Timing of antiretroviral therapy. Use of Markov modeling and decision analysis to evaluate the long-term implications of therapy

Quantitative Evidence Synthesis Methods for the Assessment of the Effectiveness of Treatment Sequences for Clinical and Economic Decision Making: A Review and Taxonomy of Simplifying Assumptions

Sequential use of alternative treatments for chronic conditions represents a complex intervention pathway; previous treatment and patient characteristics affect both the choice and effectiveness of subsequent treatments. This paper critically explores the methods for quantitative evidence synthesis of the effectiveness of sequential treatment options within a health technology assessment (HTA) or similar process. It covers methods for developing summary estimates of clinical effectiveness or the clinical inputs for the cost-effectiveness assessment and can encompass any disease condition. A comprehensive review of current approaches is presented, which considers meta-analytic methods for assessing the clinical effectiveness of treatment sequences and decision-analytic modelling approaches used to evaluate the effectiveness of treatment sequences. Estimating the effectiveness of a sequence of treatments is not straightforward or trivial and is severely hampered by the limitations of the evidence base. Randomised controlled trials (RCTs) of sequences were often absent or very limited. In the absence of sufficient RCTs of whole sequences, there is no single best way to evaluate treatment sequences; however, some approaches could be re-used or adapted, sharing ideas across different disease conditions. Each has advantages and disadvantages, and is influenced by the evidence available, extent of treatment sequences (number of treatment lines or permutations), and complexity of the decision problem. Due to the scarcity of data, modelling studies applied simplifying assumptions to data on discrete treatments. A taxonomy for all possible assumptions was developed, providing a unique resource to aid the critique of existing decision-analytic models.

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.

A decision tree to help determine the best timing and antiretroviral strategy in HIV-infected patients

Optimal antiretroviral strategies for HIV-infected patients still need to be established. To this end a decision tree including different antiretroviral strategies that could be adopted for HIV-infected patients was built. A 10-year follow-up was simulated by using transitional probabilities estimated from a large cohort using a time-homogeneous Markov model. The desired outcome was for patients to maintain a CD4 cell count of >500 cells/mm3 without experiencing AIDS or death. For patients with a baseline HIV viral load ⩾5 log10 copies/ml, boosted protease inhibitor-based immediate highly active antiretroviral therapy (HAART) allowed them to spend 12% more time with CD4 ⩾500/mm3 than did delayed HAART (6·40 vs. 5·69 and 5·57 vs. 4·90 years for baseline CD4 ⩾500 and 350–499/mm3, respectively). In patients with a baseline HIV viral load ⩽3·5 log10 copies/ml, delayed HAART performed better than immediate HAART (6·43 vs. 6·26 and 5·95 vs. 5·18 for baseline CD4 ⩾500 and 350–499/mm3, respectively). Immediate HAART is beneficial in patients with a baseline HIV viral load ⩾5 log10 copies/ml, whereas deferred HAART appears to be the best option for patients with CD4 ⩾350/mm3 and baseline HIV viral load <3·5 log10 copies/ml.

Epidemiologic study of human immunodeficiency virus (HIV) Infection in the patients referred to health centers in Hamadan province, Iran

Acquired immunodeficiency syndrome (AIDS) is one of the most important infectious diseases threatening the world's population today. The main aim of this study was to assess the epidemiologic features of HIV/AIDS from January 1989 to March 2007 in Hamadan province, Iran. In a cross-sectional study, epidemiodemographic characteristics of HIV/AIDS-positive patients during a period of 17 years were collected from health centers in Hamadan province. This study showed that about 1.8% of HIV/AIDS cases in Iran involved people who lived in Hamadan province. Further study is needed to determine the reasons for this. From January 1989 to March 2007, 285 individuals including 275 males and 10 females were infected with HIV in this province. The study showed that 88% of patients lived in urban areas while 12% involved a rural population. Hamadan city had the highest rate of HIV/AIDS infection and death with 191 and 33 individuals, respectively. The main transmission route was intravenous drug use with 78%. From 28 patients who were entered into the AIDS phase, only 10 patients returned to health centers to be covered under definite treatment. The establishment of the Triangular Clinic can be presented as the starting point in the organization of infected people to detect HIV/AIDS. Altogether, efforts in reducing the impact of HIV in this province to date can be considered beneficial. Continuous laboratory diagnostic strategies may lead in time to therapeutic approaches that result in appropriate outcomes.

