Pharmacology & Pharmacy, 2013, 4, 651-662 Published Online December 2013 (http://www.scirp.org/journal/pp) http://dx.doi.org/10.4236/pp.2013.49092 Open Access PP 651 Tenofovir Renal Toxicity: Evaluation of Cohorts and Clinical Studies—Part One Adikwu Elias*, Ogbuehi Ijeoma, Nkereuwem Jonathan Edikpo, Deo Oputiri, Oru-Bo Precious Geoffrey Department of Pharmacology, Faculty of Basic Medical Sciences, University of Port Harcourt, Choba, Rivers State, Nigeria. Email: *adikwuelias@gmail.com Received September 11th, 2013; revised October 24th, 2013; accepted November 8th, 2013 Copyright © 2013 Adikwu Elias et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT Tenofovir is one of the most commonly used antiretrovirals in adolescents and adults because of its potency and favor- able pharmacokinetic and relative safety toxicological profile. It has been combined successfully with antiretroviral drugs from classes such as protease inhibitors, non-nucleoside reverse transcriptase inhibitors and nucleoside reverse transcriptase inhibitors to achieve virologic suppression in a high percentage of recipients. Despite its therapeutic suc- cess, quite a number of cohorts and clinical studies have associated tenofovir with the development of renal toxicity with few studies on the opposing end. This stimulated us to review reported cohorts and clinical studies on tenofovir renal toxicity. In this study it was observed that literature reported incidence of tenofovir renal toxicity falls within the range of 0.7% - 17%. Available studies gave different appellations to tenofovir renaltoxicity, which include fanconis syndrome, proximal tubule dysfunction, acute renal failure, chronic renal failure, chronic kidney disease and nephro- genic diabetes insipidus. Markers of renal toxicity (tubulopathy) which include glycosuria, hyperaminoaciduria, pro- teinuria, hyperphosphaturia, hyperuricosuria, retinol-binding protein, beta2-microglobulinuria, decreased creatinine clearance and decreased glomerular filtration rate were also reported. In some studies renal biopsy demonstrated cyto- plasmic vacuolization, apical localization of nuclei and reduction of the brush border on proximal tubule epithelial cells. This study observed that tenofovir renal toxicity could be reversible on discontinuation of tenofovir therapy despite contrary views by some studies. Regardless of tenofovir reported renal toxicity, it is well tolerated with a relative safety profile but it is advised that renal profile of patients should be evaluated before and routinely during tenofovir therapy. Keywords: Tenofovir; Pharmacology; Renal; Toxicity; Cohorts 1. Introduction The human immunodeficiency virus (HIV-1) is a retro- virus of the lentivirus genus that primarily infects cells of the host immune system. Once an individual is infected, HIV-1 replication takes place in several steps. In the first step, the virion attaches itself and fuses with the host cell membrane using co-receptors and releases two single- stranded RNA molecules and three different viral en- zymes into the host cell cytoplasm. The introduced viral RNA is transcribed by viral reverse transcriptase enzyme into DNA and the viral DNA is transported into the nu- cleus. The viral DNA is processed and incorporated by the viral integrase enzyme into the host genome. The integrated viral DNA (aprovirus) is transcribed and translated by the host system to produce viral proteins and single-stranded RNA for new virions. After assem- blage, the new virions bud off and mature using the viral protease, completing the HIV-1 lifecycle [1]. One of the key principles of antiretroviral therapy is the inhibition of the above mentioned HIV replication stages. These have led to the combination of at least three antiviral drugs, preferably from at least two different classes as the standard practice and are known as highly active antiretroviral therapy (HAART) which is currently the therapy of choice for HIV infected patients [2]. Dif- ferent types of antiretroviral combination therapies are available and use of a particular therapy depends on the tolerability, the cost, and the therapeutic objectives [3]. However, despite remarkable viral replication suppres- sion, immune response restoration and decreased mortal- ity, long-term HAART appears to be associated with the development of some toxicological effects like cardio- toxicity, hepatotoxicity and nephrotoxicity [4,5]. These *Corresponding author.
