Development of drug resistance in patients receiving combinations of zidovudine, didanosine and nevirapine

OBJECTIVE

To evaluate the development of phenotypic and genotypic resistance to zidovudine, didanosine and nevirapine as a function of the virologic response to therapy in a group of drug-naive individuals receiving various combinations of these agents.

DESIGN

All patients were enrolled in a double-blind controlled randomized trial (the INCAS study) and were selected for detailed resistance studies based on specimen availability and virologic response.

METHODS

Within the three study groups (zidovudine/nevirapine, zidovudine/didanosine or zidovudine/nevirapine/didanosine), 16, 19 and 24 patients, respectively, had evaluable baseline isolates and remained in the study > 24 weeks. Phenotypic resistance to all three drugs was evaluated using the VIRCO recombinant virus assay. Genotypic sequencing was done on selected specimens from patients receiving zidovudine/nevirapine/didanosine.

RESULTS

After 24 weeks, all available isolates taken from patients receiving nevirapine were resistant to this agent, while 18/21 (86%) patients receiving triple therapy carried such isolates at 30--60 weeks. At 24 weeks, zidovudine resistance developed in 4/40 isolates but was more frequent after 30--60 weeks, especially in patients on two drugs. The degree of zidovudine resistance (rise in concentration required for 50% inhibition) appeared lower in the triple therapy group compared with zidovudine/didanosine (P = 0.0004). All nevirapine-resistant isolates that were sequenced carried at least one mutation associated with resistance, most often K103N and/or Y181C.

CONCLUSION

The use of highly active drug therapies may be associated with a beneficial effect on the development of antiretroviral drug resistance. The characteristics of virologic suppression that must be maintained to avoid resistance are currently being studied in hypothesis-driven clinical trials.

The steady-state pharmacokinetics of efavirenz and nevirapine when used in combination in human immunodeficiency virus type 1-infected persons

The steady-state pharmacokinetics of efavirenz and nevirapine, when used in combination to treat human immunodeficiency virus type 1 (HIV-1)-infected subjects, were investigated. HIV-1-infected persons who had used efavirenz (600 mg once daily) for > or =2 weeks were eligible for study inclusion. The plasma pharmacokinetics of efavirenz were determined over 24 h. Subsequently, nevirapine (400 mg once daily) was added to the regimen. After 4 weeks, the pharmacokinetics of efavirenz and nevirapine were assessed over 24 h. The differences between the pharmacokinetic parameters of efavirenz with and without nevirapine were analyzed, and the pharmacokinetics of nevirapine were compared with those in historical control patients. The exposure to efavirenz when combined with nevirapine was significantly decreased by 22% (area under the plasma concentration vs. time curve), 36% (minimum plasma concentration), and 17% (maximum plasma concentration). Nevirapine pharmacokinetics appear to be unaffected by coadministration of efavirenz, compared with data from historical control patients.

High exposure to nevirapine in plasma is associated with an improved virological response in HIV-1-infected individuals

OBJECTIVE

To explore relationships between exposure to nevirapine and the virological response in HIV-1-infected individuals participating in the INCAS trial.

METHODS

The elimination rate constant of plasma HIV-1 RNA (k) was calculated during the first 2 weeks of treatment with nevirapine, zidovudine and didanosine in 51 antiretroviral-naive HIV-1-infected patients. The relationships between the value of k, the time to reach an undetectable HIV-1 RNA concentration in plasma (< 20 copies/ml) and the success of therapy after 52 weeks of treatment as dependent variables and the exposure to nevirapine, baseline HIV-1 RNA and baseline CD4 cell count as independent variables, were explored using linear regression analyses, proportional hazard models and logistic analyses, respectively.

RESULTS

The value of k for HIV-1 RNA in plasma was positively and significantly associated with the mean plasma nevirapine concentration during the first 2 weeks of therapy (P = 0.011) and the baseline HIV-1 RNA (P = 0.008). Patients with a higher exposure to nevirapine reached undetectable levels of HIV-1 RNA in plasma more rapidly (P = 0.03). From 12 weeks on, the median nevirapine plasma concentration was significantly correlated with success of therapy after 52 weeks (P < 0.02).

