Tenofovir disoproxil fumarate

Tenofovir-induced kidney injury

Tenofovir disoproxil fumarate is a nucleotide reverse transcriptase inhibitor with activity against both HIV and the hepatitis B virus. It has had minimal nephrotoxic effects in early clinical trials, but as clinical use has widened, case reports describing tenofovir-induced renal tubular damage, Fanconi's syndrome and diabetes insipidus have been described. The authors review the pharmacokinetics, mechanism of action and clinical uses of tenofovir disoproxil fumarate. The large clinical trials, as well as the case reports of tenofovir-induced kidney injury, are also reviewed. The potential mechanism of renal damage is discussed and recommendations for evaluation and treatment of tenofovir-induced kidney injury are given.

Neuropsychiatric Adverse Events after Switching from An Antiretroviral Regimen Containing Efavirenz without Tenofovir to An Efavirenz Regimen Containing Tenofovir: A Report of Nine Cases

The combination of tenofovir (TDF) and efavirenz (EFV) has not been associated with any pharmakokinetic interaction or with enhancement of neuropsychiatric disturbances. We report nine cases of neuropsychiatric intolerance occurring early after a switch from an antiretroviral regimen without TDF to an EFV and TDF-containing regimen. Nine HIV-1-infected patients were treated with an EFV-containing regimen for a median duration of 31 months without any EFV-related central nervous system (CNS) effects. They were switched to an EFV-TDF-containing regimen because of lipodystrophy (n=2) and/or the wish to simplify to a once-daily regimen ( n=9). Moderate to severe neuropsychiatric events occurred immediately (<48 hours) after TDF initiation in five patients and 2 weeks to 24 months after the switch in the remaining four patients. Treatment modifications occurred in six patients (switch to EFV-nevirapine [ n=3], TDF-zidovudine [ n=2] or treatment discontinuation [ n=1]), leading to a marked improvement of CNS intolerance. Treatment remained unchanged in three patients; two patients experienced chronic persistent sleeping disorders and one patient underwent a spontaneous improvement of symptoms within 2 weeks. EFV plasma concentrations, which were available in two patients before the switch and in four patients after the switch, remained in the therapeutic range. Although the exact mechanism of these symptoms remains hypothetical, neuropsychiatric disorders could be either a consequence of an unexplained interaction between EFV and TDF or an infrequent TDF-related side effect. The incidence of these side effects needs to be evaluated in large databases or pharmacokinetic studies.

Longitudinal study on mitochondrial effects of didanosine-tenofovir combination

Tenofovir disoproxil fumarate (TDF) has been reported to be free of adverse effects on mitochondria. We evaluate the effects of the introduction of TDF in a didanosine (ddI)-based highly active antiretroviral therapy (HAART) on mitochondrial DNA (mtDNA) content, mitochondrial mass (MM), and cytochrome c oxidase (COX) activity of the oxidative phosphorylation (OXPHOS) system over a 12-month period. Forty-four asymptomatic HIV patients with undetectable viral load receiving a ddI-based HAART were recruited and switched to ddI plus TDF (ddI + TDF) and nevirapine (n = 22) or maintained with the same baseline ddIbased HAART scheme (n = 22). Peripheral blood mononuclear cells were obtained at 0, 6, and 12 months. COX activity and MM were determined by spectrophotometry and the mtDNA content by quantitative realtime PCR. The mtDNA content showed a progressive decrease over the 12-month period of the study for the two groups with respect to baseline, with such a decrease statistically significant only in the ddI + TDF group (55% decrease, p < 0.001). In addition, the decrease of mtDNA content over time was statistically different between both groups (p < 0.001). Consistently, MM and COX activity decreased significantly at 12 months with respect to baseline only in the ddI < TDF group (28% decrease for MM, p < 0.05; 47% decrease for COX activity, p < 0.001). We conclude that switching to a HAART regimen containing ddI + TDF is associated with evolutive mitochondrial damage expressed as mtDNA depletion, loss of MM, and decrease in COX efficiency. The particular relevance of either ddI, TDF, or any interaction between them in such a mitochondrial dysfunction remains to be established.

