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At least 163 records · Page 9Linked to original sources
PubMed2006

Role of parametric resonance in virological failure during HIV treatment interruption therapy.

We present a novel hypothesis that could explain virological failure to structured treatment interruptions (STI). We analysed a classic mathematical model of HIV within-host viral dynamics and found that non-linear parametric resonance occurs when STI are added to the model; resonance is observed as virological failure. We simulated clinical trial data and calculated patient-specific resonant spectra. We gained two important insights. First, within an STI trial, patients who begin with similar viral loads can be expected to show very different virological responses as a result of resonance. Second, and more importantly, virological failure is not simply due to STI or patients' characteristics; instead it is the result of complex interaction between STI and the patient's viral dynamics. Hence, our analyses show that no universal regimen with periodic interruptions will be effective for all patients.

CD4 Lymphocyte Count↗
PubMed1979

Viruses in drinking-water. Reconsideration of evidence for postulated health hazard and proposals for virological standards of purity.

Stringent virological standards for drinking-water have been proposed by the World Health Organisation and by others, but there is no evidence of the spread of virus infection by drinking-water that has been adequately treated to conventional bacteriological standards. There is evidence for waterborne transmission of hepatitis and viral gastroenteritis but the case for the introduction of virological standards is critically examined. It is concluded that there is no evidence that drinking-water in the U.K. contributes to the spread of virus infection, and that the introduction of virological standards for drinking-water could not at present be justified. Moreover, in the absence of any information relating the degree of viral contamination to disease, there is no logical basis on which to set the level of a practical virological standard.

Disease Outbreaks↗
PubMed1999

Improved correlation between multiple mutations within the NS5A region and virological response in European patients chronically infected with hepatitis C virus type 1b undergoing combination therapy.

BACKGROUND/AIMS: Studies from Japan showed that HCV-1b isolates with at least four amino acid changes within NS5A2209-2248 compared with the prototype sequence HCV-J are more sensitive to interferon than isolates with a prototype sequence. However, the data were not unequivocally confirmed in studies from other geographical areas. These discrepancies may be explained by differences in the prevalence of multiple mutations within the NS5A2209-2248 and/or the treatment efficacy. METHODS: In the present study, we therefore investigated the correlation between NS5A2209-2248 sequences of HCV-1b isolates and sustained virological response in 72 European patients treated with 3x6 MU interferon-a per week with (n = 26) and without (n = 46) ribavirin (1000-1200 mg/day). Serum HCV RNA was amplified by reverse transcription-polymerase chain reaction (RT-PCR) and the NS5A2209-2248 region was analyzed by sequencing of PCR products or individual clones. RESULTS: Compared with HCV-1b prototype sequences, 19 patients (26%) had no amino acid changes (prototype), 47 patients (65%) had 1-3 mutations (intermediate type) and six patients (8%) had at least 4 mutations in the NS5A2209-2248 region (mutant type). Nine of the 12 patients with sustained virological response were infected with an intermediate type HCV-1b, the remaining three patients revealed a mutant type HCV-1b. A sustained virological response was achieved in three of four patients with a mutant type HCV-1b treated with interferon-alpha and ribavirin, but in none of the mutant type HCV-1b infected patients treated with interferon-a alone. Quasispecies analysis of HCV in the NS5A2209-2248 region showed only minor heterogeneity of the amino acid sequence. CONCLUSIONS: The prevalence of mutant type HCV-1b isolates in European patients is low. In patients treated with combination therapy interferon-a and ribavirin, a correlation between mutant type HCV-1b isolates and sustained virological response was observed. The discrepancies between previous studies appear to be related to the efficacy of antiviral treatment and to the low prevalence of mutant type HCV-1b isolates in Western countries.

Adult↗
PubMed1999

Treatment of chronic hepatitis C: comparative virologic response rates among the different interferons.

End-treatment and sustained virologic response rates are similar in large, comparative controlled trials which have compared the standard dosing regimens of interferon alpha-2b to interferon alpha-nl and consensus interferon, as well as to virologic response rates recently reported with interferon alpha-2b monotherapy for 24 weeks. For patients who have responded and relapsed after an initial course of alpha interferon, retreatment with consensus interferon for 48 weeks demonstrates a high sustained virologic response rate, similar to that reported with interferon alpha-2b combined with ribavirin for 24 weeks. Based on available pharmacokinetic and pharmacodynamic data, pegylation of interferon alpha-2a shows promise in demonstrating high sustained serum levels and 2',5' OAS activity. Preliminary data from a Phase II clinical trial of a 48-week treatment in naive patients demonstrates end-treatment and sustained virologic response rates similar to that seen with interferon alpha-2b combined with ribavirin for 48 weeks.

