Predictors of kidney tubular dysfunction in HIV-infected patients treated with tenofovir: a pharmacogenetic study

Vitamin D3 decreases parathyroid hormone in HIV-infected youth being treated with tenofovir: a randomized, placebo-controlled trial

BACKGROUND

The study goal was to determine the effect of vitamin D (VITD) supplementation on tubular reabsorption of phosphate (TRP), parathyroid hormone (PTH), bone alkaline phosphatase (BAP), and C-telopeptide (CTX) in youth infected with human immunodeficiency virus (HIV) receiving and not receiving combination antiretroviral therapy (cART) containing tenofovir disoproxil fumarate (TDF).

METHODS

This randomized, double-blind, placebo-controlled multicenter trial enrolled HIV-infected youth 18-25 years based on stable treatment with cART containing TDF (n = 118) or no TDF (noTDF; n = 85), and randomized within those groups to vitamin D3, 50 000 IU (n = 102) or placebo (n = 101), administered at 0, 4, and 8 weeks. Outcomes included change in TRP, PTH, BAP, and CTX from baseline to week 12 by TDF/noTDF; and VITD/placebo.

RESULTS

At baseline, VITD and placebo groups were similar except those on TDF had lower TRP and higher PTH and CTX. At week 12, 95% in the VITD group had sufficient serum 25-hydroxy vitamin D (25-OHD; ≥20 ng/mL), increased from 48% at baseline, without change in placebo (P < .001). PTH decreased in the TDF group receiving VITD (P = .031) but not in the noTDF group receiving VITD, or either placebo group. The decrease in PTH with VITD in those on TDF occurred with insufficient and sufficient baseline 25-OHD (mean PTH change, -7.9 and -6.2 pg/mL; P = .031 and .053, respectively).

CONCLUSIONS

In youth on TDF, vitamin D3 supplementation decreased PTH, regardless of baseline 25-OHD concentration.

CLINICAL TRIALS REGISTRATION

NCT00490412.

Individualization of antiretroviral therapy

Antiretroviral therapy (ART) has evolved considerably over the last three decades. From the early days of monotherapy with high toxicities and pill burdens, through to larger pill burdens and more potent combination therapies, and finally, from 2005 and beyond where we now have the choice of low pill burdens and once-daily therapies. More convenient and less toxic regimens are also becoming available, even in resource-poor settings. An understanding of the individual variation in response to ART, both efficacy and toxicity, has evolved over this time. The strong association of the major histocompatibility class I allele HLA-B*5701 and abacavir hypersensitivity, and its translation and use in routine HIV clinical practice as a predictive marker with 100% negative predictive value, has been a success story and a notable example of the challenges and triumphs in bringing pharmacogenetics to the clinic. In real clinical practice, however, it is going to be the exception rather than the rule that individual biomarkers will definitively guide patient therapy. The need for individualized approaches to ART has been further increased by the importance of non-AIDS comorbidities in HIV clinical practice. In the future, the ideal utilization of the individualized approach to ART will likely consist of a combined approach using a combination of knowledge of drug, virus, and host (pharmacogenetic and pharmacoecologic [factors in the individual’s environment that may be dynamic over time]) information to guide the truly personalized prescription. This review will focus on our knowledge of the pharmacogenetics of the efficacy and toxicity of currently available antiretroviral agents and the current and potential utility of such information and approaches in present and future HIV clinical care.

Genetic variants of ABCC10, a novel tenofovir transporter, are associated with kidney tubular dysfunction

BACKGROUND

Tenofovir (TFV) causes kidney tubular dysfunction (KTD) in some patients, but the mechanism is poorly understood. Genetic variants in TFV transporters are implicated; we explored whether ABCC10 transports TFV and whether ABCC10 single-nucleotide polymorphisms (SNPs) are associated with KTD.

METHODS

TFV accumulation was assessed in parental and ABCC10-transfected HEK293 cells (HEK293-ABCC10), CD4(+) cells and monocyte-derived macrophages (MDMs). Substrate specificity was confirmed by cepharanthine (ABCC10 inhibitor) and small interfering RNA (siRNA) studies. Fourteen SNPs in ABCC10 were genotyped in human immunodeficiency virus-positive patients with KTD (n = 19) or without KTD (controls; n = 96). SNP and haplotype analysis was performed using Haploview.

RESULTS

TFV accumulation was significantly lower in HEK293-ABCC10 cell lines than in parental HEK293 cells (35% lower; P = .02); this was reversed by cepharanthine. siRNA knockdown of ABCC10 resulted in increased accumulation of TFV in CD4(+) cells (18%; P = .04) and MDMs (25%; P = .04). Two ABCC10 SNPs (rs9349256: odds ratio [OR], 2.3; P = .02; rs2125739, OR, 2.0; P = .05) and their haplotype (OR, 2.1; P = .05) were significantly associated with KTD. rs9349256 was associated with urine phosphorus wasting (P = .02) and β2 microglobulinuria (P = .04).

