The use of highly active antiretroviral therapy (HAART) has contributed in great part to converting HIV into a chronic disease.1 Short-term toxicity and, particularly, long-term toxicity are important limitations of HAART, however.2-4 Morphologic and lipid abnormalities are observed in a considerable percentage of treated patients, generating concern about a possible increased risk of cardiovascular events in this population.5-8
The morphologic changes that can occur, also referred to as HIV-associated lipodystrophy, consist of a lipoatrophic process in peripheral areas, such as the arms, legs, buttocks, and face, and fat accumulation (lipoaccumulation) at the abdominal, breast, and dorsocervical regions. Despite the high prevalence of fat distribution change and its negative impact among the HIV-infected population receiving HAART, the pathogenesis of this condition is not completely understood. Although clinical signs of lipoatrophy and lipoaccumulation can be seen together in the same patient, there is growing evidence that these processes are distinct entities with different underlying pathophysiologic mechanisms.4,9 In fact, some authors have recently questioned the actual existence of a lipoaccumulation process in HIV-infected individuals and suggest that lipoatrophy is the distinguishing trait of HIV lipodystrophy.10
A number of factors, including certain antiretroviral families or specific drugs, virologic control, time from infection, duration of HAART, and demographics, have been associated with the development of HIV-associated lipodystrophy. Mitochondrial toxicity is thought to play a role in the lipoatrophy process.11 This may be the mechanism by which stavudine, and, to a lesser degree, other nucleoside analogues, such as zidovudine, are linked to lipoatrophy.12-15 The potential toxicity on mitochondrial DNA of other nucleosides, such as abacavir and lamivudine, and the nucleotide tenofovir seems to be lower. Hence, it is thought that there would be a smaller incidence of lipoatrophy with the use of these drugs. In a recent study, significantly less total limb fat was observed in the stavudine-containing arm as compared to the alternative tenofovir-containing option.16 Also, a more favorable change in the lipid profile from baseline was noted in the tenofovir group.
Abacavir is a potent well-tolerated nucleoside analogue that was licensed in the United States in 1999. A few randomized studies have recently proved its efficacy and tolerability in antiretroviral-naive patients.17,18 Few data on its potential contribution to morphologic and metabolic HAART-related abnormalities have been reported in this population, however.19
We present the results of the first randomized trial designed to compare the incidence of lipoatrophy between antiretroviral regimens as the primary endpoint. In this 2-year randomized multicenter trial initiated in 2001, the standard-of-care regimen of stavudine, lamivudine, and efavirenz was compared with a regimen substituting abacavir for stavudine. In addition, the virologic and immunologic efficacy, associated metabolic changes, and tolerability of the 2 regimens were compared.
Study Design and Patient Population
The Abacavir vs. d4T (stavudine) plus efavirenz (ABCDE) study was a randomized, open, multicenter trial conducted in 17 Spanish hospitals. The study was approved by the ethics committees of each hospital and by the Spanish Health Authorities (Agencia Española del Medicamento). Adult HIV-1-infected antiretroviral-naive patients with a viral load >500 copies/mL who gave written informed consent were recruited between January 2001 and June 2002 for participation.
Intervention and Follow-Up
Patients were centrally stratified according to HIV-1 RNA > or ≤30,000 copies/mL and CD4 counts > or ≤200 cells/μL and randomized to one of these arms: (1) 300 mg of abacavir twice daily, plus 150 mg of lamivudine twice daily, plus 600 mg of efavirenz once daily; or (2) 30 mg of stavudine twice daily (according to < or >60 kg of body weight) plus lamivudine and efavirenz at the same doses. The use of treatments other than the allocated ones, including lipid-lowering agents, was left to the researchers' discretion and was recorded for later analysis.
Clinical assessment and laboratory parameter controls were performed at baseline, at weeks 4 and 12, and every 12 weeks thereafter up to 96 weeks of follow-up.