CONCLUSIONS

A high exposure to nevirapine (in a twice daily regimen) is significantly associated with improved virological response in the short as well as in the long term. These findings suggest that optimization of nevirapine concentration might be used as a tool to improve virological outcome in (antiretroviral-naive) patients treated with nevirapine.

Health related quality of life among persons with HIV after the use of protease inhibitors

OBJECTIVE

This study was conducted to determine the effect of the use of HIV protease inhibitors on the quality of life among persons infected with HIV.

METHODS

Subjects were participants in the British Columbia Centre for Excellence in HIV/AIDS Drug Treatment Program who had completed two annual participant surveys, one prior to initiating therapy with a protease inhibitor and one after. Quality of life was measured using the Medical Outcomes Study Short Form Health Survey (MOS-SF). Statistical analyses were conducted using parametric and multivariate methods.

RESULTS

Our analysis was based on 179 HIV-positive individuals. Compared to quality of life at baseline, we found no statistically significant changes in the health perception, pain, physical, role and social functioning MOS-SF subscale scores at follow-up. The measure of mental health was the only component to decline significantly over time. Subanalyses found significant increases in the measures of health perception (p = 0.004), physical (p = 0.037), role (p < 0.001) and social functioning (p = 0.053) for individuals with a low baseline quality of life. For those with a higher quality of life before starting a protease inhibitor containing regimen we observed a significant decline in the subscales of mental health (p = 0.001), physical (p = 0.007), role (p = 0.021) and social functioning (p = 0.003) over the study period.

CONCLUSIONS

Our findings indicate that despite strict dosage requirements and adverse side effects associated with protease inhibitor use patients are on the whole maintaining their quality of life after starting on a protease inhibitor containing regimen. Continued follow-up of this cohort will be required to determine the long term implications of these observations.

HIV protease and reverse transcriptase variation and therapy outcome in antiretroviral-naive individuals from a large North American cohort

OBJECTIVE

To assess the effect of baseline HIV reverse transcriptase (RT) and protease sequence variation on virologic outcomes in a large cohort of antiretroviral-naive patients in British Columbia, Canada.

METHODS

Population sequencing of RT and protease was performed on baseline viral RNA of all antiretroviral-naive patients first seeking treatment in British Columbia between June 1997 and August 1998 (n = 479). Relative risks of virological failure associated with genotypic differences from a 'standard' HIV strain (HXB2) were assessed for up to 18 months.

RESULTS

The prevalence of key baseline mutations known to confer resistance to RT and protease inhibitors (PI) was 3.4 and 3.8%, respectively. No statistically significant impact on virologic outcomes could be established for these patients. However, the data suggest that some individuals (harboring a M184V mutation in RT or a V82I in protease) may have benefited from pre-therapy resistance tests. 'Secondary' mutations in the protease associated with resistance (e.g. codons 10, 36 or 63) were common, but the presence of these secondary mutations, either alone or in combination, did not appear to result in early loss of therapeutic virological suppression. Preliminary analyses suggest that an amino acid change at codon 35 in the protease may be associated with early treatment failure.

CONCLUSIONS

The results suggest that routine genotyping of naive patients about to start antiretroviral therapy would be of benefit to a relatively small proportion of the population. Secondary mutations associated with resistance to PI alone were not found to affect virologic outcomes significantly.

[Current status of the treatment of HIV infection]

The antiretroviral therapeutic strategy changed in 1996, when the prognostic value of the plasma viral load and the CD4 cell counts were confirmed. Two nucleosides, plus a protease inhibitor or a non-nucleoside, are currently the initial preferred options. Viral resistance, and pharmacokinetic problems, however, have limited the efficacy of these schemes. It should be emphasized that continued use of triple drug therapy regimens have been associated with a decrease of morbidity and mortality associated to AIDS. We have analyzed the different drug combinations used in clinical trials and their results, the definition of therapeutic failure, and its consequences to control the treatment. With the currently available regimens, the virus cannot be totally eradicated from the organism and treatment should be continued for life. The combination of drugs in a single tablet, and the decrease in the number of daily intakes can help the patient with adherence, and allow for supervised treatment programs like the ones already applied with success in the treatment of tuberculosis. The use of virus resistance assays and pharmacokinetic assays will help to select the most appropriate treatment in the near future.

