Efavirenz liquid formulation in human immunodeficiency virus-infected children

Antiretroviral treatment in HIV-1 infected pediatric patients: focus on efavirenz

Efavirenz is a non-nucleoside reverse transcriptase inhibitor (NNRTI), used for the treatment of human immunodeficiency virus (HIV)-1 infection. Approved by the US Food and Drug Administration in 1998, its indication was recently extended to include children as young as 3 months of age. The World Health Organization and many national guidelines consider efavirenz to be the preferred NNRTI for first-line treatment of children over the age of 3 years. Clinical outcomes of patients on three-drug antiretroviral regimens which include efavirenz are as good as or better than those for patients on all other currently approved HIV medications. Efavirenz is dosed once daily and has pediatric-friendly formulations. It is usually well tolerated, with central nervous system side effects being of greatest concern. Efavirenz increases the risk of neural tube defects in nonhuman primates and therefore its use during the first trimester of pregnancy is limited in some settings. With minimal interactions with antituberculous drugs, efavirenz is preferred for use among patients with HIV/tuberculosis coinfection. Efavirenz can be rendered inactive by a single point mutation in the reverse transcriptase enzyme. Newer NNRTI drugs such as etravirine, not yet approved for use in children under the age of 6 years, may maintain their activity following development of efavirenz resistance. This review highlights key points from the existing literature regarding the use of efavirenz in children and suggests directions for future investigation.

Etravirine in treatment-experienced, HIV-1-infected children and adolescents: 48-week safety, efficacy and resistance analysis of the phase II PIANO study

OBJECTIVES

PIANO (Paediatric study of Intelence As an NNRTI Option; TMC125-C213; NCT00665847) assessed the safety/tolerability, antiviral activity and pharmacokinetics of etravirine plus an optimized background regimen (OBR) in treatment-experienced, HIV-1-infected children (≥ 6 to < 12 years) and adolescents (≥ 12 to < 18 years) over 48 weeks.

METHODS

In a phase II, open-label, single-arm study, 101 treatment-experienced patients (41 children; 60 adolescents) with screening viral load (VL) ≥ 500 HIV-1 RNA copies/mL received etravirine 5.2 mg/kg (maximum dose 200 mg) twice a day (bid) plus OBR.

RESULTS

Sixty-seven per cent of patients had previously used efavirenz or nevirapine. At week 48, the most common treatment-related grade ≥ 2 adverse event (AE) was rash (13%); 12% experienced grade 3 AEs. Only two grade 4 AEs occurred (both thrombocytopaenia, not etravirine related). At week 48, 56% of patients (68% children; 48% adolescents) achieved a virological response (VL<50 copies/mL; intent-to-treat, noncompleter=failure). Factors predictive of response were adherence > 95%, male sex, low baseline etravirine weighted genotypic score and high etravirine trough concentration (C0h ). Seventy-six patients (75%) completed the trial; most discontinuations occurred because of protocol noncompliance or AEs (8% each). Sixty-five per cent of patients were > 95% adherent by questionnaire and 39% by pill count. Forty-one patients experienced virological failure (VF; time-to-loss-of-virological-response non-VF-censored algorithm) (29 nonresponders; 12 rebounders). Of 30 patients with VF with paired baseline/endpoint genotypes, 18 (60%) developed nonnucleoside reverse transcriptase inhibitor (NNRTI) mutations, most commonly Y181C. Mean etravirine area under the plasma concentration-time curve over 12 h (AUC0-12h ; 5216 ng h/mL) and C0h (346 ng/mL) were comparable to adult target values.

CONCLUSIONS

Results with etravirine 5.2 mg/kg bid (with OBR) in this treatment-experienced paediatric population and etravirine 200 mg bid in treatment-experienced adults were comparable. Etravirine is an NNRTI option for treatment-experienced paediatric patients.

Antiretroviral use in Italian children with perinatal HIV infection over a 14-year period

BACKGROUND

Information on the use of new antiretroviral drugs in children in the real setting of clinical fields is largely unknown.

METHODS

Data from 2554 combined antiretroviral therapy (cART) regimens administered to 911 children enrolled in the Italian Register for HIV infection in children, between 1996 and 2009, were analysed. Factors potentially associated with undetectable viral load and immunological response to cART were explored by Cox regression analysis.

