Predisposition to nevirapine hypersensitivity associated with HLA-DRB1*0101 and abrogated by low CD4 T-cell counts

The clinical implications of antiretroviral pharmacogenomics

Heterogeneity exists in the effectiveness and toxic effects of antiretroviral agents between individuals and populations. Although patient-related clinical variables such as age, sex and ethnic origin have been associated with drug response, inherited predispositions may have a significant effect on treatment outcome. The role of host and pathogen pharmacogenomics is gaining increasing interest in the field of both antiretrovirals in development, such as the chemokine (C-C motif) receptor 5 (CCR5) inhibitors, and in established therapies where toxicity and efficacy may be predicted. Despite numerous studies available in the literature, the interpretation of the relationship between genetic polymorphisms and clinical outcomes is often posed with many confounding variables, making clinical interpretations of these results difficult. This review summarizes the key findings in the growing knowledge between human genetics and response to antiretroviral drugs and how these findings may be effectively applied in a clinical context.

Pharmacogenetics of nevirapine-associated hepatotoxicity: an Adult AIDS Clinical Trials Group collaboration

Associations have been reported between an MDR1 variant and responses to nonnucleoside reverse-transcriptase inhibitors. We explored associations between MDR1, CYP2B6, and CYP3A polymorphisms and nevirapine hepatotoxicity. Among participants in a randomized study in South Africa (FTC-302), MDR1 3435C-->T was significantly associated with decreased risk of hepatotoxicity (risk ratio, 0.30; P=.016).

Drug transporter and metabolizing enzyme gene variants and nonnucleoside reverse-transcriptase inhibitor hepatotoxicity

This nested case-control study examined relationships between MDR1, CYP2B6, and CYP3A4 variants and hepatotoxicity during antiretroviral therapy with either efavirenz- or nevirapine-containing regimens. Decreased risk of hepatotoxicity was associated with MDR1 3435C-->T (odds ratio, 0.254; P=.021). An interaction between MDR1 and hepatitis B surface antigen status predicted risk with 82% accuracy (P<.001).

HLA-dependent hypersensitivity to nevirapine in Sardinian HIV patients

BACKGROUND

Hypersensitivity reaction to nevirapine, which in some cases can be fatal, shows a higher prevalence in Sardinia in comparison with other Italian regions.

OBJECTIVE

This study demonstrates that hypersensitive reaction to nevirapine in Sardinian HIV-infected patients is associated with the HLA Cw8-B14 haplotype. These two HLA class I antigens are in strong linkage disequilibrium in the Sardinian population.

METHODS

Forty-nine Sardinian HIV-positive patients treated with nevirapine were studied. Thirteen (26%), developed a hypersensitive reaction thus requiring the drug to be discontinued. HLA class I and II molecular typing was performed in both nevirapine-hypersensitive and nevirapine-tolerant patients. To avoid biased representation of the allele frequencies in the two groups of treated patients, molecular typing was also performed in 82 HIV-positive patients who had not been treated with nevirapine.

RESULTS

Considerable overlap was observed for the clinical, immunological and demographic characteristics of the 13 hypersensitive patients and 36 tolerant patients. Clinical parameters included viral load, status of HIV infection, CD4 and CD8 cell counts, hepatitis C virus/hepatitis B virus co-infections. Forty-six percent (6/13) of the nevirapine-hypersensitive subjects had the HLA-Cw8 and HLA-B14(65) antigens compared with 5% (2/36) of the nevirapine-tolerant group (P = 0.004; Pc = 0.05).

CONCLUSION

In agreement with other recent reports, the utility of HLA typing in HIV patients to identify genetic factors that may confer susceptibility to drug-induced hypersensitive reaction was confirmed. A careful choice of antiretroviral therapy in susceptible individuals should significantly reduce the risk of severe hypersensitive reaction.

Safety of nevirapine-containing antiretroviral triple therapy regimens to prevent vertical transmission in an African cohort of HIV-1-infected pregnant women

OBJECTIVE

To assess the incidence and consequences of adverse reactions among African HIV-positive pregnant women treated with fixed-dose combinations of a nevirapine-containing antiretroviral (ARV) triple therapy.

METHODS

A retrospective analysis of the clinical files of 703 HIV-1-positive pregnant women treated with a nevirapine-containing regimen between May 2002 and July 2004 was conducted. Selection criteria for inclusion in the analysis were: (a) taking ARV for more than 14 days; (b) baseline values of transaminases below the threshold of 2.5 times the upper limit of normal (ULN). The women were on a nevirapine-containing regimen for a median of 127 days [interquartile range (IQR) 86-190 days], starting on average at the 27th week of gestation (standard deviation+/-9.5) and continuing up to a maximum of 6 months after delivery. All women were offered formula milk to feed the babies. Highly active antiretroviral therapy (HAART) was continued beyond 6 months only if the patient qualified on the first visit. The main outcome measures were incidence of hepatotoxicity, skin rashes and Stevens-Johnson syndrome. Multivariate analysis to assess the impact of several factors on the adverse reaction rate was performed.

