JJ, Bosch RJ, Rosenkranz SL, Cramer YS, Ussery M, Flexner C. Effect of hydroxyurea and dideoxyinosine on intracellular 3'-deoxyadenosine-5'-triphosphate concentrations in HIV-infected patients

Hydroxyurea (HU) significantly enhances the antiretroviral effects of the adenosine analog reverse transcriptase inhibitor dideoxyinosine (ddI). This is believed to be due to a reduction in intracellular de-oxyadenosine triphosphate (dATP) concentrations resulting from HU-mediated inhibition of ribonucleotide reductase (RnR). The effect of combined HU-ddI treatment on intracellular dATP pools in vivo has not been examined. We measured intracellular dATP concentrations in peripheral blood mononuclear cells (PBMCs) from 69 HIV-infected patients receiving 1000 or 1500 mg HU daily for 14 days, 200 mg ddI twice daily for 14 days, or a combination of the two drugs. Median intracellular dATP concentrations decreased from base-line to day 14 by 46% in the ddI + 1000 mg HU arm and by 62% in the ddI + 1500 mg HU arm. When compared to the HU monotherapy arms, these changes proved statistically significant (p = 0.018; stratified Wilcoxon rank-sum test). These findings support reduced intracellular dATP as the mechanism of ddI-HU synergistic activity, and indicate that changes in intracellular nucleotides contribute to HU activity and toxicity in patients. Since a significant reduction in dATP was measurable only when ddI was combined with HU, the antiretroviral activity of ddI may be more complex than previously assumed.

Amprenavir and Lopinavir Pharmacokinetics following Coadministration of Amprenavir or Fosamprenavir with Lopinavir/Ritonavir, with or without Efavirenz

Background

Amprenavir (APV), fosamprenavir (FPV), lopinavir (LPV), ritonavir (RTV) and efavirenz (EFV) are to varying degrees substrates, inducers and inhibitors of CYP3A4. Coadministration of these drugs might result in complex pharmacokinetic drug-drug interactions.

Methods

Two prospective, open-label, non-randomized studies evaluated APV and LPV steady-state pharmacokinetics in HIV-infected patients on APV 750 mg twice daily + LPV/RTV 533/133 mg twice daily with EFV ( n=7) or without EFV ( n=12) + background nucleosides (Study 1) and after switching FPV 1,400 mg twice daily for APV ( n=10) (Study 2).

Results

In Study 1 EFV and non-EFV groups did not differ in APV minimum plasma concentration (Cmin; 1.10 versus 1.06μg/ml, P=0.89), area under the concentration-time curve (AUC; 17.46 versus 24.34μg•h/ml, P=0.22) or maximum concentration (Cmax; 2.61 versus 4.33 μg/ml, P=0.08); for LPV there was no difference in Cmin (median: 3.66 versus 6.18μg/ml, P=0.20), AUC (81.84 versus 93.75 μg•h/ml, P=0.37) or Cmax (10.36 versus 10.93 μg/ml, P=0.61). In Study 2, after switching from APV to FPV, APV Cmin increased by 58% (0.83 versus 1.30 μg/ml, P=0.0001), AUC by 76% (19.41 versus 34.24 μg•h/ml, P=0.0001), and Cmax by 75% (3.50 versus 6.14, P=0.001). Compared with historical controls, LPV and RTV pharmacokinetics were not changed. All treatment regimens were well tolerated. Seven of eight completers (88%) maintained HIV-1 RNA <400 copies/ml 12 weeks after the switch (1 lost to follow up).

Conclusions

EFV did not appear to significantly alter APV and LPV pharmacokinetic parameters in HIV-infected patients taking APV 750 mg twice daily + LPV 533/133 mg twice daily. Switching FPV 1,400 mg twice daily for APV 750 mg twice daily resulted in an increase in APV Cmin, AUC, and Cmax without changing LPV or RTV pharmacokinetics or overall tolerability.

