Alternative switching strategies based on regimens with a low genetic barrier: do clinicians have a choice nowadays?

Clinicians sometimes use switching strategies based on regimens such as RAL + ABC/3TC or RPV + ABC/3TC in order to resolve tolerability or safety issues associated with conventional recommended first-line strategies. Despite the low genetic barrier of these regimens, high safety and efficacy rates have been reported in retrospective studies.

Tenofovir vs lamivudine plus adefovir in chronic hepatitis B: TENOSIMP-B study.

AIM: To demonstrate the non-inferiority (15% non-inferiority limit) of monotherapy with tenofovir disoproxil fumarate (TDF) vs the combination of lamivudine (LAM) plus adefovir dipivoxil (ADV) in the maintenance of virologic response in patients with chronic hepatitis B (CHB) and prior failure with LAM. METHODS: This study was a Phase IV prospective, randomized, open, controlled study with 2 parallel groups (TDF and LAM+ADV) of adult patients with hepatitis B e antigen (HBeAg)-negative CHB, prior failure with LAM, on treatment with LAM+ADV for at least 6 mo, without prior resistance to ADV and with an undetectable viral load at the start of the study, in 14 Spanish hospitals. The follow-up time for each patient was 48 wk after randomization, with quarterly visits in which the viral load, biochemical and serological parameters, adverse effects, adherence to treatment and consumption of hospital resources were analysed. RESULTS: Forty-six patients were evaluated [median age: 55.4 years (30.2-75.2); 84.8% male], including 22 patients with TDF and 24 with LAM+ADV. During study development, hepatitis B virus DNA (HBV-DNA) remained undetectable, all patients remained HBeAg negative, and hepatitis B surface antigen (HBsAg) positive. Alanine aminotransferase (ALT) values at the end of the study were similar in the 2 groups (25.1 ± 7.65, TDF vs 24.22 ± 8.38, LAM+ADV, P = 0.646). No significant changes were observed in creatinine or serum phosphorus values in either group. No significant differences between the 2 groups were noted in the identification of adverse effects (AEs) (53.8%, TDF vs 37.5%, LAM+ADV, P = 0.170), and none of the AEs which occurred were serious. Treatment adherence was 95.5% and 83.3% in the TDF and the LAM+ADV groups, respectively (P = 0.488). The costs associated with hospital resource consumption were significantly lower with the TDF treatment than the LAM+ADV treatment (€4943 ± 1059 vs €5811 ± 1538, respectively, P < 0.001). CONCLUSION: TDF monotherapy proved to be safe and not inferior to the LAM+ADV combination therapy in maintaining virologic response in patients with CHB and previous LAM failure. In addition, the use of TDF generated a significant savings in hospital costs.

Conjugates of phosphorylated zalcitabine and lamivudine with SiO2 nanoparticles: Synthesis by CuAAC click chemistry and preliminary assessment of anti-HIV and antiproliferative activity.

Conjugates of phosphorylated dideoxynucleoside antiviral drugs dideoxycytidine (zalcitabine) and lamivudine with SiO2 nanoparticles were obtained via the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry between a nucleoside triphosphate containing an alkynyl group at the γ-phosphate or azidothymidine triphosphate and SiO2 nanoparticles containing alkyl azide or alkynyl groups, respectively. 4-(Prop-2-yn-1-yloxy)butylamino group has been attached to the γ-phosphate group of dideoxycytidine (zalcitabine) and lamivudine 5'-triphosphates via the phosphoramidate linkage. New compounds were shown to be potent killers of human colon carcinoma cells. Anti-HIV activity of the conjugates was demonstrated as well. The conjugates of phosphorylated lamivudine and dideoxycytidine (zalcitabine) showed higher potency than the parent nucleosides. The conjugate of phosphorylated azidothymidine was less active against HIV-1 than the parent nucleoside probably because of the replacement of its 3'-azido group by 1,2,3-triazole ring. These results show an opportunity for using SiO2 nanoparticles as a transport for delivering phosphorylated nucleosides to cells in order to increase their efficiency as antiviral and anticancer drugs.