Complications in treating chronic hepatitis B in patients with HIV

The management of chronic hepatitis B virus (HBV) poses specific problems in the presence of HIV infection, as therapeutic approaches have to consider both HBV and HIV. There are currently four drugs approved for the treatment of chronic HBV: IFN-alpha, lamivudine, adefovir and entecavir. Furthermore, the dual antiviral activity against HIV and HBV of antiretrovirals such as tenofovir and emtricitabine broadens the armamentarium against HBV in the HIV-coinfected population. Nucleotide analogues adefovir and tenofovir have the advantage of a higher genetic barrier for resistance when compared with the nucleoside analogues lamivudine and emtricitabine. Fortunately, the two families do not share resistance mutations, allowing salvage therapy and the consideration of combination therapy for drug-naive individuals. Although response to IFN-alpha is poorer in HBV/HIV-coinfected patients compared with HBV-monoinfected individuals, the more potent pegylated forms of IFN-alpha have brought new hopes.

Pharmacokinetic properties of nucleoside/nucleotide reverse transcriptase inhibitors

Options for antiretroviral therapy in patients infected with HIV continue to expand as new drugs are integrated into treatment regimens. Nonetheless, nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs/NtRTIs) remain the backbone of highly active antiretroviral therapy (HAART). With the approval of emtricitabine in 2003, there are now 8 Food and Drug Administration (FDA)-approved NRTIs/NtRTIs. Several of these agents are effective as once-daily therapy, including didanosine, lamivudine, extended-release stavudine (FDA approved, but not currently available), tenofovir DF, and emtricitabine. Recent results from pharmacokinetic and clinical trials indicate that another NRTI, abacavir, may also be effective as a once-daily therapy, and FDA approval of once-daily dosing is anticipated. NRTIs are inactive as administered, requiring anabolic phosphorylation within target cells to achieve their antiretroviral effects. All NRTIs are converted to nucleoside triphosphates, which serve as the active metabolites (the NtRTI, tenofovir DF, only requires conversion to the diphosphate form). Frequency of drug administration is closely related to the pharmacokinetic properties of a drug. The key parameter is the half-life; however, the plasma elimination half-life of the NRTIs/NtRTIs as administered is of little use in developing a dosing schedule. Rather, the intracellular half-life of the nucleoside triphosphate is the relevant parameter. This article reviews the pharmacokinetic properties, particularly those of the various phosphorylation steps, of the NRTIs/NtRTIs.

Protective effect of the acyclic nucleoside phosphonate tenofovir toward human T-cell leukemia/lymphotropic virus type 1 infection of human peripheral blood mononuclear cells in vitro

9-(R)-[(2-Phosphonomethoxy)propyls]adenine (tenofovir), is an acyclic nucleoside phosphonate known to inhibit HIV replication in vitro and to reduce viremia in HIV-infected patients. Here we have investigated whether tenofovir is able to protect peripheral blood mononuclear cells (PBMCs) from healthy donors against human T-cell leukemia/lymphotropic virus type 1 (HTLV-1) infection in vitro. PBMCs were pre-treated with tenofovir and infected by exposure to an irradiated cell line chronically harbouring HTLV-1. Measurements of viral DNA, as well as viral gene and protein expression, at 4 weeks after infection, revealed that tenofovir at concentrations of 1 microM and higher completely protected PBMCs against HTLV-1; lower concentrations did not fully prevent HTLV-1 infection of the cultures. Nevertheless, in the long term, cell growth of infected PBMCs was inhibited in vitro even by 0.1 microM tenofovir. In addition, tenofovir directly inhibited HTLV-1 reverse transcriptase activity, in a cell-free assay that utilizes a crude preparation from HTLV-1 viral particles as a source of the enzyme. The selectivity index of tenofovir for HTLV-1, was about four times higher than that of azidothymidine. Taken together our results strongly encourage further studies to investigate the real impact of tenofovir towards HTLV-1 infection.

The pharmacology of antiretroviral nucleoside and nucleotide reverse transcriptase inhibitors: implications for once-daily dosing

The trend toward once-daily dosing in HIV antiretroviral therapy is based on the association between adherence, treatment outcome, and patient preferences. Patients prefer simpler treatments, fewer pills, less frequent dosing, and no food restrictions. When a regimen meets a patient's preferences, the patient is more likely to be adherent, and with good adherence, the regimen is more likely to be effective. Nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) have been a prime focus for developing once-daily therapies primarily because they form the backbone of most current regimens. Within the NRTI class, however, drugs differ in their pharmacokinetic properties, such as plasma and intracellular half-lives, and thus in their suitability for once-daily dosing. For example, newer NRTIs, such as tenofovir and emtricitabine, combine longer plasma half-lives with longer intracellular half-lives, prolonging exposure and the period of pharmacologic activity. Of equal importance, the clinical impact of systemic and intracellular interactions between concomitant drugs defines which once-daily drugs may be combined in once-daily regimens. To construct simplified and effective therapies for individual patients, clinicians require an understanding of the plasma and intracellular pharmacokinetic properties of NRTIs and how these properties determine a drug's appropriateness for once-daily dosing and placement within a once-daily regimen.

