The model allows tracking of patient's outcomes, including calculating survival time and average time on first-line and second-line cART. The model simulates changes in patient's outcomes when prescribed a new drug regimen, with either improved toxicity or virological failure profiles, two potential targets for future drug development.
The incidence of switching regimens has declined between the periods of 2000–2005 and 2005–2010 (Fig. 1), suggesting that cART regimens have improved considerably over the course of the last decade. The decline is particularly evident in first-line cART (Fig. 1a). Incidence of virological failure and switching due to simplification/new medication becoming available more than halved, from 31 events [95% confidence interval (CI), 25–38] and 94 events (95% CI, 83–106) in 2000–2005 to 13 (95% CI, 10–17) and 38 (95% CI, 32–44) events per 1000 person-years in 2005–2010, respectively. Incidence of switching due to toxicity and for other reasons decreased from 161 events (95% CI, 147–177) and 46 events (95% CI, 38–54) in 2000–2005 to 90 (95% CI, 82–99) and 31 (95% CI, 26–36) events per 1000 person-years in 2005–2010, respectively.
Analysis of the Dutch ATHENA data found that among Dutch-born men, diagnosed with HIV from 1996 onward, the main reason for switching current first-line and second-line regimens was toxicity, accounting for around 50% of switching first-line and second-line cART (Fig. 1). Despite the decline in the incidence of switching from first-line cART between 2000–2005 and 2005–2010, toxicity is still the dominant reason for switching cART regimens.
We simulated the impact of a new drug regimen, with improved profile on patient's outcomes using a mathematical model. Model simulations found that a new drug regimen would have the highest impact if it had an improved toxicity profile (Fig. 1c). A new drug regimen with a 50% reduction (from 90 to 45 events per 1000 person-years) in incidence of toxicity compared with current cART would result in three additional life-months per patient (Fig. 1c) to an average survival time of 32 years after start of treatment. In comparison, a 50% reduction in virological failure would add less than 1 month to patient's survival time after treatment initiation (Fig. 1c).
The results further showed that a new drug regimen would have the highest impact if used as first-line cART. Used as first-line, a new drug regimen with a 50% reduction (from 90 to 45 events per 1000 person-years) in incidence of toxicity can potentially add 5 months to patient's survival time compared with no change in survival time if used as second-line.
A new first-line drug regimen would also simplify patient management, as fewer patients experience problems with their regimen and therefore remain on first-line cART for longer. A new drug regimen with a 50% reduction in incidence of toxicity compared with current treatment regimens could reduce the number of patients, who have to switch first-line cART by 16% and increase the average duration on first-line cART by nine months per patient.
Among HIV-infected men in the Netherlands, the main reason for switching regimens is toxicity, and model simulations found that use of a new drug regimen with a reduction in these toxicity rates could translate into a potential increase in survival time and time on first-line cART, to the benefit of patient management. The model highlighted the importance of using new improved drug regimens as first-line cART in order to maximise clinical outcomes and simplify patient management. The relatively low impact a new drug regimen can have on survival is due to the high performance of existing regimens as evident by the improvement in performance shown by the analysis of ATHENA data and marked increase in life-expectancy of HIV-infected individuals in European countries, including the Netherlands since 1996 [1,15,16]. Moreover, patients, who experience toxicity could switch regimen without experiencing virological failure, thus having little impact on survival. However, although newer, bettertolerated regimens may have a limited impact on patients’ survival, they will simplify patient management and improve patient's quality of life.
Our findings are consistent with other studies. Research conducted into the reasons for switching treatment suggests that toxicity is the main reason patients switch their regimens [17–20]. Model results are consistent with studies documenting that effective treatment has increased patients’ life expectancy [1,16,21,22]. There may be a number of mechanisms driving the increased mortality rate in patients switching first-line due to toxicity. Patients could have difficulty adhering to the regimen because of the side effects and consequently do less well virologically and/or clinically. These could be patients who are more likely to experience side effects, for example due to their reduced body mass, so that higher concentrations of the medication are in the body [19,23].
To our knowledge, this analysis of ATHENA data is the first attempt to look at the factors that drive switching cART and the potential impact of new drug regimens in the Netherlands. Coupled with the model, it provides a valuable insight into the potential of new drug regimens and the impact these can have on patients’ outcomes and patient management in the Netherlands in the future. The results suggest that the data requires further analysis to identify the side effects that result in switching, as well as their effect on patients’ long-term outcome. Interpretation of the model output would be wrong if switching and reduced survival on second-line is entirely due to switching being a marker for low adherence. The model analysis is limited by its reliance on assumptions and on data from the literature, in which ATHENA data was not available or sufficient, especially for biological assumptions regarding disease progression. The model uses long-term extrapolations from the patient data and assumes that switching rates are independent of CD4 cell count. The mathematical model did not include certain complexities, for example the inclusion of failure rates for different treatment regimens, as it has been well documented that earlier regimens, such as stavudine and some zidovudine-based regimens are associated with high toxicity rates [24–26] or including time-dependent variation of switching rates, as the incidence of these have been shown to vary during the first and subsequent years on cART [27,28]. Incorporation of individual-based adherence into the model, which has been shown to be associated with the development of resistance [27,29–31], could assist in investigating the reason for poor response to second-line treatment . However, we believe that this model provides a suitable framework with which to describe potentials of new drug regimens in the future.
In conclusion, new drug regimens with improved toxicity profiles will have the greatest impact on patient prognosis and patient management in the Netherlands.
M.S. would like to thank the Medical Research Council for funding this research.
M.S. formulated the research question, constructed the model, interpreted results and wrote the first draft of the article. C.S. carried out the data analysis of the ATHENA cohort for the data and model part of the work. I.C. assisted in the model construction. G.P.G., T.H. and F.W. contributed to the formulation of the research question, and the interpretation of the data and model output. All authors contributed to the re-drafting of the article and in the process of approving the final draft.
Conflicts of interest
Conflict of interest and source of funding: The funder had no role in the analysis or the decision to publish. There are no conflicts of interest.
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antiretroviral therapy; ATHENA; mathematical models; new drug regimens; toxicity
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