Chemoprophylaxis with tenofovir disoproxil fumarate provided partial protection against infection with simian human immunodeficiency virus in macaques given multiple virus challenges

Direct stringency comparison of two macaque models (single-high vs. repeat-low) for mucosal HIV transmission using an identical anti-HIV chemoprophylaxis intervention

BACKGROUND

In our previous work, oral chemoprophylaxis with tenofovir disoproxil fumarate (TDF) provided partial protection in rhesus macaques against repeated low-dose (RL) intrarectal SHIV162p3 exposure.

METHODS

Here, we make a direct comparison of these previous findings with data generated using a single high (SH)-dose challenge strategy.

RESULTS

All 5 (100%) control macaques were infected after a SH challenge and only three of five (60%) TDF-treated macaques became infected. The remaining two TDF-treated macaques remained virus-negative and were susceptible to virus infection upon re-challenge in the absence of oral TDF. Thus, two of five (40%) TDF-treated macaques were protected by the pre-exposure chemoprophylaxis regimen. By comparison with the RL challenge system, only one of four (25%) of TDF-treated macaques were protected from infection, whereas four of four (100%) control macaques became infected using RL challenges.

CONCLUSION

Taken together, these findings indicate that the stringency of the RL challenge model for testing antiretroviral interventions is not lower and possibly greater than that of the SH challenge model.

Potential impact of antiretroviral chemoprophylaxis on HIV-1 transmission in resource-limited settings

Background

The potential impact of pre-exposure chemoprophylaxis (PrEP) on heterosexual transmission of HIV-1 infection in resource-limited settings is uncertain.

Methodology/Principle Findings

A deterministic mathematical model was used to simulate the effects of antiretroviral PrEP on an HIV-1 epidemic in sub-Saharan Africa under different scenarios (optimistic, neutral and pessimistic) both with and without sexual disinhibition. Sensitivity analyses were used to evaluate the effect of uncertainty in input parameters on model output and included calculation of partial rank correlations and standardized rank regressions. In the scenario without sexual disinhibition after PrEP initiation, key parameters influencing infections prevented were effectiveness of PrEP (partial rank correlation coefficient (PRCC) = 0.94), PrEP discontinuation rate (PRCC = −0.94), level of coverage (PRCC = 0.92), and time to achieve target coverage (PRCC = −0.82). In the scenario with sexual disinhibition, PrEP effectiveness and the extent of sexual disinhibition had the greatest impact on prevention. An optimistic scenario of PrEP with 90% effectiveness and 75% coverage of the general population predicted a 74% decline in cumulative HIV-1 infections after 10 years, and a 28.8% decline with PrEP targeted to the highest risk groups (16% of the population). Even with a 100% increase in at-risk behavior from sexual disinhibition, a beneficial effect (23.4%–62.7% decrease in infections) was seen with 90% effective PrEP across a broad range of coverage (25%–75%). Similar disinhibition led to a rise in infections with lower effectiveness of PrEP (≤50%).

Conclusions/Significance

Mathematical modeling supports the potential public health benefit of PrEP. Approximately 2.7 to 3.2 million new HIV-1 infections could be averted in southern sub-Saharan Africa over 10 years by targeting PrEP (having 90% effectiveness) to those at highest behavioral risk and by preventing sexual disinhibition. This benefit could be lost, however, by sexual disinhibition and by high PrEP discontinuation, especially with lower PrEP effectiveness (≤50%).

Antiretroviral drug exposure in the female genital tract: implications for oral pre- and post-exposure prophylaxis

OBJECTIVES

To describe first dose and steady state antiretroviral drug exposure in the female genital tract.

DESIGN

Non-blinded, single center, open-label pharmacokinetic study in HIV-infected women.

METHOD

Twenty-seven women initiating combination antiretroviral therapy underwent comprehensive blood plasma and cervicovaginal fluid sampling for drug concentrations during the first dose of antiretroviral therapy and at steady-state. Drug concentrations were measured by validated HPLC/UV or HPLC-MS/MS methods. Pharmacokinetic parameters were estimated for 11 drugs by non-compartmental analysis. Descriptive statistics and 95% confidence intervals were generated using Intercooled STATA Release 8.0 (Stata Corporation, College Station, Texas, USA).

RESULTS

For all antiretroviral drugs, genital tract concentrations were detected rapidly after the first dose. Drugs were stratified according to the genital tract concentrations achieved relative to blood plasma. Median rank order of highest to lowest genital tract concentrations relative to blood plasma at steady state were: lamivudine (concentrations achieved were 411% greater than blood plasma), emtricitabine (395%), zidovudine (235%) tenofovir (75%), ritonavir (26%), didanosine (21%), atazanavir (18%), lopinavir (8%), abacavir (8%), stavudine (5%), and efavirenz (0.4%).

CONCLUSIONS

This is the first study to comprehensively evaluate antiretroviral drug exposure in the female genital tract. These findings support the use of lamivudine, zidovudine, tenofovir and emtricitabine as excellent pre-exposure/post-exposure prophylaxis (PrEP/PEP) candidates. Atazanavir and lopinavir might be useful agents for these applications due to favorable therapeutic indices, despite lower genital tract concentrations. Agents such as stavudine, abacavir, and efavirenz that achieve genital tract exposures less than 10% of blood plasma are less attractive PrEP/PEP candidates.