Markov modelling of HIV infection evolution in the HAART era

The aim was to investigate the impact of the main prognostic factors on HIV evolution. A multi-state Markov model was applied in a cohort of 2126 patients to estimate impact of these factors on patients' clinical and immunological evolutions. Clinical progression and immunological deterioration shared most of their prognostic factors: male gender, intravenous drug use, weight loss, low haemoglobin level (<110 g/l), CD8 cell count (<500/mm(3)) and HIV viral load (>5 log(10) copies/ml). Highly active retroviral therapy reduced the risks of clinical progression and immune deterioration whatever patients' CD4 cell count. Risk reductions were 41-60% for protease inhibitor-based and 27-68% for non-nucleoside reverse transcriptase inhibitor-based regimens. Three-year transition probabilities showed that only patients with a CD4 cell count >or=350 CD4/mm(3) could in most cases maintain their immunity. This model provides 'real life' transition probabilities from one immunological stage to another, allowing decision analyses that could help determine the beneficial therapeutic strategies for HIV-infected patients.

Agreement of decision analyses and subsequent clinical studies in infectious diseases

PURPOSE

Decision analysis techniques can compare management strategies when there are insufficient data from clinical studies to guide decision making. We compared the outcomes of decision analyses and subsequent clinical studies in the infectious disease literature to assess the validity of the conclusions of the decision analyses.

METHODS

A search strategy to identify decision analyses in infectious disease topics published from 1990 to 2005 was developed and performed using PubMed. Abstracts of all identified articles were reviewed, and infectious disease-related decision analyses were retained. Subsequent clinical trials and observational studies that corresponded to these decision analyses were identified using prespecified search strategies. Clinical studies were considered a match for the decision analysis if they assessed the same patient population, intervention, and outcome. Agreement or disagreement between the conclusions of the decision analysis and clinical study were determined by author review.

RESULTS

The initial PubMed search yielded 318 references. Forty decision analyses pertaining to 29 infectious disease topics were identified. Of the 40, 16 (40%) from 13 infectious disease topics had matching clinical studies. In 12 of 16 (75%), conclusions of at least 1 clinical study agreed with those of the decision analysis. Three of the 4 decision analyses in which conclusions disagreed were from the same topic (management of febrile children).

CONCLUSIONS

There was substantial agreement between the conclusions of decision analyses and clinical studies in infectious diseases, supporting the validity of decision analysis and its utility in guiding management decisions.

[Recommendations from the GESIDA/Spanish AIDS Plan regarding antiretroviral treatment in adults with human immunodeficiency virus infection (update January 2007)]

OBJECTIVE

This consensus document is an update of antiretroviral therapy (ART) recommendations for adult patients infected with the human immunodeficiency virus (HIV-1).

METHODS

To formulate these recommendations, a panel composed of members of the Grupo de Estudio de Sida (GESIDA; AIDS Study Group) and the Plan Nacional sobre el Sida (PNS; Spanish AIDS Plan) reviewed the advances in the current understanding of the pathophysiology of HIV, the safety and efficacy findings from clinical trials, and the results from cohort and pharmacokinetic studies published in biomedical journals or presented at scientific meetings over the last years. Three levels of evidence were defined according to the source of the data: randomized studies (level A), cohort or case-control studies (level B), and expert opinion (level C). The decision to recommend, consider or not recommend ART was established in each situation.

RESULTS

Currently, the treatment of choice for chronic HIV infection is the combination of three drugs of two different classes, including 2 nucleosides or nucleotide analogs (NRTI) plus 1 non-nucleoside (NNRTI) or 1 boosted protease inhibitor (PI/r). Initiation of ART is recommended in patients with symptomatic HIV infection. In asymptomatic patients, initiation of ART is recommended on the basis of CD4+ lymphocyte counts and plasma viral load, as follows: 1) therapy should be started in patients with CD4+ counts of < 200 cells/microl; 2) therapy should be started in most patients with CD4+ counts of 200-350 cells/microl, although it can be delayed when CD41 count persists at around 350 cells/microL and viral load is low, and 3) initiation of therapy can be delayed in patients with CD4+ counts of > 350 cells/microL. The initial objective of ART is to achieve an undetectable viral load. Adherence to therapy plays an essential role in maintaining the antiviral response. Therapeutic options are limited with the development of cross resistance and ART failure. Genotype studies are useful in these cases. More information regarding the studies analyzed and the panel recommendations for adherence, toxicity, treatment during pregnancy, patients with hepatitis B or C virus co-infection, and post-exposure prophylaxis can be accessed at www.gesida.seimc.org.

CONCLUSIONS

CD4+ lymphocyte count is the most important reference factor for initiating ART in asymptomatic patients. The large number of available drugs, the increased sensitivity of tests to monitor viral load, and the ability to determine viral resistance is leading to a more individualized approach to therapy.

Early initiation of highly active antiretroviral therapies for AIDS: dynamic choice with endogenous and exogenous learning

Criteria for initiation of highly active antiretroviral treatments (HAART) in HIV-infected patients remain a matter of debate world-wide because short-term benefits have to be balanced with costs of these therapies, and restrictions placed on future treatment options if resistant viral strains develop. On the other hand, postponing the introduction of HAART may involve a therapeutic opportunity cost if a patient's health is allowed to deteriorate to such an extent of becoming unable to benefit from new treatments currently under development when they become available. We introduce a two period model where period one treatment adoption is an irreversible act with future, but uncertain, consequences. New information, both endogenous and exogenous, arises over time and shapes the conditions surrounding the second period therapeutic decision. A surprising result is that, under conditions that appear close to those surrounding the HAART debate, the magnitude of the feared resistance effect has no effect on leaves the optimal treatment decision as far as it is high enough.