Phase 2 Study of the Safety and Efficacy of Vicriviroc, a CCR5 Inhibitor, in HIV‐1–Infected, Treatment‐Experienced Patients: AIDS Clinical Trials Group 5211

BACKGROUND

Vicriviroc, an investigational CCR5 inhibitor, demonstrated short-term antiretroviral activity in a phase 1 study.

METHODS

The present study was a double-blind, randomized phase 2 study of vicriviroc in treatment-experienced, human immunodeficiency virus (HIV)-infected subjects experiencing virologic failure while receiving a ritonavir-containing regimen with an HIV-1 RNA level >or=5000 copies/mL and CCR5-using virus. Vicriviroc at 5, 10, or 15 mg or placebo was added to the failing regimen for 14 days, after which the antiretroviral regimen was optimized. The primary end point was the change in plasma HIV-1 RNA levels at day 14; secondary end points included safety/tolerability and HIV-1 RNA changes at week 24.

RESULTS

One hundred eighteen subjects were randomized with a median HIV-1 RNA level of 36,380 (4.56 log(10)) copies/mL and a median CD4 cell count of 146 cells/mm(3). At 14 days and 24 weeks, mean changes in HIV-1 RNA level (log(10) copies/mL) were greater in the vicriviroc groups (-0.87 and -1.51 [5 mg], -1.15 and -1.86 [10 mg], and -0.92 and -1.68 [15 mg]) than in the placebo group (+0.06 and -0.29) (P<.01). Grade 3/4 adverse events were similar across groups. Malignancies occurred in 6 subjects randomized to vicriviroc and in 2 to placebo.

CONCLUSIONS

In HIV-1-infected, treatment-experienced patients, vicriviroc demonstrated potent virologic suppression through 24 weeks. The relationship of vicriviroc to malignancy is uncertain. Further development of vicriviroc in treatment-experienced patients is warranted.

Beneficial Pharmacokinetic Interaction Between Atazanavir and Lopinavir/Ritonavir

BACKGROUND

The combination of lopinavir/ritonavir (LPV/r) and atazanavir (ATV) with nucleoside reverse transcriptase inhibitors has been used as a salvage regimen in HIV-infected patients. Because these agents, to various degrees, are substrates, inducers, and inhibitors of CYP450 3A4, there is concern for alterations in the pharmacokinetics (PK) of these combined agents.

OBJECTIVE

To determine the steady-state PK interactions between ATV, ritonavir (RTV), and LPV when coadministered at various doses.

METHODS

HIV-negative subjects (n = 15) received a combination of ATV, RTV, and LPV in the following sequence: period I (days 1-10), ATV/r at a dose of 300/100 mg once daily; period II (days 11-24), ATV at a dose of 300 mg once daily plus LPV/r at a dose of 400/100 mg twice daily; and period III (days 25-34), ATV/r at a dose of 300/100 mg once daily plus LPV/r at a dose of 400/100 mg twice daily. Intensive PK analysis was performed on days 10, 24, and 34. A paired t test was used for pairwise comparison of log-transformed PK parameters of ATV and LPV.