Diagnosis and management of acute HIV infection

HIV infection starts as an acute, systemic infection, followed by a chronic period of clinical latency, usually lasting 3 to 10 years, which precedes the eventual collapse of the immune system. It is increasingly recognized that events occurring during acute HIV infection may determine the natural course of the disease. The very dynamic events of acute HIV infection provide multiple opportunities for biologic interventions, such as anti-retroviral or immune-based therapies. Similarly, the implementation of public health measures during acute HIV infection could help control epidemics or outbreaks. Many of the dramatic possibilities for intervention in acute HIV infection remain unproved, not the least because of traditional difficulty of diagnosing patients during this early period. This article reviews the natural history, pathogenesis and clinical presentation of acute HIV infection, and suggests a diagnostic and therapeutic approach to guide clinicians dealing with patients with suspected or confirmed acute HIV infection.

Tenofovir disoproxil fumarate for prevention of HIV infection in women: a phase 2, double-blind, randomized, placebo-controlled trial

OBJECTIVES

The objective of this trial was to investigate the safety and preliminary effectiveness of a daily dose of 300 mg of tenofovir disoproxil fumarate (TDF) versus placebo in preventing HIV infection in women.

DESIGN

This was a phase 2, randomized, double-blind, placebo-controlled trial.

SETTING

The study was conducted between June 2004 and March 2006 in Tema, Ghana; Douala, Cameroon; and Ibadan, Nigeria.

PARTICIPANTS

We enrolled 936 HIV-negative women at high risk of HIV infection into this study.

INTERVENTION

Participants were randomized 1:1 to once daily use of 300 mg of TDF or placebo.

OUTCOME MEASURES

The primary safety endpoints were grade 2 or higher serum creatinine elevations (>2.0 mg/dl) for renal function, grade 3 or 4 aspartate aminotransferase or alanine aminotransferase elevations (>170 U/l) for hepatic function, and grade 3 or 4 phosphorus abnormalities (<1.5 mg/dl). The effectiveness endpoint was infection with HIV-1 or HIV-2.

RESULTS

Study participants contributed 428 person-years of laboratory testing to the primary safety analysis. No significant differences emerged between treatment groups in clinical or laboratory safety outcomes. Study participants contributed 476 person-years of HIV testing to the primary effectiveness analysis, during which time eight seroconversions occurred. Two were diagnosed in participants randomized to TDF (0.86 per 100 person-years) and six in participants receiving placebo (2.48 per 100 person-years), yielding a rate ratio of 0.35 (95% confidence interval = 0.03-1.93), which did not achieve statistical significance. Owing to premature closures of the Cameroon and Nigeria study sites, the planned person-years of follow-up and study power could not be achieved.

CONCLUSION

Daily oral use of TDF in HIV-uninfected women was not associated with increased clinical or laboratory adverse events. Effectiveness could not be conclusively evaluated because of the small number of HIV infections observed during the study.

Postexposure prophylaxis after sexual exposure to HIV

Increasing numbers of international, national and state/provincial health organizations in the developed and developing world recommend postexposure prophylaxis (PEP) following potential sexual exposure to HIV. The evidence for these policies is extrapolated from occupational healthcare worker, perinatal prophylaxis and animal studies. There is no direct evidence of PEP efficacy after sexual exposures. Studies addressing potential increases in risk behavior, toxicities and cost–effectiveness are encouraging. Considerations for offering PEP include the timing and characteristics of the exposure and the HIV status of the source and exposed individuals. PEP includes 28 days of a combination antiretroviral drug regimen containing two or more drugs and associated laboratory testing, counseling and referrals. PEP service delivery challenges include ensuring adequate access to services, optimizing PEP adherence and facilitating follow-up HIV testing and counseling. Men who have sex with men, sexual assault survivors, children and adolescents, and individuals in resource-limited settings present unique needs and challenges.

Postexposure prophylaxis after sexual exposure to HIV

PURPOSE OF REVIEW

HIV postexposure prophylaxis is often recommended following potential sexual exposure to HIV. Recent data address the effectiveness of postexposure prophylaxis and prevention counseling, cost-effectiveness, antiretroviral options, challenges with nonoccupational postexposure prophylaxis among adolescents and children and following sexual assault in high HIV prevalence areas, and a successful program in Amsterdam.

RECENT FINDINGS

Postexposure prophylaxis is not completely protective. Seroconversion may result from antiretroviral failure or from ongoing exposures. Postexposure prophylaxis associated risk reduction counseling results in reductions in subsequent risk behavior. Programs that target outreach and limit prescriptions to those with exposure sources who are at risk of being HIV infected are cost-effective. Less restrictive guidelines result in more prescriptions for low-risk exposures; this practice is not cost-effective. The ideal antiretrovirals for postexposure prophylaxis use have not been established. Tenofovir has several attractive properties. Developing systems to support the effective delivery of postexposure prophylaxis among children and adolescents and following sexual assault in high HIV prevalence, resource limited settings is challenging.

SUMMARY

Numerous national and international guidelines recommend postexposure prophylaxis following potential sexual exposure to HIV. Maximizing adherence and minimizing subsequent HIV exposures will be critical to enhancing the effectiveness of this HIV prevention intervention.