Antiviral Agents↗
PubMed2003

High rate of long-term virological response after a 1-year course of interferon +/- ribavirin in chronic hepatitis C relapsers. Results of a 191 patients randomized trial.

UNLABELLED: We investigated the long-term efficacy of a 12-month course of interferon (IFN)+ribavirin in chronic hepatitis C relapsers. We randomized 191 relapsers with a 2:1 ratio to receive 3 million units three times a week of interferon alpha (IFN alpha)-2b+ribavirin (1-1.2 g/day) (group A=127 patients) or IFN alpha-2b (group B=60 patients) of same dosage and duration for 1 year. General and hepatitis C data of group A and B patients were similar. The main goal of the study was to determine the rate of sustained virological response evaluated 1 year after treatment. RESULTS: Virological sustained response (SR) was 61% and 12% for groups A and B, respectively (P<0.001). A significant histological improvement was observed in both treatment groups. The Metavir activity score became significantly lower in the IFN+ribavirin group than in the IFN group (P<0/0001). The Metavir fibrosis scores remained unchanged. Also, at the end of the treatment, the virological response was 69% (88/127) for group A and 33% (20/60) for group B (P<0.001). CONCLUSION: One-year retreatment of relapsers with the combination of IFN+ribavirin led to 61% of virological SR and to a significant improvement of histological activity. Therefore, the therapeutic schedule presented here can be considered of particular interest for the retreatment of relapsers.

Administration, Oral↗
PubMed2001

NS5A mutations predict biochemical but not virological response to interferon-alpha treatment of sporadic hepatitis C virus infection in European patients.

The NS5A region of the hepatitis C virus (HCV) genome has been reported by Japanese but not European investigators to be a significant factor in predicting interferon (IFN) response patients with HCV of genotype 1. We correlated the NS5A region with treatment outcome in patients with sporadic HCV infection. Twenty-eight patients (10 men, 18 women, mean age 60 +/- 2 years) with histologically proven HCV chronic hepatitis, genotype 1b, were treated with 6 MU IFN-alpha for 6 months. The 6954-7073 area of the NS5A region was directly sequenced for nucleotide and amino acids mutations and the results were related to biochemical and virological response. None of the patients had a strain with nucleotide sequence identical to the Japanese HCV-J. However, in five strains the nucleotide mutations led to synonymous amino acids and the amino acid sequences were identical to the prototype Japanese strain. Only 2/28 patients had four or more amino acid mutations (mutant strains) while 21 demonstrated an intermediate type and five belonged to the wild-type. The most frequent non-synonymous substitution was at position 6982 (A-->G) corresponding to an amino acid change at codon 2218 (His-->Arg). All patients with the wild-type were biochemical nonresponders while the two patients with the mutant strains had a sustained biochemical response. Twenty-three percent of the intermediate type had a sustained biochemical response. NS5A mutations predict the biochemical but not the virological response of patients. Virological response was poor and unrelated to the type of HCV strain. Biochemical responders had significantly lower amino acid mutations (1.14 +/- 0.19) compared with nonresponders (2.57 +/- 1.4, P < 0.003) as well as lower aminotransferase values (P < 0.01). Hence, mutational analysis of the NS5A region showed that our patients have a mutational profile similar to the European studies with a wild-type that is slightly different from the Japanese HCV-J sequence. The biochemical, but not the virological response to IFN-alpha is similar to the Japanese studies, with no response of the patients with wild-type sequence, a good response in the limited number of patients with mutant strains and 23% response rate in the patients with intermediate type sequences.

Amino Acid Sequence↗
PubMed2004

Interferon treatment improves survival in chronic hepatitis C patients showing biochemical as well as virological responses by preventing liver-related death.