RESULTS

As of 1 August 2004, 554 pregnancies reached term, 96 women were still pregnant, and 53 women dropped out of the programme before giving birth. After 2 months of therapy the percentage of patients with a viral load less than 1000 HIV-1 RNA copies/mL increased to 78.6%; average CD4 cell counts increased from 490 cells/microL before therapy to 630 after therapy. The incidence of grade 3-4 adverse reactions (hepatotoxicity, skin rashes and Stevens-Johnson syndrome) was 6.5, 2.4 and 1.1%, respectively. Five women died during pregnancy (0.88%). Only one of the deaths could be associated with ARV treatment.

CONCLUSION

Nevirapine-containing regimens in pregnant woman, at all CD4 cell count levels, appear to be safe in African settings.

Hepatotoxicity of antiretrovirals: incidence, mechanisms and management

One of the toxicities linked to the use of antiretrovirals is the elevation of transaminases. Liver toxicity is a cause of morbidity, mortality, and treatment discontinuation in HIV-infected patients. While several antiretrovirals have been reported to cause fatal acute hepatitis, they most often cause asymptomatic elevations of transaminases. Liver toxicity is more frequent among subjects with chronic hepatitis C and/or B. The incidence of drug-induced liver toxicity is not well known for most antiretrovirals. The contribution of each particular drug to the development of hepatotoxicity in a HAART regimen is difficult to determine. Possible pathogenic mechanisms involved in hepatotoxicity are multiple, including direct drug toxicity, immune reconstitution in the presence of HCV and/or HBV co-infections, hypersensitivity reactions with liver involvement, and mitochondrial toxicity. Other pathogenic pathways may be involved, such as insulin resistance caused by several antiretrovirals, which may contribute to the development of steatohepatitis. The management of liver toxicity is based mainly on its clinical impact, severity and pathogenic mechanism.

Drug-Specific T Cells in An HIV-Positive Patient with Nevirapine-Induced Hepatitis

Background

Nevirapine is associated with idiosyncratic reactions such as skin rash, hepatitis and hypersensitivity syndrome, which have the hallmarks of being immune mediated. However, there is little laboratory evidence to support an immune pathogenesis.

Methods

A HIV-positive individual who developed hepatitis within 6 weeks of starting nevirapine, in the absence of any cutaneous manifestations, is described. Other causes of hepatitis were excluded, and the patients liver function normalized on withdrawal of nevirapine. Lymphocytes from the patient, and six individuals with HIV who were on nevirapine without adverse effects, were exposed to nevirapine and its metabolites, and lymphocyte proliferation assessed by 3H-thymidine incorporation on day 5.

Results

The T cells taken from the nevirapine-hypersensitive patient proliferated in the presence of nevirapine with a stimulation index of greater than 2. There was no proliferation with nevirapine metabolites. T cells taken from HIV-positive control individuals showed no proliferation with either nevirapine or its metabolites.

Conclusion

The results from our patient suggest that T cells may be involved in the pathogenesis of nevirapine-induced hepatitis. Larger numbers of patients need to be studied to fully evaluate the role of T cells in nevirapine-induced hepatitis and nevirapine hypersensitivity syndrome.

Predicting and diagnosing abacavir and nevirapine drug hypersensitivity: from bedside to bench and back again

There is a growing discussion surrounding the issue of personalized approaches to drug prescription based on an individual's genetic makeup. This field of investigation has focused primarily on identifying genetic factors that influence drug metabolism and cellular disposition, thereby contributing to dose-dependent toxicities and/or variable drug efficacy. However, pharmacogenetic approaches have also proved valuable in predicting drug hypersensitivity reactions in selected patient populations, including HIV-infected patients receiving long-term antiretroviral therapy. In this instance, susceptibility has been strongly linked to genetic loci involved in antigen recognition and presentation to the immune system--most notably within the major histocompatibility complex (MHC) region--consistent with the notion that hypersensitivity reactions represent drug-specific immune responses that are largely dose independent. Here the authors describe their experiences with the development of pharmacogenetic approaches to hypersensitivity reactions associated with abacavir and nevirapine, two commonly prescribed antiretroviral drugs. It is demonstrated that prospective screening tests to identify and exclude individuals with a certain genetic makeup may be largely successful in decreasing or eliminating incidence of these adverse drug reactions in certain populations. This review also explores the broader implications of these findings.