Participants underwent an extensive physical examination to detect clinical signs of peripheral fat wasting (lipoatrophy) and central adiposity (lipoaccumulation) at weeks 48 and 96. Lipoatrophy features consisted of decreased subcutaneous fat tissue in the face, buttocks, and extremities, whereas lipoaccumulation features included increased abdominal girth, breast enlargement, and dorsal fat accumulation. The morphologic abnormality at the precise site was diagnosed when reported by the patient and confirmed by medical examination. For the purpose of the analysis, body fat abnormalities were categorized as lipoatrophy or lipoaccumulation. Therefore, patients with fat loss and fat accumulation were included in both categories.
Anthropometric measurements were done at baseline and at 48 and 96 weeks according to standard techniques described elsewhere20 and included height, weight, and circumferences at 4 body sites (waist, hip, midarm, and midthigh). An experienced nurse in the coordinating center trained participating physicians in the anthropometric procedures before the study began. The ratio between the waist and hip circumferences was also calculated. Additionally, a dual-energy x-ray absorptiometry (DEXA; Lunar DPX-L Equipment, Madison, WI) substudy was undertaken to determine the changes in total and regional body fat. Patients giving informed consent from 6 participating centers located near the DEXA center Centro Tecnico de Isotopos Radioactivos (CETIR) were enrolled for this purpose. Scans were performed at baseline and at the 48- and 96-week visits. Data from the DEXA scans were analyzed by an independent observer blinded to the patients' study arm.
At each visit, blood samples were drawn in the morning after an overnight fast. Blood cells; biochemical parameters, including alanine aminotransferase (ALT), alkaline phosphatase, gamma-glutamyl transpeptidase (GGT), creatinine, and amylase; and CD4 cell counts (except for week 4) were measured according to routine methods at each center. A complete lipid profile, including total cholesterol (TC) and high-density lipoprotein cholesterol (HDLc), triglycerides, and apolipoproteins A1 and B, was determined at baseline and every 6 months from stored samples (−70°C). These measurements were centralized in the laboratory of the coordinating center (Hospital Universitari de Bellvitge) using standardized procedures. Low-density lipoprotein cholesterol (LDLc) was estimated with the Friedewald formula.
HIV-1 RNA was determined in each center using a polymerase chain reaction (PCR), branched DNA (bDNA), or nucleic acid sequence-based amplification (NASBA) method. When HIV-1 RNA was undetectable by any of these techniques in baseline and follow-up samples, results were confirmed by centralized determinations in the coordinating center with the 3.0 bDNA technique.
The 1993 Centers for Disease Control and Prevention (CDC) classification was used for AIDS-defining diseases. A diagnosis was considered definite when the disease was confirmed histologically and/or microbiologically and probable when only the clinical presentation plus the response to therapy were available. HIV-related symptoms, adverse effects, and other events were recorded, and a predefined short questionnaire was administered at every visit to assess adherence to antiretroviral therapy.21
The primary endpoint of the study was the presence of at least 1 clinical sign of lipoatrophy as defined previously, and the secondary endpoints were the presence of clinical lipoaccumulation signs; lipid changes; virologic, clinical, and immunologic efficacy; and tolerability.
All endpoints were analyzed using intent-to-treat (ITT) and on-treatment (OT) approaches. In the ITT analyses of toxicity, any adverse event occurring during follow-up was computed with the initially assigned regimen (missing values were not computed), and in the ITT analyses of virologic efficacy, switch equaled failure. Unless otherwise stated, the data presented are from the ITT analysis.
Estimation of sample size was based on the assumption that 20% of patients on stavudine and 5% on abacavir would present with lipoatrophy as assessed by clinical examination. To detect a difference of at least 15 percentage points, with 80% power and a significance level of 0.05, the sample size was determined to be 116 patients per arm, a figure that includes 20% of patients that might lost to follow-up.