Interferon therapy for chronic hepatitis C reduces the risk of hepatocellular carcinoma, especially among virological and biochemical responders. However, little is known about the effect of interferon therapy on mortality. We studied the long-term effect of interferon therapy on mortality in patients with chronic hepatitis C. For this retrospective cohort study, 2954 patients with chronic hepatitis C were recruited, of whom 2698 received interferon therapy and 256 did not. The effect of interferon therapy on survival was assessed by standardized mortality ratio (SMR) based on published mortality data for the general Japanese population and by risk ratio calculated by proportional hazard regression. Over 6.0 +/- 2.2 years follow-up, death from liver-related diseases was observed in 69 (68%) of 101 deaths among interferon-treated patients and in 42 (81%) of 52 deaths among untreated patients. Compared with the general population, overall mortality was high among untreated patients (SMR: 2.7; 95% CI: 2.0-3.6) but not among interferon-treated patients (SMR: 0.9; 95% CI: 0.7-1.1). Liver-related mortality was extremely high among untreated patients (SMR: 22.2; 95% CI: 16.0-30.0) and less among interferon-treated patients (SMR: 5.5; 95% CI: 4.3-6.9). The risk of death from all causes was lower for interferon-treated than untreated patients (risk ratio: 0.47; 95% CI: 0.261-0.836; P = 0.01). The risk of death from liver-related diseases was significantly lower for sustained virological responders (risk ratio: 0.04; 95% CI: 0.005-0.301; P = 0.002) compared with untreated patients, but not for nonsustained virological responders. Sustained biochemical responders (risk ratio: 0.03; 95% CI: 0.004-0.230; P < 0.001) and transient biochemical responders (risk ratio: 0.18; 95% CI: 0.063-0.532; P = 0.002) showed a significantly reduced risk of death from liver-related death, whereas biochemical nonresponders did not. Hence interferon treatment improved survival in chronic hepatitis C patients showing a biochemical as well as a virological response by preventing liver-related deaths.

Adult↗
PubMed2002

Favorable impact of virological response to highly active antiretroviral therapy on survival in patients with AIDS-related lymphoma.

We have retrospectively studied the influence of highly active antiretroviral therapy (HAART) on the outcome of AIDS-related lymphomas (ARL) as well as the possible influence of the virological response to HAART on complete response (CR) rate and survival in our series of ARL treated with CHOP. Two groups of patients were studied: (1) 44 patients who did not take HAART when the lymphoma was diagnosed, and (2) 26 patients treated with HAART concomitantly and after chemotherapy. There were 4 (9%) women in group 1 versus 11 (42%) in group 2 (P = 0.01), and serum lactate dehydrogenase (LDH) level was lower in group 2. The response rate to CHOP was higher in group 2 patients (15 out of 23, 65%) than in those of group 1 (16 out of 44, 36%) (P = 0.025). The factors associated with improvement of CR in the multivariate analysis were the administration of HAART (P = 0.004) and International Prognostic Index (IPI) score < or = 2 (P = 0.006). Among group 2 patients, those with a virological response to HAART and with IPI score < or = 2 had better response rate to chemotherapy (odds ratios 9.3 and 11.8, respectively). The median (95% CI) overall survival (OS) for group 1 patients was 7 (3-11) months, whereas it has not been reached for group 2 (P = 0.002). The only parameters influencing OS in the multivariate analysis were HAART (0.003), as a protective factor and IPI score > 2 (P = 0.015) with negative influence. Among patients treated with HAART, those with virological response had higher OS probability (P = 0.004), whereas those with IPI score > 2 had an unfavorable prognosis (P = 0.014). The only variable with statistical significance for disease free survival (DFS) in the univariate and multivariate analyses was HAART (P = 0.0168 and P = 0.028, respectively). We conclude that HAART is an independent prognostic factor for CR attainment, OS and DFS in patients with ARL treated with CHOP. Those patients with virological response to HAART had a better survival.

Adult↗
PubMed2004

Long-term virological effect of highly active antiretroviral therapy on cerebrospinal fluid and relationship with genotypic resistance.

The objective of this study was to assess the long-term virological response in cerebrospinal fluid (CSF) in patients treated with highly active antiretroviral therapy (HAART) and to compare this response to CSF and plasma human immunodeficiency virus (HIV) drug resistance profiles. Paired CSF and plasma specimens were drawn from 18 patients receiving HAART at baseline and after 9 to 70 months of therapy. At baseline, median HIV-1 RNA concentrations were 4.13 log10 copies/ml in CSF and 5.31 log10 copies/ml in plasma. At the time of on-therapy CSF sampling, HIV-1 RNA was undetectable in CSF from 13/18 patients (72%), and in plasma from 9/18 patients (50%). The genotypic analysis at baseline revealed reverse transcriptase (RT) resistance mutations in 7 of 11 (64%) CSF samples and in 8 of 11 (73%) plasma samples. No patient had protease resistance mutations, except for secondary mutations. At the time of virological failure in CSF, new RT and protease resistance mutations were found in both CSF and plasma of the two patients with both baseline and on-treatment paired evaluations. At long-term follow-up, the proportion of patients failing to respond virologically was lower in CSF than in plasma. Virological failure in CSF was associated with failure to respond in plasma and onset of new drug resistance mutations in both compartments.

