IL28B, HLA-C, and KIR variants additively predict response to therapy in chronic hepatitis C virus infection in a European Cohort: a cross-sectional study

BACKGROUND

To date, drug response genes have not proved as useful in clinical practice as was anticipated at the start of the genomic era. An exception is in the treatment of chronic hepatitis C virus (HCV) genotype 1 infection with pegylated interferon-alpha and ribavirin (PegIFN/R). Viral clearance is achieved in 40%-50% of patients. Interleukin 28B (IL28B) genotype predicts treatment-induced and spontaneous clearance. To improve the predictive value of this genotype, we studied the combined effect of variants of IL28B with human leukocyte antigen C (HLA-C), and its ligands the killer immunoglobulin-like receptors (KIR), which have previously been implicated in HCV viral control.

METHODS AND FINDINGS

We genotyped chronic hepatitis C (CHC) genotype 1 patients with PegIFN/R treatment-induced clearance (n = 417) and treatment failure (n = 493), and 234 individuals with spontaneous clearance, for HLA-C C1 versus C2, presence of inhibitory and activating KIR genes, and two IL28B SNPs, rs8099917 and rs12979860. All individuals were Europeans or of European descent. IL28B SNP rs8099917 "G" was associated with absence of treatment-induced clearance (odds ratio [OR] 2.19, p = 1.27×10(-8), 1.67-2.88) and absence of spontaneous clearance (OR 3.83, p = 1.71×10(-14), 2.67-5.48) of HCV, as was rs12979860, with slightly lower ORs. The HLA-C C2C2 genotype was also over-represented in patients who failed treatment (OR 1.52, p = 0.024, 1.05-2.20), but was not associated with spontaneous clearance. Prediction of treatment failure improved from 66% with IL28B to 80% using both genes in this cohort (OR 3.78, p = 8.83×10(-6), 2.03-7.04). There was evidence that KIR2DL3 and KIR2DS2 carriage also altered HCV treatment response in combination with HLA-C and IL28B.

CONCLUSIONS

Genotyping for IL28B, HLA-C, and KIR genes improves prediction of HCV treatment response. These findings support a role for natural killer (NK) cell activation in PegIFN/R treatment-induced clearance, partially mediated by IL28B.

The progressive ankylosis protein regulates cementum apposition and extracellular matrix composition

BACKGROUND/AIMS

Tooth root cementum is sensitive to modulation of inorganic pyrophosphate (PP(i)), an inhibitor of hydroxyapatite precipitation. Factors increasing PP(i) include progressive ankylosis protein (ANK) and ectonucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) while tissue nonspecific alkaline phosphatase hydrolyzes PP(i). Studies here aimed to define the role of ANK in root and cementum by analyzing tooth development in Ank knock-out (KO) mice versus wild type.

MATERIALS AND METHODS

Periodontal development in KO versus control mice was analyzed by histology, histomorphometry, immunohistochemistry, in situ hybridization, electron microscopy, and nanoindentation. Cementoblast cultures were used in vitro to provide mechanistic underpinnings for PP(i) modulation of cell function.

RESULTS

Over the course of root development, Ank KO cervical cementum became 8- to 12-fold thicker than control cervical cementum. Periodontal ligament width was maintained and other dentoalveolar tissues, including apical cementum, were unaltered. Cervical cementum uncharacteristically included numerous cells, from rapid cementogenesis. Ank KO increased osteopontin and dentin matrix protein 1 gene and protein expression, and markedly increased NPP1 protein expression in cementoblasts but not in other cell types. Conditional ablation of Ank in joints and periodontia confirmed a local role for ANK in cementogenesis. In vitro studies employing cementoblasts indicated that Ank and Enpp1 mRNA levels increased in step with mineral nodule formation, supporting a role for these factors in regulation of cementum matrix mineralization.

CONCLUSION

ANK, by modulating local PP(i), controls cervical cementum apposition and extracellular matrix. Loss of ANK created a local environment conducive to rapid cementogenesis; therefore, approaches modulating PP(i) in periodontal tissues have potential to promote cementum regeneration.