Overview of the pharmacogenetics of HIV therapy

The administration of standard doses of most antiretroviral drugs results in significant variations in plasma drug concentrations among different individuals, influencing antiviral activity as well as incidence of drug-related toxicities. The reasons for this large inter-individual variability in drug levels are multifactorial, and involve differences in metabolism related to gender, concomitant medications, drug compliance, underlying diseases and genetic factors. Pharmacogenetics is the discipline that analyses the genetic basis for the inter-individual variation in the body disposition of drugs. One of its main goals is to give grounds to individualized treatment. The majority of pharmacogenetic traits so far have involved drug metabolism. This is the case for the inherited variation in the pharmacokinetics and pharmacodynamics of drugs such as hydralazine or isoniazid, which is due to polymorphisms in the N-acetyltransferase-2 (NAT2) gene, which allows splitting the population into three categories: slow, intermediate, and fast metabolizers. Pharmacogenetic studies conducted so far with antiretroviral drugs have focussed on metabolizer enzymes at the liver and on transporter proteins on cell membranes. Herein, we review the most relevant metabolizer enzymes and protein transporters, along with the genetic polymorphisms, which seem to influence the pharmacokinetics of antiretroviral drugs, ultimately determining its efficacy and toxicity.

The nonnucleoside reverse transcriptase inhibitors efavirenz and nevirapine in the treatment of HIV

Clinical trial data and real-world experience have shown the nonnucleoside reverse transcriptase inhibitors (NNRTIs) to be an important class of agents for the treatment of HIV. Given their long plasma half-lives, in vitro and in vivo potency against HIV, low pill burdens, and ability to be safely combined with other commonly used medications, the NNRTIs nevirapine and efavirenz are widely used in combination antiretroviral therapies. Observational, retrospective cohort studies among antiretroviral treatment (ART)-naive patients have suggested that efavirenz may be superior to nevirapine in terms of efficacy. Recently, data from the 2NN study, a large, multicenter, multinational, prospective, randomized, head-to-head trial comparing efavirenz and nevirapine, have been reported. The results from this study indicate that ART-naive patients achieved good antiviral response after 48 weeks of treatment with nucleoside reverse transcriptase inhibitors (NRTIs) combined with either efavirenz or nevirapine (viral load >50 copies/mL: efavirenz, 70%; nevirapine bid, 65.4%; nevirapine qd, 70%). Even though central nervous system disturbances occurred more frequently among efavirenz-treated patients and nonclinically significant transaminitis occurred more frequently among nevirapine-treated patients, these adverse events were not statistically significant or mutually exclusive. Given the results of the 2NN study, the selection of one agent or the other for use in clinical practice will depend more upon patient-specific factors than expected differences in antiviral responses.

Sensitivity to Bee Venom Antigen Phospholipase A2: Association With Specific HLA Class I and Class II Alleles and Haplotypes in Beekeepers and Allergic Patients

Bee venom hypersensitivity is a clinical entity of outstanding importance because bee stings are a leading cause of mortality worldwide. Individuals with immediate-type bee venom hypersensitivity, beekeepers, and healthy controls were examined for HLA-DRB1, DQB1, and DQA1 alleles by sequence-specific oligonucleotide probe typing. Defined hypersensitivity to bee venom antigen phospholipase A2 (vbPLA2) is significantly associated with the presence of susceptible HLA class II alleles: DRB1*0101 (RR = 2.7, p < 3 x 10(-3)), DRB1*0103 (RR = 21.2, p < 7.5 x 10(-11)), DQA1*0101 (RR = 1.2, p < 38.52 x 10(-10)), and DQB1*0501 (RR = 4, p < 2.18 x 10(-10)). Some HLA class I alleles were also associated with risk to bee venom allergy: A*01 (RR = 2.4, p < 7.5 x 10(-4)), B*57 (RR = 35.1, p < 3.5 x 10(-7)), and B*5901 (p < 3.5 x 10(-5)), but they are probably of secondary significance. Three- (DRB1*0103-DQA1*0101-DQB1*0501) (RR = 21.24, p < 7.5 x 10(-11)) and five-loci (A*01-B*59-DRB1*0103-DQA1*0101-DQB1*0501) (p < 2.3 x 10(-6)) extended haplotypes are also significantly carried by vbPLA2 allergic patients. When HLA allele frequencies from patients are compared with those from beekeepers, only HLA-DRB1*0103 (RR = 11.7, p < 8.5 x 10(-5)) and HLA-DQA1*0101 (p < 0.02) were significantly increased in the former. These observations emphasize the importance of the DRB1*0103-DQA1*0101-DQB1*0501 haplotype as a strong candidate for susceptibility to vbPLA2 hypersensitivity, at least in our region.

Are Adverse Events of Nevirapine and Efavirenz Related to Plasma Concentrations?

Objective

The relationships between adverse events (AEs) and plasma concentrations of nevirapine (NVP) and efavirenz (EFV) were investigated as part of the large, international, randomized 2NN study.