RESULTS

In period II, the ATV minimum concentration (Cmin) geometric mean (GM) was higher compared with period I (GM: 0.75 vs. 0.51 microg/mL, geometric mean ratio (GMR) = 1.45, 90% confidence interval [CI]: 1.19 to 1.77; P = 0.006). The ATV area under the concentration-time curve from dosing to 24 hours after the dose (AUC0-24; GM: 36.40 vs. 39.62 microg.h/mL, GMR = 0.92, 90% CI: 0.80 to 1.05; P = 0.28) did not differ, however. The addition of 100 mg of RTV in period III did not significantly increase the ATV Cmin (GM: 0.84 vs. 0.75 microg/mL, GMR = 1.13, 90% CI: 0.91 to 1.40; P = 0.34) or ATV AUC0-24 (GM: 39.59 vs. 36.40 microg.h/mL, GMR = 1.09, 90% CI: 0.99 to 1.20; P = 0.14) compared with period II. The additional RTV in period III resulted in a higher LPV Cmin (GM: 5.12 vs. 3.99 microg/mL, GMR = 1.28, 90% CI: 1.15 to 1.43; P = 0.001), but the LPV areas under the concentration-time curve from dosing to 12 hours after the dose and maximum concentration were not significantly different. LPV PK parameters in period II were comparable to those of historical control subjects receiving LPV/r at a dose of 400/100 mg twice daily. All studied regimens were well tolerated. Indirect hyperbilirubinemia was the only grade 3 and 4 abnormality reported, which was expected given that ATV competitively inhibits UGTIA1 and has not been shown to result in other hepatic abnormalities.

CONCLUSIONS

The combination of ATV at a dose of 300 mg once daily plus LPV/r at a dose of 400/100 mg twice daily resulted in an appropriate PK profile for ATV and LPV and could be further evaluated in treatment-experienced patients requiring a dual-boosted protease inhibitor-containing regimen.

Multiple-dose escalation study of the safety, pharmacokinetics, and biologic activity of oral AMD070, a selective CXCR4 receptor inhibitor, in human subjects

AMD070 is an oral CXCR4 antagonist with in vitro activity against X4-tropic human immunodeficiency virus type 1. Thirty fasting healthy male volunteers received oral doses of AMD070 ranging from a single 50-mg dose to seven 400-mg doses given every 12 h (q12h). Nine subjects received a 200-mg dose during fasting and prior to a meal. Subjects were monitored for safety and pharmacokinetics. AMD070 was well tolerated, without serious adverse events. Transient headaches (13 subjects) and neurocognitive (8 subjects) and gastrointestinal (7 subjects) symptoms were the most common complaints. Seven subjects had sinus tachycardia, and two were symptomatic. AMD070 plasma concentrations peaked 1 to 2 h after patient dosing. The estimated terminal half-life ranged from 11.2 to 15.9 h among cohorts. Dose proportionality was not demonstrated. Less than 1% of the drug appeared unchanged in the urine. Food reduced the maximum concentration of drug in serum and the area under the concentration-time curve from 0 to 24 h by 70% and 56%, respectively (P < or = 0.01). A dose-dependent elevation of white blood cells (WBC) demonstrated a maximum twofold increase over baseline (95% confidence interval, 2.0- to 2.1-fold) in an E(max) model. In healthy volunteers, AMD070 was well tolerated and demonstrated mixed-order pharmacokinetics, and food reduced drug exposure. AMD070 induced a dose-related elevation of WBC which was attributed to CXCR4 blockade. Using leukocytosis as a surrogate marker for CXCR4 inhibition, this dose-response relationship suggests that the doses used in this study were active in vivo, though not maximal, throughout the dosing interval. Trough concentrations with the 400-mg dose q12h exceeded the antiviral in vitro 90% effective concentration of AMD070.

Balancing justice and autonomy in clinical research with healthy volunteers

In clinical research, ethics review generally first examines whether study risks are reasonable in light of benefits provided. Through informed consent, then, prospective subjects consider whether the risk/benefit balance and procedures are reasonable for them. Unique ethics issues emerge in clinical research with healthy volunteers. Certain types of studies only recruit healthy volunteers as participants. Phase 1 studies, for example, including first time in human studies of investigational drugs and vaccines, generally are conducted in healthy volunteers. Although such research carries inherent and often unknown risks, healthy subjects provide the most efficient target population in which to conduct such research, as these volunteers generally are free of concurrent diseases or medications that could confound interpretation of toxicity. Other studies enrolling healthy volunteers often are simply looking for the most scientifically sound population for the study of normal human physiology.