An initial assessment of correlations between host- and virus-related factors affecting analogues antiviral therapy in HBV chronically infected patients.

BACKGROUND: Success in treating hepatitis B virus (HBV) infection with nucleoside analogues drugs is limited by the emergence of drug-resistant viral strains upon prolonged therapy. In addition to mutation patterns in the viral polymerase gene, host factors are assumed to contribute to failure of treatment in chronic HBV infections. The aim of this study was to analyze the correlation between efficacy of antiviral therapy and the prevalence of HBV pretreatment drug-resistant variants. We also analyzed the role of heterogeneity in the promoter region of the IL-10 on the HBV pol/s gene polymorphisms and efficacy of analogues-driven therapy. MATERIAL AND METHODS: HBV DNA was extracted from 54 serum samples from chronic hepatitis B (CHB) patients. Drug-resistance mutations were analyzed using MALDI-TOF mass spectrometry technology (MALDI-TOF MS) and Multi-temperature single-strand conformation polymorphism (MSSCP). IL-10 gene promoter region polymorphisms at positions -1082, -819, and -592 were determined in allele-specific PCR reactions (AS-PCR). RESULTS: Drug-resistance mutations were detected in 74% of naïve and 93% of experienced patients, but the effect of pre-existence of drug-resistant HBV variants on antiviral therapy was not statistically significant (p=0.86). The role of polymorphisms at positions -1082 (p=0.88), -819 (p=0.26), and -592 (p=0.26) of IL-10 promoter region polymorphisms was excluded from the response-predicting factors. The main host factors predicting successful response to antiviral therapy were female sex (p=0.007) and young age (p=0.013). CONCLUSIONS: The presence of drug-resistant HBV variants in baseline is not a viral predictor of good response to nucleoside/nucleotide analogues therapy. Only low HBV viral load predicted positive response to antiviral therapy. The ideal candidate for antiviral therapy is an immunocompetent, young female with low HBV viral load and elevated ALT activity.

The stress response resolution assay. II. Quantitative assessment of environmental agent/condition effects on cellular stress resolution outcomes in epithelium.

Cellular stress responses consist of a complex network of pathways and linked processes that, when perturbed, are postulated to have roles in the pathogenesis of various human diseases. To assess the impact of environmental insults upon this network, we developed a novel stress response resolution (SRR) assay for investigation of cellular stress resolution outcomes and the effects of environmental agents and conditions thereupon. SRR assay-based criteria identified three distinct groups of surviving cell clones, including those resembling parental cells, those showing Hprt/HPRT mutations, and a third type, "Phenotype-altered" clones, that occurred predominantly in cells pretreated with a chemical mutagen, was heterogeneous in nature, and expressed significant alterations in cell morphology and/or function compared with parental cells. Further evaluation of Phenotype-altered clones found evidence of various alterations that resembled epithelial-to-mesenchymal transition, phenotype switching, checkpoint dysfunction, senescence barrier bypass, and/or epigenetic reprogramming. Phenotype-altered clones were found to occur spontaneously in a cell line with a mutator phenotype, to represent the major surviving clone type in a variation of the SRR assay, and to be tumorigenic in nude mice. Assessment of SRR assay final results showed that pretreatment with a chemical mutagen induced significant changes in cellular stress response prosurvival capacity, in damage avoidance versus damage tolerance stress resolution outcomes, and in the damage burden in the final surviving cell populations. Taken together, these results support the conclusion that use of the SRR assay can provide novel insights into the role of environmental insults in the pathogenesis of cancer and other human diseases.

The stress response resolution assay. I. Quantitative assessment of environmental agent/condition effects on cellular stress resolution outcomes in epithelium.