Tenofovir Renal Toxicity: Evaluation of Cohorts and Clinical Studies—Part One 652 have impaired therapeutic success via poor adherence, loss of serum HIV suppression, development of drug- resistant HIV strains, and increased probability of illness progression [6]. Among these HAART associated toxi- cological effects is renal toxicity which was reported to be pronounced in tenofovir (TDF) containing antiretro- viral regimen [7]. Tenofovir is one of the most commonly used antiret- rovirals (ARVs) in adolescents and adults because of its potency and a favorable pharmacokinetic (PK) profile that allows it to be dosed once daily [8,9]. Tenofovir has been found to be effective in many combination regi- mens for the treatment of HIV infection, both in previ- ously untreated and in treated individuals. It has been combined successfully with antiretroviral drugs from classes like protease inhibitors. Non-nucleoside reverse transcriptase inhibitors and nucleoside reverse transcrip- tase inhibitors to achieve virologic suppression in a high percentage of recipients, but researches have associated tenofovir with renal toxicity and decreased mineral bone density [10]. Due to increased reports on tenofovir in- duced renal toxicity and its place in the management of HIV, this work which is the first part (Part 1) of two parts investigated reported cohorts and clinical studies on the renal profile of tenofovir. 2. Pharmadynamics and Pharmacokinetics of Tenofovir Tenofovir was approved by the US Food and Drug Ad- ministration (FDA) on October, 29, 2001 as a once-daily 300 mg tablet for individuals aged 18 years and above for the treatment of HIV-1 infection in combination with other ARVs [11]. It is a 9-R-2-phosphonomethoxypropyl adenine (PMPA) that belonging to the acyclic nucleoside phosphonate family [12]. It is an ester prodrug and is orally administered. Due to the presence of a phospho- nate group, tenofovir is negatively charged at neutral pH, which limits its oral bioavailability [13]. When adminis- tered, it is first hydrolyzed by carboxylesterase and phosphodiesterase during its first passage through the liver to producedtenofovir [14,15]. Tenofovir is later phosphorylated in the cell by adenylate kinase to produce tenofovir monophosphate (TFV-MP). TF-MP undergoes conversion by nucleotide diphosphate kinase to produce tenofovir diphosphate (TFV-DP). TFV-DP has antiviral property and it competes with the naturally nucleotide counterpart deoxyadenosine 5’-triphosphate to inhibit viral reverse transcriptase. The incorporation of TFV-DP into the viral DNA chain terminates DNA elongation and stops further DNA synthesis [16]. Tenofovir has a relatively long half-life of 12 - 18 hours [17]. The oral bioavailability in fasted patients is approximately 25%. Administration of food (high fat meal) increases the oral bioavailability, with an increase in the AUC of approximately 40%. The binding of teno- fovir to human plasma or serum proteins is less than 7.2%. The volume of distribution at steady-state is 1.3 ± 0.6 L/kg and 1.2 ± 0.4 L/kg, following intravenous ad- ministration of tenofovir 1.0 mg/kg and 3.0 mg/kg re- spectively [18]. Tenofovir is not metabolized by liver enzymes but is extensively and rapidly eliminated as unchanged drug in the urine TDF is eliminated by a combination of glomerular filtration and active tubular secretion. There may be competition with other com- pounds that are also excreted through the kidney [19]. TDF associated toxicities include a decline in mineral density of bone, renal increase in parathyroid hormone (PTH) secretion, phosphaturia and hypophosphataemia while fatal lactic acidosis has been reported when TDF was added to a regimen containing didanosine due to TDF induced increase indidanosine concentration [20]. The use of TDF is associated with proximal tubular dysfunction with or without decreased renal function. Renal impairments, including cases of acute renal failure and Fanconi’s syndrome, have been reported with the use of TDF in clinical practice [21]. The pharmacokinetics of tenofovir are altered in patients with renal impairment and patients with creatinine clearance <50 mL/min or with end-stage renal disease (ESRD) requiring dialysis. It is recommended that the dosing interval for tenofovir be modified in patients with creatinine clearance <50 mL/ min or in patients with ESRD who require dialysis [22]. Renal tubular dysfunction and tubular toxicity have been associated with increased TDF plasma concentration. TDF-associated elevations of PTH have been found in- dependent of vitamin D deficiency and have also been linked to vitamin D deficiency in studies of adults with HIV [23,24]. Tenofovir is recommended as one of the preferred nu- cleotide reverse transcriptase inhibitors (NRTIs) for first-line ART in adults. It is available as a co-formula- tion with other ARVs to make dual or triple fixed-dose combinations. Tenofovir exhibited synergistic and addi- tive activity when combined with certain antiretrovirals and demonstrates no antagonistic interactions in their presence. Strong synergism has been seen with zi- dovudine and nevirapine. Additive inhibition has been reported when co-administered with abacavir, lami- vudine and emteicitabine [25,26]. There are reports of HIV-1 isolates with reduced susceptibility to tenofovir in vitro. These viruses expressed a K65R mutation in re- verse transcriptase and showed a 3 - 4 fold reduction in susceptibility to tenofovir [27]. 3. HIV Associated Renal Disease Renal functions abnormalities are present in a large per- centage of patients with HIV infection especially those with very high viral load and comobidities. HIV-associ- Open Access PP
Tenofovir Renal Toxicity: Evaluation of Cohorts and Clinical Studies—Part One 653 ated renal disease has become a relatively frequent cause of end-stage renal disease (ESRD) requiring dialysis and seems to be associated with progression to AIDS and death. Kidney disease associated with HIV is a signifi- cant challenge to patients and clinicians by increasing the risk for AIDS-defining illness, hospitalization, and death [28,29]. Due to morbidity and mortality as a result of HIV associated renal disease, in this section we critically examine reported cases of renal disease attributed to HIV. One of the first cases of kidney disease associated with HIV as reported in 1984 by Rao et al. [30] was charac- terized by nephrotic syndrome with focal and segmental glomerulosclerosis in nine cases of acquired immunode- ficiency syndrome (AIDS). Naicker and colleagues in their work also attested to the fact that the association between HIV and renal disease was first reported in 1984 in New York City and Miami. These groups showed that HIV-positive individuals have proteinuria and progres- sion to end-stage renal disease which occurs within 8 - 16 weeks; death rate approached 100% within 6 months of diagnosis [31]. Subsequently, various glomerular and renal syndromes were described in histology or autopsy studies [32]. Dif- ferent types of renal diseases associated with HIV have been reported this include classic Human immunodefi- ciency virus associated nephropathy (HIVAN), HIV- associated thrombotic microangiopathy, and immune- mediated glomerulonephritis which were discussed in the second part of this work. A survey conducted during the period 1995 through 1999 showed an increasing preva- lence of HIV associated renal disease from 6.3% to 9.1% in HIV patients [33]. Another report revealed that preva- lence of chronic kidney disease in HIV patients may be between 5% to 15% depending on the series. However, some studies revealed that the prevalence of renal histo- logical involvement ranged from 1% - 15% depending on the different autopsy series [34,35]. Similar increase in prevalence was also reported by Deti and colleagues who showed that incidence rate of chronic renal failure were 1.27 cases per 100 person- years. This tends to rise with time: 1.9% at one year, 3.3% at two years, 4% at three years, and 4.4% at four years [36]. Rates of ARF in HIV outpatients were re- ported at 2.9% in 1995 and 6.0% in 2003 in a study of 25,114 patients which shows an increase in trend [37]. Data from the US Renal Database System (USRDS) showed that every year, approximately 800 - 900 new cases of end-stage renal disease (ESRD) attributed to HIVAN are recorded in the US and nearly 90% are re- ported in African-Americans [38]. Szczech in her study also reported CKD correlated with proteinuria and ele- vated creatinine level in 7% to 32% of HIV-seropositive patients and were associated with an increased rate of death in a study of 2038 female HIV-infected patients [39]. Another study that showed the prevalence of HIV infection in renal disease is the report from the Veterans Affairs Medical System. This report showed that the overall incidence of end-stage renal disease was 3.9 cases/1000 person-years among HIV-infected veterans. In this report a higher incidence of end-stage renal dis- ease was observed among HIV-infected African-Ameri- cans which may suggests genetic predisposition in HIV associated renal disease [40]. A similar incidence of higher end-stage renal disease in blacks was also reported in a single-center study from Johns Hopkins, with an 18-fold higher risk for progres- sion to ESRD among HIV infected African-Americans compared with HIV-infected Caucasians [41]. Haile- mariam et al. (2001) [42] reported series of 239 autopsies performed on patients with AIDS in Switzerland from 1981 to 1989 (before the introduction of HAART). Vari- ous renal abnormalities were reported among the 228 white patients. However, the only case of HIVAN in this series was detected in one of six African patients in- cluded in the study. The prevalence of higher HIV asso- ciated kidney disease in black population is supported by a study which employed varying criteria for diagnosis of kidney disease. This study reported a variable prevalence of these diseases in patients with HIV in sub-Saharan Africa: 6% in South Africa, 38% in Nigeria, 26% in Côte d'Ivoire, 28% in Tanzania, 25% in Kenya, 20% - 48.5% in Uganda and 33.5% in Zambia. Results from these studies also suggested that a broader spectrum of histo- pathological lesions in HIV-associated kidney disease exists in African populations than previously thought [43]. A study conducted on an urban US HIV population found evidence of CKD in 24% of the patients. Forty patients which represents (10%) had CKD stage 1, 19 patients which represents (4%) had stage 2, 29 patients (7%) stage 3, four patients (1%) stage 4, and eight pa- tients (2%) stage 5 [44]. Another study carried out in Baltimore, Maryland supported the involvement of HIV in renal disease. In their work they measured CKD incidence, GFR slope, and progression to ESRD in 3332 African American and 927 white HIV-infected subjects. A total of 284 subjects developed CKD, 35% of whom subsequently developed ESRD [45]. In a cross-sectional study of another urban HIV-infected population in New York City, 22% of Af- rican-American patients (versus 11.4% of whites) had either CKD or ESRD; 4.1% of the studied population including Caucasians and Hispanics had ESRD [46]. Rollins et al., 2006 [47] reported that HIV-associated nephropathy is caused by focal sclerosing glomerulopa- thy with is characterized by proteinuria, renal failure, and rapid progression to ESRD. It is said to have a genetic predisposition because it is very common in Africans Open Access PP
Tenofovir Renal Toxicity: Evaluation of Cohorts and Clinical Studies—Part One 654 infected with HIV. It occurs late in the course of HIV-1 infection and includes a CD4 cell count 200 cells/mm3 and a high viral burden. But with the advent of HAART in the treatment of HIV, the incidence of HIV associated renal disease must have decreased due to decline in mor- bidity and mortality rate. 4. Tenofovir Renal Toxicity Tenofovir is one of the widely prescribed antiretroviral drugs and is an essential part of all the regimen (HAART) use in the treatment of HIV-1 adults. TDF has achieved very wide acceptability because it is easy to be adminis- tered, efficacious, and relatively favorable toxicological profile. These qualities have increase the choice and use of TDF as one of the widely prescribed antiretroviral drugs for the treatment of HIV-1. Despite its therapeutic success some reports have associated TDF with devel- opment of renal toxicity which include proximal tubular dysfunction, Fanconi syndrome, acute kidney injury, acute renal failure and chronic renal failure. Reports of renal toxicity attributed to TDF have been published as case reports, cohorts and clinical studies. This section analyzed “with all degree of clarity” these reported co- horts and clinical studies taking into cognizance, the in- cidence, reversibility of tenofovir renal toxicity and dis- crepancy in reports. 4.1. Epidemiology The incidence of a disease could be fundamentally cor- related with its morbidity and mortality rate hence the incidence of tenofovir associated renal toxicity can’t be overemphasized. Studies have reported different inci- dence. This portion evaluated reported incidence of ten- ofovir associated renal toxicity. We will start by looking at a retrospective review of the Food and Drug Admini- stration Adverse Events Reporting System from 2001 through 2006 which registered 164 subjects who had Fanconi’s syndrome. Report showed that 83% of subject with Fanconi syndrome received tenofovir with protease inhibitors [48]. Evaluation of 754 HIV infected subject treated with tenofovir by SCOLTA reported 2.5% inci- dence of creatinine elevations over 1.5-fold the upper limit of normal in a mean followup of 19.5 months [49,50]. Similar observation was reported when a total of 172 patients receiving tenofovir disoproxil fumarate (TDF) for a median of 16 months were evaluated. Seven (4%) patients developed grade 1 increases in serum creatinine (SCr). Fifteen (8.7%) patients had an increase in SCr of greater