Multiple drug rescue therapy for HIV-infected individuals with prior virologic failure to multiple regimens

OBJECTIVES

To characterize the antiviral response and tolerability of a multi-drug rescue therapy (MDRT) among heavily pretreated patients.

METHODS

Observational study conducted in a single, university-based tertiary referral clinic. Patients (n = 106) who failed several prior regimens started MDRT including at least five antiretroviral (ARV) drugs between August 1997 and June 1998. The most common starting regimen included three nucleoside reverse transcriptase inhibitors and two protease inhibitors, which was prescribed to 45 (42.5%) patients. Virologic response was defined as plasma viral load < 400 copies/ml on at least two consecutive visits.

RESULTS

Median prior ARV exposure was seven drugs over a median time of 43 months. Fifty-nine percent of the patients were phenotypically (VIRCO Antivirogram) resistant at baseline to seven or more ARV. Median plasma viral load change following initiation of MDRT was -1.04 log10 copies/ml over a median of 15 months. Using intention-to-treat analysis 40% of patients had plasma viral load values < 400 copies/ml between weeks 47 and 57 of follow-up. Twenty-six patients (25%) experienced severe laboratory abnormalities or subjective adverse drug effects and six of these participants discontinued therapy.

CONCLUSION

MDRT induced a substantial antiviral response in this heavily pretreated group of patients despite extensive phenotypic resistance at baseline. Adverse effects were frequent but generally manageable. Our data suggest that relying exclusively on historical, clinical and laboratory evidence may not be sufficient to rule out a possible antiviral response when multiple drug regimens are used in this heavily pretreated patient population.

The cost effectiveness of antiretroviral regimens for the treatment of HIV/AIDS

OBJECTIVE

To estimate survival, the number of life-years gained and cost effectiveness of antiretroviral therapy (ART) regimens, denoted as ERA-I [zidovudine + (didanosine or zalcitabine)]; ERA-II [stavudine + (didanosine or zalcitabine) or lamivudine + (zidovudine or didanosine or zalcitabine or stavudine)]; and ERA-III [2 nucleoside reverse transcriptase inhibitors + (1 protease inhibitor or 1 non-nucleoside reverse transcriptase inhibitor)].

DESIGN

Modelling of drug cost, cost of opportunistic diseases and survival of HIV positive men and women in the province of British Columbia who were first prescribed any ART between October 1992 and June 1996. A 'reference cohort' was modelled upon individuals in a longitudinal cohort of homosexual men followed since 1982. PERSPECTIVE AND SETTING: Third-party payer perspective in British Columbia, Canada.

PATIENTS

All HIV-positive men and women aged > or =18 years with CD4+ counts < or =350 cells/microL who were enrolled in the province-wide drug treatment programme.

MAIN OUTCOME MEASURES

Annual costs, survival and cost-effectiveness ratios of successive ART regimens.

RESULTS

Total costs [1997 Canadian dollars ($Can)] at 12 months under ERA-I, -II and -III were $Can4897, $Can6620 and $Can 11 914, respectively. Survival at 12 months under ERA-I, -II and -III was 89.6%, 91.0% and 97.6%, respectively. The annual incremental cost (estimated by the total incremental cost at 12 months) between ERA-II and ERA-I was $Can1723. The incremental cost-effectiveness ratios between ERA-III and ERA-I, and between ERA-III and ERA-II were $Can58 806 and $Can46 971 per life-year gained, respectively.

CONCLUSION

We found the cost effectiveness of ERA-III ART regimens well within the range of currently funded therapies for the treatment of other chronic diseases.

Full suppression of viral load is needed to achieve an optimal CD4 cell count response among patients on triple drug antiretroviral therapy

OBJECTIVE

To characterize the relationship between plasma viral load (pVL) suppression and triple drug antiretroviral therapy, and the accompanying changes in CD4 cell counts.