Baseline characteristics were compared using the χ2 or Mann-Whitney U test, as appropriate. Proportions of patients with lipoatrophy or lipoaccumulation were compared using the Fisher exact test. The within- and between-group statistical comparisons of continuous data were performed using the Wilcoxon rank sum test and Mann-Whitney U test, respectively. Continuous data are reported as the mean (range). A 2-sided P value <0.05 was considered statistically significant. Statistical analyses were performed with the use of SPSS software, version 12.0 (SPSS, Chicago, IL).
A total of 257 patients were randomized, and among them, 237 (115 in the abacavir arm and 122 in the stavudine arm) were considered eligible for analysis (Fig. 1).
There were no statistically significant differences in baseline characteristics between arms, except for TC levels (Table 1). No differences were observed in any other hematologic or biochemical parameter (data not shown). More than 70% of the patients were men, approximately 90% were white, and approximately 40% had acquired HIV through heterosexual intercourse. In the abacavir and stavudine arms, respectively, 18% and 28% had prior AIDS, the median CD4 counts were 175 cells/μL and 201 cells/μL, and the median viral loads were 4.96 copies/mL and 4.92 copies/mL. Although the proportion of patients who acquired HIV through intravenous drug use was similar (30% in the abacavir arm and 28% in the stavudine arm), a trend to a higher proportion with hepatitis C virus (HCV) infection was observed in the abacavir arm (45% vs. 32%; P = 0.053).
At the study end, 56 patients had been lost to follow-up and morphologic data were not collected in 16 of the remaining patients. Hence, lipodystrophy was assessed in 165 (84 in the abacavir arm and 81 in the stavudine arm [70%]) of the 237 patients enrolled (Table 2). Among these 165 patients, 113 (68.5%) showed no clinical signs of lipodystrophy, 23 (13.9%) had lipoatrophy alone, 17 (10.3%) had lipoaccumulation alone, and 12 (7.3%) presented with the mixed form.
Four (4.8%) patients in the abacavir arm and 31 (38.3%) in the stavudine arm developed 1 or more clinical signs of lipoatrophy (difference of 33.5%, 95% confidence interval [CI]: 22% to 45%; P < 0.001). The OT analysis produced similar results (3 in the abacavir arm [4.3%] and 19 in the stavudine arm [32.2%], difference of 27.9%, 95% CI: 15.1% to 40.7%; P < 0.001). With regard to lipoaccumulation, fewer patients in the abacavir arm developed clinical signs of this alteration (9 in the abacavir arm [10.7%] vs. 20 in the stavudine arm 20 [24.7%], difference of 14%, 95% CI: 2.5% to 25.5%; P < 0.023; see Table 2).
Anthropometric Assessments and Dual-Energy X-Ray Absorptiometry Scans
During the first year of the study, both treatment groups presented with similar weight gains (3.13 kg in the abacavir group and 3.21 kg in the stavudine group). Between 48 and 96 weeks, however, weight continued to increase in the abacavir patients (1.57 kg, 4.70 from baseline), whereas a weight reduction occurred in the stavudine patients (−0.96 kg, 2.25 from baseline), which is a common finding in the course of peripheral fat loss.15
Regarding the measured body girths, both regimens exhibited significant increases at all sites, except at the hip in the stavudine group (Table 3). A significantly lower increase in the waist-to-hip ratio was observed in the abacavir group as compared to the group receiving stavudine (1.2% vs. 4.5%; P = 0.002). This difference was driven by a significant increase in waist girth in both arms accompanied by an increase in hip girth only in the abacavir arm.
At the end of study, patients with clinical signs of lipoatrophy presented with greater decreases in the hip (−1.1 vs. 2.1; P = 0.022), arm (0.0 vs. 1.7; P = 0.020), and leg (−0.8 vs. 2.3; P = 0.017) circumferences as compared to the remaining patients. Similarly, those with clinical signs of abdominal lipoaccumulation presented with greater increases in the waist perimeter (6.8 vs. 2.9; P = 0.005).