CONCLUSIONS

TFV is a substrate for ABCC10, and genetic variability within the ABCC10 gene may influence TFV renal tubular transport and contribute to the development of KTD. These results need to be replicated in other cohorts.

Severe acute renal failure in an HIV-infected patient after only 2 weeks of tenofovir-based antiretroviral therapy

We report a 46-year-old man who has sex with men (MSM) patient, of Scottish descent, who had no history of arterial hypertension, diabetes, or illicit drug use, was hepatitis C virus (HCV) negative but underwent right nephrectomy for urothelial tumor in 2006. Before starting antiretroviral therapy, he had a CD4 cell count of 316/mm(3) and plasma HIV RNA level was 1,020,537 copies per milliliter. He developed acute renal failure only 2 weeks after introduction of tenofovir-based antiretroviral therapy and then required 3 months of hemodialysis. After the end of hemodialysis, antiviral therapy was resumed with abacavir (300 mg×2/day), lamivudine (300 mg every day), and lopinavir/ritonavir (400/100 mg twice daily). Renal biopsy revealed severe and diffuse toxic acute tubular necrosis Two years after tenofovir discontinuation, the patient's renal function remained subnormal. Although severe renal toxicity due to tenofovir is rare, patients receiving tenofovir must be monitored closely for renal dysfunction especially during the first weeks of tenofovir therapy.

Impact of small body weight on tenofovir-associated renal dysfunction in HIV-infected patients: a retrospective cohort study of Japanese patients

Background

Treatment with tenofovir is sometimes associated with renal dysfunction. Limited information is available on this side effect in patients with small body weight, although the use of tenofovir will spread rapidly in Asia and Africa, where patients are likely to be of smaller body weight.

Methods

In a single-center cohort, Japanese patients with HIV infection who started tenofovir-containing antiretroviral therapy were retrospectively analyzed. The incidence of tenofovir-associated renal dysfunction, defined as more than 25% decrement of estimated glomerular filtration rate (eGFR) from the baseline, was determined. The effects of small body weight and body mass index (BMI) on tenofovir-associated renal dysfunction, respectively, were estimated in univariate and multivariate Cox hazards models as the primary exposure. Other possible risk factors were evaluated by univariate analysis and those found significant were entered into the multivariate analysis.

Results

The median weight of 495 patients was 63 kg. Tenofovir-related renal dysfunction occurred in 97 (19.6%) patients (incidence: 10.5 per 100 person-years). Univariate analysis showed that the incidence of tenofovir-related renal dysfunction was significantly associated with smaller body weight and BMI, respectively (per 5 kg decrement, HR = 1.23; 95% CI, 1.10–1.37; p<0.001)(per 1 kg/m² decrement, HR = 1.14; 95% CI, 1.05–1.23; p = 0.001). Old age, high baseline eGFR, low serum creatinine, low CD4 count, high HIV viral load, concurrent nephrotoxic drugs, hepatitis C infection, and current smoking were also associated with tenofovir-related renal dysfunction. Multivariate analysis identified small body weight as a significant risk (adjusted HR = 1.13; 95% CI, 1.01–1.27; p = 0.039), while small BMI had marginal significance (adjusted HR = 1.07; 95% CI 1.00–1.16; p = 0.058).

Conclusion

The incidence of tenofovir-associated renal dysfunction in Japanese patients was high. Small body weight was identified as an independent risk factor for tenofovir-associated renal dysfunction. Close monitoring of renal function is advocated for patients with small body weight treated with tenofovir.

Tenofovir nephrotoxicity: 2011 update

Tenofovir is an acyclic nucleotide analogue reverse-transcriptase inhibitor structurally similar to the nephrotoxic drugs adefovir and cidofovir. Tenofovir is widely used to treat HIV infection and approved for treatment of hepatitis B virus. Despite initial cell culture and clinical trials results supporting the renal safety of tenofovir, its clinical use is associated with a low, albeit significant, risk of kidney injury. Proximal tubular cell secretion of tenofovir explains the accumulation of the drug in these mitochondria-rich cells. Tenofovir nephrotoxicity is characterized by proximal tubular cell dysfunction that may be associated with acute kidney injury or chronic kidney disease. Withdrawal of the drug leads to improvement of analytical parameters that may be partial. Understanding the risk factors for nephrotoxicity and regular monitoring of proximal tubular dysfunction and serum creatinine in high-risk patients is required to minimize nephrotoxicity. Newer, structurally similar molecular derivatives that do not accumulate in proximal tubules are under study.

