Implementing the number needed to harm in clinical practice: risk of myocardial infarction in HIV-1-infected patients treated with abacavir

Cardiovascular toxicity of abacavir: a clinical controversy in need of a pharmacological explanation

: There is a long-lasting controversy surrounding an association between abacavir (ABC) and an increased risk of cardiovascular disease in HIV-positive patients. Although differing in their specifics, a number of published cohort studies and clinical trials support such an association, usually relating it to recent exposure to the drug, independently of traditional predisposing factors. However, other clinical trials have failed to reveal such a relation and have pointed to methodological differences to explain discrepancies. Significantly, the controversy has been fueled by the lack of a credible mechanism of action to justify the putative detrimental actions of ABC. There is a myriad of contradictory clinical indicators which are not clearly compatible with known profiles of either vascular physiopathology or pharmacological interference. However, basic research has recently hinted at altered homeostatic mechanisms, though this requires clinical validation. In particular, recurrent evidence - both clinical and experimental - relates ABC with vascular inflammation, a leading contributor to the atherosclerotic plaque and thrombosis. ABC's chemical structure is very close to that of endogenous purines (ATP, ADP and AMP), major paracrine signaling molecules capable of triggering prothrombotic and proinflammatory vascular programs. Other proposed mechanisms are a competitive inhibition of guanylyl cyclase in platelets and a subsequent decrease in cyclic guanosine monophosphate (cGMP). The present review aims to shed light on this complex subject by summarizing and critically evaluating all the available clinical data regarding a relationship between ABC and cardiovascular disease, and to put forward potential pharmacological explanations compatible with both the clinical scenario and experimental findings.

Cardiovascular disease risk scores' relationship to subclinical cardiovascular disease among HIV-infected and HIV-uninfected men

OBJECTIVE

To study cardiovascular disease risk score utility, we compared the association between Framingham Risk Score (FRS)/pooled cohort equation (PCE) categories and coronary artery plaque presence by HIV serostatus and evaluated whether D : A : D risk category more accurately identifies plaque in HIV-infected men.

DESIGN

Cross-sectional analysis within a substudy of the Multicenter AIDS Cohort Study.

METHODS

Cardiac computed tomography was performed to assess coronary plaque. We evaluated the association of plaque with increasing cardiovascular disease risk score category, stratified by HIV serostatus, using logistic regression. Receiver operating characteristic curves compared the discrimination of the scores for plaque by HIV serostatus. The sensitivity and specificity of the risk scores were compared in HIV-infected men.

RESULTS

The risk score category - plaque associations were stronger among HIV-uninfected men than HIV-infected men, except for noncalcified plaque. For example, the odds of coronary artery calcium more than 0 were 7.03 (95% confidence interval 4.21, 11.76) times greater among men in the PCE high-risk versus low-risk category among HIV-uninfected men, compared with just 3.13 (95% confidence interval 2.13, 4.61) times greater among men in the high-risk versus low-risk category among HIV-infected men. Among HIV-infected men, high-risk category by PCE identified the greatest percentage of men with plaque/stenosis, but with lower specificity than D : A : D and FRS. The prevalence of coronary artery calcium more than 0 among men in the PCE low-risk category was 26.5% (HIV-uninfected men) and 36.0% (HIV-infected men).

CONCLUSIONS

FRS and PCE categories associate with plaque burden better in HIV-uninfected men. No risk score delivered both high sensitivity and specificity among HIV-infected men.

Cause-Specific Mortality in HIV-Positive Patients Who Survived Ten Years after Starting Antiretroviral Therapy

OBJECTIVES

To estimate mortality rates and prognostic factors in HIV-positive patients who started combination antiretroviral therapy between 1996-1999 and survived for more than ten years.

METHODS

We used data from 18 European and North American HIV cohort studies contributing to the Antiretroviral Therapy Cohort Collaboration. We followed up patients from ten years after start of combination antiretroviral therapy. We estimated overall and cause-specific mortality rate ratios for age, sex, transmission through injection drug use, AIDS, CD4 count and HIV-1 RNA.