AIDS Dementia Complex↗
PubMed2000

Determinants of virological response to antiretroviral therapy: implications for long-term strategies.

A variety of factors can contribute to the failure of combination antiretroviral therapy to durably suppress viral replication in patients infected with human immunodeficiency virus (HIV). Patients who have a low CD4(+) T cell count or high plasma viral load before therapy is initiated are at high risk for subsequent virological failure. Previous therapy is also a strong determinant of subsequent virological response, presumably because of pre-existing viral resistance. Drug exposure, as determined by adherence, drug absorption, and drug metabolism, has a significant impact on future long-term virological responses. Although definitive proof is lacking, some tissues may have limited drug penetration, thus allowing for ongoing viral replication. Understanding why combination therapy fails for HIV-infected patients may allow clinicians to individualize treatment strategies. Unfortunately, almost any factor (drug, host, or viral) that leads to virological failure of an initial combination regimen is likely to persist-and perhaps become more challenging-once a salvage regimen is initiated.

Anti-HIV Agents↗
PubMed2000

Human immunodeficiency virus-infected persons with mutations conferring resistance to zidovudine show reduced virologic responses to hydroxyurea and stavudine-lamivudine.

The baseline predictors of poor virologic response (<0.5 log decrease in plasma virus load) were examined in two 1996 pilot trials of combination nucleoside-analogue therapy. One trial examined the addition of hydroxyurea to didanosine therapy; the other examined stavudine-lamivudine in combination. In both, predictors of virologic response included the presence of mutations associated with zidovudine resistance. For hydroxyurea, the odds ratio (OR) of failure to achieve a short-term (4 weeks) virologic response in a bivariate logistic regression model was 30.8 (95% confidence interval [CI], 1.75-543; P=.02) for use of lower dose hydroxyurea (500 mg/day) and 14.7 (95% CI, 1.1-200; P=.04) for the presence of a zidovudine-related mutation. For the stavudine-lamivudine study, the OR of failure to achieve a virologic response at 4 weeks in a multivariate logistic regression model was 23 (95% CI, 2.7-199; P=.004) for the presence of a mutation at codon 215.

Anti-HIV Agents↗
PubMed2001

Secondary mutations in the protease region of human immunodeficiency virus and virologic failure in drug-naive patients treated with protease inhibitor-based therapy.

The role of mutations in protease (PR) and reverse-transcriptase (RT) of human immunodeficiency virus (HIV) in predicting virologic failure was assessed in 248 antiretroviral-naive HIV-positive patients who began a PR inhibitor-containing antiretroviral regimen. Genotypic testing was performed on plasma samples stored before the start of therapy. Twenty-seven patients (10.9%) had mutations in the RT, 5 (2%) carried primary mutations in the PR, and 131 (52.8%) showed only secondary PR mutations. Virologic failure at week 24 occurred in 62 (25.0%) of 248 patients. There was a statistically significant correlation between virologic failure and the number of PR mutations (P= .04, chi(2) test). Mutations at codons 10 and 36 of PR (present in 39.3% and 40.0% of patients in whom treatment failed, respectively) were identified by stepwise logistic regression as the strongest predictors of virologic failure (odds ratio, 2.20; 95% confidence interval, 1.30-3.75; P= .004). If confirmed in independent studies, this result may justify the increased use of HIV genotyping in drug-naive patients requiring antiretroviral therapy.

Acute Disease↗
PubMed2004

Predictors of virologic failure and resistance in HIV-infected patients treated with nevirapine- or efavirenz-based antiretroviral therapy.