Risk factors of chronic kidney disease in HIV-infected patients

BACKGROUND AND OBJECTIVES

The main aim of this study was determining the risk factors of chronic kidney disease (CKD) in HIV-1-infected patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Patients were followed from seven large HIV reference centers in France that maintain prospective databases on HIV-1-infected patients. The main outcome was the time to CKD defined as two consecutive measures of estimated GFR ≤60 ml/min per 1.73 m² over ≥3 months. A Cox's model with delayed entry was used to search predictive factors of time to CKD.

RESULTS

From 1993 to 2006, 349 out of 7378 patients were found to have CKD. Of these, 166 had hypertension, 33 had diabetes, and 26 were antiretroviral therapy-naïve. Occurrence of acute kidney injury (hazard ratio [HR] = 2.40) and hypertension (HR = 2.39) were strongly associated with an increased risk of CKD. Patients with a durable level of CD4 count >200 cells/mm³ had a lower risk of CKD (HR = 0.63). Recent exposure to indinavir (HR = 2.03), totenofovir (HR = 1.55), and abacavir (HR = 1.37) were associated with an increased risk of CKD. Past exposure to tenofovir was also associated with an increased risk of CKD (HR = 2.23), and a trend toward significance was observed for past exposure to indinavir (HR = 1.28).

CONCLUSIONS

CKD was not rare in HIV-infected patients and occurs preferentially in HIV-infected patients exposed to certain ARVs, specifically abacavir, indinavir and tenofovir. This requires closer monitoring of renal function in patients exposed to one of these drugs.

Increased risk of abnormal proximal renal tubular function with HIV infection and antiretroviral therapy

Abnormal kidney function is common in the course of human immunodeficiency virus (HIV) infection. Here, we performed a cross-sectional analysis using 399 patients within the Aquitaine cohort (a hospital-based cohort of HIV-1-infected patients receiving routine clinical management) to estimate the prevalence of proximal renal tubular dysfunction (PRTD) associated with HIV infection. These patients did not differ statistically by sociodemographics, median age, years since HIV diagnosis, AIDS stage, or median CD4 cell count from the entire 3080 patient cohort. Antiretroviral therapy was received by 352 patients, with 256 given tenofovir (TDF); 325 had undetectable HIV plasma viral load, and 26 were diagnosed with PRTD. In multivariate analysis, significant independent associations were found between PRTD and age (odds ratio (OR) 1.28 per 5-year increase), atazanavir (OR 1.28 per year of exposure), and TDF (OR 1.23 per year) treatment. Among patients having received TDF-containing regimens over a 5-year period, PRTD remained significantly associated with TDF exposure when treatment was ongoing (OR 5.22) or had been discontinued (OR 11.49). Thus, cumulative exposure to TDF and/or atazanavir was associated with an increased risk of PRTD, with concern about its reversibility in patients with HIV.

Novel nephrotoxins

Drug and xenobiotic toxicity is an important cause of kidney injury, especially in vulnerable patients. Nephrotoxic syndromes include functional disorders; vascular injury, such as thrombotic microangiopathy; glomerular injury resulting in nephrotic syndrome or glomerulonephritis; acute tubular necrosis; acute interstitial nephritis; and crystalopathy/nephrolithiasis. Recently reported nephrotoxins are reviewed in the context of these syndromes of kidney injury.

Secondary complications and co-infections in the HIV-infected adolescent in the antiretroviral era

PURPOSE OF REVIEW

The number of HIV-infected adolescents is increasing dramatically. With combination antiretroviral therapy, they are expected to live well into adulthood. However, complications are emerging at a higher rate in the HIV-infected population compared to the general population. HIV-infected adolescents are also at a high risk of sexually transmitted co-infections. This article reviews the main secondary complications and co-infections in the HIV-infected adolescent.

RECENT FINDINGS

HIV-infected adolescents are at a high risk of sexually transmitted infections. A careful, age-appropriate and developmentally appropriate inquiry into the individual's sexual behavior to assess risk is paramount, in addition to regular screening at medical visits. Treating co-infections is not only important for HIV-infected individuals, but also limits HIV transmission to others. In addition, monitoring and addressing modifiable secondary risk factors for complications such as renal disease, osteopenia or osteoporosis, and cardiovascular disease are critical, well before the onset of clinically apparent disease. Using antiretroviral therapy to suppress viral replication and inflammation appears to be a promising strategy for decreasing secondary complication risk, and likely overshadows the toxicities associated with the long-term use of certain antiretrovirals.

SUMMARY

Assessing and addressing the risk of secondary complications and co-infections in the HIV-infected adolescent is crucial for optimal length and quality of life.