RESULTS

During 50,593 person years 656/13,011 (5%) patients died. Older age, male sex, injecting drug use transmission, AIDS, and low CD4 count and detectable viral replication ten years after starting combination antiretroviral therapy were associated with higher subsequent mortality. CD4 count at ART start did not predict mortality in models adjusted for patient characteristics ten years after start of antiretroviral therapy. The most frequent causes of death (among 340 classified) were non-AIDS cancer, AIDS, cardiovascular, and liver-related disease. Older age was strongly associated with cardiovascular mortality, injecting drug use transmission with non-AIDS infection and liver-related mortality, and low CD4 and detectable viral replication ten years after starting antiretroviral therapy with AIDS mortality. Five-year mortality risk was <5% in 60% of all patients, and in 30% of those aged over 60 years.

CONCLUSIONS

Viral replication, lower CD4 count, prior AIDS, and transmission via injecting drug use continue to predict higher all-cause and AIDS-related mortality in patients treated with combination antiretroviral therapy for over a decade. Deaths from AIDS and non-AIDS infection are less frequent than deaths from other non-AIDS causes.

Effect of Cumulating Exposure to Abacavir on the Risk of Cardiovascular Disease Events in Patients From the Swiss HIV Cohort Study

BACKGROUND

Patients with HIV exposed to the antiretroviral drug abacavir may have an increased risk of cardiovascular disease (CVD). There is concern that this association arises because of a channeling bias. Even if exposure is a risk, it is not clear how that risk changes as exposure cumulates.

METHODS

We assess the effect of exposure to abacavir on the risk of CVD events in the Swiss HIV Cohort Study. We use a new marginal structural Cox model to estimate the effect of abacavir as a flexible function of past exposures while accounting for risk factors that potentially lie on a causal pathway between exposure to abacavir and CVD.

RESULTS

A total of 11,856 patients were followed for a median of 6.6 years; 365 patients had a CVD event (4.6 events per 1000 patient-years). In a conventional Cox model, recent--but not cumulative--exposure to abacavir increased the risk of a CVD event. In the new marginal structural Cox model, continued exposure to abacavir during the past 4 years increased the risk of a CVD event (hazard ratio = 2.06; 95% confidence interval: 1.43 to 2.98). The estimated function for the effect of past exposures suggests that exposure during the past 6-36 months caused the greatest increase in risk.

CONCLUSIONS

Abacavir increases the risk of a CVD event: the effect of exposure is not immediate, rather the risk increases as exposure cumulates over the past few years. This gradual increase in risk is not consistent with a rapidly acting mechanism, such as acute inflammation.

Current Efavirenz (EFV) or ritonavir-boosted lopinavir (LPV/r) use correlates with elevate markers of atherosclerosis in HIV-infected subjects in Addis Ababa, Ethiopia

BACKGROUND

HIV patients on antiretroviral therapy have shown elevated incidence of dyslipidemia, lipodystrophy, and cardiovascular disease (CVD). Most studies, however, focus on cohorts from developed countries, with less data available for these co-morbidities in Ethiopia and sub-Saharan Africa.

METHODS

Adult HIV-negative (n = 36), treatment naïve (n = 51), efavirenz (EFV)-treated (n = 91), nevirapine (NVP)-treated (n = 95), or ritonavir-boosted lopinavir (LPV/r)-treated (n=44) subjects were recruited from Black Lion Hospital in Addis Ababa, Ethiopia. Aortic pressure, augmentation pressure, and pulse wave velocity (PWV) were measured via applanation tonometry and carotid intima-media thickness (cIMT) and carotid arterial stiffness, and brachial artery flow-mediated dilation (FMD) were measured via non-invasive ultrasound. Body mass index, waist-to-hip circumference ratio (WHR), skinfold thickness, and self-reported fat redistribution were used to quantify lipodystrophy. CD4+ cell count, plasma HIV RNA levels, fasting glucose, total-, HDL-, and LDL-cholesterol, triglycerides, hsCRP, sVCAM-1, sICAM-1, leptin and complete blood count were measured.

RESULTS

PWV and normalized cIMT were elevate and FMD impaired in EFV- and LPV/r-treated subjects compared to NVP-treated subjects; normalized cIMT was also elevated and FMD impaired in the EFV- and LPV/r-treated subjects compared to treatment-naïve subjects. cIMT was not statistically different across groups. Treated subjects exhibited elevated markers of dyslipidemia, inflammation, and lipodystrophy. PWV was associated with age, current EFV and LPV/r used, heart rate, blood pressure, triglycerides, LDL, and hsCRP, FMD with age, HIV duration, WHR, and glucose, and cIMT with age, current EFV use, skinfold thickness, and blood pressure.