The events or factors that lead from normal cell function to conditions and diseases such as aging or cancer reflect complex interactions between cells and their environment. Cellular stress responses, a group of processes involved in homeostasis and adaptation to environmental change, contribute to cell survival under stress and can be resolved with damage avoidance or damage tolerance outcomes. To investigate the impact of environmental agents/conditions upon cellular stress response outcomes in epithelium, a novel quantitative assay, the "stress response resolution" (SRR) assay, was developed. The SRR assay consists of pretreatment with a test agent or vehicle followed later by a calibrated stress conditions exposure step (here, using 6-thioguanine). Pilot studies conducted with a spontaneously-immortalized murine mammary epithelial cell line pretreated with vehicle or 20 µg N-ethyl-N-nitrososurea/ml medium for 1 hr, or two hTERT-immortalized human bronchial epithelial cell lines pretreated with vehicle or 100 µM zidovudine/lamivudine for 12 days, found minimal alterations in cell morphology, survival, or cell function through 2 weeks post-exposure. However, when these pretreatments were followed 2 weeks later by exposure to calibrated stress conditions of limited duration (for 4 days), significant alterations in stress resolution were observed in pretreated cells compared with vehicle-treated control cells, with decreased damage avoidance survival outcomes in all cell lines and increased damage tolerance outcomes in two of three cell lines. These pilot study results suggest that sub-cytotoxic pretreatments with chemical mutagens have long-term adverse impact upon the ability of cells to resolve subsequent exposure to environmental stressors.

Rapid identification of YVDD mutants of hepatitis B virus using smart amplification process with competition probe.

Accurate and timely detection of drug-associated viral mutants is important during antiviral therapy. Combining Smart Amplification Process (SMAP) with competition probe, an assay specifically designed to detect point mutation at codon 204 of the hepatitis B virus (HBV) polymerase gene was developed. This assay was sensitive to detect 20 copies of mutant/reaction and recognize as little as 1% of minor mutants in the viral population. The comparison of direct sequencing and SMAP method on 35 clinical specimens showed the concordance in 88% of the cases. This method provides an efficient alternative for rapid identification of HBV mutation associated with lamivudine resistance.

Mechanism of entecavir resistance of hepatitis B virus with viral breakthrough as determined by long-term clinical assessment and molecular docking simulation.

The mechanism by which entecavir resistance (ETVr) substitutions of hepatitis B virus (HBV) can induce breakthrough (BT) during ETV therapy is largely unknown. We conducted a cross-sectional study of 49 lamivudine (LVD)-refractory patients and 59 naïve patients with chronic hepatitis B. BT was observed in 26.8% of the LVD-refractory group during weeks 60 to 144 of ETV therapy. A line probe assay revealed ETVr substitutions only in the LVD-refractory group, i.e., in 4.9% of patients at baseline, increasing to 14.6%, 24.4%, and 44.8% at weeks 48, 96, and 144, respectively. Multivariate logistic regression analysis adjusted for age, gender, HBV DNA levels, and LVD resistance (LVDr) (L180M and M204V, but not M204I) indicated that T184 substitutions and S202G (not S202C) were a significant factor for BT (adjusted odds ratio [OR], 141.12, and 95% confidence interval [CI], 6.94 to 2,870.20; OR, 201.25, and 95% CI, 11.22 to 3608.65, respectively). Modeling of HBV reverse transcriptase (RT) by docking simulation indicated that a combination of LVDr and ETVr (T184L or S202G) was characterized by a change in the direction of the D205 residue and steric conflict in the binding pocket of ETV triphosphate (ETV-TP), by significantly longer minimal distances (2.2 A and 2.1 A), and by higher potential energy (-117 and -99.8 Kcal/mol) for ETV-TP compared with the wild type (1.3 A; -178 Kcal/mol) and LVDr substitutions (1.5 A; -141 Kcal/mol). Our data suggest that the low binding affinity of ETV-TP for the HBV RT, involving conformational change of the binding pocket of HBV RT by L180M, M204V plus T184L, and S202G, could induce BT.

Effect of prophylactic lamivudine for chemotherapy-associated hepatitis B reactivation in lymphoma: a meta-analysis of published clinical trials and a decision tree addressing prolonged prophylaxis and maintenance.