Tenofovir-induced renal toxicity in 324 HIV-infected, antiretroviral-naïve patients

To better evaluate the renal safety profile of tenofovir, we performed a retrospective study of HIV-infected antiretroviral-naïve patients starting a first antiretroviral therapy between July 2004 and July 2008, and followed-up for 24 months. The glomerular filtration rate (GFR) was calculated using the MDRD formula, and tubular dysfunction was diagnosed with 2 or more of the following: proteinuria, glucosuria, hypouricemia, hypophosphatemia and hypokalemia. Overall, 324 patients were enrolled: 201 were tenofovir-exposed and were compared with 123 tenofovir-unexposed subjects. In both the unadjusted and adjusted analyses, tenofovir-exposed subjects had a significantly greater decline in GFR and a significantly higher incidence of proximal tubular dysfunction through 24 months. Reduced glomerular and tubular functions were significantly associated with older age, diabetes, hypertension and concomitant therapy with a protease inhibitor.

Tenofovir-associated kidney toxicity in HIV-infected patients: a review of the evidence

Tenofovir (TDF) is an effective and widely used treatment for both human immunodeficiency virus (HIV) and hepatitis B virus infection. Although studies suggest that TDF has a low overall toxicity profile and only a modest effect on estimated glomerular filtration rate, numerous case reports have since appeared in the literature describing TDF-associated renal tubular dysfunction, and this is now a significant source of HIV-related referrals to nephrologists. The main target of toxicity appears to be the proximal tubule, and in severe cases, patients can develop renal Fanconi syndrome. We review findings from recent studies in this area performed by ourselves and others and discuss our direct experience as practicing nephrologists. In particular, we discuss: (1) the nature and extent of TDF-associated kidney toxicity in the HIV-infected population, (2) potential underlying mechanisms of toxicity in the proximal tubule, (3) risk factors for developing tubular dysfunction, and (4) suggested strategies to monitor patients on TDF therapy.

Biomarkers of impaired renal function

PURPOSE OF REVIEW

Renal disease is increasingly common as life expectancy of HIV-infected persons continues to improve. Several biomarkers are available for monitoring renal function, although no consensus exists on how best to apply these tools in HIV infection. This review describes recent findings for the more common renal biomarkers.

RECENT FINDINGS

Although widely used in clinical practice, creatinine-based estimates of glomerular filtration rate have not been validated in HIV infection. Serum cystatin C has been proposed as a more sensitive marker of renal dysfunction in HIV infection, although it may also reflect systemic inflammation. Screening for proteinuria and albuminuria allows identification of patients at higher risk of kidney disease and other adverse outcomes. Fanconi syndrome, which has been associated with tenofovir use, is associated with severe tubular proteinuria, and several low molecular weight proteins, including retinol-binding protein, β2-microglobulin, and neutrophil gelatinase-associated lipocalin have been studied as markers of tubular dysfunction. Studies have reported a high prevalence of subclinical proximal tubular dysfunction in patients receiving antiretroviral therapy.

SUMMARY

Future studies are needed to determine the optimal biomarkers for the detection and monitoring of renal disease in HIV.

Pharmacological considerations for tenofovir and emtricitabine to prevent HIV infection

The use of antiretroviral medications in HIV-negative individuals as pre-exposure prophylaxis (PrEP) is a promising approach to prevent HIV infection. Tenofovir disoproxil fumarate (TDF) and emtricitabine exhibit desirable properties for PrEP including: favourable pharmacokinetics that support infrequent dosing; few major drug-drug or drug-food interactions; an excellent clinical safety record; and pre-clinical evidence for efficacy. Several large, randomized, controlled clinical trials are evaluating the safety and efficacy of TDF and emtricitabine for this new indication. A thorough understanding of variability in drug response will help determine future investigations in the field and/or implementation into clinical care. Because tenofovir and emtricitabine are nucleos(t)ide analogues, the HIV prevention and toxicity effects depend on the triphosphate analogue formed intracellularly. This review identifies important cellular pharmacology considerations for tenofovir and emtricitabine, which include drug penetration into relevant tissues and cell types, race/ethnicity/pharmacogenetics, gender, cellular activation state and appropriate episodic or alternative dosing strategies based on pharmacokinetic principles. The current state of knowledge in these areas is summarized and the future utility of intracellular pharmacokinetics/pharmacodynamics for the PrEP field is discussed.

Prospective study of renal function in HIV-infected pediatric patients receiving tenofovir-containing HAART regimens

AIM

to describe the impact of tenofovir disoproxil fumarate (TDF) use on renal function in HIV-infected pediatric patients.

DESIGN

it is a prospective, multicenter study. The setting consisted of five third-level pediatric hospitals in Spain. The study was conducted on patients aged 18 years and younger who had received TDF for at least 6 months. The intervention was based on the study of renal function parameters by urine and serum analyses. The main outcome measures were renal function results following at least 6 months of TDF therapy.