Growth and Structure of Metallic Barrie Laye and Interconnect Films I: Exeriments

We present experimental results directed at understanding the growth and structure of metallic barrier layer and interconnect films. Numerical simulation results associated with this experimental work are presented in an accompanying paper in these proceedings. Here, thin films of Al, Ti, Cu and Ta have been grown by magnetron sputtering onto oxidized Si substrates. Using a specially-constructed substrate holder, the orientation of the substrate with respect to the growth direction was varied from horizontal to vertical. Films were grown at both low and high argon pressure; in the case of Ta, the cathode power was varied as well. The film structure and in particular the surface roughness was measured by X-ray reflectance and also by atomic force microscopy. We find that the surface roughness increases markedly with orientation angle in the case of Ta and Cu films, and in Ti films grown at high argon pressure. At low pressure, however, the Ti film surface roughness remains constant for all substrate orientations. No variation in roughness with either orientation angle or argon pressure was observed in the Al films. These results suggest that, under certain circumstances, shadowing effects and/or grain orientation (i.e., texture) competition during growth can give rise to lower density, more porous (and thus more rough) films, particularly at large orientation angles, as on sidewalls in sub-micron trenches.

Discovery of potent, soluble and orally active TRPV1 antagonists. Structure-activity relationships of a series of isoxazoles

Systematic optimisation of a poorly soluble lead series of isoxazole-3-carboxamides was conducted. Substitution of the 4-position with specific polar functionality afforded the requisite balance of potency, solubility and physicochemical properties. Compound 21a was found to be efficacious in the rat Capsaicin Hargreaves assay following oral administration.

Risk factors for fatality in HIV-infected patients with dideoxynucleoside-induced severe hyperlactataemia or lactic acidosis

BACKGROUND

Lactic acidosis (LA) and severe hyperlactataemia (HL) are infrequent but serious complications of antiretroviral therapy that have been associated with a high fatality rate.

METHODS

In a multinational retrospective cohort study, LA was defined as arterial blood pH<7.35, bicarbonate <20 mmol/l and lactate above normal, and HL as confirmed blood lactate >5 mmol/l. Logistic regression was used to identify factors associated with fatality. Sensitivity and specificity of different case definitions as predictors of death were compared.

RESULTS

The overall case-fatality rate was 19/110 (17.3%), but among acidotic patients it was 33% (16/49 cases). There were 10 asymptomatic patients and none of them died as a consequence of the event. The median lactate for fatal, non-fatal and all patients was 8.3 mmol/l (IQR 7.2-13.1), 6.4 mmol/l (IQR 5.4-7.8) and 6.7 mmol/l (IQR 5.5-8.1), respectively. After adjusting for age and current CD4(+) T-cell count, lactate >7 mmol/l (OR 6.27, 95% CI 1.13-34.93), blood bicarbonate <12 mmol/l (OR 10.02 relative to >18 mmol/l, 95% CI 1.33-75.65) and concurrent opportunistic infections (OR 8.69, 95% CI 1.45-52.22) were independently associated with case fatality. Blood lactate >7 mmol/l showed a sensitivity of 84% for fatality with a specificity of 60%, whereas bicarbonate <12 mmol/l showed a better specificity (85%) but a poorer sensitivity (42%). Bicarbonate <18 mmol/l appears to be as good as lactate <7 mmol/l at predicting death (sensitivity 90% and specificity 54%).

CONCLUSIONS

Our data suggest that blood lactate >7 mmol/l and blood bicarbonate <18 mmol/l appear to predict death and might help clinicians in selecting patients who may benefit from more intense monitoring.

Positive and negative drug selection pressures on the N348I connection domain mutation: new insights from in vivo data

BACKGROUND

There is conflicting evidence on specific reverse transcriptase inhibitors to which the N348I mutation in the connection domain of HIV type-1 reverse transcriptase confers resistance. Here, we examined associations between the emergence of N348I and antiretroviral history in a large clinical database.