Lamivudine prophylaxis is an effective strategy in HbSAg-positive patients receiving cancer chemotherapy. Recent data indicate that a lamividune-prophylaxis strategy results in a decrease of hepatitis B virus (HBV) reactivation rates, though its effect on HBV-mortality remains equivocal. This report evaluates the benefits from this strategy among lymphoma patients and develops a management approach for patients with prolonged immunosuppression. A Medline search was conducted to retrieve published trials on HBsAg-positive lymphoma patients receiving prophylactic lamivudine during chemotherapy. Basic inclusion criterion was to report HBV-reactivation rates with and without lamivudine prophylaxis. A meta-analysis of the risk of HBV-reactivation and HBV-related mortality was conducted, and the pooled effect was calculated as risk ratio (RR). We found that lamivudine prophylaxis is associated with a significant reduction in hepatitis B virus reactivation (RR 0.21, 95%CI 0.13-0.35) and a trend in reducing HBV-related mortality (RR 0.68, 95%CI 0.19-2.49). In order to study the long-term effects of anti-HBV prophylaxis when prolonged immunosuppression is needed, we used our findings to model a decision tree. Overall survival was the main outcome used in the analysis. Rituximab maintenance in B-cell lymphomas was used as a paradigm of prolonged immunosuppression. We found that extended anti-HBV prophylaxis can improve survival rates by 2.4% in HBsAg-positive patients. If 1,000 HBsAg-positive lymphoma patients receive prophylaxis, one will die from hepatitis B virus reactivation versus 25/1,000 if no prophylaxis is administered. This effect is probably mediated through a reduction of hepatitis B virus reactivation and HBV-related mortality. The ideal antiviral agent needs to be determined.

Non-occupational postexposure prophylaxis for HIV: a systematic review.

OBJECTIVES: To review the evidence on the clinical effectiveness and cost-effectiveness of non-occupational postexposure prophylaxis (PEP) for HIV. DATA SOURCES: Eleven electronic databases were searched from inception to December 2007. REVIEW METHODS: Selected studies were assessed, subjected to data extraction using a standard template and quality assessment using published criteria. Studies were synthesised using a narrative approach with full tabulation of results from all included studies. RESULTS: One clinical effectiveness study meeting the inclusion criteria was identified, a cohort study of PEP in a high-risk HIV-negative homosexual male cohort in Brazil. The quality of the study was generally weak. Seroincidence in the cohort as a whole (2.9 per 100 person-years) was very similar to that expected in this population (3.1 per 100 person-years, p > 0.97), despite the seroconversion to HIV being 1/68 in the PEP group and 10/132 in the group not receiving PEP. High-risk sexual activities declined over time for both PEP and non-PEP users. Four economic evaluations met the inclusion criteria of the review. The methodological quality of the studies was mixed. The studies are constrained by a lack of published data on the clinical effectiveness of PEP after non-occupational exposure, with effectiveness data derived from one study of occupational PEP. Their generalisability to the UK is not clear. Results suggest that PEP following non-occupational exposure to HIV was cost saving for men who have unprotected receptive anal intercourse with men, whether the source partner is known to be HIV positive or not; heterosexuals after unprotected receptive anal intercourse; and intravenous drug users sharing needles with a known HIV-positive person. PEP following non-occupational exposure to HIV was cost-effective for all male-male intercourse (unprotected receptive and insertive anal intercourse, unprotected receptive oral sex, and 'other') and was possibly cost-effective for intravenous drug users and high-risk women. Four additional studies were identified giving further information about adverse events associated with PEP after non-occupational exposure to HIV. The majority of participants experienced adverse events with the most common being nausea and fatigue. Rates were generally higher in participants receiving triple therapy than in participants receiving dual therapy. Completion of PEP therapy was variable, ranging from 24% to 78% of participants depending on type of therapy. Toxicity was the main reason for discontinuation of treatment. CONCLUSIONS: It is not possible to draw conclusions on the clinical effectiveness of non-occupational PEP for HIV because of the limited evidence available. The review of cost-effectiveness suggests that non-occupational PEP may be cost-effective, especially in certain population subgroups; however, the assumptions made and data sources used in the cost-effectiveness studies mean that their results should be used with caution.

In vivo fitness cost of the M184V mutation in multidrug-resistant human immunodeficiency virus type 1 in the absence of lamivudine.