RESULTS

forty patients were included (32 were white and 26 were diagnosed with AIDS). Median (range) duration of TDF treatment was 77 months (16-143). There were no significant changes in the estimated creatinine clearance. Urine osmolality was abnormal in eight of 37 patients, a decrease in tubular phosphate absorption was documented in 28 of 38 patients, and 33 of 37 patients had proteinuria. A statistically significant decrease in serum phosphate and potassium concentrations was observed during treatment (P = 0.005 and P = 0.003, respectively), as well as a significant relationship between final phosphate concentration and tubular phosphate absorption (P = 0.010). A negative correlation was found between phosphate concentration and time on TDF.

CONCLUSIONS

TDF use showed a significant association with renal tubular dysfunction in HIV-infected pediatric patients. Periodic assessment of tubular function may be advisable in the follow-up of this population.

Association of pharmacogenetic markers with premature discontinuation of first-line anti-HIV therapy: an observational cohort study

BACKGROUND

Poor tolerance and adverse drug reactions are main reasons for discontinuation of antiretroviral therapy (ART). Identifying predictors of ART discontinuation is a priority in HIV care.

METHODS

A genetic association study in an observational cohort to evaluate the association of pharmacogenetic markers with time to treatment discontinuation during the first year of ART. Analysis included 577 treatment-naive individuals initiating tenofovir (n = 500) or abacavir (n = 77), with efavirenz (n = 272), lopinavir/ritonavir (n = 184), or atazanavir/ritonavir (n = 121). Genotyping included 23 genetic markers in 15 genes associated with toxicity or pharmacokinetics of the study medication. Rates of ART discontinuation between groups with and without genetic risk markers were assessed by survival analysis using Cox regression models.

RESULTS

During the first year of ART, 190 individuals (33%) stopped 1 or more drugs. For efavirenz and atazanavir, individuals with genetic risk markers experienced higher discontinuation rates than individuals without (71.15% vs 28.10%, and 62.5% vs 14.6%, respectively). The efavirenz discontinuation hazard ratio (HR) was 3.14 (95% confidence interval (CI): 1.35-7.33, P = .008). The atazanavir discontinuation HR was 9.13 (95% CI: 3.38-24.69, P < .0001).

CONCLUSIONS

Several pharmacogenetic markers identify individuals at risk for early treatment discontinuation. These markers should be considered for validation in the clinical setting.

Renal impairment after switching from stavudine/lamivudine to tenofovir/lamivudine in NNRTI-based antiretroviral regimens

BACKGROUND

During stavudine phase-out plan in developing countries, tenofovir is used to substitute stavudine. However, knowledge regarding whether there is any difference of the frequency of renal injury between tenofovir/lamivudine/efavirenz and tenofovir/lamivudine/nevirapine is lacking.

METHODS

This prospective study was conducted among HIV-infected patients who were switched NRTI from stavudine/lamivudine to tenofovir/lamivudine in efavirenz-based (EFV group) and nevirapine-based regimen (NVP group) after two years of an ongoing randomized trial. All patients were assessed for serum phosphorus, uric acid, creatinine, estimated glomerular filtration rate (eGFR), and urinalysis at time of switching, 12 and 24 weeks.

RESULTS

Of 62 patients, 28 were in EFV group and 34 were in NVP group. Baseline characteristics and eGFR were not different between two groups. At 12 weeks, comparing mean ± SD measures between EFV group and NVP group were: phosphorus of 3.16 ± 0.53 vs. 2.81 ± 0.42 mg/dL (P = 0.005), %patients with proteinuria were 15% vs. 38% (P = 0.050). At 24 weeks, mean ± SD phosphorus and median (IQR) eGFR between the corresponding groups were 3.26 ± 0.78 vs. 2.84 ± 0.47 mg/dL (P = 0.011) and 110 (99-121) vs. 98 (83-112) mL/min (P = 0.008). In NVP group, comparing week 12 to time of switching, there was a decrement of phosphorus (P = 0.007) and eGFR (P = 0.034). By multivariate analysis, 'receiving nevirapine', 'old age' and 'low baseline serum phosphorus' were associated with hypophosphatemia at 24 weeks (P < 0.05). Receiving nevirapine and low baseline eGFR were associated with lower eGFR at 24 weeks (P < 0.05).

CONCLUSION

The frequency of tenofovir-associated renal impairment was higher in patients receiving tenofovir/lamivudine/nevirapine compared to tenofovir/lamivudine/efavirenz. Further studies regarding patho-physiology are warranted.