METHODS

We analysed 5,353 resistance tests (that were sequenced beyond codon 348) among 2,266 antiretroviral-experienced patients. Associations between N348I and individual antiretroviral drug exposure were estimated using a matched case-control approach. Cases were defined as the first resistance test where N348I was detected; for each case, the 10 closest (in calendar time) N348N tests were selected as controls. Odds ratios (ORs) adjusted for effects of all other drugs were estimated by conditional logistic regression.

RESULTS

N348I was detected in 198 (8.7%) cases. Drugs that were statistically significantly positively associated with N348I were efavirenz (OR 1.55, 95% confidence interval [CI] 1.08-2.23; P=0.017) and nevirapine (OR 2.06, 95% CI 1.49-2.85; P<0.001). Tenofovir disoproxil fumarate (TDF) was significantly negatively associated (OR 0.27, 95% CI 0.15-0.48; P<0.001) with N348I. Similar findings were observed when the analysis was repeated to include only those tests within 2 years of the resistance test. Effects for zidovudine and stavudine were evident only in an additional analysis, which considered exposure to both drugs jointly within 2 years prior to the resistance test: exposure to zidovudine alone (OR 4.61, 95% CI 1.83-11.61; P<0.001) and exposure to stavudine alone (OR 3.39, 95% CI 1.32-8.71; P=0.011).

CONCLUSIONS

This is the first clinical evidence to suggest that efavirenz might select for N348I in addition to nevirapine, that stavudine might select for N348I in addition to zidovudine and that TDF might protect against the mutation.

Impact of transmitted drug-resistance on treatment selection and outcome of first-line Highly Active Antiretroviral Therapy (HAART)

OBJECTIVE

The study aim was to determine how resistance testing influences outcome of first-line highly active antiretroviral therapy (HAART) in routine practice in the United Kingdom.

METHODS

The prevalence of transmitted drug resistance and the genotypic sensitivity score (GSS) of first-line HAART regimens were determined using data from the UK Collaborative HIV Cohort(CHIC) Study. Factors associated with starting a regimen with a reduced GSS and subsequent virological responses were analyzed by logistic and Cox regression.

RESULTS

Amongst patients tested in 1999–2006, 116 of 1175 (10%) had $1 resistance mutation; 64 patients (5.4%) had $1 mutation associated with resistance to drugs in the initial HAART regimen and 54 (4.6%) showed a GSS, 3. Factors independently associated with a GSS, 3 were starting HAART in 1999–2001 vs. 2004–2006 (odds ratio = 2.63; 95% confidence interval: 1.19 to 5.83) and use of ritonavir-boosted protease inhibitor (PI/r)–based vs. nonnucleoside reverse transcriptase inhibitor–based regimens (1.97; 1.06 to 3.64). AGSS .3 was independently associated with virological suppression(hazard ratio for GSS, 3 = 0.60; 95% confidence interval 0.41 to 0.87).

CONCLUSIONS

Most patients starting HAART after undergoing resistance testing received regimens with a GSS $3. PI/r-based therapy was often selected in patients with resistance to the nucleoside reverse transcriptase inhibitor backbone. Low GSS predicted poor virological suppression and the association persisted after adjusting for PI/r use.

Routine versus clinically driven laboratory monitoring of HIV antiretroviral therapy in Africa (DART): a randomised non-inferiority trial

BACKGROUND

HIV antiretroviral therapy (ART) is often managed without routine laboratory monitoring in Africa; however, the effect of this approach is unknown. This trial investigated whether routine toxicity and efficacy monitoring of HIV-infected patients receiving ART had an important long-term effect on clinical outcomes in Africa.