HIV type 1 chemokine coreceptor use among antiretroviral-experienced patients screened for a clinical trial of a CCR5 inhibitor: AIDS Clinical Trial Group A5211

BACKGROUND

Chemokine coreceptor use impacts both the natural history of human immunodeficiency virus type 1 (HIV-1) disease and the potential use of a new class of antiretroviral agents, the CCR5 inhibitors.

METHODS

We analyzed HIV-infected patients who were screened for participation in Acquired Immunodeficiency Syndrome (AIDS) Clinical Trial Group protocol A5211, a phase 2b study of the investigational CCR5 inhibitor vicriviroc involving antiretroviral-experienced subjects. Screening CD4(+) cell count, HIV-1 plasma RNA level, HIV-1 genotype, and chemokine coreceptor use phenotype were determined. The univariate and multivariate association of subject characteristics with coreceptor use was assessed by logistic regression.

RESULTS

Coreceptor use was determined for 391 subjects: 197 (50%) had virus that used the CCR5 coreceptor (the R5 group), 178 [corrected] (46%) had dual-tropic or mixed HIV-1 populations that used both CCR5 and CXCR4 coreceptors (the D/M group), and 16 (4%) had virus that used the CXCR4 coreceptor (the X4 group). The D/M group had a significantly lower median CD4(+) cell count than the R5 virus group (103 cells/ micro L vs. 170 cells/ mu L; P<.001). No other characteristics were independently associated. Among 118 subjects who entered A5211 having R5 virus, 12 (10%) had D/M virus according to the results of a second coreceptor test conducted prior to starting treatment with the study drug.

CONCLUSIONS

Infection with dual-tropic or mixed HIV-1 populations that use both CCR5 and CXCR4 is common among highly treatment-experienced patients, but infection with virus using CXCR4 alone is uncommon. Subjects in the D/M group had significantly lower CD4(+) cell counts than subjects in the R5 group. Evaluating coreceptor use will be important in the clinical development of CCR5 and CXCR4 inhibitors.

Amprenavir and lopinavir pharmacokinetics following coadministration of amprenavir or fosamprenavir with lopinavir/ritonavir, with or without efavirenz

BACKGROUND

Amprenavir (APV), fosamprenavir (FPV), lopinavir (LPV), ritonavir (RTV) and efavirenz (EFV) are to varying degrees substrates, inducers and inhibitors of CYP3A4. Coadministration of these drugs might result in complex pharmacokinetic drug-drug interactions.

METHODS

Two prospective, open-label, non-randomized studies evaluated APV and LPV steady-state pharmacokinetics in HIV-infected patients on APV 750 mg twice daily + LPV/RTV 533/133 mg twice daily with EFV (n=7) or without EFV (n=12) + background nucleosides (Study 1) and after switching FPV 1,400 mg twice daily for APV (n=10) (Study 2).

RESULTS

In Study 1 EFV and non-EFV groups did not differ in APV minimum plasma concentration (Cmin; 1.10 versus 1.06 microg/ml, P = 0.89), area under the concentration-time curve (AUC; 17.46 versus 24.34 microg x h/ml, P = 0.22) or maximum concentration (Cmax; 2.61 versus 4.33 microg/ml, P = 0.08); for LPV there was no difference in Cmin, (median: 3.66 versus 6.18 microg/ml, P = 0.20), AUC (81.84 versus 93.75 microg x h/ml, P = 0.37) or Cmax (10.36 versus 10.93 microg/ml, P = 0.61). In Study 2, after switching from APV to FPV, APV Cmin increased by 58% (0.83 versus 1.30 microg/ml, P = 0.0001), AUC by 76% (19.41 versus 34.24 micorg x h/ml, P = 0.0001), and Cmax by 75% (3.50 versus 6.14, P = 0.001). Compared with historical controls, LPV and RTV pharmacokinetics were not changed. All treatment regimens were well tolerated. Seven of eight completers (88%) maintained HIV-1 RNA <400 copies/ml 12 weeks after the switch (1 lost to follow up).