Renal toxicity associated with tenofovir use

IMPORTANCE OF THE FIELD

Tenofovir (TFV) is a nucleotide analogue widely used for the treatment of HIV infection. Despite its proven efficacy and safety, cases of kidney tubular dysfunction have increasingly been reported and concern exists about the risk of nephrotoxicity associated with the long-term use of TFV.

AREAS COVERED IN THIS REVIEW

Evidences about the renal toxicity associated with TFV use as well as predictors are examined. The most relevant publications assessing TFV safety and those which have reported cases of tubular dysfunction were identified and carefully revised.

WHAT THE READER WILL GAIN

Renal damage of clinical significance caused by TFV is uncommon in the short-mid-term. It occurs more frequently in subjects with underlying kidney conditions. TFV primarily results in kidney tubular dysfunction and less frequently in glomerular abnormalities. Kidney damage may progress over time under long-term TFV exposure but is reversible in most cases on drug discontinuation.

TAKE HOME MESSAGE

Severe renal damage associated with TFV use is uncommon and of multifactorial origin. However, mild tubular dysfunction is recognized in a substantial proportion of TFV-treated individuals and tends to increase with cumulative exposure.

Randomized comparison of renal effects, efficacy, and safety with once-daily abacavir/lamivudine versus tenofovir/emtricitabine, administered with efavirenz, in antiretroviral-naive, HIV-1-infected adults: 48-week results from the ASSERT study

BACKGROUND

Abacavir/lamivudine and tenofovir/emtricitabine fixed-dose combinations are commonly used first-line antiretroviral therapies, yet few studies have comprehensively compared their safety profiles.

METHODS

Forty-eight-week data are presented from this multicenter, randomized, open-label study comparing the safety profiles of abacavir/lamivudine and tenofovir/emtricitabine, both administered with efavirenz, in HLA-B*5701-negative HIV-1-infected adults.

RESULTS

Three hundred eighty-five subjects were enrolled in the study. The overall rate of withdrawal was high (28%). Changes in estimated glomerular filtration rate from baseline were similar between arms [difference 0.953 mL.min.1.73 m (95% confidence interval: -1.445 to 3.351), P = 0.435]. Urinary excretion of retinol-binding protein and beta-2 microglobulin increased significantly more in the tenofovir/emtricitabine arm (+50%; +24%) compared with the abacavir/lamivudine arm (no change; -47%) (P < 0.0001). A lower proportion achieved viral load <50 copies per milliliter in the abacavir/lamivudine arm (114 of 192, 59%) compared with the tenofovir/emtricitabine arm (137 of 193, 71%) [difference 11.6% (95% confidence interval: 2.2 to 21.1)]. The overall virological failure rate was low. The adverse event rate was similar between arms (except drug hypersensitivity, reported more in the abacavir/lamivudine arm).

CONCLUSIONS

The study showed no difference in estimated glomerular filtration rate between the arms, however, increases in markers of tubular dysfunction were observed in the tenofovir/emtricitabine arm, the long-term consequence of which is unclear. A significant difference in efficacy favoring tenofovir/emtricitabine was observed.

Recent developments in HIV-related kidney disease

Although kidney disease has been a recognized complication of HIV infection since the beginning of the HIV epidemic, its epidemiology, underlying causes and treatment have evolved in developed countries where HAART has been widely available. HIV-associated nephropathy and HIV immune complex-mediated kidney disease were the prominent renal diagnoses in the earlier period of the HIV epidemic. While HIV immune complex-mediated kidney disease remains a common finding among HIV-infected individuals with kidney disease, the incidence of HIV-associated nephropathy has been diminishing in developed countries. The role of the metabolic effects of long-term HAART exposure and nephrotoxicity of certain antiretroviral medications on the development and progression of chronic kidney disease is now of increasing concern. The long-term clinical implications of acute kidney injury among HIV-infected persons are increasingly recognized. Kidney disease in HIV-infected persons continues to be a major risk factor for morbidity and mortality in this patient population; therefore, early recognition and treatment of kidney disease are imperative in lessening the impact of kidney disease on the health of HIV-infected individuals. This review focuses on recent developments and ongoing challenges in the understanding, diagnosis and management of HIV-related kidney disease.