METHODS

In this open, non-inferiority trial in three centres in Uganda and one in Zimbabwe, 3321 symptomatic, ART-naive, HIV-infected adults with CD4 counts less than 200 cells per microL starting ART were randomly assigned to laboratory and clinical monitoring (LCM; n=1659) or clinically driven monitoring (CDM; n=1662) by a computer-generated list. Haematology, biochemistry, and CD4-cell counts were done every 12 weeks. In the LCM group, results were available to clinicians; in the CDM group, results (apart from CD4-cell count) could be requested if clinically indicated and grade 4 toxicities were available. Participants switched to second-line ART after new or recurrent WHO stage 4 events in both groups, or CD4 count less than 100 cells per microL (LCM only). Co-primary endpoints were new WHO stage 4 HIV events or death, and serious adverse events. Non-inferiority was defined as the upper 95% confidence limit for the hazard ratio (HR) for new WHO stage 4 events or death being no greater than 1.18. Analyses were by intention to treat. This study is registered, number ISRCTN13968779.

FINDINGS

Two participants assigned to CDM and three to LCM were excluded from analyses. 5-year survival was 87% (95% CI 85-88) in the CDM group and 90% (88-91) in the LCM group, and 122 (7%) and 112 (7%) participants, respectively, were lost to follow-up over median 4.9 years' follow-up. 459 (28%) participants receiving CDM versus 356 (21%) LCM had a new WHO stage 4 event or died (6.94 [95% CI 6.33-7.60] vs 5.24 [4.72-5.81] per 100 person-years; absolute difference 1.70 per 100 person-years [0.87-2.54]; HR 1.31 [1.14-1.51]; p=0.0001). Differences in disease progression occurred from the third year on ART, whereas higher rates of switch to second-line treatment occurred in LCM from the second year. 283 (17%) participants receiving CDM versus 260 (16%) LCM had a new serious adverse event (HR 1.12 [0.94-1.32]; p=0.19), with anaemia the most common (76 vs 61 cases).

INTERPRETATION

ART can be delivered safely without routine laboratory monitoring for toxic effects, but differences in disease progression suggest a role for monitoring of CD4-cell count from the second year of ART to guide the switch to second-line treatment.

FUNDING

UK Medical Research Council, the UK Department for International Development, the Rockefeller Foundation, GlaxoSmithKline, Gilead Sciences, Boehringer-Ingelheim, and Abbott Laboratories.

Factors influencing lopinavir and atazanavir plasma concentration

BACKGROUND

The protease inhibitors lopinavir and atazanavir are both recommended for treatment of HIV-infected patients. Considerable inter-individual variability in plasma concentration has been observed for both drugs. The aim of this study was to evaluate which demographic factors and concomitant drugs are associated with lopinavir and atazanavir plasma concentration.

METHODS

Data from the Liverpool TDM (therapeutic drug monitoring) Registry were linked with the UK Collaborative HIV Cohort (CHIC) study. For each patient, the first measurement of lopinavir (twice daily) or atazanavir [once daily, ritonavir boosted (/r) or unboosted] plasma concentration was included. Linear regression was used to evaluate the association of dose, gender, age, weight, ethnicity and concomitant antiretroviral drugs or rifabutin with log-transformed drug concentration, adjusted for time since last intake.

RESULTS

Data from 439 patients on lopinavir (69% 400 mg/r, 31% 533 mg/r; 3% concomitant rifabutin) and 313 on atazanavir (60% 300 mg/r, 32% 400 mg/r, 8% 400 mg) were included. Multivariable models revealed the following predictors for lopinavir concentration: weight (11% decrease per additional 10 kg; P = 0.001); dose (25% increase for 533 mg/r; P = 0.024); and rifabutin (116% increase; P < 0.001). For atazanavir the predictors were dose (compared with 300 mg/r: 40% increase for 400 mg/r, 67% decrease for 400 mg; overall P < 0.001) and efavirenz (32% decrease; P = 0.016) but not tenofovir (P = 0.54).

CONCLUSIONS

This analysis confirms that efavirenz decreases atazanavir concentrations, and there was a negative association of weight and lopinavir concentrations. The strong impact of rifabutin on lopinavir concentration should be studied further.