CONCLUSIONS

EFV did not appear to significantly alter APV and LPV pharmacokinetic parameters in HIV-infected patients taking APV 750 mg twice daily + LPV 533/133 mg twice daily. Switching FPV 1400 mg twice daily for APV 750 mg twice daily resulted in an increase in APV Cmin, AUC, and Cmax without changing LPV or RTV pharmacokinetics or overall tolerability.

HIV/AIDS: Interactions between Natural Health Products and Antiretroviral Drugs: Pharmacokinetic and Pharmacodynamic Effects

Concurrent use of natural health products (NHPs) with antiretroviral drugs (ARVs) is widespread among human immunodeficiency virus-infected patients. This article reviews the clinical pharmacokinetic and pharmacodynamic interactions between NHPs and ARVs. Many NHPs are complex mixtures and are likely to contain organic compounds that may induce and/or inhibit drug metabolizing enzymes and drug transporters. Although the weight of evidence for the effects of certain NHPs varies and many studies of these products lack scientific rigor, it has been observed that St. John's wort clearly induces cytochrome P450 3A4 and P-glycoprotein and reduces protease inhibitor and nonnucleoside reverse-transcriptase inhibitor concentrations, thereby increasing the likelihood of therapeutic failure. Limited clinical research suggests that intake of garlic and vitamin C results in reductions in ARV concentrations. The intake of milk thistle, Echinacea species, and goldenseal inhibits cytochrome P450 enzymes in vitro and may increase ARV concentrations, but by clinically unimportant amounts. Intake of fish oil reduces ARV-induced hypertriglyceridemia without significantly affecting lopinavir concentrations. Before recommending the use of NHPs as adjuncts to ARV use, studies should first exclude significant pharmacokinetic interactions and ensure that ARV efficacy is maintained.

Psychological distress and physical pain appear to have no short-term adverse impact on plasma HIV-1 RNA levels in patients on successful HAART

PURPOSE

Previous studies have linked depression and stressful life events in HIV disease with a more rapid decline in CD4 count and progression to AIDS. However, the short-term effect of psychological and physical distress on HIV-1 RNA levels in patients on successful HAART has not been well studied.

METHOD

Ten asymptomatic HIV-infected adults with suppression of viremia to <50 copies/mL on a stable HAART regimen for > or =6 months were studied. Participants donated blood every 2-3 days over a 3-4 month period for duplicate independent viral load measurements and drug level monitoring. At each time point, psychological distress was measured using the Mental Health Inventory-5 (MHI-5) and an 11-point numeric rating scale for emotional stress. Physical pain was assessed using an 11-point numeric rating scale.

RESULTS

All patients maintained successful viral suppression throughout the study. Twenty-six of 713 (3.6%) viral load measurements were >50 copies/mL. Psychological distress and physical pain were not associated with episodes of detectable viremia.

CONCLUSION

Using frequent monitoring of HIV-1 RNA levels and patient ratings of mood, stress, and pain, we found that psychological distress and physical pain had no short-term adverse impact on HIV-1 RNA levels in highly adherent patients with stable suppression of viremia on HAART.

Marked Intraindividual Variability in Antiretroviral Concentrations May Limit the Utility of Therapeutic Drug Monitoring

BACKGROUND

Effective therapeutic drug monitoring for antiretrovirals requires a better understanding of intraindividual variability in pharmacokinetics.

METHODS

We determined concentrations of human immunodeficiency virus (HIV) protease and nonnucleoside reverse-transcriptase inhibitors for 10 patients with undetectable plasma HIV RNA levels who had been receiving stable regimens for > or = 11 months. Plasma samples were collected at the same time of day 3 times per week for up to 4 months. Patients were instructed to take their antiretrovirals at the same time every day. Plasma protease and nonnucleoside reverse-transcriptase inhibitor concentrations were determined using high-performance liquid chromatographic methods. Pharmacokinetic variability was expressed as intraindividual percentage coefficient of variation (ICV), which was calculated as the patient's standard deviation divided by the mean drug concentration for that patient.