Resistance to nonnucleoside reverse transcriptase inhibitors (NNRTIs) increases with the wider use of this class of antiretroviral therapy. The association between adherence and resistance to NNRTI-based regimens is poorly understood. Predictors of virologic failure and resistance according to a baseline evaluation of nonadherence risk factors were determined in a cohort of 71 human immunodeficiency virus (HIV)-infected patients with early virologic response who received an NNRTI-based regimen. During the median follow-up of 29 months, 20 (28%) of 71 patients experienced virologic failure with an NNRTI-based regimen. Virologic failure was associated with repeated drug holidays (> or =48 h of unplanned drug cessation), depression, younger age, and low adherence to therapy during baseline evaluation. Moreover, repeated drug holidays was the only risk factor for developing a major mutation conferring cross-resistance to the NNRTI class (hazard ratio, 22.5; 95% confidence interval, 2.8-180.3; P<.0001). Patients' previous adherence to therapy and drugs genetic barriers, not only the number of pills or doses involved, should be taken into consideration in the decision to simplify highly active antiretroviral therapy.

Adult↗
PubMed2001

Impact of HIV type 1 protease, reverse transcriptase, cleavage site, and p6 mutations on the virological response to quadruple therapy with saquinavir, ritonavir, and two nucleoside analogs.

Genotype alterations of HIV-1 protease, reverse transcriptase, cleavage sites p7/p1 and p1/p6, as well as p6(gag) and transframe protein p6* were studied in an observational cohort of 42 individuals who received antiretroviral therapy consisting of saquinavir, ritonavir, and two nucleoside analogs. In a multivariate logistic regression analysis, the prior protease inhibitor experience (odds ratio, 6.20; 95% CI, 1.22-31.38) and the presence of primary protease mutations (odds ratio, 9.99; 95% CI, 1.05-94.72) were independently associated with virological failure. Moreover, a trend was observed in that individuals with N-terminal amino acid insertions in the proline-rich motif of the p6(gag) protein were less likely to experience virological failure (OR, 0.17; 95% CI, 0.02-1.35; p = 0.09). In contrast, the presence of secondary protease, reverse transcriptase, or cleavage site mutations was not independently associated with treatment failure. However, mutations at cleavage site p7/p1 (p = 0.01) and C-terminal p6* mutations (p = 0.02) were both associated with primary protease mutations. In conclusion, the presence of primary protease mutations was the most important predictor of the subsequent virological response. Moreover, there is some evidence that insertions in the proline-rich area of the p6(gag) protein may affect the virological response. The relationship between mutations of cleavage sites or C-terminal p6* residues and protease mutations suggests that these alterations may serve a compensatory role, increasing viral fitness.

Adult↗
PubMed2001

Impact of HIV type 1 drug resistance mutations and phenotypic resistance profile on virologic response to salvage therapy.

This study examines the association between presence of drug resistance mutations and phenotypic resistance at baseline to virologic response to salvage therapy in a community setting. The study population consisted of 58 antiretroviral drug-experienced patients with HIV-1 infection who had recently switched therapy because of virologic failure. Drug resistance mutations in the reverse transcriptase- and protease-coding regions and phenotypic susceptibility to 13 antiretroviral drugs were assessed at baseline. Plasma HIV-1 RNA levels were assessed at baseline and at subsequent clinic visits. Results showed that three variables were significant in predicting virologic response: HIV-1 levels at baseline, number of protease mutations, and phenotypic sensitivity score for the regimen at baseline. For four drugs there was a significant association between the presence of specific drug resistance mutations and >10-fold phenotypic resistance to that drug. With phenotypic resistance defined as >4-fold resistance, the association between specific drug resistance mutations and phenotypic resistance was significant for seven drugs. Overall, these data show that phenotypic susceptibility and absence of drug resistance mutations, particularly protease mutations, are significant predictors of virologic response. For several drugs, specific combinations of drug resistance mutations are associated with decreased phenotypic susceptibility and might provide useful clinical guidelines in selecting therapeutic options.

Adult↗
PubMed2002

Immunologic and virologic consequences of temporary antiretroviral treatment interruption in clinical practice.