Resistencias genotípicas en pacientes con infección por el virus de la inmunodeficiencia humana. Correlación con las pautas terapéuticas empleadas en su tratamiento

BACKGROUND AND OBJECTIVE

Our goal was to establish the different therapeutic regimens used in our clinical setting, and to determine the prevalence of genotypic resistances in patients under antiretroviral therapy, analyzing the relationship between the appearance of mutations and treatments along with other HIV related variables.

MATERIAL AND METHOD

191 samples from the same number of patients who were on antiretroviral therapy and virological failure were analyzed. Samples were processed by means of the genotypic technique LiPA in order to study the presence of mutations in the reverse transcriptase (RT) and the protease (P) genes. Prescribed therapeutic regimens and epidemiological variables relevant in HIV infection were also analyzed.

RESULTS

Overall resistance prevalence was 72.32%. By LiPA, RT mutations were detected in 71.43% of patients, being M184V, T215Y and L41M the most frequent ones. Moreover, P mutations were detected in 59.38% of cases, being V82A, L90M and I84V the most frequent ones. 61.02% of the patients presented one or more mutations against the reverse transcriptase inhibitors included in their treatment. With regard to protease inhibitors, this fact was documented in 28.81% of cases, and in 23.73% of patients receiving both reverse transcriptase inhibitors and protease inhibitors.

CONCLUSIONS

Although the analysis of the mutation patterns by LiPA has known limitations, the prevalence of resistances in our study was different from that reported by other authors, being lower in the P gene and higher in the RT one. Of note, a high proportion of patients showed mutations against the drugs included in their prescribed treatment.

Natural histories of hepatitis C virus infection in men and women simulated by the Markov model

The Markov model was introduced to simulate natural histories of hepatitis C virus (HCV) infection in men and women. The data set was constructed on 942 HCV carriers who were examined at least once a year without receiving antiviral therapies. Based on 2,251 patient-year data, the probabilities of transition between any two of the four clinical states, i.e., asymptomatic carrier state, chronic hepatitis, liver cirrhosis and hepatocellular carcinoma in 1 year were calculated. Hepatocellular carcinoma was defined as the absorbing state from where no transitions occur. Probability matrices thus obtained on six each subsets of HCV infection (asymptomatic carrier state, chronic hepatitis and liver cirrhosis in men and women) in their forties, fifties, and sixties, were used to simulate long-term outcomes of HCV infection. Male asymptomatic carriers aged 40 years were expected to retain the asymptomatic carrier state in 2.6%, evolve into chronic hepatitis in 48.4%, liver cirrhosis in 14.6% and hepatocellular carcinoma in 34.4% after 30 years when they reached 70 years of age, in contrast to 1.9%, 45.3%, 32.8% and 20.0%, respectively, of female asymptomatic carriers. Likewise, male patients with chronic hepatitis aged 40 years were expected to remain with chronic hepatitis in 43.8%, evolve into liver cirrhosis in 15.0% and hepatocellular carcinoma in 41.1%, contrasting with 38.9%, 32.7% and 22.0%, respectively, of female patients during 30 years. The Markov model could simulate the outcomes of 153 HCV carriers identified among blood donors after 5 years. The Markov simulation would help in assessing the long-term outcome of HCV infection and making decisions in the management of HCV carriers toward prevention of hepatocellular carcinoma.

Treatment for primary HIV infection: projecting outcomes of immediate, interrupted, or delayed therapy

With limited data available on the optimal treatment of primary HIV infection, disease modeling can be used to project clinical outcomes and inform decision makers. The authors developed a simulation model to evaluate the clinical outcomes and life expectancy projections for three primary HIV infection treatment strategies: 1) continuous antiretroviral therapy (ART) initiated at CD4 count <350 cells/mm(3); 2) continuous ART initiated immediately on diagnosis of primary HIV infection; and 3) ART initiated on diagnosis followed by structured treatment interruption. Projected life expectancies for the three strategies were 23.92, 24.46, and 26.07 years, respectively. The impact of key variables was assessed in sensitivity analysis, with the structured treatment interruption strategy remaining the most effective over a broad range of inputs. The immunologic benefit associated with immediate therapy and the potential for antiretroviral resistance due to structured treatment interruption have the most important impact on the optimal strategy. Based on current data, immediate treatment on diagnosis of primary HIV infection followed by structured treatment interruption will likely yield the best outcome. These results can assist decision makers and those planning clinical trials in defining evidence-based performance measures for primary HIV infection treatment and future trials.