Lamivudine therapy selects for the M184V mutation. Although this mutation reduces the replicative capacity of human immunodeficiency virus in vitro, its impact on viral fitness in vivo has not been well defined. We used quantitative allele-specific PCR to precisely calculate the fitness differences between the mutated M184V virus and one that had reverted to the wild type in a cohort of patients by selectively interrupting reverse transcriptase inhibitor therapy, and we found that the M184V variants were consistently 4 to 8% less fit than the wild type in the absence of drug. After a lag phase of variable duration, wild-type variants emerged due to continued evolution of pol and back mutation rather than through emergence of an archived wild-type variant.

Assessment of selective real-time PCR for quantitation of lamivudine and adefovir hepatitis B virus-resistant strains and comparison with direct sequencing and line probe assays.

A selective real-time PCR (sPCR) assay has been developed to detect the rtM204V/I and rtN236T mutations of hepatitis B virus (HBV) associated with resistance to lamivudine and adefovir. Using mixtures of mutant and wild-type plasmids, this sPCR was able to detect 0.1% of mutated strain in a total plasmid population of 10(5) copies and was more sensitive in detecting resistant strains than the line probe INNO-LiPA-DR-v2 assay and a direct sequencing assay. The comparison of these methods on 20 clinical specimens from treated patients confirmed the plasmid results: the three methods were concordant for the detection of the mutant strains in 72% of the cases and the discrepant results were caused mainly by the sequencing assay's lack of sensitivity. The line probe assay was more sensitive for detecting mutations than sPCR when the viral load was less than 10(4) copies/ml; conversely, the sPCR provided a more sensitive detection when the viral load was greater than 10(4) copies/ml. Although difficult to perform in clinical practice, sPCR appears to be a reliable technique for detecting and quantifying quasi-species resistant to lamivudine (LAM) and adefovir (ADV) and can be useful to gain a better understanding of the natural history of antiviral resistance during the treatment of chronic hepatitis B (CHB).

Hepatitis B virus quantification and detection of YMDD mutants in a single reaction by real-time PCR and annealing curve analysis.

BACKGROUND: Long-term antiviral therapy, although effective for treatment of hepatitis B, might select the emergence of drug-resistant hepatitis B virus (HBV) mutants. Detection of HBV mutants and determination of viral titre are two crucial parameters for monitoring treatment response and occurrence of mutants. In this study, we take lamivudine resistance as an example to develop a method that can determine both parameters in a single-tube PCR reaction. METHODS: The method contained two consecutive steps: in the first step, real-time PCR was used for quantification; in the second step, a novel annealing curve analysis was used for detecting YMDD mutants. For accurate quantification, PCR primers and hybridization probes were chosen from highly conserved regions to ensure the equivalent amplification of all HBV genotypes. Within the sensor probe, there were signature nucleotide polymorphisms that could effectively differentiate YMDD mutants from wild type by distinct melting temperatures (Tm) values. The clinical applicability of the assay was tested in serial samples from 90 patients receiving lamivudine treatment. RESULTS: This assay could readily differentiate YMDD, YIDD and YVDD mutants by their distinct Tm values. The quantification results showed great consistency in a linear range from 10(3) to 10(11) copies/ml. Moreover, this assay could detect YMDD mutants accounting for < or = 10% of the total viral population. Its clinical feasibility has been verified in primary specimens. CONCLUSIONS: The newly designed YMDD detection method is simple, sensitive, cost-effective, time-saving and provides a useful tool for follow-up of patients treated with lamivudine or other antiviral drugs.

An efficient tool for surveying CRF01_AE HIV type 1 resistance in Thailand to combined stavudine-lamivudine-nevirapine treatment: mutagenically separated PCR targeting M184I/V.

