Modelling the impact of treatment with individual antiretrovirals

HIV Treatment and Prevention: A Simple Model to Determine Optimal Investment

OBJECTIVE

To create a simple model to help public health decision makers determine how to best invest limited resources in HIV treatment scale-up and prevention.

METHOD

A linear model was developed for determining the optimal mix of investment in HIV treatment and prevention, given a fixed budget. The model incorporates estimates of secondary health benefits accruing from HIV treatment and prevention and allows for diseconomies of scale in program costs and subadditive benefits from concurrent program implementation. Data sources were published literature. The target population was individuals infected with HIV or at risk of acquiring it. Illustrative examples of interventions include preexposure prophylaxis (PrEP), community-based education (CBE), and antiretroviral therapy (ART) for men who have sex with men (MSM) in the US. Outcome measures were incremental cost, quality-adjusted life-years gained, and HIV infections averted.

RESULTS

Base case analysis indicated that it is optimal to invest in ART before PrEP and to invest in CBE before scaling up ART. Diseconomies of scale reduced the optimal investment level. Subadditivity of benefits did not affect the optimal allocation for relatively low implementation levels. The sensitivity analysis indicated that investment in ART before PrEP was optimal in all scenarios tested. Investment in ART before CBE became optimal when CBE reduced risky behavior by 4% or less. Limitations of the study are that dynamic effects are approximated with a static model.

CONCLUSIONS

Our model provides a simple yet accurate means of determining optimal investment in HIV prevention and treatment. For MSM in the US, HIV control funds should be prioritized on inexpensive, effective programs like CBE, then on ART scale-up, with only minimal investment in PrEP.

Factors associated with short-term changes in HIV viral load and CD4(+) cell count in antiretroviral-naive individuals

Objectives:

Among antiretroviral therapy (ART)-naive individuals, viral load levels tend to increase and CD4⁺ cell counts decline over time. We sought to explore the rate of change and influence of other factors associated with these markers of HIV progression.

Design:

An observational cohort collaboration study.

Methods:

A total of 158 385 pairs of consecutive viral load and CD4⁺ cell count simultaneously measured from 34 384 ART-naive individuals in the COHERE database were analysed. Annual changes and factors associated with these changes were estimated using generalized estimating equations.

Results:

Viral load continued to rise at a mean [95% confidence interval (CI)] rate of 0.091 (0.086–0.096) log₁₀ copies/ml per year. A faster rise in viral load was significantly associated with older age, such that for every 10 years older, it was a mean 0.022 log₁₀ copies/ml per year greater. The mean (95% CI) CD4⁺ cell count change was −78.0 (−80.1 to −76.0) cell/μl per year and it was strongly associated with a higher current viral load: for every 1 log₁₀ copies/ml higher, CD4⁺ cell count declined by an additional 37.6 cells/μl per year (P < 0.001). Current viral load was a stronger predictor of CD4⁺ cell count depletion than baseline viral load. Neither sex, race nor transmission by injecting drug use was associated with change in either the viral load or CD4⁺ cell count.

Discussion:

We found that in ART-naive individuals, viral load continues to increase over time and more sharply in those who are older. Our results also suggest that higher current viral load is strongly associated with ongoing rate of CD4⁺ cell count depletion.

A methodological review of models used to estimate the cost effectiveness of antiretroviral regimens for the treatment of HIV infection

The aim of this article was to perform a detailed methodological review of models used to estimate the cost effectiveness of drug treatment regimens for HIV infection in Europe and North America and assess the relationship between the different modeling approaches or key structural assumptions and the results. Electronic searches in three databases (MEDLINE, EMBASE, and the Cochrane Library) identified the cost-effectiveness models. Modeling approaches and structural assumptions were abstracted for all models. For three case studies of multiple analyses that compared the cost effectiveness of two drug regimens using the same clinical data inputs, differences in results were compared with differences in modeling approaches and structural assumptions. Forty-one model publications were reviewed. Recent models included Monte Carlo simulations, Markov models, or discrete-event simulation models, all including multiple lines of therapy and capturing the long-expected duration of efficacy of highly active antiretroviral therapy. In the three case studies, assumptions about the duration of efficacy after the trial time period, whether differences between the two regimens persist after the trial time period, the sequence of regimens after initial regimen failure, and the cost and utility assigned to adverse events, but not the modeling approach, were the most important factors in explaining differences in the results. As the models and treatment pathways get more complex, models should be validated using clinical trial data and local observational databases. The results of sensitivity analyses testing the impact of the structural assumptions that might change the results as identified in this review should also be presented in modeling papers.

Antiviral agents and HIV prevention: controversies, conflicts, and consensus

Antiviral agents can be used to prevent HIV transmission before exposure as preexposure prophylaxis (PrEP), after exposure as postexposure prophylaxis, and as treatment of infected people for secondary prevention. Considerable research has shed new light on antiviral agents for PrEP and for prevention of secondary HIV transmission. While promising results have emerged from several PrEP trials, the challenges of poor adherence among HIV-negative clients and possible increase in sexual risk behaviors remain a concern. In addition, a broader pipeline of antiviral agents for PrEP that focuses on genital tract pharmacology and safety and resistance issues must be developed. Antiretroviral drugs have also been used to prevent HIV transmission from HIV-infected patients to their HIV-discordant sexual partners. The HIV Prevention Trials Network 052 trial demonstrated nearly complete prevention of HIV transmission by early treatment of infection, but the generalizability of the results to other risk groups - including intravenous drug users and MSM - has not been determined. Most importantly, the best strategy for use of antiretroviral agents to reduce the spread of HIV at either the individual level or the population level has not been developed, and remains the ultimate goal of this area of investigation.

A literature review of reporting standards of HIV progression models

OBJECTIVE

We conducted a systematic review of HIV progression models to identify the mathematical structures used, the main research questions and key model aspects in terms of quality and robustness.

METHODS

We searched for articles published before February 2009 that described models of HIV progression in humans. We included two strategies of search with and without MeSH terms. We classified the models by their mathematical structure and research question. We created a checklist of desirable features of the models, reviewed and classified the articles to inform our conclusions.

RESULTS

Among 3491 articles found, 93 met the inclusion criteria. Among the selected articles, 60 used transition models, 25 applied differential equations, and eight had other structures. We did not find a relation between the type of question explored and the modeling method used. None of the studies complied with the complete set of items in the checklist, but 6.5% cover at least 90% of them.

CONCLUSION

There is an enormous heterogeneity of HIV modeling exercises in terms of methods used and topics addressed, as well as in the presentation of key aspects of the articles in terms of quality and robustness.

HIV-1 treatment as prevention: the good, the bad, and the challenges

PURPOSE OF REVIEW

This work focuses on the use of antiretroviral agents to prevent the sexual transmission of HIV-1.

RECENT FINDINGS

Two randomized clinical trials demonstrated that antiretroviral agents provided before exposure to HIV-1 offer substantial protection, ostensibly directly proportional to the concentration of antiretroviral therapy (ART) in the genital secretions. Intense focus on the use of HIV treatment as prevention has led to publication of modeling exercises, ecological studies, and observational studies, most of which support the potential benefits of ART. However, the logistical requirements for successful use of ART for prevention are considerable.

SUMMARY

ART will serve as a cornerstone of combination prevention of HIV-1. Continued research will be essential to measure anticipated benefits and to detect implementation barriers and untoward consequences of such a program, especially increases in primary ART resistance.