than 1.5 times baseline values. Four (2.3%) pa- tients discontinued TDF due to increase in SCr and/or abnormal urinalysis. Of 62 patients with urinalysis, twenty-eight which represents (16%) and 11 which represents (6%) of the patients developed grade 1 and grade 2 hypophosphataemia respectively [51]. Some studies have identified rising incidence of hy- pophosphatemia in patients treated with tenofovir a prevalence of 9.8% among tenofovir-treated patients, 6.7% among non tenofovir, HAART-treated patients and 2.6% among treatment-naive, HIV-infected individuals were reported. This observed hypophosphatamia which is a biomaker of renal toxicity may be associated with some comorbidities [52,53]. An outstanding incidence was reported by retrospective cohort analysis of HIV-infected adults who received tenofovir at the Themba Lethu in South Africa. Of 890 patients initiated on tenofovir, 573 (64.4%) had normal renal function had mild renal dys- function and 46 (5.2%) had moderate renal dysfunction. 2.4% experienced nephrotoxicity, 7.8% died and 9.7% were lost during 48-months of follow-up. Incidence of tenofovir associated renal toxicity can be seen from an evaluation of 10,343 tenofovir-treated patients [54]. Another study showed 8.4% of patients attained a greater than 1.5-fold increase in SCr within 6 months of starting tenofovir therapy [55]. One of the studies that could have correlated incidence of tenofovir renal toxic- ity, risk and exposure was the evaluation of association of cumulative and ever exposure to tenofovir on kidney outcomes in 10,841 HIV-infected patients. After multi- variable adjustment, each year of exposure to tenofovir was associated with 34% increased risk of proteinuria 11% increased risk of rapid decline and 33% increased risk of CKD [56]. In a cohort Of 4183 HIV-positive pa- tients, 1058 patients were exposed to tenofovir DF, Only 84 (8%) patients experienced a creatinine value >120 μmol/L [57]. Some incidence as reported by some au- thors include 0.7% by Cooper et al., (2010) [58] 1.65% by Padilla et al., ( 2005) [59] 0.78% and 2% by Gupta et al., (2012) [60]. 4.2. Cohorts and Clinical Studies Tenofovir has been associated with development of renal toxicity in humans and animals. Quite a number of co- horts, case reports and clinical studies have reported dif- ferent forms of tenofovir associated renal toxicity. In this section, we critically looked at various cohorts andclini- cal studies to evaluate the profile of tenofovir on the re- nal system. Verhelst et al. (2002) [61] was the first to describe a patient who was treated with tenofovir and developed reversible Fanconi syndrome, nephrogenic diabetes insipidus, and acute renal failure. Renal biopsy demonstrated cytoplasmic vacuolization, apical localiza- tion of nuclei, and reduction of the brush border on proximal tubule epithelial cells. Subsequently more re- ports on tenofovir associated renal toxicity were rolled out from various studies. One of these reports is a retro- spective cohort analysis of 1647 patients enrolled in the Open Access PP
Tenofovir Renal Toxicity: Evaluation of Cohorts and Clinical Studies—Part One 655 Kaiser Permanente Health Maintenance Organization during 2002 to 2005. In this study tenofovir exposure was found to be significantly associated with a decline in GFR and proximal tubular dysfunction [62]. Another cohort that showed the nephrotoxic effect of tenofovir was performed by Milinkovic and colleagues. They evaluated 1293 patients and reported that 103 pa- tients stopped tenofovir therapy in which 29 discontinued due to renal toxicity [63]. In the ANRS CO3 Aquitaine Cohort, 2613 HIV-infected patients were followed-up between 2004 and 2008 to estimate the incidence of chronic renal failure and related risk factors. The inci- dence rate of chronic renal failure was much higher (12.7 cases for 1000 person-years) which is said to be associ- ated with factors like immunodeficiency and tenofovir exposure [64]. The above reports are in agreement with the work of Wood ward and friends who evaluated the renal profile of 5687 patients in a clinical centre provid- ing HIV care services. They identified 22 patients with TDF associated renal toxicity of which 21 were males and one female [65]. Also a similar Swiss HIV Cohort Study found a consistent evidence for a significant re- duction in GFR associated with tenofovir use [66]. The incidence of CKD was also investigated in the Euro-SIDA Cohort Study, which included 6843 HIV- infected persons that were followed-up from 2004 on- wards. Progression to chronic nephropathy was observed in 225 patients among 