DEXA scans were performed in a subset of 57 patients (25 in the abacavir arm and 32 in the stavudine arm). Within this subgroup, both arms presented baseline characteristics similar to those of the total study population except for serum cholesterol concentration (data not shown). DEXA scans showed a net limb fat gain after 96 weeks in patients assigned to abacavir (913 g, range: 150-1677 g) as opposed to patients randomized to stavudine (−1578 g, range: −2294 to −862), with the difference being statistically significant (P < 0.001; Fig. 2). The scans also showed a marked difference in limb fat changes when comparing patients with or without clinical signs of lipoatrophy (−2103 vs. 45 g; P = 0.002). Regarding central fat, patients with abdominal lipoaccumulation presented with higher trunk fat increases than those without (3413 g, range: 656-7511 g vs. 817 g, range: −4076-7976 g; P = 0.014). The DEXA measurements (abacavir, 1225 g, range: −2840- 7976 g and stavudine, 996 g, range: −4076-7511 g; P = 0.58) did not confirm the difference between arms observed in the clinical examination (see Table 2).
Lipid Metabolism Changes
At 96 weeks, both treatments were associated with significant increases in the following parameters: TC (stavudine: 0.89 mmol/L [34 mg/dL]; P < 0.001 and abacavir: 1.09 mmol/L [42 mg/dL]; P < 0.001), LDLc (stavudine: 0.43 mmol/L [16.6 mg/dL]; P = 0.001 and abacavir: 0.56 mmol/L [21.6 mg/dL]; P < 0.001), HDLc (stavudine: 0.20 mmol/L [7.7 mg/dL]; P = 0.001 and abacavir: 0.47 mmol/L [18.2 mg/dL]; P < 0.001), triglycerides (stavudine: 0.85 mmol/L [75 mg/dL]; P < 0.001 and abacavir: 0.28 mmol/L [25 mg/dL]; P < 0.05), apolipoprotein A1 (stavudine: 0.17 g/L; P = 0.001 and abacavir: 0.31 g/L; P < 0.001), and apolipoprotein B (stavudine: 0.12 g/L; P = 0.001 and abacavir: 0.12 g/L; P < 0.001) (Fig. 3).
In the comparison between treatments, the abacavir patients presented with a lower increase in triglyceride levels (P = 0.03), a greater increase in HDLc and apolipoprotein A1 (P < 0.001), and a greater reduction in the TC/HDLc ratio (−1.51 vs. −0.06; P = 0.005). At the end of the study, a higher percentage of patients in the stavudine group had received lipid-lowering agents as compared to the abacavir group (17% vs. 4%; P = 0.002): statins (15% vs. 4%; P = 0.008) and fibrates (4% vs. 1%, P = 0.21).
Drug discontinuation (1 or more of the drugs received) attributable to adverse events was required in 20 (17.4%) abacavir patients (rash/hypersensitivity in 13, central nervous system symptoms in 5, peripheral neuropathy in 1, and opiate withdrawal in 1) and in 33 (27%) stavudine patients (mitochondrial toxicity in 23 [lipoatrophy in 14, peripheral neuropathy in 5, and symptomatic hyperlactatemia/metabolic acidosis in 4], central nervous system symptoms in 6, gastrointestinal disturbance in 1, dyslipidemia in 1, increased GGT level in 1, and opiate withdrawal in 1) (P = 0.075). Although “allergic symptoms” were observed in 13 patients receiving abacavir, a hypersensitivity reaction to abacavir19 was diagnosed in only 8 of them (7%).
Regarding grade 3 and 4 adverse events and laboratory abnormalities, there were significant differences between arms only in the frequency of increased GGT levels (23% vs. 12%; P = 0.022) and in the presence of rash/fever (5% vs. 0%; P = 0.011), which were higher in the abacavir arm. HCV-positive patients presented a higher rate of grade 3 or 4 GGT toxicity than HCV-negative patients (34% vs. 7%; P < 0.001).
Four patients (1.7%) died during the study period: 2 receiving stavudine (1 with cirrhosis and probable sepsis and 1 with lung adenocarcinoma) and 2 receiving abacavir (1 with acute myocardial infarction and 1 with sudden death).