METHOD

Retrospective study of 465 participants in a HIV/AIDS Treatment Program who initiated triple drug therapy between August 1996 and May 1998. Participants were divided into three groups according to their pVL response: (i) non-responders (NR; n = 112) exhibited pVL persistently > 500 copies/ml over the study period; (ii) partial responders (PR; n = 100) achieved a pVL < 100 copies/ml at least once and subsequently rebounded to > 500 copies/ml; and (iii) full responders (FR; n = 253) achieved a pVL < 500 copies/ml and sustained this level for the remainder of the study period. For each group, the accompanying changes in absolute and fractional CD4 cell counts were evaluated.

RESULTS

The median net change in pVL per person from baseline to the end of the observation period was -0.37, -2.27, and -2.56 log10 copies/ml for NR, PR and FR, respectively. During weeks 68-83, the median CD4 cell count (x 10(6) cells/l) was 150 [interquartile range (IQR) 90-370], 380 (IQR 300-480) and 525 (IQR 305-705) for NR, PR and FR, respectively. Median changes in CD4 cells (x 10(6) cells/l) were -20 (IQR -90 to 40), 150 (IQR 30-250) and 240 (IQR 110-365) for NR, PR, and FR, respectively. The net percentage change in CD4 cells per person was 0% (IQR -34-31), 54% (IQR 6-160), and 83% (IQR 39-173) for NR, PR, and FR, respectively. By weeks 68-83, the median fractional CD4 cells was 0.16 (IQR 0.07-0.22), 0.22 (IQR 0.15-0.28), and 0.26 (IQR 0.17-0.34) for NR, PR and FR respectively.

CONCLUSIONS

An optimal CD4 cell count response appears to be coupled with continued pVL suppression. Our data indicate that maximal suppression of viral replication should remain the primary goal of therapy.

The end of the line: has rapid transit contributed to the spatial diffusion of HIV in one of Canada's largest metropolitan areas?

The objective of this study is to describe the relationship between socio-demographic characteristics and the geographic distribution of persons with HIV in the metropolitan area surrounding Vancouver, British Columbia. Specifically, we sought to determine the location of persons with HIV and the population based characteristics related to the rate of anti-HIV medication use. In addition, we investigated the relationship between the distribution of persons on anti-HIV medications and the city's monorail "SkyTrain" route. The residences of persons on anti-HIV therapy were linked to Census Tracts. Data from the most recent census were used to create a socio-demographic profile of each geographic area. The spatial relationship between the distribution of persons on anti-HIV therapy and the path of the monorail was assessed by digitizing the SkyTrain route over a digital Census Tract map. Statistical analyses were used to determine the characteristics of Census Tracts associated with the rate of anti-HIV medication use. The overall rate of anti-HIV medication use in the Census Tracts that are within 1 km of SkyTrain was 66 per 100,000 population, whereas the rate was only 22 in the non-proximal Census Tracts. Multivariate analyses indicated that persons on anti-HIV therapy were significantly less likely to reside where there is a higher proportion of the population female, and were more likely to reside in areas with a higher proportion of the population of First Nations or Aboriginal descent, a higher population density, and in areas within 1 km of the SkyTrain route. Our analyses suggest that neither migration, nor a heightened access to therapy explain these findings. The environment surrounding the SkyTrain may have been conducive to the spatial diffusion of HIV, and could be the focus of targeted public health interventions. The mechanisms responsible for the clustering of persons on anti-HIV medications around the SkyTrain require further investigation.

Predicting HIV RNA virologic outcome at 52-weeks follow-up in antiretroviral clinical trials. The INCAS and AVANTI Study Groups

OBJECTIVE

To determine the ability of intermediate plasma viral load (pVL) measurements to predict virologic outcome at 52 weeks of follow-up in clinical trials of antiretroviral therapy.

METHODS

Individual patient data from three clinical trials (INCAS, AVANTI-2 and AVANTI-3) were combined into a single database. Virologic success was defined to be plasma viral load (pVL) <500 copies/ml at week 52. The sensitivity and specificity of intermediate pVL measurements below the limit of detection, 100, 500, 1000, and 5000 copies/ml to predict virologic success were calculated.

