Tenofovir/emtricitabine (TDF/FTC) is currently the most widely used nucleoside backbone for the treatment of HIV in Western countries. It has shown excellent efficacy when associated with either protease inhibitors or efavirenz [1,2]. However, warnings about an increased risk of early virological failure in patients treated with TDF plus FTC (or lamivudine, 3TC) in association with nevirapine (NVP) have recently been reported [3,4]. In the Daufin study, the efficacy of TDF/3TC versus zidovudine (AZT)/3TC, both in association with NVP, was compared in an open prospective trial . At month 12, when 35 patients had been included, the steering committee stopped the study because eight (22.2%) early virological failures occurred in the TDF/3TC group, whereas none had been seen in the AZT/3TC group. Failures showed drug resistance mutations M184V/I and K65R in three and six cases, respectively. Aware of this report, Lapadula et al.  performed an unplanned interim analysis in another trial at the time when only seven patients had been enrolled. This second study was designed with the goal of comparing plasma cholesterol and triglyceride levels in patients treated with NVP (200 mg twice daily after a 14-day course of 200 mg once daily) or atazanavir (300 mg once daily) plus ritonavir (100 mg once daily; ATV/r), both in association with TDF/FTC (coformulated). The interim analysis revealed that three patients, all receiving NVP, experienced virological rebound at week 12 despite showing an initial decline in plasma HIV-RNA. The authors mentioned that multiple drug resistance mutations, not present at baseline, emerged at the time of failure.
Herein, we report the results of a retrospective review of a large group of HIV-infected individuals exposed to TDF/FTC/NVP at our institution. In this observational cohort-based study, the primary objective was to describe the rate of virological failure in patients treated with TDF/FTC/NVP, either used as first-line or as part of subsequent antiretroviral regimens. The secondary objective was to describe which risk factors were associated with virological failure in patients receiving this antiretroviral combination.
All HIV-infected patients who had initiated treatment with TDF/FTC/NVP at our institution until February 2009 were identified. Briefly, the first patient had initiated TDF/FTC/NVP in September 2007. Analyses were extended until May 2009 when the last individual had completed at least 3 months of therapy. All patients were followed until they stopped the regimen for any reason, including side effects or virological failure. In all drug-naive and in antiretroviral-experienced patients who were rescued with the study regimen, results of baseline drug resistance testing were available. In contrast, it could not be obtained from patients who began this regimen as a simplification strategy. Patients for whom drug adherence was proven to be inferior to 95% using the SMAQ (simplified medication adherence questionnaire) in two consecutive visits were excluded from further analysis. Likewise, individuals who discontinued the study regimen within the first 2 weeks of treatment due to rash and/or hepatitis were excluded from further consideration. Virological failure was defined as plasma HIV-RNA of more than 50 copies/ml in two consecutive specimens separated by 10–15 days each. Measurement of plasma HIV-RNA was made using a commercial real-time PCR assay (Taqman; Roche Molecular Systems, Pleasanton, California, USA). Hepatotoxicity was defined as aminotransferase/alanine aminotransferase elevations more than two-fold the upper limit of normality or baseline values in individuals with elevated liver enzymes. Drug resistance testing was performed using a commercial population sequencing assay (Applied Biosystems, Foster City, California, USA) and NVP plasma trough concentrations were measured at the time of viral rebound in patients failing therapy. Abnormal metabolic parameters were defined as triglycerides of more than 150 mg/dl and low-density lipoprotein-cholesterol more than 130 mg/dl.
A total of 199 patients had initiated TDF/FTC/NVP at our institution. However, 21 patients were excluded based on pharmacy records and clinical history which recognized poor drug adherence (n = 13) or because treatment discontinuation had occurred due to rash and/or hepatitis (n = 8). These adverse events leading to treatment withdrawal occurred in four drug-naive and four antiretroviral-experienced patients who initiated the study medication as simplification therapy. Of the remaining 178 individuals who constituted the final study population, 78% were men, mean age was 38 years, 38% were coinfected with hepatitis C virus, and 22% were antiretroviral-naive. Among the 139 antiretroviral-experienced patients, 90% had initiated TDF/FTC/NVP as a simplification strategy and only 10% as a rescue intervention. Of note, the majority of patients (78%) received NVP 400 mg daily (q.d.) after a lead-in phase of 2 weeks with NVP 200 mg/day. In the subset of 39 antiretroviral-naive patients and 14 rescued with the study regimen, the median baseline plasma HIV-RNA was 4.57 log copies/ml [interquartile range (IQR) = 1.83–5.50].