Molecular phylodynamics of the heterosexual HIV epidemic in the United Kingdom

The heterosexual risk group has become the largest HIV infected group in the United Kingdom during the last 10 years, but little is known of the network structure and dynamics of viral transmission in this group. The overwhelming majority of UK heterosexual infections are of non-B HIV subtypes, indicating viruses originating among immigrants from sub-Saharan Africa. The high rate of HIV evolution, combined with the availability of a very high density sample of viral sequences from routine clinical care has allowed the phylodynamics of the epidemic to be investigated for the first time. Sequences of the viral protease and partial reverse transcriptase coding regions from 11,071 patients infected with HIV of non-B subtypes were studied. Of these, 2774 were closely linked to at least one other sequence by nucleotide distance. Including the closest sequences from the global HIV database identified 296 individuals that were in UK-based groups of 3 or more individuals. There were a total of 8 UK-based clusters of 10 or more, comprising 143/2774 (5%) individuals, much lower than the figure of 25% obtained earlier for men who have sex with men (MSM). Sample dates were incorporated into relaxed clock phylogenetic analyses to estimate the dates of internal nodes. From the resulting time-resolved phylogenies, the internode lengths, used as estimates of maximum transmission intervals, had a median of 27 months overall, over twice as long as obtained for MSM (14 months), with only 2% of transmissions occurring in the first 6 months after infection. This phylodynamic analysis of non-B subtype HIV sequences representing over 40% of the estimated UK HIV-infected heterosexual population has revealed heterosexual HIV transmission in the UK is clustered, but on average in smaller groups and is transmitted with slower dynamics than among MSM. More effective intervention to restrict the epidemic may therefore be feasible, given effective diagnosis programmes.

Since 1995, HIV among heterosexuals in the UK increased to the point where the total number of heterosexuals infected with HIV, predominantly of non-B subtypes, exceeds the number of HIV-positive homosexual men. To understand the dynamics of this epidemic, we have applied the novel technique of phylodynamics to the analysis of viral sequences taken in the course of routine clinical care from approximately 40% of the HIV-infected heterosexual population in the UK. Phylodynamics reconstructs the pattern of viral sequence divergence in time, revealing the size of transmission clusters and the dynamics of transmission within them. Of 11,071 patients studied, 296 were linked to at least two others in the UK. There were 8 clusters comprising 10 or more individuals among these, yielding a total of 143 or 5% of all individuals with links, much lower than seen earlier among homosexual men (25%). Viral transmissions within clusters also occurred less rapidly, only 2% being dated to the first 6 months of infection, compared to 25% among homosexual men. Overall, transmission clusters exist in the UK heterosexual HIV epidemic but they are generally smaller than among homosexuals; onward transmission occurs less rapidly and is not associated with acute HIV infection.

Virological response to initial antiretroviral regimens containing abacavir or tenofovir

Patients with a baseline viral load >100,000 copies/mL receiving abacavir (ABC) as part of the nucleoside-backbone component of their first highly active antiretroviral therapy (HAART) regimen have been reported to have a greater failure rate than those receiving tenofovir (TDF). We analyzed short-term outcomes of the use of HAART combinations that included ABC or TDF. The mean 2-8-week change in viral load was calculated using linear regression. In total, 1136 patients started ABC, and 412 started TDF. After adjustment for baseline viral load and other factors, there was no difference in the change in viral load between the patients who started ABC and those who started TDF (0.03 [95% confidence interval, -0.07 to 0.12]) log copies/mL; P = .59). Furthermore, there was no evidence that this effect differed according to baseline viral load (P = .88 for the interaction between pre-HAART viral load and nucleoside started). Likewise, there was no difference in rates of virological failure between the 2 drugs at 24-48 weeks after starting HAART.

Effect of HIV-1 subtype on virologic and immunologic response to starting highly active antiretroviral therapy

BACKGROUND

It has been proposed that subtype-related human immunodeficiency virus type 1 (HIV-1) variability may influence virologic and immunologic responses to highly active antiretroviral therapy (HAART). Studies to date, however, have described treatment outcomes predominantly in persons with subtype B infection or compared subtype B with diverse non-B subtypes grouped together.