21,482 person-years which repre- sents an incidence of 1.05/100 person-years. After ad- justment for traditional risk factors, exposure to tenofovir was significantly associated with a higher incidence of CKD [67]. This is consistent with a study that evaluated 281 HIV infected patients receiving TDF followed up for 4 - 6 weeks, 3, 6, 9 and 12 months, result showed asso- ciation between TDF and renal toxicity [68]. It is out- standing to know that in a retrospective cohort study conducted by Manosuthi et al. one hundred and thirty patients were evaluated. Report showed that the overall incidence of renal failure was 0.26 per 100 persons/ month [69]. Also a cross-sectional study involving 845 HIV-infected outpatients showed a prevalence of chronic renal failure higher than that of the general population, and significant predictors of lower GFR in multivariate analyses were found to be associated with the use of ten- ofovir or stavudine [70]. Cao and others investigated the impact of tenofovir containing regiment in 75 HIV-positive patients. Their results showed that tenofovir containing regimen resulted in greater renal function decline over 48 weeks [71]. This may agree with an observational cohort of renal evalua- tion of patients on TDF performed by Patel and core- searchers. In this cohort, 1271 patients were evaluated, 83 developed renal dysfunction of which 79 had im- paired serum creatinine and 5 had faconis syndrome. Renal dysfunction was higher in tenofovir and PI con- taining regimen [72]. Soler-Palacin and co researchers in their study also showed the capability of tenofovir to induced renal toxicity. The evaluated 40 patients on TDF for a median duration of 77 months and reported signifi- cant association between TDF and renal tubular dysfunc- tion in HIV infected children [73]. In a cross-sectional study of 99 HIV-infected patients who used tenofovir had increased urine retinol-binding protein/creatinine ratio and protein/creatinine ratio, showing a subclinical renal tubulopathy [74]. This can be correlated with a cross-sectional study of plasma and 24-hour urine markers of tubulopathy (glycosuria, hy- peraminoaciduria, hyperphosphaturia, hyperuricosuria, and beta2-microglobulinuria) in 284 HIV-positive pa- tients who demonstrated a significant relationship be- tween exposure to tenofovir and tubular dysfunction in the absence of impaired glomerular function [75]. Simi- lar findings were reported in the ASSERT study, a mul- ticenter, randomized, open-label trial comparing the safety profiles of tenofovir/emtricitabine and abacavir/ lamivudine in association with efavirenz in 385 HIV- infected subjects. After a 48-week follow-up, no differ- ence in eGFR was observed between the arms, but mark- ers of tubular damage (urinary excretion of retinol-bind- ing protein and beta2-microglobulin) increased signifi- cantly in the tenofovir/emtricitabine group [76]. Compel et al., also added their voices to affirm the re- nal toxicity of tenofovir by evaluating 843 patients on TDF containing ART. They discovered that 26 patients developed chronic kidney disease. Those who developed CKD were older and 85% of participants had other risk factor for progression [77]. Decrease in renal function via was also reported in a study involving 40 patients starting a TDF-containing regimen and 388 patients starting regimen not containing TDF, and followed during 42 months. Between baseline and 12 months, the eGFR de- creased significantly in patients receiving TDF (−10.40 ml/min), After 12 months, patients receiving TDF ex- perienced a higher rate of transition from mild renal im- pairment (60 - 90 ml/min/1.73 m2) to moderate renal im- pairment (30 - 60 ml/min/1.73 m2) when compared with patients not receiving TDF [78]. Cohorts studies performed in African countries are consistent with reports from other countries on renal tox- icity associated with tenofovir and this can be correlated with report of higher incidence of tenofovir nephrotoxic- ity in blacks [79]. In a cohort that took place in Zambia involving 10485 patients on ART in which 6900 were on TDF containing regimens available result showed that exposure to TDF was associated with a mean decrease of −14.7 ml/min in crcl from baseline of 6 months [80]. Another study of 324 ARVnaıve patients found a greater incidence of proximal tubular dysfunction and greater Open Access PP