RESULTS

ICV was determined for 6 drugs for 10 patients, for a total of 17 different patient-drug combinations, using 600 total samples. ICV was unexpectedly high for most patients who were receiving protease inhibitors (ICVs for individual patients taking lopinavir/ritonavir were 24%, 33%, 51%, and 92%; for patients taking nelfinavir/M8 metabolite, they were 30%/44% and 39%/54%; for patients taking ritonavir, they were 34% and 43%; for patients taking saquinavir, they were 52% and 55%). ICVs for patients receiving nonnucleoside reverse-transcriptase inhibitors were lower (for patients receiving efavirenz, they were 7%, 13%, 29%, and 51%; for a patient receiving nevirapine, it was 25%). The median ICV for all patients receiving protease inhibitors (n = 12) was 43.5%, and for all patients receiving nonnucleoside reverse-transcriptase inhibitors (n = 5), the median ICV was 25%.

CONCLUSIONS

Intraindividual variability in concentrations of antiretrovirals was surprisingly high in virologically suppressed patients. Possible contributors include food effects, concomitant use of prescription and herbal medications, assay variability, or medication timing, which was assessed by self-report. High intraindividual pharmacokinetic variability may limit the utility of single measurements in therapeutic drug monitoring for some antiretroviral agents.

Therapeutic Drug Monitoring and Drug–Drug Interactions Involving Antiretroviral Drugs

The consensus of current international guidelines for the treatment of HIV infection is that data on therapeutic drug monitoring (TDM) of non-nucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors (PIs) provide a framework for the implementation of TDM in certain defined scenarios in clinical practice. However, the utility of TDM is considered to be on an individual basis until more data are obtained from large clinical trials showing the benefit of TDM.

In April 2004, a panel of experts met for the second time in Rome, Italy. This was following the inaugural meeting in Perugia, Italy, in October 2000, which resulted in the manuscript published in AIDS 2002, 16(Suppl 1):S5–S37. The objectives of this second meeting were to review and update the numerous questions surrounding TDM of antiretroviral drugs and discuss the clinical utility, current concerns and future prospects of drug concentration monitoring in the care of HIV-1-infected individuals. A major focus of the meeting was to discuss and critically analyse recent and precedent clinical drug–drug interaction data to provide a clear framework of the pharmacological basis of how one drug may impact the disposition of another.

This report, which has been updated to include material published or presented at international conferences up to the end of December 2004, reviews recent pivotal pharmacokinetic interaction data and provides advice to clinical care providers on how some drug–drug interactions may be prevented, avoided or managed, and, when data are available, on what dose adjustments and interventions should be performed.

Current Status and Future Prospects of Therapeutic Drug Monitoring and Applied Clinical Pharmacology in Antiretroviral Therapy

The consensus of current international guidelines for the treatment of HIV infection is that data on therapeutic drug monitoring (TDM) of non-nucleoside reverse transcriptase inhibitors and protease inhibitors provide a framework for the implementation of TDM in certain defined scenarios in clinical practice. However, the utility of TDM is considered to be on an individual basis until more data are obtained from large clinical trials showing the benefit of TDM.

In April 2004, a panel of experts met in Rome, Italy. This followed an inaugural meeting in Perugia, Italy, in October 2000, which resulted in the article published in AIDS 2002, 16(Suppl 1):S5–S37. The objectives of this second meeting were to review the questions surrounding TDM of antiretroviral drugs and discuss the clinical utility, current concerns and future prospects of drug concentration monitoring in the care of HIV-1-infected individuals.