METHODS

With use of data from the linked UK Collaborative Group on HIV Drug Resistance and the UK Collaborative HIV Cohort Study databases, time to viral load undetectability (viral load, <50 copies/mL), time to virologic rebound (viral load, >1000 copies/mL), and increases in the CD4 cell count were compared for a median of 39 months (interquartile range, 23-67 months) in drug-naive patients infected with subtype B (n=1550), subtype C (n=272), subtype A (n=66), circulating recombinant form AG (n=57), or subtype D (n=41) disease who started HAART.

RESULTS

Overall, 1906 (90%) of 2116 patients achieved viral load undetectability within 12 months after they started HAART, of whom 335 (18%) subsequently experienced virologic rebound. In adjusted analyses, viral load suppression occurred more rapidly in patients infected with subtype C (hazard ratio, 1.16; 95% confidence interval, 1.01-1.33; P=.04) and subtype A (hazard ratio, 1.35; 95% confidence interval, 1.04-1.74; P=.02) relative to subtype B infection. The virologic rebound occurred marginally more rapidly in patients with subtype C infection (hazard ratio, 1.40; 95% confidence interval, 1.00-1.95; P=.05), but the hazard of virologic rebound was similar with other subtypes. Although persons with subtype B infection showed higher baseline CD4 cell counts and maintained the advantage throughout therapy, CD4 cell count recovery occurred at similar rates with all subtypes.

CONCLUSIONS

Patients infected with prevalent non-B subtypes were as likely to achieve viral load suppression as persons infected with subtype B and showed comparable rates of CD4 cell count recovery. HAART achieves excellent outcomes regardless of the infecting subtype.

Young people in the United Kingdom and Ireland with perinatally acquired HIV: the pediatric legacy for adult services

Children with perinatally acquired HIV-1 infection are surviving into adolescence and increasingly transitioning toward adult services. Planning appropriate services in adult life requires an understanding of their progress through pediatric care. We describe the demographic features, disease progression, antiretroviral therapy (ART), and resistance in young people aged 10 years or more living in the United Kingdom and Ireland reported to the National Study of HIV in Pregnancy and Childhood (NSHPC) with prospective annual follow-up in the Collaborative HIV Paediatric Study (CHIPS) between 1996 and September 2007. Six hundred fifty-four perinatally infected young people were identified; 76% black African, 57% born abroad. Median age at presentation and duration of follow-up was 1 and 11 years, respectively, if born in the United Kingdom/Ireland, and 8 and 5 years if born elsewhere. One hundred sixty-nine (26%) ever had an AIDS-defining illness. Ten died during adolescence. At last follow-up, 64% were on ART, 18% off treatment having previously received ART and 18% were ART naive. Of 518 who had received highly active antiretroviral therapy (HAART), 47% were triple class experienced. At last follow-up 77 (12%) had CD4 counts less than 200 per microliter; of those on HAART, 78% had HIV-1 RNA </=400 copies per milliliter, median CD4 count 554 (interquartile range [IQR] 324-802). Among 166 with resistance assays on HAART, 52% and 12% had dual- and triple-class HIV-1-associated resistance mutations, respectively. One hundred three (16%) young people had transferred to adult services. Young adults with perinatally acquired HIV-1 infection require coordinated multidisciplinary transitional care services and careful long-term follow-up in adult life.

Luring houseflies (Musca domestica) to traps: do cuticular hydrocarbons and visual cues increase catch?

Houseflies (Musca domestica L.) are a major pest species of livestock units and landfill sites. Insecticide resistance has resulted in an increased emphasis on lure-and-kill control methods, but the success of this approach relies on the effective attraction of houseflies with olfactory or visual stimuli. This study examined the efficacy of olfactory (cuticular hydrocarbons) or visual (colours and groups of flies) attractants in a commercial poultry unit. Despite simulating the cuticular hydrocarbon profiles of male and female houseflies, we found no significant increase in the number of individuals lured to traps and no sex-specific responses were evident. The use of target colours selected to match the three peaks in housefly visual spectral sensitivity yielded no significant increase in the catch rate of traps to which they were applied. This study also demonstrated that male and female flies possess significantly different spectral reflectance (males are brighter at 320-470 nm; females are brighter at 470-670 nm). An experiment incorporating groups of recently killed flies from which cuticular hydrocarbons were either removed by solvent or left intact also failed to show any evidence of olfactory or visual attraction for houseflies of either sex. This study concluded that variations of the most commonly applied methods of luring houseflies to traps in commercial livestock units fail to significantly increase capture rates. These results support commonly observed inconsistencies associated with using olfactory or visual stimuli in lure-and-kill systems, possibly because field conditions lessen the attractant properties observed in laboratory experiments.