Methods

Treatment-naive, HIV-1-infected patients received NVP (once or twice daily), EFV or their combination, each in combination with lamivudine and stavudine. Blood samples were collected on day 3 and weeks 1, 2, 4, 24 and 48. Concentrations of NVP and EFV were quantitatively assessed by a validated HPLC assay. Individual Bayesian estimates of the area under the plasma concentration–time curve over 24 h (AUC24h), and minimum and maximum plasma concentrations (Cmin and Cmax) as measures for drug exposure of NVP and EFV, were generated using a previously developed population pharmacokinetic model. Pharmacokinetic parameters were compared for patients with and without central nervous system (CNS) and psychiatric AEs, hepatic events, liver enzyme elevations (LEEs) and rash. Furthermore, it was investigated whether a clear cut-off for a pharmacokinetic parameter could be identified above which the incidence of AEs was clearly increased. AEs were also related to demographic parameters and baseline characteristics.

Results

In total, from 1077 patients, NVP (3024 samples) and EFV (1694 samples) plasma concentrations and AE data (825 observations) were available. For all patients Cmin, Cmax and AUC24h were determined. When corrected for known covariates of gender, CD4 cell count at baseline, region, hepatitis coinfection and possible interactions between these factors, no significant associations between AEs and any tested exposure parameter of NVP was observed. Also, no target Cmin value, above which patients were at increased risk for AEs, could be established. On the other hand, geographical region, hepatitis coinfection, CD4 cell count and gender were found to be significantly related with the incidence of CNS and psychiatric AEs, hepatic events, LEEs and rash during the treatment with NVP. The occurrence of elevated liver enzymes during the first 6 weeks in the EFV-containing arm was significantly ( P=0.036) correlated to the exposure of EFV (Cmin). Only hepatitis coinfection impacted on LEEs during the first 6 weeks of treatment. With an EFV Cmin above 2.18 mg/l during the induction phase, patients were 4.4 (range 1.3–15.5) times more at risk for elevated liver enzymes. No other correlations between AEs and EFV pharmacokinetics or patient characteristics could be identified.

Conclusions

Pharmacokinetic parameters of NVP did not have a relationship to AEs in the 2NN trial when corrected for known covariates. The value of periodical drug monitoring of NVP as a way to prevent toxicity is therefore limited. Treating physicians should instead focus on factors that are more predictive of AEs (gender, CD4 count and hepatitis coinfection). High EFV Cmin levels resulted in elevated liver enzyme values during the first 6 weeks of treatment. Regular measurement of EFV levels and liver enzymes at the start of therapy may therefore be advised.

Antiretroviral-associated hepatotoxicity

The use of highly active antiretroviral therapy has dramatically reduced HIV-associated morbidity and mortality. As a result, patients are often being treated longer and with more complex medical regimens than ever before, increasing the risk for drug interactions and toxicities. In particular, hepatotoxicity caused by antiretroviral use has become an increasingly appreciated potential complication of drug treatment. All classes of antiretrovirals have been reported to induce liver enzyme abnormalities. However, certain antiretrovirals appear much more likely to be associated with drug-induced hepatotoxicity. The risk of antiretroviral-related hepatotoxicity may be associated with patient-specific risk factors, including pre-existing viral hepatitis, baseline elevated liver function test results, female gender, and substance abuse. In addition, complex drug-drug interactions may potentate the risk of antiretroviral-associated hepatotoxicity. Coinfection with hepatitis B or hepatitis C appears to increase the risk of antiretroviral-related hepatotoxicity.

Do Non-Nucleoside Reverse Transcriptase Inhibitors Contribute to Lipodystrophy?

Lipodystrophy complications, including lipoatrophy (pathological fat loss) and metabolic complications, have emerged as important long-term toxicities associated with antiretroviral therapy in the current era. The wealth of data that has accumulated over the past 6 years has now clarified the contribution of specific antiretroviral drugs to the risk of these clinical endpoints, with evidence that lipoatrophy is strongly associated with the choice of nucleoside reverse transcriptase inhibitor therapy (specifically, stavudine and to a lesser extent zidovudine). The aetiological basis of metabolic complications of antiretroviral therapy has proven to be complex, in that the risk appears to be modulated by a number of lifestyle factors that have made the metabolic syndrome highly prevalent in the general population, with additional contributions from HIV disease status itself, as well as from individual drugs within the HIV protease inhibitor class. The currently licensed non-nucleoside reverse transcriptase inhibitor (NNRTI) drugs, efavirenz and nevirapine, have been proven to have a favourable safety profile in terms of lipodystrophy complications. However, it must be noted that NNRTI drugs also have individual toxicity profiles that must be accounted for when considering and/or monitoring their use in the treatment of HIV infection.