay rate was positively correlated with CD4+ cell increases. No significant correlation was found between viral decay rates and longer term (24 weeks) virologic responses, and no difference in viral decay rates was found among the 5 study regimens. These data suggest that the potency of the 5 treatment regimens was similar and was not predictive of long-term virologic failure.

Determining the antiviral activity of tenofovir disoproxil fumarate in treatment-naive chronically HIV-1-infected individuals

OBJECTIVE

To assess the efficacy of tenofovir disoproxil fumarate (TDF) monotherapy by following the initial rate of decline in plasma viral load, which is a measure of the efficacy of therapy in blocking viral replication.

DESIGN

An open-label, single-site study of TDF monotherapy in 10 antiretroviral drug-naive chronically HIV-1-infected individuals.

METHODS

Antiviral responses were assessed at baseline and during 21 days of monotherapy with TDF by measuring plasma HIV-1 RNA levels. The rate of change in HIV-1 RNA from baseline was determined both by linear regression and by fitting to a published model. Slopes were compared with those previously determined for ritonavir monotherapy.

RESULTS

Over 21 days, mean plasma HIV-1 RNA levels in the TDF-treated patients fell 1.5 log(10) copies/ml (range, 0.7-2.0). The initial rates of decline in plasma HIV-1 RNA in the 10 TDF-treated patients and in 25 protease inhibitor-naive subjects treated with ritonavir monotherapy were nearly identical.

CONCLUSIONS

The reduction in plasma HIV-1 RNA with TDF monotherapy was comparable with the decline observed in previous studies of protease inhibitor monotherapy. TDF is a potent antiretroviral agent and has comparable inherent antiviral activity with that of ritonavir, a potent protease inhibitor. These data support further study of TDF-based regimens in simplified combinations of antiviral agents as initial treatment for chronic HIV-1 infection.

Early factors in successful anti-HIV treatment

Rapid suppression of plasma HIV RNA and sustained increase in CD4 cell count following highly active antiretroviral therapy (HAART) regimens can be prognostic indicators of long-term virologic treatment success. Routine measurement of plasma HIV RNA levels (viral load or VL) at four and eight or 12 weeks is recommended after initiating treatment because favorable changes are predictive of durable success at six months and longer. Early favorable response of VL, as soon as six days after HAART initiation, can signify that the patient is initially adherent to treatment, which is necessary in the long term for a successful regimen. Early favorable response is also an indicator of adequate pharmacokinetic profile and potent antiviral activity of the drug regimen. It also can indicate that the predominant HIV strain infecting the patient is sensitive to the treatment regimen. These factors of adherence, drug levels, potency, and susceptibility favor a long-term durable response. Evaluation of early treatment responses may create the opportunity to promptly change the HAART regimen in the event of an anticipated long-term failure, delaying or preventing the evolution of drug resistance, and improving the effectiveness of treatment overall.

Modelling viral and immune system dynamics

During the past 6 years, there have been substantial advances in our understanding of human immunodeficiency virus 1 and other viruses, such as hepatitis B virus and hepatitis C virus, that cause chronic infection. The use of mathematical modelling to interpret experimental results has made a significant contribution to this field. Mathematical modelling is also improving our understanding of T-cell dynamics and the quantitative events that underlie the immune response to pathogens.

Correlation between reduction in plasma HIV-1 RNA concentration 1 week after start of antiretroviral treatment and longer-term efficacy

BACKGROUND

Early assessment of antiretroviral drug efficacy is important for prevention of the emergence of drug-resistant virus and unnecessary exposure to ineffective drug regimens. Current US guidelines for changing therapy are based on measurements of plasma HIV-1 RNA concentrations 4 or 8 weeks after the start of treatment with cut-off points of 0.75 or 1.00 log, respectively. We investigated the possibility of assessing drug efficacy from measurements of plasma HIV-1 concentrations made during the first week on therapy.

METHODS

The kinetics of virus decay in plasma during the first 12 weeks of treatment was analysed for 124 HIV-1-infected patients being treated for the first time with a protease inhibitor. Patients with a continuous decline of HIV-1 concentrations and in whom HIV-1 was either undetectable or declined by more than 1.5 log at 12 weeks were defined as good responders; the rest were poor responders.

FINDINGS

The individual virus decay rate constants (k) at day 6 correlated significantly (r>0.66, p<0.0001) with changes in HIV-1 concentrations at 4, 8, and 12 weeks, and correctly predicted 84% of the responses with a cut-off value of k=0.21 per day (in log scale). Reduction in plasma HIV-1 of less than 0.72 log by day 6 after initiation of therapy predicted poor long-term responses in more than 99% of patients.

INTERPRETATION

These results suggest that changes in HIV-1 concentration at day 6 after treatment initiation are major correlates of longer-term virological responses. They offer a very early measure of individual long-term responses, suggesting that treatment could be optimised after only a few days of therapy.