CONCLUSIONS

Current EFV- or LPV/r-treatment, but not NVP-treatment, correlated with elevated markers of atherosclerosis, which may involve mechanisms distinct from traditional risk factors.

Effects of combination antiretroviral therapies on the risk of myocardial infarction among HIV patients

BACKGROUND

Cohort studies have demonstrated greater risk of myocardial infarction (MI) associated with specific antiretroviral use, while meta-analyses of randomized controlled trials (RCTs) have not. These differences may be due to inherent biases in the observational study design or to the limited duration of randomized trials. We conducted a new-user, active-comparator cohort study emulating an RCT comparing the initiation of several antiretrovirals as part of combination antiretroviral therapy (cART) and MI.

METHODS

We included North Carolina (NC) Medicaid beneficiaries infected with human immunodeficiency virus between 2002 and 2008 who were previously untreated with cART. We compared hazard ratios (HRs) and 95% confidence intervals (CIs) of MI between abacavir and tenofovir recipients, and lopinavir-ritonavir or atazanavir recipients and nonnucleoside reverse transcriptase inhibitor (NNRTI) recipients. We adjusted for confounding through inverse probability weighting methods.

RESULTS

There were 3481 NC Medicaid new cART recipients who contributed 6399 person-years and experienced 38 MI events. Receiving abacavir compared with tenofovir as part of cART was associated with an increased rate of MI (unadjusted HR = 2.70 [95% CI = 1.24-5.91]; adjusted HR = 2.05 [0.72-5.86]). Point estimates also suggest a relationship between receipt of atazanavir or lopinavir-ritonavir compared with an NNRTI and MI, although estimates were imprecise.

CONCLUSIONS

We found an increased rate of MI among patients initiating abacavir compared with tenofovir, although the association was decreased after confounding adjustment. Without a very large prospective comparative clinical trial, a much larger observational study of patients initiating cART would be needed to better define this apparent association.

When to start antiretroviral therapy: the need for an evidence base during early HIV infection

BACKGROUND

Strategies for use of antiretroviral therapy (ART) have traditionally focused on providing treatment to persons who stand to benefit immediately from initiating the therapy. There is global consensus that any HIV+ person with CD4 counts less than 350 cells/μl should initiate ART. However, it remains controversial whether ART is indicated in asymptomatic HIV-infected persons with CD4 counts above 350 cells/μl, or whether it is more advisable to defer initiation until the CD4 count has dropped to 350 cells/μl. The question of when the best time is to initiate ART during early HIV infection has always been vigorously debated. The lack of an evidence base from randomized trials, in conjunction with varying degrees of therapeutic aggressiveness and optimism tempered by the risks of drug resistance and side effects, has resulted in divided expert opinion and inconsistencies among treatment guidelines.

DISCUSSION

On the basis of recent data showing that early ART initiation reduces heterosexual HIV transmission, some countries are considering adopting a strategy of universal treatment of all HIV+ persons irrespective of their CD4 count and whether ART is of benefit to the individual or not, in order to reduce onward HIV transmission. Since ART has been found to be associated with both short-term and long-term toxicity, defining the benefit:risk ratio is the critical missing link in the discussion on earlier use of ART. For early ART initiation to be justified, this ratio must favor benefit over risk. An unfavorable ratio would argue against using early ART.

SUMMARY

There is currently no evidence from randomized controlled trials to suggest that a strategy of initiating ART when the CD4 count is above 350 cells/μl (versus deferring initiation to around 350 cells/μl) results in benefit to the HIV+ person and data from observational studies are inconsistent. Large, clinical endpoint-driven randomized studies to determine the individual health benefits versus risks of earlier ART initiation are sorely needed.

T-cell phenotypes, apoptosis and inflammation in HIV+ patients on virologically effective cART with early atherosclerosis

Objective

We investigated the potential relationship between T-cell phenotype, inflammation, endotoxemia, and atherosclerosis evaluated by carotid intima-media thickness (IMT) in a cohort of HIV-positive patients undergoing long-term virologically suppressive combination antiretroviral therapy (cART).

Design

We studied 163 patients receiving virologically suppressive cART.

