Comparison of the efficacy and safety of tenofovir vs. d4T when used in combination with 3TC and efavirenz in ARV-naive patients

Mark Nelson,


The 903 study compared tenofovir (TDF, Viread) against d4T (stavudine, Zerit) in combination with 3TC (lamivudine, Epivir) and efavirenz (EFV, Sustiva). Two hundred and ninety-nine individuals received TDF/3TC/EFV and d4T placebo, and 301 individuals received d4T/3TC/EFV with TDF placebo. Patients were stratified by plasma viral load below or greater than 100,000 and CD4 count less or greater than 200 cells. This study is due to continue for 144 weeks.


Patients who entered this study had a mean age of 36 years and, although the majority were white males, approximately 25% of study participants were female. Forty-six percent of participants in the TDF arm had a viral load above 100,000, while 43% in the d4T arm had viral loads above 100,000. Similarly, 39% of participants in the TDF arm had a low CD4 count and 38% in the d4T arm had less than 200 cells respectively. A very high number of patients continued this study for 48 weeks, with only 9% in each arm discontinuing the study.

This low discontinuation rate contributed to the rates of success seen in both arms, with 87% of individuals having a viral load less than 400 copies/ml, and 82% and 81% less than 50 copies/ml at 48 weeks. The CD4 count rise was 169 cells in the TDF arm, and 167 cells in the d4T arm. There was no effect of viral load or CD4 count on the efficacy in each arm.

Percentage of Patients With HIV-1 RNA <400 copies/mL at Week 48 by Baseline Strata

(n = 299) (n = 301)
≤100,000 c/mL HIV-1 RNA 87% 89%
>100,000 c/mL HIV-1 RNA 86% 85%
≤200 CD4 cells 84% 81%
>200 CD4 cells 88% 90%
Grade 3 and 4 adverse events did not differ through 48 weeks. In particular, there was some concern over the issue of the possibility of osteopenia and bone fracture in patients treated with TDF, however in this study only one patient developed a fracture in the TDF arm and, in fact, four fractured bones in the d4T arm.
Concerning laboratory events, there were marked differences between TDF and d4T in the incidence of raised triglycerides, cholesterol and lactic acid.
TDF+3TC+EFV d4T+3TC+EFV p-value
Mean Change in Triglycerides (mg/dL) +0.14 + 0.95 -0.0001
Mean Change in Cholesterol (mg/dL) + 0.75 +1.47 -0.0001
Percent Lactate >2.2 mg/dL 4% 27% -0.0001

There was also an attempt to quantify mitochondrial DNA reduction, which may lead to toxicities, including peripheral neuropathy, lactic acidosis, pancreatitis and, perhaps, most importantly, lipodystrophy. Mitochondrial DNA was quantified by nucleic acid extraction from PBMC in a sub group of patients in each arm and compared with a control group of 49 HIV-negative men. At baseline, individuals within both arms had lower mitochondrial DNAs than the HIV-negative males. This fact has already been noted in previous studies. When individuals are treated, mitochondrial DNA tends to increase, and individuals in the TDF arm returned to the same level as the HIV-negative men, while those in the d4T arm, although having increases in mitochondrial DNA, remained below the level of the HIV-negative and TDF-treated groups. This may explain the mitochondrial toxicities seen in the two groups.

Toxicities Potentially Associated With Mitochondrial Dysfunction Through Week 48

(n = 299) (n = 301)
(All grades) 9 (3%)* 30 (10%)*
Patients (%) with events 6 (2%)** 20 (7%)**
Peripheral Neuritis/Neuropathy 3 (1%) 11 (4%)
Lipodystrophy 0 3 (1%)
Pancreatitis 0 0

*p <0.001
** p = 0.013


High proportions of individuals in both arms achieved virological success and there were significant increases in CD4 counts. Both arms had a remarkably low discontinuation rate compared with other studies. Individuals who received TDF had fewer toxicities associated with mitochondrial dysfunction, potentially secondary to a greater increase in mitochondrial DNA than those treated with d4T. In addition, the TDF arm had smaller increases in cholesterol and triglycerides.

Clinical implications

Both the TDF and d4T arm achieved remarkable success, paving the way for us to say that the drugs that we have are sufficiently active and that the reasons for virological failure more and more are fear of development of toxicity and compliance issues. Both of the arms are or will soon be available as once-daily therapy. 3TC is now licensed to be utilised once daily and d4TXR will soon be licensed giving us the potential for two highly effective regimens.

However, the major reason for regimen failure both in cohort and clinical studies is toxicity. The lower rates of toxicity with TDF, particularly those associated with mitochondrial dysfunction would suggest that this may be a better choice of initial therapy than d4T. The lower increases in triglyceride and cholesterol may be explained by the fact that rather than d4T causing hyperlipidemia, TDF is protecting against the hyperlipidemia known to be associated with EFV. This theory would be backed up from unpublished data from the 902 and 907 studies suggesting that individuals who received TDF rather than placebo, in addition to background therapy, had a decrease from baseline of their lipids.

Whether the reduction in the increase in lipids in the TDF arm is of clinical significance can only be found by long-term follow up. Significantly fewer patients on the TDF arm than in the d4T arm had raised cholesterol, LDL and triglycerides as defined by limits of the National Cholesterol Education Program Adult Treatment Panel.


Anton Pozniak, Schlomo Staszewski, Joel Gallant et al. Comparison of the Efficacy and Safety of Tenofovir Disoproxil Fumarate (TDF) Versus Stavudine (d4T) When Used in Combination With Lamivudine (3TC) and Efavirenz (EFV) in HIV-1 Infected Patients Naive to Antiretroviral Therapy (ART) After 48 Weeks of Treatment (Study 903). 6th International Congress on Drug Therapy in HIV Infection 17-21 November 2002, Glasgow, UK. Abstract P1.


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