Tenofovir nephrotoxicity: acute tubular necrosis with distinctive clinical, pathological, and mitochondrial abnormalities

Tenofovir, a widely prescribed antiretroviral medication for treatment of HIV-1 infection, is infrequently associated with renal dysfunction and biopsy findings of acute tubular necrosis. We examined the clinical and pathological findings in 13 cases of tenofovir nephrotoxicity (7 men and 6 women, mean age of 51.1±9.6 years). Patients received tenofovir therapy for a mean of 19.6 months (range, 3 weeks to 8 years; median 8 months). Nine patients presented with acute kidney injury, and four had mild renal insufficiency with subnephrotic proteinuria. Mean baseline serum creatinine was 1.3±0.3 mg/dl, reaching 5.7±4.0 mg/dl at the time of biopsy, with mean proteinuria of 1.6±0.3 g/day. Glycosuria was documented in seven patients, five of whom were normoglycemic. Renal biopsy revealed toxic acute tubular necrosis, with distinctive proximal tubular eosinophilic inclusions representing giant mitochondria visible by light microscopy. Electron microscopy showed mitochondrial enlargement, depletion, and dysmorphic changes. Clinical follow-up after tenofovir discontinuation was available for 11 of 13 patients (mean duration 13.6 months). Significant recovery of renal function occurred in all patients, including four who required transient hemodialysis. Our study shows that tenofovir nephrotoxicity is a largely reversible form of toxic acute tubular necrosis targeting proximal tubules and manifesting distinctive light microscopic and ultrastructural features of mitochondrial injury.

Impairment in kidney tubular function in patients receiving tenofovir is associated with higher tenofovir plasma concentrations

Tenofovir (TFV) is a nucleotide analogue active against HIV and hepatitis B virus. Although TFV rarely affects the glomerular function, abnormalities in the kidney tubular function appear to be quite common. The relationship between TFV exposure and kidney tubular dysfunction (KTD) was examined prospectively in 92 HIV-infected individuals. Median TFV plasma trough concentration was higher in patients with KTD than in the rest (182 vs. 106 ng/ml; P = 0.001). This dose-dependent effect further supports an involvement of TFV in KTD.

[Diagnosis, treatment and prevention of renal diseases in HIV infected patients. Recommendations of the Spanish AIDS Study Group/National AIDS Plan]

The incidence of opportunistic infections and tumours in HIV-infected patients has sharply declined in the HAART era. At the same time there has been a growing increase of other diseases not directly linked to immunodeficiency. Renal diseases are an increasing cause of morbidity and mortality among HIV-infected patients. In the general population, chronic renal failure has considerable multiorgan repercussions that have particular implications in patients with HIV infection. The detection of occult or subclinical chronic kidney disease is crucial since effective measures for delaying progression exist. Furthermore, the deterioration in glomerular filtration should prompt clinicians to adjust doses of some antiretroviral agents and other drugs used for treating associated comorbidities. Suppression of viral replication, strict control of blood pressure, dyslipidemia and diabetes mellitus, and avoidance of nephrotoxic drugs in certain patients are fundamental components of programs aimed to prevent renal damage and delaying progression of chronic kidney disease in patients with HIV. Renal transplantation and dialysis have also special implications in HIV-infected patients. In this article, we summarise the updated clinical practice guidelines for the evaluation, management and prevention of renal diseases in HIV-infected patients from a panel of experts in HIV and nephrologists on behalf of the Spanish AIDS Study Group (GESIDA) and the National AIDS Plan.

Impact of ATP-binding cassette transporters on human immunodeficiency virus therapy

Even though potent antiretrovirals are available against human immunodeficiency virus (HIV)-1 infection, therapy fails in a significant fraction of patients. Among the most relevant reasons for treatment failure are drug toxicity and side effects, but also the development of viral resistance towards the drugs applied. Efflux by ATP-binding cassette (ABC-) transporters represents one major mechanism influencing the pharmacokinetics of antiretroviral drugs and particularly their distribution, thus modifiying the concentration within the infected cells, that is, at the site of action. Moreover, drug-drug interactions may occur at the level of these transporters and modulate their activity or expression thus influencing the efficacy and toxicity of the substrate drugs. This review summarizes current knowledge on the interaction of antiretrovirals used for HIV-1 therapy with ABC-transporters and highlights the impact of ABC-transporters for cellular resistance and therapeutic success. Moreover, the suitability of different cell models for studying the interaction of antiretrovirals with ABC-transporters is discussed.

Impact of tenofovir on renal function in HIV-infected, antiretroviral-naive patients

OBJECTIVE

To better characterize the long-term effects of tenofovir on renal function in a large managed care organization.

METHODS

We performed a retrospective cohort analysis in Kaiser Permanente for years 2002 to 2005 comparing renal function among antiretroviral naïve patients initiating a tenofovir-containing regimen (964 patients) or tenofovir-sparing regimens (683 patients). We evaluated glomerular filtration rate (GFR, [Modification of Diet in Renal Disease equation]), serum creatinine, and the development of renal proximal tubular dysfunction. We report multivariable hazard ratios (HR, Cox modeling) and linear outcomes (repeated measures) with predictors retained if P < 0.10 (backward selection). Potential predictor variables included in multivariate models were age, sex, Black race, baseline laboratories (including CD4 count), history of diabetes mellitus, hypertension, malignancy, hepatitis, and concurrent medications.