Methods

We measured IMT (carotid ultrasound); CD4+/CD8+ T-cell activation (CD38, CD45R0), differentiation (CD127), apoptosis (CD95), and senescence (CD28, CD57) (flow cytometry); plasma sCD14, IL-6, TNF- α, sVCAM-1, hs-CRP, anti-CMV IgG (ELISA); LPS (LAL). The results were compared by Mann-Whitney, Kruskal-Wallis or Chi-square tests, and factors associated with IMT were evaluated by multivariable logistic regression.

Results

Of 163 patients, 112 demonstrated normal IMT (nIMT), whereas 51 (31.3%) had pathological IMT (pIMT: ≥1 mm). Of the patients with pIMT, 22 demonstrated an increased IMT (iIMT), and 29 were shown to have plaques. These patient groups had comparable nadir and current CD4+, VLs and total length of time on cART. Despite similar proportions of CD38-expressing CD8+ cells (p = .95), pIMT patients exhibited higher activated memory CD8+CD38+CD45R0+ cells (p = .038) and apoptotic CD4+CD95+ (p = .01) and CD8+CD95+ cells (p = .003). In comparison to nIMT patients, iIMT patients tended to have lower numbers of early differentiated CD28+CD57− memory CD4+ (p = .048) and CD28–CD57−CD8+ cells (p = .006), both of which are associated with a higher proliferative potential. Despite no differences in plasma LPS levels, pIMT patients showed significantly higher circulating levels of sCD14 than did nIMT patients (p = .046). No differences in anti-CMV IgG was shown. Although circulating levels of sCD14 seemed to be associated with a risk of ATS in an unadjusted analysis, this effect was lost after adjusting for classical cardiovascular predictors.

Conclusions

Despite the provision of full viral suppression by cART, a hyperactivated, pro-apoptotic T-cell profile characterizes HIV-infected patients with early vascular damage, for whom the potential contribution of subclinical endotoxemia and anti-CMV immunity should be investigated further.

Long-term exposure to combination antiretroviral therapy and risk of death from specific causes: no evidence for any previously unidentified increased risk due to antiretroviral therapy

BACKGROUND

Despite the known substantial benefits of combination antiretroviral therapy (cART), cumulative adverse effects could still limit the overall long-term treatment benefit. Therefore we investigated changes in the rate of death with increasing exposure to cART.

METHODS

A total of 12 069 patients were followed from baseline, which was defined as the time of starting cART or enrolment into EuroSIDA whichever occurred later, until death or 6 months after last follow-up visit. Incidence rates of death were calculated per 1000 person-years of follow-up (PYFU) and stratified by time of exposure to cART (≥3 antiretrovirals): less than 2, 2-3.99, 4-5.99, 6-7.99 and more than 8 years. Duration of cART exposure was the cumulative time actually receiving cART. Poisson regression models were fitted for each cause of death separately.

RESULTS

A total of 1297 patients died during 70,613 PYFU [incidence rate 18.3 per 1000 PYFU, 95% confidence interval (CI) 17.4-19.4], 413 due to AIDS (5.85, 95% CI 5.28-6.41) and 884 due to non-AIDS-related cause (12.5, 95% CI 11.7-13.3). After adjustment for confounding variables, including baseline CD4 cell count and HIV RNA, there was a significant decrease in the rate of all-cause and AIDS-related death between 2 and 3.99 years and longer exposure time. In the first 2 years on cART the risk of non-AIDS death was significantly lower, but no significant difference in the rate of non-AIDS-related deaths between 2 and 3.99 years and longer exposure to cART was observed.

CONCLUSION

In conclusion, we found no evidence of an increased risk of both all-cause and non-AIDS-related deaths with long-term cumulative cART exposure.

Lipid metabolism in treated HIV Infection

Patients infected with the human immunodeficiency virus (HIV) are prone to a great number of lipid and lipoprotein disturbances, as a result of both the infection itself and direct effects on lipid metabolism from the drugs used to treat HIV infection. These lipid disorders account for at least part of the increased risk of cardiovascular disease seen in this population. In general, evaluation and interventions for dyslipidemia in HIV-infected individuals should follow guidelines established for the general population. Special consideration, however, must be given to the potential for adverse drug interactions between lipid lowering drugs and the agents used to treat HIV infection. In this review, we summarize what is known about the relative tendency of different antiretroviral drugs to alter lipid levels, and suggest an approach to intervention for dyslipidemia in this population.