This report, which has been updated to include material published or presented at international conferences up to the end of September 2004, reviews pharmacokinetic and pharmacodynamic data and reports the issues discussed by the panel, offering advice to clinical care providers who may be currently, or are considering incorporating TDM into the routine care of their patients. In addition, the panel formulated a series of position statements that are relevant to the interpretation of current data and can aid the design of future clinical trials.

Part 2 of this Special article, Therapeutic drug monitoring and drug–drug interactions involving antiretroviral drugs, will be published in Antiviral Therapy 10(4).

Intermittent HIV-1 viremia (Blips) and drug resistance in patients receiving HAART

CONTEXT

Many patients infected with human immunodeficiency virus type 1 (HIV-1) and receiving highly active antiretroviral therapy experience intermittent episodes of detectable viremia ("blips"), which may raise concerns about drug resistance, lead to costly repeat measurements of viral RNA, and sometimes trigger alterations in therapy.

OBJECTIVE

To test the hypothesis that blips represent random biological and statistical variation around mean steady-state HIV-1 RNA levels slightly below 50 copies/mL rather than biologically significant elevations in viremia.

DESIGN, SETTING, AND PATIENTS

Between June 19, 2003, and February 9, 2004, patients receiving therapy underwent intensive sampling (every 2-3 days) over 3 to 4 months to define the frequency, magnitude, and duration of blips and their association with drug levels and other clinical variables. Blips were defined as HIV-1 RNA measurements greater than or equal to 50 copies/mL preceded and followed by measurements less than 50 copies/mL without a change in treatment. To determine whether blips result from or lead to drug resistance, an ultrasensitive genotyping assay was used to detect drug resistance mutations before, during, and after blips. Patients were 10 HIV-1-infected asymptomatic adults recruited by clinicians and followed up in the Moore Clinic at the Johns Hopkins Hospital. Patients had suppression of viremia to below 50 copies/mL while receiving a stable antiretroviral regimen for 6 months or longer.

MAIN OUTCOME MEASURES

At each time point, plasma HIV-1 RNA levels were measured in 2 independent laboratories and drug resistance mutations were analyzed by clonal sequencing.

RESULTS

With the intensive sampling, blips were detected in 9 of 10 patients. Statistical analysis was consistent with random assay variation around a mean viral load below 50 copies/mL. Blips were not concordant on independent testing and had a short duration (median, <3 days) and low magnitude (median, 79 copies/mL). Blip frequency was not associated with demographic, clinical, or treatment variables. Blips did not occur in relation to illness, vaccination, or directly measured antiretroviral drug concentrations. Blips were marginally associated (P = .08) with reported episodes of nonadherence. Most importantly, in approximately 1000 independent clones sequenced for both protease and reverse transcriptase, no new resistance mutations were seen before, during, or shortly after blips.

CONCLUSION

Most blips in this population appear to represent random biological and statistical variation around mean HIV-1 levels below 50 copies/mL rather than clinically significant elevations in viremia.

Therapeutic drug monitoring and drug-drug interactions involving antiretroviral drugs

The consensus of current international guidelines for the treatment of HIV infection is that data on therapeutic drug monitoring (TDM) of non-nucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors (Pls) provide a framework for the implementation of TDM in certain defined scenarios in clinical practice. However, the utility of TDM is considered to be on an individual basis until more data are obtained from large clinical trials showing the benefit of TDM. In April 2004, a panel of experts met for the second time in Rome, Italy. This was following the inaugural meeting in Perugia, Italy, in October 2000, which resulted in the manuscript published in AIDS 2002, 16(Suppl 1):S5-S37. The objectives of this second meeting were to review and update the numerous questions surrounding TDM of antiretroviral drugs and discuss the clinical utility, current concerns and future prospects of drug concentration monitoring in the care of HIV-1-infected individuals. A major focus of the meeting was to discuss and critically analyse recent and precedent clinical drug-drug interaction data to provide a clear framework of the pharmacological basis of how one drug may impact the disposition of another. This report, which has been updated to include material published or presented at international conferences up to the end of December 2004, reviews recent pivotal pharmacokinetic interaction data and provides advice to clinical care providers on how some drug-drug interactions may be prevented, avoided or managed, and, when data are available, on what dose adjustments and interventions should be performed.