[Assessment of renal abnormalities in 107 HIV patients treated with tenofovir]

OBJECTIVES

The objectives of our study were to assess frequency, severity and outcome of renal abnormalities, as well as to determine the risk of developing hypophosphataemia in HIV-infected patients receiving tenofovir.

METHODS

An observational study was conducted in real-life conditions, during a 6-month period, in 107 HIV patients receiving tenofovir.

RESULTS

Mild-to-moderate hypophosphataemia (<0.77 mmol/L) occurred during follow-up, at least once in 43% of patients and at least twice in 27%. Antiretroviral therapy including ritonavir + lopinavir was significantly associated with the occurrence of hypophosphataemia (relative risk = 2.6; p = 0.03). Frequency of abnormal proteinuria was 22%.

CONCLUSION

Creatinine clearance, phosphataemia, proteinuria and glycosuria should be closely monitored in patients receiving tenofovir therapy.

Management of patients co-infected with hepatitis B virus and HIV

The management of chronic hepatitis B virus (HBV) infection poses specific problems in the presence of HIV co-infection, since therapeutic approaches have to consider both HBV and HIV infections. There are currently four drugs approved for the treatment of chronic HBV infection (interferon alpha, lamivudine, adefovir, and entecavir); the dual antiviral activity of tenofovir and emtricitabine broadens the armamentarium against HBV in HBV/HIV co-infected patients. Nucleotide analogues--eg, adefovir and tenofovir--have the advantage of a higher genetic barrier to the development of resistance compared with nucleoside analogues--eg, lamivudine and emtricitabine. Fortunately, the two families do not share resistance mutations, allowing salvage therapy and the possibility of combination therapy for drug-naive individuals. Although response to interferon alpha is poorer in HBV/HIV co-infected patients compared with HIV-negative individuals, especially in hepatitis B e antigen-negative HBV infection, the more potent pegylated forms of interferon alpha have brought new hope.

Strategies to improve oral drug bioavailability

Efforts to improve oral drug bioavailability have grown in parallel with the pharmaceutical industry. As the number and chemical diversity of drugs has increased, new strategies have been required to develop orally active therapeutics. The past two decades have been characterised by an increased understanding of the causes of low bioavailability and a great deal of innovation in oral drug delivery technologies, marked by an unprecedented growth of the drug delivery industry. The advent of biotechnology and consequent proliferation of biopharmaceuticals have brought new challenges to the drug delivery field. In spite of the difficulties associated with developing oral forms of this type of therapeutics, significant progress has been made in the past few years, with some oral proteins, peptides and other macromolecules currently advancing through clinical trials. This article reviews the approaches that have been successfully applied to improve oral drug bioavailability, primarily, prodrug strategies, lead optimisation through medicinal chemistry and formulation design. Specific strategies to improve the oral bioavailability of biopharmaceuticals are also discussed.

Tenofovir disoproxil fumarate: a review of its use in the management of HIV infection

Tenofovir disoproxil fumarate (tenofovir DF; Viread), an ester prodrug of the nucleotide reverse transcriptase inhibitor (NRTI) tenofovir, is indicated in combination with other antiretroviral agents in the treatment of HIV infection. As a component of an antiretroviral regimen, oral tenofovir DF 300 mg once daily effectively reduces viral load in patients with HIV infection who are treatment-experienced with baseline NRTI resistance mutations or treatment-naive. Tenofovir DF provides a simple and convenient once-daily dosage regimen, and is generally well tolerated and able to produce sustained suppression of viral replication.

The Steady-State Pharmacokinetics of Nelfinavir in Combination with Tenofovir in HIV-Infected Patients

Background

The nucleotide analogue, tenofovir, has been shown to lower plasma atazanavir levels in pharmacokinetic trials, an interaction that may be partly reversed by the addition of ritonavir, whereas plasma tenofovir levels are themselves raised when the drug is combined with lopinavir/ritonavir.

Objective

To investigate the effect of tenofovir coadministration on the steady-state pharmacokinetics of nelfinavir in HIV-infected patients.