RESULTS

The sensitivity, specificity, and positive and negative predictive values of a pVL measurement <1000 copies/ml at week 16 to predict virologic outcome at week 52 were 74%, 74%, 48%, and 90%, respectively, for patients on double therapy. For patients on triple therapy, the sensitivity, specificity, and positive and negative predictive values of a pVL measurement <50 copies/ml at week 16 to predict virologic outcome were 68%, 68%, 80%, and 47%, respectively.

CONCLUSIONS

For patients receiving double therapy, a poor virologic result at an intermediate week of follow-up is a strong indicator of virologic failure at 52 weeks whereas intermediate virologic success is no guarantee of success at 1 year. For patients on triple therapy, disappointing intermediate results do not preclude virologic success at 1 year and intermediate successes are more likely to be sustained.

Clinical uses of non-nucleoside reverse transcriptase inhibitors

Three non-nucleoside reverse transcriptase inhibitors (NNRTIs) are currently available for treatment of HIV-1 as part of combination antiretroviral therapy. Oral dosing is administered three times daily for delavirdine (DLV), twice daily for nevirapine (NVP), and once daily for efavirenz (EFV). Rash is a common side effect of all three NNRTIs, and early CNS side effects are also frequent with EFV. Hepatotoxicity is relatively uncommon but requires appropriate monitoring. Drug interactions mediated by the cytochrome P450 system are an important consideration when the NNRTIs are administered concomitantly with other drugs, including protease inhibitors (PIs). HIV strains with reduced susceptibility to NNRTIs can occur with a single mutation in the reverse transcriptase (RT) gene. The available NNRTIs exhibit overlapping genotypic resistance patterns, but newer agents may overcome this problem. NNRTIs have been studied in combination with nucleoside RT inhibitors for first-line HIV therapy, where they have shown at least equivalent antiviral efficacy compared with PI-based regimens over 1-2 years of therapy. NVP and EFV have also been studied as a replacement for a PI within a virologically successful regimen, with the aim of preventing or reducing PI toxicities and simplifying the dosing regimen. Such 'switch' strategies are successful for certain patients in maintaining virologic suppression for 6 months or more and result in varying degrees of improvement in PI-associated toxicities. NNRTIs may offer a benefit when included in salvage regimens for patients failing PI-based therapy, particularly in patients who have not previously been treated with NNRTIs. NVP has been shown to have a substantial favourable impact on the rate of vertical HIV-1 transmission with a simple, cost-effective regimen.

Extent to which low-level use of antiretroviral treatment could curb the AIDS epidemic in sub-Saharan Africa

BACKGROUND

Despite growing international pressure to provide HIV-1 treatment to less-developed countries, potential demographic and epidemiological impacts have yet to be characterised. We modelled the future impact of antiretroviral use in South Africa from 2000 to 2005.

METHODS

We produced a population projection model that assumed zero antiretroviral use to estimate the future demographic impacts of the HIV-1 epidemic. We also constructed four antiretroviral-adjusted scenarios to estimate the potential effect of antiretroviral use. We modelled total drug cost, cost per life-year gained, and the proportion of per-person health-care expenditure required to finance antiretroviral treatment in each scenario.

FINDINGS

With no antiretroviral use between 2000 and 2005, there will be about 276,000 cumulative HIV-1-positive births, 2,302,000 cumulative new AIDS cases, and the life expectancy at birth will be 46.6 years by 2005. By contrast, 110,000 HIV-1-positive births could be prevented by short-course antiretroviral prophylaxis, as well as a decline of up to 1 year of life expectancy. The direct drug costs of universal coverage for this intervention would be US$54 million--less than 0.001% of the per-person health-care expenditure. In comparison, triple-combination treatment for 25% of the HIV-1-positive population could prevent a 3.1-year decline in life expectancy and more than 430,000 incident AIDS cases. The drug costs of this intervention would, however, be more than $19 billion at present prices, and would require 12.5% of the country's per-person health-care expenditure.

INTERPRETATION

Although there are barriers to widespread HIV-1 treatment, limited use of antiretrovirals could have an immediate and substantial impact on South Africa's AIDS epidemic.

Antiretroviral medication use among injection drug users: two potential futures

OBJECTIVE

To model the potential impact of HIV infection rates and the use of antiretroviral medication on life expectancy and mortality in the Downtown Eastside of Vancouver, British Columbia, Canada, from 1999 to 2006.