Tenofovir Renal Toxicity: Evaluation of Cohorts and Clinical Studies—Part One 656 decline in eGFR over 24 months in tenofovir-treated pa- tients [81]. In a cohort analysis of 512 patients on tenofovir con- taining antiretroviral regimen for 26 months it was ob- served that TDF induced AKI developed in 25 patients. On stopping TDF 15 patients had complete recovery of renal function, 5 had partial recovery while 5 patients died [82]. This is in agreement with a study involving 324 patients in which 201 TDF exposed patients were compared with 123 tenofovir un-exposed subjects. Re- sults showed that tenofovir exposed patients had a sig- nificant greater decline in glomerular filtration rate and a significant higher incidence of proximal tubular dysfunc- tion through 24 months [83]. Similarly, both current and past tenofovir use were associated with increased risk of proximal renal tubular dysfunction in a cross-sectional study of 399 HIV infected persons [84]. A single-centre cohort study of 503 Japanese patients administered either tenofovir or abacavir base ART was performed by Nishijima et al. and incidence of renal function was defined as more than 25% fall in estimated glomerular filtration rate from the base line. Result showed that incidence of renal dysfunction in tenofovir arm was higher than the abacavir arm per 100 persons- year [85]. This report is consistent with an evaluation of 226 patients on TDF containing regimen in which 18 patients had a decline in renal function [86]. This can be correlated with a European multicenter cohort study in- volving 78 HBV infected patients exposed to TDF for 76 weeks and reported significant renal damage [87]. Johns Hopkins cohort data showed significant reductions in creatinine clearance at 180 days, 270 days, and 360 days over a 360-day follow-up in 344 patients receiving teno- fovir compared with 314 patients who received nRTIs other than tenofovir [88]. 4.3. Is It Reversible? Still on tenofovir associated renal toxicity, there are dis- crepancies in reports on the reversibility of tenofovir renal toxicity. Some studies have reported the reversibil- ity of tenofovir associated renal toxicity. These studies include a research that evaluated the association between tenofovir use and renal abnormality in HIV-1-infected children on antiretroviral therapy; the biochemistry re- sults for 456 ART-exposed children were evaluated. Re- sults showed that twenty out of 456 (4.4%) had hypo- phosphataemia, and one had eGFR less than 60 ml/min per 1.73 m2. The hypophosphataemia incidence rate was 4.3/100 person-years in the TDF group versus 0.9/100 person-years in those not exposed to TDF. They con- cluded that hypophosphataemia was uncommon (4%), but was associated with prolonged TDF use, and was generally reversible following TDF withdrawal [89]. Another study in which patients received tenofovir therapy for a mean of 19.6 months show that nine pa- tients presented with acute kidney injury, and four had mild renal insufficiency with subnephrotic proteinuria,. 11 of 13 patients who discontinued tenofovir showed significant recovery of renal function including four who required transient hemodialysis [90]. The progress of renal damage after discontinuation of tenofovir (TDF) in patients who started therapy with normal renal parame- ters was also assessed by Bonjoch and colleagues. They evaluated 183 patients who were exposed to TDF for 39 (22 - 63) months. After 22 (13 - 49.5) months of TDF discontinuation, renal parameters returned to normal values in 59% of patients [91]. Kelly and colleagues also reported that proteinuria was reversible in 11 of 12 pa- tients who discontinued tenofovir because of proteinuria without altering other medications [92]. Other cases of reversible tubular dysfunction, includ- ing Fanconi syndrome, nephrogenic diabetes insipidus, and/or ARF, have also been reported, with onset usually within 5 to 12 months after starting therapy and recovery usually occurring within a few months after tenofovir discontinuation [93,94]. Another study that supports the reversibility of tenofovir nephrotoxicity is a cohort of 1286 HIV patients treated with tenofovir containing regimens and followed up for 48 weeks results showed an incidence of 0.39 per 100/year which was reversed on cessation of therapy [95]. Some studies gave contrary views on the reversibility of tenofovir renal toxicity. One of these studies was per- formed by McKelvey who evaluated the renal function of 24 HIV positive patients treated with tenofovir for greater than 3 months and reported that the use of TDF is associated with impairment of renal function. This im- pairment was not fully reversible in the majority of pa- tients following cessation of TDF [96]. This is consistent with a study by Wever and colleagues which evaluated the reversibility of TDF-related nephrotoxicity in 24 HIV-infected male outpatients who ceased TDF due to renal impairment and observed that TDF-related renal toxicity was not always fully reversible [97]. Zimmer- man and co researchers in their work reported that teno- fovir-associated ARF manifests as acute tubular necrosis that may not resolve with tenofovir withdrawal [98]. Comparatively more studies gave credence to the re- versibility of tenofovir associated nephrotoxicity. 