Current status and future prospects of therapeutic drug monitoring and applied clinical pharmacology in antiretroviral therapy

The consensus of current international guidelines for the treatment of HIV infection is that data on therapeutic drug monitoring (TDM) of non-nucleoside reverse transcriptase inhibitors and protease inhibitors provide a framework for the implementation of TDM in certain defined scenarios in clinical practice. However, the utility of TDM is considered to be on an individual basis until more data are obtained from large clinical trials showing the benefit of TDM. In April 2004, a panel of experts met in Rome, Italy. This followed an inaugural meeting in Perugia, Italy, in October 2000, which resulted in the article published in AIDS 2002, 16(Suppl 1):S5-S37. The objectives of this second meeting were to review the questions surrounding TDM of antiretroviral drugs and discuss the clinical utility, current concerns and future prospects of drug concentration monitoring in the care of HIV-1-infected individuals. This report, which has been updated to include material published or presented at international conferences up to the end of September 2004, reviews pharmacokinetic and pharmacodynamic data and reports the issues discussed by the panel, offering advice to clinical care providers who may be currently, or are considering incorporating TDM into the routine care of their patients. In addition, the panel formulated a series of position statements that are relevant to the interpretation of current data and can aid the design of future clinical trials.

Activity, safety, and immunological effects of hydroxyurea added to didanosine in antiretroviral-naive and experienced HIV type 1-infected subjects: a randomized, placebo-controlled trial, ACTG 307

We performed a 24-week, placebo-controlled, comparative trial of hydroxyurea (HU) monotherapy, didanosine(ddI) monotherapy, and the combination of ddI plus HU administered as 1000 mg qd or 1500 mg qd in antiretroviral-naive and experienced subjects with CD4+ lymphocyte counts of 200-700 cells/mm3. Enrollment included 134 subjects. HU enhanced the antiviral activity of ddI by 1.0 log10 copies/ml after 8 weeks of therapy, with sustained responses over 24 weeks. HU alone over 4 weeks had no effect. Lamivudine resistance had little impact on antiretroviral activity when examined across treatment arms. Increases in absolute CD4+ T cell counts, but not CD4+ T cell percentages, were less in subjects who received HU compared to ddI monotherapy, and lymphoproliferative responses to antigenic and mitogenic stimuli were not altered. Subjects who received HU 1500 mg were more likely to experience dose-limiting hematological toxicities compared to those who received 1000 mg, without any additional antiviral benefit. HU may continue to have a role as a component of HIV therapy.

Simplifying antiretroviral therapy

The substantial benefits conferred by HAART require strict patient adherence. Many of the initial HAART regimens consisted of a number of large pills that needed to be taken several times daily, sometimes with meal restrictions. The development of once-daily antiretroviral agents has eased some of the burden associated with the intense, difficult schedules of early HAART regimens.. The majority of regimens currently used in treatment-naive HIV-positive patients contain a mixture of agents that are taken on a once- and twice-daily basis. Although this is an improvement over past regimens, the asynchronous administration of pills throughout the day still presents a scheduling challenge for most patients. The newest advance in simplifying antiretroviral therapy is the use of regimens in which all pills are taken at the same time once a day. Choosing drugs for a fully once-daily regimen requires awareness of a number of factors, including pharmacokinetics, potency, durability of response, resistance and safety. At this time, there are a limited number of combinations that can be used as a fully once-daily regimen and few clinical trials evaluating such combinations. Results from initial clinical trials using simplified, once-daily regimens in treatment-naive patients have been promising. Additional studies should add to this experience and provide guidance on the role and timing of such regimens in the management of patients with HIV disease.