Population Trends in the Prevalence and Patterns of Protease Resistance Related to Exposure to Unboosted and Boosted Protease Inhibitors

Background

In recent years, several new drugs from the protease inhibitor (PI) class designed to treat HIV infection have become available and the use of ritonavir-boosting has increased in popularity. These changes might be expected to affect the prevalence and patterns of protease resistance in the population of patients who experience treatment failure.

Methods

The UK HIV Drug Resistance Database aims to capture the results of all genotypic resistance tests conducted nationally. Tests on antiretroviral therapy-experienced patients were identified through linkage with the UK Collaborative HIV Cohort Study, from which detailed clinical information on these patients, including a full antiretroviral therapy history, was obtained.

Results

Analyses were on the basis of 8,553 genotypic resistance tests carried out between 1998 and 2005, during which time the overall prevalence of protease resistance halved from 35% to 16%. Substantial declines were observed regardless of whether the patient had been exposed to unboosted PIs and/or boosted PIs. The frequency of protease resistance among patients who had received boosted PIs fell sharply until 2002 with a weaker trend thereafter, falling to 12% in 2005. Individual mutations L33F, M46I/L, V82A/F/T/S/L and I84V became relatively more frequent over the period of study.

Conclusions

The decline in protease resistance was partly due to increasing use of ritonavir-boosting. Nonetheless, the prevalence of resistance was higher than suggested by clinical trials, indicating that prolonged exposure to a boosted PI could ultimately select for major protease mutations.

Factors Influencing Efavirenz and Nevirapine Plasma Concentration: Effect of Ethnicity, Weight and Co-Medication

Background

The aim of this study was to examine factors influencing plasma concentration of efavirenz and nevirapine.

Methods

Data from the Liverpool Therapeutic Drug Monitoring (TDM) registry were linked with the UK Collaborative HIV Cohort (CHIC) Study. For each patient, the first measurement of efavirenz (600 or 800 mg/day) or nevirapine (400 mg/day) plasma concentration was included. Linear regression was used to evaluate the association of dose, gender, age, weight, ethnicity and concomitant antiretroviral drugs or rifampicin with log-transformed drug concentration, adjusted for time since last intake.

Results

Data from 339 patients on efavirenz (34% black, 17% rifampicin) and 179 on nevirapine (27% black, 6% rifampicin) were included. Multivariable models revealed the following predictors for efavirenz concentration: black ethnicity (59% higher; P<0.001), weight (10% lower per additional 10 kg; P=0.002), 800 mg/day (52% higher; P=0.027), rifampicin (35% lower; P=0.039), and zidovudine (25% lower; P=0.010). Notably, without adjustment for other factors, patients on rifampicin had 48% higher efavirenz concentration, as these patients were mostly black and on 800 mg/day. For nevirapine the predictors were black ethnicity (39% higher; P=0.002), rifampicin (40% lower; P=0.002), protease inhibitor (28% higher; P=0.008) and tenofovir (22% higher; P=0.024).

Conclusions

We observed clear associations between ethnicity and concentrations of nevirapine and efavirenz. Our analyses confirm that concomitant rifampicin substantially decreases concentration of both efavirenz and nevirapine; however, for efavirenz this effect was more than counterbalanced by the effect of ethnicity and increased efavirenz dose. There was also an additional impact of weight, which should be considered when determining optimal dosage. Other associations from our analysis (between tenofovir or protease inhibitor and nevirapine, and zidovudine and efavirenz), require confirmation in formal pharmacokinetic studies.