DESIGN

Population projections were made to estimate the population of the Downtown Eastside in the year 2006.

METHODS

Two scenarios were modelled to predict the impact of HIV infection and antiretroviral use on mortality and life expectancy. The use of antiretroviral therapy was estimated to be 80% in the first scenario and 20% in the second. The prevalence of HIV by age and sex, and by year infected was estimated using data from the Vancouver Injection Drug User Study.

RESULTS

If the level of antiretroviral therapy use among HIV-positive individuals was 80% at baseline, then we estimate that the life expectancy at birth in the year 2006 will be 60.8 years for men and 72.8 years for women, and 172 AIDS deaths will occur between 1999 and 2006. In contrast, if the present level of antiretroviral medication use persists, the life expectancy at birth in the year 2006 will be 56.9 years for men and 68.6 years for women, and 503 AIDS deaths will occur between 1999 and 2006.

CONCLUSION

Our analysis suggests that if the low levels of antiretroviral therapy use persist, life expectancy in Vancouver's Downtown Eastside will soon be on a par with many of the world's least developed countries. Our findings highlight the large health status decline that can be expected in many inner city neighbourhoods if low levels of antiretroviral use persist. Although reasonable coverage targets for injection drug users (IDU) have not been established, the expanded use of antiretroviral medication is urgently needed to avert a drastic decline in health status.

Role of hydroxyurea in treatment of disease due to human immunodeficiency virus infection

The potential role of hydroxyurea in the treatment of human immunodeficiency virus (HIV) infection was first supported by in vitro experiments that demonstrated control of viral production in activated and resting T cells. More recently, controlled clinical trials demonstrated that the addition of hydroxyurea to nucleoside-including regimens (chiefly of didanosine but also of stavudine and lamivudine) enhances their antiviral potency. It is believed that the cytostatic effect of hydroxyurea is at least partially responsible for its antiviral effect, through the down-modulation of cellular proliferation. Such an effect has also been credited for the blunted CD4 T cell responses that are characteristically observed when hydroxyurea is added to nucleoside-including regimens. The adjunctive antiviral effect of hydroxyurea-as well as its favorable dosing schedule, safety profile, and cost-makes it a very attractive addition to our therapeutic armamentarium. Further research is urgently needed to delineate the most appropriate use of this compound in the setting of HIV antiretroviral therapy.

Depressive symptoms decline among persons on HIV protease inhibitors

OBJECTIVE

To ascertain whether initiation of protease inhibitors was associated with a change in depressive symptoms among persons infected with HIV.

METHODS

Study subjects included men and women who were enrolled in the HIV/AIDS Drug Treatment Program and who had completed an annual participant survey before and after initiating triple combination therapy with a protease inhibitor. Depressive symptoms were assessed using the Centre for Epidemiologic Studies-Depression scale (CES-D). Statistical analyses to determine the change in CES-D total and subscale scores before and after protease inhibitor use were conducted using parametric and multivariate methods.

RESULTS

Our analysis was restricted to 453 participants. Of these 234 (52%) were depressed at baseline (CES-D score > or = 16). Compared with nondepressed participants, depressed participants were slightly younger (p = .048), less likely to be employed (p < .001) and more likely to have an annual income less than $10,000 per annum (p < .001). After adjusting for CD4 count, employment status, income, age, and CES-D total or subscale score at baseline, we found a significant improvement in total scale score (p = .001) and depressive mood (p = .002), positive affects (p = .005), and somatic symptoms (p = .011) subscale scores at follow-up. There was no significant change in the interpersonal relations score over the study period.

CONCLUSION

Our findings indicate that in addition to conferring impressive clinical benefits, protease inhibitor use is associated with a significant improvement in HIV-positive individuals' mental health.

Determinants of hospital admission among HIV-positive people in British Columbia

BACKGROUND

This study was initiated to evaluate the demographic and clinical determinants of admission to hospital among HIV-positive men and women receiving antiretroviral therapy in British Columbia.

