This study was conducted based on retrospective data from PWLH followed in various centers in Türkiye. Our findings indicate the advantages of TDF-containing regimens in terms of CD4 cell count increase and normalization of ALT levels. In contrast, during the initial 24 months, TAF regimens were advantageous regarding HIV RNA reduction and phosphorus metabolism. Evaluation of lipid profiles revealed disadvantages in non-HDL cholesterol, total cholesterol, and triglyceride parameters among patients using TAF. These findings suggest that TDF and TAF treatment regimens have different effects, emphasizing the importance of considering individual patient characteristics and needs in treatment selection.
Our study showed no significant difference in HIV RNA levels between TDF and TAF groups at baseline and within the first 24 months of treatment [6, 7]. However, at the 24-month follow-up, we observed higher HIV RNA levels in the TDF group compared to the TAF group (14218.43 ± 233947.64 vs. 3247.15 ± 55371.53, p < 0.001), but this difference was not significant at 36 and 48 months (P > 0.05). Various studies have reported no significant differences in viral load reduction between TDF and TAF groups [8]. However, some studies have indicated significant differences in HIV RNA reduction with TAF regimens [8]. These discrepancies may stem from differences in study methodologies, patient populations, and treatment protocols. Our findings suggest that while TDF and TAF exhibit similar virologic efficacy, treatment duration, and patient populations may influence the observed differences at specific time points.
In our study, over the 48-month follow-up period, TDF participants demonstrated a more significant increase in CD4 levels than those using TAF. Despite lower baseline CD4 levels in the TDF group, improvement in CD4 levels over the 48-month follow-up was superior to that in the TAF group. A literature review reveals insufficient direct comparison data on CD4 level increases between TDF and TAF. However, some studies have yielded different results in evaluations of CD4 increases. For instance, in a study comparing Elvitegravir/Cobicistat/FTC/TAF regimen with Elvitegravir/Cobicistat/FTC/TDF regimen, the increase per microliter based on initial CD4 + cell counts varied [9].
It is known that TAF use maintains plasma tenofovir levels 91% lower, while intracellular tenofovir levels are four times higher compared to TDF. This suggests that the concentration of plasma tenofovir may be higher with TDF use. Some studies have found that, although not statistically significant, groups using TDF showed faster CD4 increases than those using TAF [10] [11]. Meta-analyses have not found significant differences in CD4 levels between TDF and TAF groups. However, these contradictory findings in the literature may be attributed to different pharmacokinetic properties of the drugs. For example, a substantial decrease in plasma tenofovir concentrations has been observed when switching from TDF to TAF. This factor could be significant in explaining their effects on CD4 levels [12]. These findings appear consistent with the knowledge that plasma concentrations of tenofovir are significantly higher with TDF than with TAF. For instance, a transition from TDF to TAF showed a 90% reduction in plasma tenofovir concentration. Plasma tenofovir concentrations in TDF users averaged 99.98 (2.24) ng/mL, whereas in TAF users, it was 10.2 (1.6) ng/mL [13]. In a recent study investigating the effectiveness of Pre-Exposure Prophylaxis (PREP), it was demonstrated that plasma tenofovir concentration is closely associated with the risk of HIV infection development [14]. These findings suggest higher plasma tenofovir concentrations may confer an advantage regarding CD4 level improvement. However, it should be emphasized that new research is needed to understand better the role of plasma tenofovir concentrations in the effectiveness of HIV prevention strategies.
Our study observed that the mean age in the TDF/FTC/BIC subgroup (39.2611.92) was significantly lower compared to other subgroups. This could be attributed to the fact that this drug is the most recently introduced medication in our country, and it is predominantly initiated in younger patients newly diagnosed with HIV. When analyzing the gender distribution among subgroups, it was determined that the proportion of females in the TDF/FTC/RAL subgroup (35.1%) was significantly higher compared to other subgroups. The TDF/FTC/RAL combination is known to be a reliable option, especially during pregnancy, and it may be associated with its initiation in women with childbearing potential.
In our study, weight gain associated with antiretroviral therapy (ART), metabolic disturbances, and cardiovascular diseases remains a significant concern. It has been previously reported that switching from TDF to TAF may lead to the development of hyperlipidemia. Studies suggest that transitioning to TAF may be associated with a higher incidence of dyslipidemia [3, 15]. Our research observed more favorable outcomes in cholesterol and non-HDL cholesterol levels among the TDF group. One possible explanation for this finding could be the self-statin-like effect of TDF, which has been shown to reduce blood lipid concentrations directly [16]. However, other studies suggest that this effect may stem directly from TAF use. A recent study found that transitioning to TAF resulted in increased cholesterol and LDL levels, which play a crucial role in the etiology of atherosclerosis [17]. The increase in LDL-C and TC due to TAF is particularly significant, as LDL cholesterol is considered a primary driver of cardiovascular risk [18]. Changes in cardiovascular risk are directly proportional to changes in LDL cholesterol levels and the achieved LDL cholesterol level [19].
Additionally, similar cardiovascular risk reductions have been observed regardless of the method used to lower LDL cholesterol (lifestyle changes, diet, or lipid-lowering drugs) [20]. Our study results indicate a significant increase in both cholesterol and non-HDL cholesterol levels among patients using TAF [16, 19]. In a recent study, it was observed that transitioning from TDF to TAF in individuals living with HIV resulted in a significant increase in BMI, total cholesterol, and LDL values [20]. In the same study, the median Atherosclerotic Cardiovascular Disease (ASCVD) risk score increased from 6.9–8.1% after switching to TAF (P < 0.01). Adjustments made for age, gender, race, other medications that may contribute to weight gain, and duration of living with HIV showed that transitioning from TDF to TAF was associated with an average 13% increase in ASCVD risk score (95% CI, 4–23%). Following the transition to TAF, the average 13% increase in ASCVD risk score led to 50.7% of participants surpassing the 7.5% statin initiation threshold. Considering the increases in BMI and cholesterol levels, changes in ASCVD risk scores may be associated with an increased risk of cardiovascular disease in individuals transitioning from TDF to TAF. Therefore, we believe that evaluating non-TAF options may be safer for patients with a history of cardiovascular risk factors [21].