RESULTS

Overall, tenofovir-exposed patients had a larger relative decline in GFR through 104 weeks (-7.6 mL/min/1.73 m(2) relative to tenofovir-sparing, P < 0.001); the degree of the difference varied by baseline GFR, with the greatest effect seen in those patients with GFR greater than 80 mL/min/1.73 m(2). Tenofovir-exposed patients had greater development of proximal tubular dysfunction over time (at 52 wk: HR(adjusted) = 1.95 [P = 0.01] and at 104 wk: HR(adjusted) = 5.23 [P = 0.0004]) and had greater risk of medication discontinuation (HR(adjusted) = 1.21, P = 0.02), especially as renal function worsened. Viral control and CD4 count changes were similar between the two groups.

CONCLUSIONS

Tenofovir is associated with greater effect on decline in renal function and a higher risk of proximal tubular dysfunction in antiretroviral naïve patients initiating antiretroviral therapy.

Understanding and managing the adverse effects of antiretroviral therapy

Highly active antiretroviral therapy (HAART) has changed the landscape of HIV disease in a way that seemed unthinkable a decade ago; from an almost uniformly fatal disease to a chronic manageable one. The first HAART regimens worked in suppressing virus, but were encumbered by a variety of short term and long term side effects. More recent regimens became simpler, easier to take, and with fewer adverse events. As we look to people living perhaps a normal life span with HIV, the increasing number of antiretroviral agents available means that individualizing treatment has become more feasible and the longer downstream adverse events related to HAART, such as its effect on cardiovascular disease and diabetes, renal and hepatic disease, have begun to dominate our choice of drugs. A knowledge of both the short and long term adverse events associated with HAART is essential for providers and for patients. For new drugs to be acceptable in the current field, they will have to pass a litmus test of tolerability. Since adverse events are often remarkably idiosyncratic, pharmacogenomics may offer a way of predicting side effects and their severity from a particular drug or drug class in individual patients. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol. 85, issue 1, 2010.

Steady-state amprenavir and tenofovir pharmacokinetics after coadministration of unboosted or ritonavir-boosted fosamprenavir with tenofovir disoproxil fumarate in healthy volunteers

Objective An open-label, three-period pharmacokinetic study was conducted to investigate the drug interaction potential between fosamprenavir (FPV) and tenofovir disoproxil fumarate (TDF). Methods Thirty-six healthy subjects received TDF 300 mg once daily (qd) for 7 days (period 1), and then were randomized to 14 days of either FPV 1400 mg twice daily (bid) or FPV/ritonavir (RTV) 700/100 mg bid alone or with TDF (period 2). Subjects continued their randomized dose of FPV for 14 more days, adding or removing TDF based upon its receipt in period 2 (period 3). Twenty-four-hour pharmacokinetic sampling was carried out on day 7 of period 1 and on day 14 of periods 2 and 3. Steady-state plasma amprenavir (APV) and tenofovir (TFV) pharmacokinetics were assessed by noncompartmental analysis and parameter values observed with each regimen were compared using geometric mean ratios with 90% confidence intervals. Results After TDF coadministration, APV geometric mean minimum concentration (C(min)), maximum concentration (C(max)), and area under the plasma concentration-time curve (AUC) increased by 31, 3 and 7% above values observed with unboosted FPV alone; they also increased by 31, 4 and 16% above values observed with FPV/RTV alone. TFV C(min), C(max) and AUC decreased by 12, 25 and 15% after FPV coadministration and by 9, 18 and 7% after FPV/RTV coadministration. No significant changes in RTV pharmacokinetics were observed. No differences were noted in adverse events among dosing periods. Conclusions In this evaluation of the interaction between FPV and TDF, increases in APV exposures and modest decreases in TFV exposures were observed. These were unlikely to be clinically significant.

Pharmacogenetics of tenofovir treatment

Tenofovir disoproxil fumarate (TDF) is a nucleotide analog used as part of HIV therapy. Its favorable profile in terms of high efficacy, low toxicity and once-daily dosing makes TDF one of the most attractive antiretroviral agents, and therefore, it is widely used. However, cases of kidney tubular dysfunction have been reported and concern exists regarding the long term use of TDF. Owing to the high interindividual variability in the presentation of kidney function abnormalities, research has recently focused on host genetic factors predisposing to TDF-associated renal dysfunction. Transporter proteins involved in the renal elimination of TDF, such as organic anion transporter 1 or multidrug resistant protein 2 or 4, seem to be involved importantly and several genetic polymorphisms in these proteins have been associated with an increased risk of kidney tubulopathy in patients treated with TDF. In this review, all relevant pharmacogenetic factors that may play a role in the risk of renal toxicity associated with the use of tenofovir are summarized.