Methods

Eighteen patients received nelfinavir 1250 mg twice daily plus prescribed nucleoside reverse transcriptase inhibitors for at least 14 days, with pharmacokinetic measurements performed on day 15. Treatment with nelfinavir was continued for another 7 days with the addition of 300 mg tenofovir once daily. Pharmacokinetic measurements were repeated on day 22. Plasma samples were analysed by liquid chromatography–tandem mass spectrometry for nelfinavir, its primary metabolite, M8, and tenofovir. The parameters AUC0–12, C0, Cmax and Tmax were compared for nelfinavir with and without tenofovir by calculating geometric mean ratios (GMRs) of the pharmacokinetic parameters with associated 95% confidence intervals (95% CIs). Safety was assessed throughout the study.

Results

The addition of tenofovir to the nelfinavir-based regimen had no effect on the pharmacokinetics of nelfinavir. The GMR of the nelfinavir AUC0–12 values was 0.97 (95% CI: 0.80–1.17). There was a slight decrease in M8 metabolite (AUC0–12 ratio, 0.87; 95% CI: 0.68–1.11) but this was not significant. No serious adverse events occurred through the study period.

Conclusion

Nelfinavir does not require dose adjustment when coadministered with tenofovir and appears to be well-tolerated by HIV-infected patients.

Increasing number of anti-HIV drugs but no definite cure. Review of anti-HIV drugs

AIM

This review surveys the different classes of drugs.

METHOD

We searched electronic databases and selected articles about pharmacotherapy with anti-retroviral drugs.

RESULTS

We discuss anti-retroviral drugs: the nucleotide reverse transcriptase inhibitors (NRTIs), the non-nucleoside reverse transcriptase inhibitors (NNRTIs), and the protease inhibitors (PIs). The combination of a PI and two NRTIs is very effective and lowers the viral load to below the limit of detection. However, it is not yet possible to eliminate the virus completely. Recently, the first member of a brand new class of drugs has become available, the fusion inhibitor enfuvirtide. We also discuss the problems associated with combining anti-retroviral drugs, such as compliance, resistance and serious side effects.

DISCUSSION

It is important to investigate new combinations with new classes of drugs, like the fusion inhibitors, for better effectiveness and fewer side effects.

Interactions between atazanavir-ritonavir and tenofovir in heavily pretreated human immunodeficiency virus-infected patients

The aim of the present study was to assess the pharmacokinetic behavior of atazanavir-ritonavir when it is coadministered with tenofovir disoproxil fumarate (DF) in human immunodeficiency virus (HIV)-infected patients. Eleven patients enrolled in Agence Nationale de Recherche sur le SIDA (National Agency for AIDS Research, Paris, France) trial 107 were included in this pharmacokinetic study. They received atazanavir at 300 mg and ritonavir at 100 mg once a day (QD) from day 1 to the end of study. For the first 2 weeks, their nucleoside analog reverse transcriptase inhibitor (NRTI) treatments remained unchanged. Tenofovir DF was administered QD from day 15 to the end of the study. Ongoing NRTIs were selected according to the reverse transcriptase genotype of the HIV isolates from each patient. The values of the pharmacokinetic parameters for atazanavir and ritonavir were measured before (day 14 [week 2]) and after (day 42 [week 6]) initiation of tenofovir DF and are reported for the 10 patients who completed the study. There was a significant decrease in the area under the concentration-time curve from 0 to 24 h (AUC(0-24)) for atazanavir with the addition of tenofovir DF (AUC(0-24) ratio, 0.75; 90% confidence interval, 0.58 to 0.97; P = 0.05). There was a trend for a decrease in the minimum concentrations of atazanavir and ritonavir in plasma when they were combined with tenofovir, but none of the differences reached statistical significance. The median decreases in the HIV RNA loads at week 2 and week 6 were 0.1 and 0.2 log copies/ml, respectively. In summary, our data are consistent with the existence of a significant interaction between atazanavir and tenofovir DF.

Once-Daily Administration of Antiretrovirals

Adherence to therapy is of critical importance for the long-term success of the treatment of HIV infection. Once-daily administration of antiretroviral agents is appealing, as it may increase patient's adherence. The pharmaceutical industry is making huge efforts to develop drugs or combinations of drugs with pharmacokinetic properties allowing once-daily administration. The major pharmacokinetic requirement for once-daily administration is that the intracellular concentration of the antiretroviral or its active metabolite remains above the minimal concentration that can inhibit viral replication during the entire 24-hour period. Soon, all three major classes of antiretroviral agents will be available as once-daily formulations. However, only a few clinical trials have yet assessed the efficacy and safety of truly once-daily antiretroviral combinations. Preliminary results from these small pilot studies suggest that once-daily administration of antiretrovirals is a feasible approach. Large comparative trials are needed before the real benefits of such a strategy can be fully assessed.