Under programs organized by the government of Thailand, HIV-1-infected patients have been treated since 2002 with several regimens, including a tablet known as GPOvir, which contains lamivudine, stavudine, and nevirapine. The aim of this study was to establish an effective assay, based on mutagenically separated PCR (MS-PCR), with the goal of surveying GPOvir-resistant HIV-1 cases. To determine the target mutation point for the assay, we analyzed the patterns of acquired drug resistance in plasma samples from GPOvir-failed cases. Of 428 HIV-1-infected individuals treated with GPOvir at Lampang Hospital in northern Thailand from 2002 to 2004, 66 had detectable viral loads after 3 months of treatment. The HIV-1 sequences of these 66 GPOvir-failed cases and 55 pre-GPOvir baseline samples were analyzed. The most prevalent drug resistance mutation among the samples was the lamivudine resistance M184I/V mutation. Based on this finding, we developed a new MS-PCR assay to detect the M184I/V mutation, and evaluated the assay performance for detecting GPOvir-resistant CRF01_AE cases. Comparing the results of M184I/V MS-PCR and sequence analyses, we found a concordance rate of 95% and an overall sensitivity of the M184I/V MS-PCR for detecting GPOvir-resistant cases of 79%. Considering the relatively low price of the assay, approximately $12.50 per sample, M184I/V MS-PCR may be a candidate for monitoring a large number of GPOvir-treated patients, particularly in developing nations.

Options for a second-line antiretroviral regimen for HIV type 1-infected patients whose initial regimen of a fixed-dose combination of stavudine, lamivudine, and nevirapine fails.

BACKGROUND: A fixed-dose combination of stavudine, lamivudine, and nevirapine is extensively used as an antiretroviral regimen in developing countries because of its affordability. Virological failure with this regimen has become more common, and a second-line regimen needs to be prepared in the national program. METHODS: Genotypic resistance testing was conducted among human immunodeficiency virus type 1 (HIV-1)-infected patients who experienced treatment failure with their first antiretroviral regimen (a fixed-dose combination of stavudine, lamivudine, and nevirapine) during 2003-2005. Patterns of resistance mutations and options for a second-line regimen were studied. RESULTS: We studied 98 patients (mean age, 35.2 years), of whom, 63% were male. The median duration of antiretroviral therapy was 20 months. The median HIV-1 RNA load at the time of virological failure detection was 4.1 log copies/mL. The prevalences of patients with > or =1 major mutation conferring drug resistance to nucleoside reverse-transcriptase inhibitors and nonnucleoside reverse-transcriptase inhibitors were 95% and 92%, respectively. M184V was the most common nucleoside reverse-transcriptase inhibitor resistance mutation (observed in 89% of patients). Thymidine analogue mutations, K65R, and Q151M were observed in 37%, 6%, and 8% of patients, respectively. Patients with an HIV-1 RNA load of >4 log copies/mL at the time of treatment failure had higher prevalence of thymidine analogue mutations (P=.041), K65R (P=.031), and Q151M (P=.008) mutations. The second-line regimen was determined in a resource-limited setting where tenofovir and enfuvirtide are not available; the options were limited for 48% of patients. CONCLUSIONS: After experiencing treatment failure with a fixed-dose combination of stavudine, lamivudine, and nevirapine, almost all patients have lamivudine and nonnucleoside reverse-transcriptase inhibitor resistance. The options for a second-line regimen are limited for one-half of these patients. In resource-limited settings where availability of antiretroviral agents is limited, strategies for prevention of HIV-1 resistance are crucial. Early detection of virological failure may provide more options and better treatment outcomes.

Two-year assessment of entecavir resistance in Lamivudine-refractory hepatitis B virus patients reveals different clinical outcomes depending on the resistance substitutions present.