After a median follow-up of 16 months (IQR = 13–19), five patients (2.8%) experienced virological failure. All of them occurred in antiretroviral-experienced patients with a history of prior virological failure to other antiretroviral regimens. Moreover, all five individuals had begun TDF/FTC/NVP as rescue therapy and none as a simplification regimen. Thus, the rate of virological failure was null in the 39 drug-naive patients but raised to 3.6% in antiretroviral-experienced patients, being null in the 125 patients on simplification but in more than one-third (5/14) of patients who received TDF/FTC/NVP as rescue therapy. Finally, all five failures were receiving NVP q.d. and median NVP plasma trough concentration at the time of failure was 5.6 μg/ml (IQR = 5.3–7.0). Virological failures were seen in all instances after week 12 of therapy, ranging from week 13–44. Drug resistance testing at failure showed resistance mutations in three patients. M184V and Y181C mutations were present in two patients, whereas M184V and 188L were seen in one. Other mutations associated with resistance to nucleos(t)ide analogues were also recognized in these individuals (Table 1). No drug resistance mutations were found at the time of virological failure neither at baseline in one patient. For the remaining individuals, nucleic acid amplification was repeatedly negative.
In the whole study population, the median CD4 count increased from 432 cells/μl (IQR = 313–724) at baseline to 561 cells/μl (IQR = 408–779) at the end of follow-up (P = 0.01). Immune recovery was significantly greater in antiretroviral-naive patients than in the rest. In the former group, the median CD4 count rose from 284 cells/μl (IQR = 212–342) to 439 cells/μl (IQR = 330–519) (P < 0.001). In antiretroviral-experienced patients, the median CD4 count rose from 546 cells/μl (IQR = 378–815) to 663 cells/μl (IQR = 454–838) (P = 0.7).
During the whole follow-up period, a total of 18 patients (10%) interrupted therapy due to side effects. As previously mentioned, eight patients presented a hypersensitivity skin reaction to NVP, two of them along with liver enzyme elevations, and 10 patients developed laboratory urine and plasma abnormalities suggestive of kidney tubular dysfunction associated to TDF . Interruptions associated with NVP exposure occurred before week 12 in all instances, whereas all discontinuations associated with TDF safety occurred after month 8 of treatment (P = 0.03). No significant changes were found between mean values at baseline and at the end of follow-up for low-density lipoprotein-cholesterol (115 ± 34 versus 118 ± 38 mg/dl), high-density lipoprotein-cholesterol (42 ± 15 versus 43 ± 16 mg/dl) and alanine aminotransferase (32 ± 20 versus 29 ± 11 IU/l).
Acknowledging as a limitation the retrospective nature of our study, the results we obtained do not support a warning for using TDF/FTC/NVP. This regimen can be confidently used as part of the HIV armamentarium. Given that significant drug–drug interactions between TDF and NVP have not been observed [6,7], a potential explanation for the high risk of early virological failure using TDF and NVP in studies such as the Daufin trial mentioned above  could be the use of 3TC instead of FTC. It has recently been appreciated that the longer half-life of FTC over 3TC might be associated with an increased genetic barrier to resistance, specially when 3TC is given once a day [8,9], and this fact could be critical in patients with high viral load exposed to NVP, another drug with low genetic barrier to resistance. The preliminary results of the ARTEN trial, a large prospective study comparing prospectively NVP and ritonavir-boosted atazanavir, both along with TDF/FTC, in drug-naive patients have recently been released and seem to confirm that there is no increased risk of early virological failure when combining NVP with TDF/FTC .
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