4.4. Discrepancy in Reports Despite reported cases of tenofovir associated renal tox- icity some few studies have attested to the safety of ten- ofovir on the renal system. One of the studies that showed the safety profile of tenofovir on the renal system is a long time follow up of 542 tenofovir exposed pa- tients in which no significant renal impairment was ob- served [99]. Another report is a 3-year study that com- Open Access PP
Tenofovir Renal Toxicity: Evaluation of Cohorts and Clinical Studies—Part One 657 pared 602 therapy-naive patients with a backbone of lamivudine and efavirenz treatment with either tenofovir or stavudine, no difference in the incidence of renal dys- function was found [100]. In a HIV Outpatient Study (HOPS), use of tenofovir-containing HAART was asso- ciated with modest decreases in GFR during the first year of therapy, but clinically significant renal toxicity was very uncommon [101] and decline in GFR in subjects with preexisting renal dysfunction was also very limited [102]. Similar observation was reported in an analysis involving a total of 514 patients receiving tenofovir which report showed that TDF containing ART was as- sociated with less renal impairment than ART without tenofovir [103]. Clinical trials and post-marketing data reported excel- lent safety profile of tenofoviron HIV + subjects includ- ing the absence of significant renal injury. This finding is supported by an in vitro experimental study [104]. A long-term analysis of renal safety in patients receiving TDF compared with d4T for 144 weeks; mean serum creatinine did not change in the TDF group compared with a 0.1 mg/dl decrease from baseline in the d4T group. No patient experienced grade 4 (1.0 mg/dl) hypophos- phatemia and no patient developed Fanconi’s syndrome or proximal renal tubular dysfunction [105]. Gallant, et al., 2009 [106] evaluated 432 antiretroviral-naive pa- tients who initiated either tenofovir or any alternative NRTI. Patients taking both tenofovir and NRTI experi- enced an initial decline in GFR during the first six months of therapy, but renal function stabilized between six and 24 months. A comparative randomized study of ABC/3TC versus TDF/FTC in 333 persons found no statistically significant differences in eGFR over 48 weeks [107]. Furthermore, tenofovir did not appear to be associated with worsening kidney function in the multicenter, ob- servational FRAM study, despite widespread use at the follow-up visit [108]. A 1-year prospective study of 424 HIV-infected persons also reported no association be- tween tenofovir use and tubular damage [109]. This is consistent with an investigation on the safety and effi- cacy of once daily doses of tenofovir administered in combination with other antiretroviral therapy in treat- ment-experienced HIV-1-infected patients. One-hundred and eighty-nine subjects were exposed to various doses of TDF for 48-weeks; no significant changes in renal function were observed [110]. Observation from a STACCATO trial where Thai pa- tients were treated with tenofovir containing antiretrovi- ral drug showed lack of renal toxicity [111]. Vigano and co researcher evaluated the renal safety of tenofovir in HIV-infected children treated with tenofovir for 96 weeks. They reported no evidence of renal toxicity in tenofovir treated HIV infected children [112]. In a cohort of 933 HIV patients treated with tenofovir containing antiretroviral regimen, followed through for 6 and 12 months showed that TDF associated renal toxicity is rare [113]. Another cohort of 53 HIV patients exposed to TDF containing antiretroviral regimens for 48 weeks performed by Gerard and co-researchers reported that TDF related severe nephrotoxicity is an uncommon event [114]. The safety and efficacy of TDF compared with placebo in 235 patients was evaluated in addition to other observations TDF had a similar safety profile with pla- cebo [115]. On the other hand, large observational stud- ies and clinical trials have shown no evidence of glome- rular or tubular damage when tenofovir is employed as a component of an initial antiretroviral regimen [116,117]. 5. 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