LDL cholesterol has traditionally been widely used as a marker for cardiovascular risk. However, non-HDL cholesterol has been suggested to be more helpful in assessing atherogenic risk due to its inclusion of proatherogenic triglyceride-rich lipoproteins (TRL) and apolipoprotein B (apoB) particles [22]. Our study observed that non-HDL cholesterol levels were significantly higher in patients using TAF than those using TDF. Similarly, a study monitoring lipid parameters after switching from TDF to TAF showed a significant increase in non-HDL cholesterol post-TAF [23]. In our cohort, we observed cholesterol elevation due to TAF use persisted for up to 24 months and then tended to decrease, possibly attributed to lifestyle changes and statin use associated with hyperlipidemia.
Furthermore, Silva et al. demonstrated that patients using TAF/FTC/c/EVG required lipid-lowering therapy twice as often as those using TDF/FTC/c/EVG [19]. When examining TAF subgroups in our study, we found that patients using bictegravir-based combinations had a higher increase in non-HDL cholesterol than those using c/EVG. Previous studies have shown that bictegravir, compared to EVG/c, presents a better lipid profile. However, these studies primarily reflect changes in patients undergoing treatment switches rather than direct head-to-head comparisons [24]. Long-term follow-up data from TAF/FTC/BIC combinations also showed total cholesterol and LDL increases, with lipid-lowering therapy initiated in ≤ 2% of patients annually after week 48 [25]. Based on these findings, lipid values should be closely monitored in patients using TAF, especially those at higher cardiovascular risk, and alternative options to TAF should be considered. Traditional risk factors for dyslipidemia, such as diabetes, high BMI, advanced age, and low CD4 + cell counts (< 350 cells/µl), should prompt close monitoring and counseling on lifestyle changes in HIV-positive individuals.
In individuals living with HIV, the infection itself, along with aging, comorbidities, and certain antiretroviral (ARV) medications, increases the risk of osteoporosis. Long-term use of TDF medications is mainly associated with reduced bone mineral density and osteoporosis [26]. Conversely, TAF is associated with lower plasma tenofovir levels, resulting in fewer bone-related side effects. When phosphorus levels were examined, TAF users were found to have significantly higher levels at 48 months compared to TDF users, which may indicate a potential positive effect of TAF on bone health. Studies have shown improvement in bone mineral density when switching from TDF to TAF [27, 28]. However, in a randomized open-label study, no change in bone mineral density was observed after 48 weeks of switching from TDF/FTC/RPV to TAF/FTC/RPV [29].
In our study, when examining TDF subgroups, we observed significant deterioration in spine DEXA results at 24 months, particularly in the TDF/FTC/c/EVG group compared to other groups. This raises the possibility that the boosting effect of cobicistat may increase TDF plasma levels and thereby contribute to bone toxicity. Similarly, another study demonstrated increased bone and kidney toxicity when TDF and cobicistat were administered together, with an area under the curve (AUC) 23% higher [30]. According to a recent meta-analysis, the risk of bone and kidney-related toxicity with TDF was associated with the concurrent use of pharmacological enhancers like cobicistat and ritonavir [30]. When TDF was used without enhancers, there was no significant difference in grade 1–4 adverse events or rates of discontinuation due to renal or bone-related treatment compared to TAF. Therefore, when conducting bone and kidney research, data should be carefully evaluated separately for enhancer use, and further studies in this area are warranted.
Our study observed that ALT levels were significantly higher in patients starting on TDF than those starting on TAF. Additionally, among patients starting on TDF, we noted that the increase in CD4 levels and the decrease in ALT levels at 48 months were better than the TAF group. In a study evaluating treatment-naive HIV patients, it was found that ALT or AST levels were > 1.25 times higher in patients with low baseline CD4 levels [31]. Interestingly, despite being taken at lower doses, TAF can achieve better concentrations in the liver. TDF, particularly effective in reducing lipids, especially in older people, may have a lesser effect on hepatic steatosis, leading to better ALT outcomes. The dyslipidemia observed in TAF users may indirectly relate to elevated liver enzymes. A study examining determinants of liver steatosis in individuals living with HIV participating in the Swiss HIV Cohort Study identified a significant relationship between BMI ≥ 25 kg/m², age 50 and older, and the use of TAF with liver steatosis [32].
In our study, subgroup analyses revealed that treatments with the most detrimental effects on cholesterol levels were TAF and BIC. DOL and TAF were independently associated with a higher likelihood of weight gain. Integrase inhibitors like efavirenz have been suggested to disrupt adipocyte function and increase proinflammatory cytokines. Our research observed that lipid profile deterioration was particularly pronounced in measurements taken within the first 24 months. The study's subgroup analyses showed that TAF and BIC therapies had the most detrimental impact on cholesterol levels [33]. Our study also indicates that lipid deterioration was particularly pronounced in measurements taken within the first 24 months. Another study highlighted that over the years, switching from TDF to TAF and especially using INSTI combinations could lead to a cascade of metabolic disorders, including metabolic syndrome, fatty liver, and eventually insulin resistance [34]. The elevation in ALT observed in cases using TAF-based combinations could be associated with hepatosteatosis. However, this issue should be investigated further with well-designed randomized controlled trials.