METHODS

The analysis was restricted to participants enrolled in the HIV/AIDS Drug Treatment Program between September 1992 and March 1997 who had completed an annual participant survey, had a viral load determination and had signed a consent form allowing electronic access to their inpatient hospital records. A record linkage was conducted with the BC Ministry of Health to obtain all records of hospital admissions from April 1991 to March 1997. Statistical analyses were carried out using parametric and nonparametric methods and multivariate logistic analyses.

RESULTS

The study sample comprised 947 participants (859 men, 88 women). Of these, 165 (17%) were admitted to hospital during the study period from May 1, 1996, to Mar. 31, 1997. The median number of admissions was 1 (interquartile range [IQR] 1-2 admissions), and the median length of stay per admission was 3 days (IQR 1-8 days). Admission to hospital was associated with being unemployed (82% of those admitted v. 58% of those not admitted), being an injection drug user (24% v. 17%), reporting a fair or poor health status (46% v. 29%) and having a physician experienced in the management of HIV/AIDS (31% v. 24%). Examination of clinical determinants demonstrated that hospital admission was associated with a previous admission (72% v. 46%), a high viral load (median 74,000 v. 14,000 HIV-1 RNA copies/mL), a low CD4 count (median 0.16 v. 0.27 x 10(9)/L) and an AIDS diagnosis (44% v. 24%). Multivariate logistic regression analysis revealed that being admitted to hospital was independently associated with being unemployed (odds ratio [OR] 2.64, 95% confidence interval [CI] 1.66-4.20), having been previously admitted to hospital (OR 2.30, 95% CI 1.53-3.46), having a high viral load at baseline (OR 1.45, 95% CI 1.16-1.80), being an injection drug user (OR 1.63, 95% CI 1.02-2.62) and having an experienced physician (OR 1.98, 95% CI 1.29-3.03).

INTERPRETATION

Hospital admission among participants in this study was found to be associated with marginalization and poor health status.

Diminished HIV-1 sensitivity to stavudine in patients on prolonged therapy occurs only at low levels and cannot be attributed to any single amino acid substitution in reverse transcriptase

To study the extent to which phenotypic resistance to stavudine occurs under therapy, we studied 18 pairs of human immunodeficiency virus type 1 (HIV-1) isolates from patients both prior to and following 24-48 weeks of treatment with stavudine monotherapy or stavudine in combination with either didanosine or lamivudine. We also used a nested polymerase chain reaction (PCR) assay to probe for the presence of specific mutations associated in culture with stavudine resistance. The results showed that resistance to stavudine (approximately 3-10 fold) was observed in nine of ten cases of monotherapy, in three of four cases of therapy involving both stavudine and didanosine, and in two of four cases involving stavudine and lamivudine. Viruses from the four patients receiving stavudine plus didanosine became resistant to didanosine in only one instance while the use of lamivudine plus stavudine yielded resistance to lamivudine each time. Whereas changes in the reverse transcriptase (RT) genes of resistant isolates were frequently observed, two mutations, previously identified with stavudine resistance in tissue culture (i.e., V75T and I50T), could not be identified in the clinical samples by either direct sequencing of the RT gene or by PCR amplification. Thus, resistance to stavudine can occur, albeit at low levels, in the context of prolonged therapy with this drug but is not associated with specific mutations in HIV RT at either codons 75 or 50 in clinical samples.

Determinants of geographic mobility among participants in a population-based HIV/AIDS drug treatment program

This study was undertaken to determine the geographic distribution and patterns of migration of persons with HIV in British Columbia. Our analysis was restricted to all HIV-positive men and women aged 18 years and over who had completed a participant survey and were enrolled in the HIV/AIDS Drug Treatment Program between September 1992 and September 1997. Patterns of migration were determined by examining participants whose postal code changed between July 1995 and September 1997. Statistical analysis were carried out using both parametric and non-parametric methodologies. Stepwise logistic regression was used to determine baseline predictors of migration. The final multivariate model revealed that residing in a census subdivision with a population less than 100,000, being heterosexual, acquiring HIV through intravenous drug use, and the absence of AIDS at baseline were all independently associated with moving census subdivisions during the period of observation. In summary, our analyses demonstrate the need for the continued study of the evolving geography and migration patterns of persons with HIV.