Entecavir (ETV) is a deoxyguanosine analog approved for use for the treatment of chronic infection with wild-type and lamivudine-resistant (LVDr) hepatitis B virus (HBV). In LVD-refractory patients, 1.0 mg ETV suppressed HBV DNA levels to below the level of detection by PCR (<300 copies/ml) in 21% and 34% of patients by Weeks 48 and 96, respectively. Prior studies showed that virologic rebound due to ETV resistance (ETVr) required preexisting LVDr HBV reverse transcriptase substitutions M204V and L180M plus additional changes at T184, S202, or M250. To monitor for resistance, available isolates from 192 ETV-treated patients were sequenced, with phenotyping performed for all isolates with all emerging substitutions, in addition to isolates from all patients experiencing virologic rebounds. The T184, S202, or M250 substitution was found in LVDr HBV at baseline in 6% of patients and emerged in isolates from another 11/187 (6%) and 12/151 (8%) ETV-treated patients by Weeks 48 and 96, respectively. However, use of a more sensitive PCR assay detected many of the emerging changes at baseline, suggesting that they originated during LVD therapy. Only a subset of the changes in ETVr isolates altered their susceptibilities, and virtually all isolates were significantly replication impaired in vitro. Consequently, only 2/187 (1%) patients experienced ETVr rebounds in year 1, with an additional 14/151 (9%) patients experiencing ETVr rebounds in year 2. Isolates from all 16 patients with rebounds were LVDr and harbored the T184 and/or S202 change. Seventeen other novel substitutions emerged during ETV therapy, but none reduced the susceptibility to ETV or resulted in a rebound. In summary, ETV was effective in LVD-refractory patients, with resistant sequences arising from a subset of patients harboring preexisting LVDr/ETVr variants and with approximately half of the patients experiencing a virologic rebound.

Development of a population simulation model for HIV monotherapy virological outcomes using lamivudine.

Current highly active antiretroviral therapy (HAART) requires the use of combinations of three drugs to minimize the early emergence of drug-resistant HIV strains. Therefore, long-term monotherapy data with new agents are unavailable. However, the development of computer models for Monte-Carlo-type simulations of antiviral monotherapy, which incorporate HIV infection dynamic distributions from previously studied populations, together with pharmacokinetics and pharmacodynamic parameters of the new agent, could serve as an important tool. The nucleoside lamivudine (3TC) was used as a representative drug to standardize an improved pharmacodynamic and infection dynamic monotherapy model. 3TC plasma concentration versus time profiles was used to drive the cellular accumulation of 3TC-triphosphate (TP) in primary human lymphocytes in the model, over a 16 week period. The fraction of HIV reverse transcription inhibited was calculated using the median inhibitory concentration and intracellular 3TC-TP levels. Virus loads and activated CD4+ T-cell counts were generated for 2,200 theoretical individuals and compared with the outcomes of an actual 3TC monotherapy trial at the same dose. Pharmacokinetic variance alone did not account for the interindividual HIV-load variability. However, selection of appropriate distributions of the various pharmacokinetic and infection dynamics parameters produced a similar range of virus load reductions to actual observations. Therefore, once parameter and variance distributions are standardized, this modelling approach could be helpful in planning clinical trials and predicting the antiviral contribution of each agent in a HAART modality.

Doctor to patient transmission of hepatitis B virus: implications of HBV DNA levels and potential new solutions.

Hepatitis B virus (HBV)-infected health care workers (HCWs) can infect patients undergoing exposure prone procedures. Until now reviews have focused on the problem of the HBeAg-positive HCWs. After transmission of HBV by HBeAg-negative surgeons, the focus of Public Health Policy in the UK and the Netherlands has changed from HBeAg status to serum HBV DNA level. Viral load and the volume of blood transmitted determine the transmission risk of HBV. We have estimated the number of infectious particles transmitted by needlesticks, in comparison with those attributed in maternal-fetal transfusion. The blood volume transmitted by needlestick is roughly 1-30% of that of delivery. As vertical transmission with maternal HBV DNA levels below 10(7) g Eq./ml is rarely documented, HBV transmission by needlesticks is, according to our assumptions, unlikely to occur with HBV DNA levels below 10(7) g Eq./ml. Sera of transmitting HCWs contained HBV DNA levels between 5.0 x 10(9) and 6.35 x 10(4) g Eq./ml. Interpretation of these levels is hampered as the sera were taken at least 3 months after transmission. To prevent both loss of expertise and nosocomial infection, highly viremic HCWs can be offered antiviral therapy. Lamivudine and alpha-interferon can now be complemented with adefovir, tenofovir and entecavir to provide effective new therapies for chronic HBV-infected HCWs.