To determine the long-term immunologic and virologic effects of antiretroviral treatment interruptions, a retrospective analysis of an ongoing observational database was performed at a university HIV clinic. All patients who began highly active antiretroviral therapy (HAART) after January 1, 1996 and (1) were HAART experienced for >/=90 days, (2) had a treatment interruption (TI) for >/=30 days, (3) resumed HAART for >/=30 days, and (4) had CD4(+) cell counts performed pre- and post-TI were included. Main outcome measures included the following: Immunologic success was defined as a post-TI CD4(+) cell count >90% of the pre-TI CD4(+) cell count (post-TI/pre-TI, >90%). Virologic success was defined as a post-TI viral load (VL) less or equal to twice the pre-TI VL (post-TI/pre-TI, </=2) or a post-TI VL of <1000 copies/ml. The pre-TI (baseline) value was the value at the start of the TI (range, -20 to +7 days); the post-TI value was the highest CD4(+) cell count and lowest VL copy achieved during the follow-up window (270 days). One thousand and eight patients were included in the analysis and 75 met the inclusion criteria. Forty-four of 75 patients (58.6%) achieved a successful immunologic outcome and 52 of 68 patients (76.5%; 7 patients did not have a VL determined within the specified periods) achieved a successful virologic outcome. No factors predicting success were identified. The median CD4(+) cell counts pre- and post-TI were 233 and 231 cells/microl, respectively; the median VLs pre- and post-TI were 11,456 and 404 copies/ml, respectively. We conclude that the majority of our patients in virologic failure who underwent a temporary TI recovered 90% of their baseline CD4(+) cell counts and returned to within 2-fold of their baseline VL when HAART was resumed.

Adult↗
PubMed2006

Efavirenz trough levels are not associated with virological failure throughout therapy with 800 mg daily and a rifampicin-containing antituberculosis regimen.

OBJECTIVES: To assess the safety and efficacy of efavirenz 800 mg daily in HIV-infected patients with tuberculosis receiving a rifampicin-containing regimen and to analyse whether a relationship exists between efavirenz Cmin and its virological efficacy. METHODS: Prospective, open-labelled study including HIV-infected patients on rifampicin and efavirenz 800 mg daily. Treatment adherence, adverse events (AEs), HIV-RNA levels, CD4 cell counts and efavirenz Cmin during and after finishing rifampicin treatment were evaluated. RESULTS: Eighty patients met the inclusion criteria. A permanent drug withdrawal due to AEs occurred in 10 patients, 5 attributable to efavirenz, and 10 patients were lost to follow-up before the third month. Efavirenz Cmin levels with 800 mg plus rifampicin were similar to those with 600 mg after withdrawing rifampicin. Sixty patients were included in the efficacy analysis, eight experiencing virological failure. No relation was observed between the rate of virological failure and efavirenz Cmin, previous antiretroviral treatment or not, baseline CD4 counts or RNA-HIV. The only variable related to virological failure was irregular adherence [odds ratio, 81 (95% CI: 5-1280); P=0.002]. CONCLUSIONS: Given the lack of a demonstrated relationship between efavirenz Cmin and its efficacy in our study, a firm recommendation cannot be made to always increase the dose to 800 mg/day when concomitantly given with rifampicin, but it seems a cautious approach to maintain the same efavirenz plasma levels as with 600 mg daily without rifampicin. Patients weighing<55 kg and also black, Asian and Hispanic subjects in whom genetic-based increased efavirenz plasma levels and rates of AEs have been observed may benefit from a dose of 600 mg.

Adult↗
PubMed2004

Clinical trial methodology and clinical cohorts: the importance of complete follow-up in trials evaluating the virological efficacy of anti-HIV medicines.

PURPOSE OF REVIEW: It has been common practice in randomized trials of HIV medicines to classify switches away from the original therapy as failures in analyses of virological effect, in line with an HIV-RNA measurement above a given level of quantification. This approach precludes the ability to identify the possible effects of a given therapy on those of a subsequent therapy. This review explores whether there have been changes in the reporting of randomized trials since the importance of continuous follow-up throughout the study period was initially raised 2 years ago. RECENT FINDINGS: Follow-up is still likely to be discontinued at a premature switch from study medication in a large number of the randomized trials published in 2002-2003. However, some studies, all initiated by investigators, did follow patients throughout the study period. In three of the studies, the proportions of patients with virological failure assessed with and without data after the premature discontinuation of randomized therapy could be elicited. Substantial differences were seen in the comparisons of two highly active antiretroviral therapy regimens according to the choice of analytical approach. In all three studies significant differences were observed between the regimens according to one approach, but not to the other. SUMMARY: The notation of treatment switch equals failure leads to an imprecise measurement of virological effect, and complete follow-up throughout the study period should be strongly encouraged, thus enabling several supplementary analyses of the virological effect of the treatment strategies being compared.

Anti-HIV Agents↗