When to start antiretroviral therapy

The unanswered question: when to initiate antiretroviral therapy in children with HIV infection

PURPOSE OF REVIEW

The question of when to initiate antiretroviral treatment for children is perhaps the most critical unanswered question in pediatric HIV therapeutics. With large numbers of children throughout the world acquiring HIV infection and with improved global access to HIV treatment it is particularly timely to consider the optimal time to initiate antiretroviral therapy in infants, children and adolescents.

RECENT FINDINGS

Early treatment can result in suppression of HIV viremia, immune preservation and prevention of disease progression. This must be balanced by the challenges of maintaining adherence to multidrug regimens, the risks of selecting drug-resistant virus, and long and short-term toxicities of medications.

SUMMARY

This review provides a framework within which to consider when to initiate children on antiretroviral treatment. A child's age and developmental status, where they live, and the goals and expectations for treatment provide a context for balancing the risks of disease progression with the risks of drug-related toxicities and viral resistance.

Considerations in the rationale, design and methods of the Strategic Timing of AntiRetroviral Treatment (START) study

BACKGROUND

Untreated human immunodeficiency virus (HIV) infection is characterized by progressive depletion of CD4+ T lymphocyte (CD4) count leading to the development of opportunistic diseases (acquired immunodeficiency syndrome (AIDS)), and more recent data suggest that HIV is also associated with an increased risk of serious non-AIDS (SNA) diseases including cardiovascular, renal, and liver diseases and non-AIDS-defining cancers. Although combination antiretroviral treatment (ART) has resulted in a substantial decrease in morbidity and mortality in persons with HIV infection, viral eradication is not feasible with currently available drugs. The optimal time to start ART for asymptomatic HIV infection is controversial and remains one of the key unanswered questions in the clinical management of HIV-infected individuals.

PURPOSE

In this article, we outline the rationale and methods of the Strategic Timing of AntiRetroviral Treatment (START) study, an ongoing multicenter international trial designed to assess the risks and benefits of initiating ART earlier than is currently practiced. We also describe some of the challenges encountered in the design and implementation of the study and how these challenges were addressed.

METHODS

A total of 4000 study participants who are HIV type 1 (HIV-1) infected, ART naïve with CD4 count > 500 cells/µL are to be randomly allocated in a 1:1 ratio to start ART immediately (early ART) or defer treatment until CD4 count is <350 cells/µL (deferred ART) and followed for a minimum of 3 years. The primary outcome is time to AIDS, SNA, or death. The study had a pilot phase to establish feasibility of accrual, which was set as the enrollment of at least 900 participants in the first year.

RESULTS

Challenges encountered in the design and implementation of the study included the limited amount of data on the risk of a major component of the primary endpoint (SNA) in the study population, changes in treatment guidelines when the pilot phase was well underway, and the complexities of conducting the trial in a geographically wide population with diverse regulatory requirements. With the successful completion of the pilot phase, more than 1000 participants from 100 sites in 23 countries have been enrolled. The study will expand to include 237 sites in 36 countries to reach the target accrual of 4000 participants.

CONCLUSIONS

START is addressing one of the most important questions in the clinical management of ART. The randomization provided a platform for the conduct of several substudies aimed at increasing our understanding of HIV disease and the effects of antiretroviral therapy beyond the primary question of the trial. The lessons learned from its design and implementation will hopefully be of use to future publicly funded international trials.

Modelling and control of HIV dynamics

Various models of HIV infection and evolution have been considered in the literature. This paper considers a variant of the Wodarz and Nowak mathematical model, adding "aggressiveness" as a new state variable in order to quantify the strength of the virus and its response to drugs. Although the model proposed is relatively simple, simulation results suggest that it may be useful in predicting the impact of the effectiveness of therapy on HIV dynamics.

Considerations in the design of randomized controlled trials evaluating the optimal time to initiate antiretroviral therapy in previously untreated HIV-1-infected patients

PURPOSE OF REVIEW

This paper addresses design issues around 'when to start' trials in adults and children and in chronic and acute HIV infection. Issues for young children treated soon after birth and recently seroconverting adults differ, and are also discussed.

RECENT FINDINGS

No trials have been published addressing this question for combination antiretroviral therapy in chronic HIV infection, and the evidence base for guidelines has largely been derived from observational studies. The biases inherent in observational data and recent results from the adult SMART trial may have moved the level of equipoise from 'unstable certainty' (mitigating against randomization) to a renewed call for a very large clinical endpoint trial of when to start therapy in the era of highly active antiretroviral therapy. Older children could also be enrolled in such a trial, as the predictive value of CD4 cell count values in children over 5 years and young adults. In acute infection, ongoing trials in adults and children is similar considering strategies of early short-term combination antiretroviral therapy compared with deferred therapy. Although not strictly 'when to start trials', these approaches could reduce life-long exposure to antiretroviral therapy while maintaining clinical and immunological well being.

SUMMARY

Issues in the design of a future randomized trial of when to start antiretroviral therapy in chronic HIV infected adults and older children are discussed, while the role of early limited therapy in primary infection awaits results of ongoing trials.