After 96 weeks, a trend favoring abacavir in the proportion of patients with an HIV-1 RNA level <50 copies/mL was observed in the ITT analysis: 60.9% versus 47.5% (difference of 13.4%, 95% CI: 0.8 to 26.0; P = 0.05), whereas no differences were detected with the OT approach: 87.5% in the abacavir arm and 85.3% in the stavudine arm (difference of 2.2%, 95% CI: −8.9 to 13.3; P = 0.81). The differences in efficacy rates in the ITT analysis were not driven by differences in adherence (95% adherence [87% in both arms]) but, instead, by the proportion of patients who discontinued therapy (34.8% in the abacavir group vs. 48.3% in the stavudine group).
A significant increase in CD4 counts was observed in both arms: 263 cells/μL in the abacavir arm and 294 cells/μL in the stavudine arm (P = 0.34).
Twenty-four AIDS-defining diseases (17 confirmed and 7 probable) were diagnosed in 20 patients after a median period of 28 days (range: 1-515 days): 15 in the abacavir arm and 5 in the stavudine arm (P = 0.013). All but 1 were diagnosed in the first 6 months after initiation of therapy.
The results of the present study show a notably lower association between abacavir and the morphologic abnormalities associated with HAART and a more beneficial lipid profile when compared with stavudine. In addition, a trend to a better efficacy rate was observed in the ITT analysis in the abacavir arm, although no differences appeared in the OT analysis. Overall, both regimens were well tolerated.
Our clinical assessments showed a substantially lower incidence of clinical lipoatrophy signs in patients receiving abacavir (4.8%) as compared to patients receiving stavudine (38.3%). These results were confirmed by anthropometric assessment. Increases in all the variables studied were observed in both arms, except for hip girth in the case of stavudine. Also, a higher increase in the waist/hip ratio was found in this arm. Finally, DEXA scans performed in a subset of the overall population showed notable limb fat loss in stavudine patients, whereas a gain was observed in the abacavir group.
Two recent trials have also reported a milder impact on the body fat compartment in naive patients initiating antiretroviral therapy with nonthymidinic regimens. Shlay et al19 found fewer marked lipoatrophy-associated morphologic changes in patients receiving abacavir/lamivudine as compared with stavudine/didanosine. It is of note that the study by Shlay et al19 was a metabolic substudy within a randomized trial, involving a smaller number of patients, with various drugs as the third compound of the regimen and combining stavudine with didanosine.
In a 3-year randomized trial, investigator-reported lipodystrophy occurred less often in patients receiving tenofovir (3%) versus stavudine (19%), both combined with lamivudine and efavirenz.16 That study, unlike ours, was not designed to evaluate body fat changes, however, and DEXA scans were only available after 2 and 3 years of follow-up.
Although some authors have found differences in abdominal fat between nucleoside regimens,19,22 the role of antiretroviral drugs in lipoaccumulation remains controversial.10 In our study, the clinical examinations showed a higher frequency of lipoaccumulation in stavudine patients, but the more reliable objective data failed to confirm these findings. A possible explanation for this discrepancy is that the abdomen may acquire a more prominent appearance when there is gradual peripheral fat loss (pseudotruncal obesity).23 Overall, the impact of treatment on central fat accumulation was substantially lower than on peripheral fat loss. These results agree with recent findings suggesting a lack of association between the phenomena of lipoatrophy and lipoaccumulation.10,24
Regarding lipid metabolism, abacavir was associated with more favorable changes in terms of triglycerides, HDLc, apolipoprotein A1, and TC/HDLc, with this last parameter being proposed by many studies as a single powerful cardiovascular risk predictor.25 Conversely, a slightly higher, although nonsignificant, increase in LDLc was observed among abacavir patients. This result was probably influenced by the substantially higher proportion of patients treated with statins in the stavudine arm (15% vs. 4%), however.
Recent studies have linked stavudine-based antiretroviral therapy with higher elevations in triglycerides and LDLc levels and smaller increases in HDLc levels than those seen in regimens containing other nucleotide/nucleosides, such as tenofovir and, possibly, zidovudine.16,22,26 A better lipid profile as compared with stavudine was shown with tenofovir in a large randomized study conducted in antiretroviral-naive patients.16 Moreover, other data suggest that replacement of stavudine by tenofovir or abacavir may be associated with lipid profile improvements.27-30
Recent data from observational studies in the HIV population have shown an independent association between the incidence of cardiovascular disease and the classic risk factors, including lipid profile alterations.6,7 Thus, the more favorable lipid changes observed in our abacavir-containing regimen may have had a positive benefit in terms of cardiovascular risk.
This study was not powered for a comparison in terms of efficacy. Our data suggest similarly favorable virologic and immunologic results by OT analysis, however, and a trend favoring the abacavir arm by ITT analysis. This may be explained by the larger proportion of patients switching therapy or lost to follow-up in the stavudine arm.
Stavudine was associated with symptoms of mitochondrial toxicity and abacavir was associated with a hypersensitivity reaction in an expected proportion of patients.2,31
Our study has some limitations that should be discussed. First, in the absence of an objective case definition tool at the time the study was designed, HIV-associated lipodystrophy features were diagnosed subjectively. To date, the data regarding the accuracy of subjective assessments remain controversial.3,27,32,33 In addition, it is possible that there may have been some partiality in the examiners' judgments, because the morphologic assessments were performed in an open-label fashion at a time when there was emerging evidence pointing to stavudine as a contributor to lipoatrophy. Second, the proportion of patients lost to follow-up was high, although it did not differ from reported rates in similar studies. Unfortunately, the main objective of this study did not allow computation of these missing data as failures, as is done in efficacy trials. Despite these factors, our clinical diagnoses showed a high level of agreement with anthropometric changes and were confirmed by the outcome of DEXA scanning performed in a subset of patients. This fact, together with the magnitude of the difference in the effect size, makes us reasonably confident about our findings. Finally, caution should be used when interpreting the lipid findings in terms of cardiovascular risk, because a number of unmeasured risk factors might also have been affected.
In conclusion, this study shows that abacavir has a substantially less deleterious effect on body fat distribution (particularly peripheral fat) and lipid metabolism than stavudine. Our data offer strong support for the concept that thymidine analogue-sparing approaches are minimally associated with limb fat loss. Abacavir/lamivudine may be a good nucleoside backbone option for initiating antiretroviral therapy with a low risk for developing lipoatrophy, at least within the first 2 years. This is important, because there is no treatment for this worrisome complication of antiretroviral therapy in HIV-infected patients.
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Other members of the ABCDE Study Team include the following: J. Cosín, and M. Ramírez, Hospital Gregorio Marañón, Madrid; M. Javaloyas, Hospital Sant Llorenç, Viladecans; C. Cepeda, and M. Torralba, Hospital 12 de Octubre, Madrid; M. J. Barberá, M. Santín, I. Ruiz, C. Faz, A. Vila, D. Buisac, and F. Gudiol, Hospital Universitari de Bellvitge, Barcelona (Coordinating Center); J. Murillas, Hospital Clinic, Barcelona; I. Ocaña and V. Falco, Hospital Vall d'Hebron, Barcelona; E. Casas, A. Arranz, and J. de Miguel, Hospital Príncipe de Asturias, Alcalá de Henares; F. Vidal, Hospital Joan XXIII, Tarragona; S. Valero, Hospital de Calella, Calella; L. Force, Hospital de Mataró, Mataró; A. Salas, and C. Villalonga, Hospital Son Dureta, Palma de Mallorca; J. Portilla and V. Boix, Hospital Gral. de Alicante, Alicante; M. A. González and B. Coll, Hospital Sant Joan de Reus, Reus; and F. Del Molino and E. Anoro, Hospital de Terrassa, Terrassa.