RESULTS

Proportion of protease inhibitor (PI)-based regimens significantly decreased from 88.0% to 51.2% and 54.9%, while proportion on non-nucleoside reverse transcriptase inhibitor (NNRTI)-based regimens increased from 4.5% to 38.8% and 40.2% in 1996-1999, 2000-2004 and 2005-2009, respectively (p < 0.0001). Significant change in the use of each antiretroviral drug occurred over the time periods (p < 0.0001). Factors independently associated with virological and immunological success were as follows: later calendar periods, younger age at regimen (only for virological success) and higher CD4(+) T-lymphocyte percentage at baseline. Use of unboosted PI was associated with lower adjusted hazard ratio (aHR) of virological or immunological success with respect to NNRTI- and boosted PI-based regimens, with no difference among these two latter types.

CONCLUSION

Use of new generation antiretroviral drugs in Italian HIV-infected children is increasing. No different viro-immunological outcomes between NNRTI- and boosted PI-based cART were observed.

Pharmacokinetics and short-term safety and tolerability of etravirine in treatment-experienced HIV-1-infected children and adolescents

OBJECTIVES

To evaluate the pharmacokinetics, weight-based dose selection and short-term safety and tolerability of etravirine in HIV-1-infected children and adolescents.

DESIGN

Phase I, nonrandomized, open-label study in two stages.

METHODS

Children and adolescents aged at least 6 years to 17 years or less on a stable lopinavir/ritonavir-based antiretroviral regimen with HIV-1 RNA plasma viral load less than 50 copies/ml were enrolled. In both stages, etravirine (4 mg/kg twice daily in stage I, 5.2 mg/kg twice daily in stage II), added to the existing antiretroviral regimen, was administered for 7 days followed by a morning dose and 12-h pharmacokinetic assessment on day 8. Pharmacokinetic parameters were determined using noncompartmental analysis. Data were compared with those previously established in HIV-1-infected adults on a similar etravirine (200 mg twice daily) combination antiretroviral regimen.

RESULTS

Twenty-one patients were recruited to each stage; 19 and 20 had evaluable pharmacokinetics in stages I and II, respectively. Mean (SD) maximum plasma concentrations in stages I and II were 495 (453) and 757 ng/ml (680), respectively; area under the plasma concentration-time curve over 12 h was 4050 (3602) and 6141 ng h/ml (5586), respectively. Statistical/qualitative comparisons showed comparable exposures with adults in stage II; however, the upper 90% confidence interval fell outside the predefined range. Plasma viral load remained undetectable on day 8 in all patients, and etravirine was well tolerated at both doses.

CONCLUSION

Etravirine 5.2 mg/kg was well tolerated in this study and this dose was selected for further investigation in clinical trials.

Role of non-nucleoside reverse transcriptase inhibitors in treating HIV-infected children

The first-generation non-nucleoside reverse transcriptase inhibitors (NNRTIs), efavirenz and nevirapine, fulfil key roles in antiretroviral therapy for HIV-infected paediatric patients, from lowering the incidence of mother-to-child transmission during pregnancy and birth to treatment throughout childhood and adolescence. Both agents have established efficacy, safety and tolerability profiles, and also offer advantages over other classes of therapy in terms of regimen simplicity and availability across different treatment settings. Although the role of NNRTIs in paediatric treatment strategies is largely determined by experience in adult patients, results of the recent phase II/III PENPACT-1 trial in infants and children aged between 30 days and 18 years have shown that there are no significant differences in 4-year virological, immunological or clinical outcomes between NNRTIs and protease inhibitors as first- and second-line agents. However, results from the IMPAACT P1060 study (cohort 2), conducted in resource-limited settings, showed that infants under 36 months unexposed to NNRTIs were significantly more likely to fail treatment when started on a nevirapine-based regimen than those on a lopinavir/ritonavir-based regimen. Unfortunately, the use of efavirenz and nevirapine in children can be limited by rapid development of high-level resistance to one or both agents, which may reduce the availability of viable treatment options, particularly in resource-limited settings. Several therapeutic strategies addressing this issue are currently under investigation, but a significant need for new NNRTI-based treatment options remains. The more recently approved NNRTI, etravirine, has demonstrated efficacy and safety benefits in HIV-1-infected, NNRTI-resistant adult patients, with a higher genetic barrier to the development of resistance relative to the first-generation NNRTIs. Another NNRTI, rilpivirine (TMC278), is approved for use in HIV-1-infected, treatment-naïve adult patients and has demonstrated an improved tolerability profile compared with efavirenz. Although available data on etravirine in children are currently limited, ongoing trials will provide important information on the potential for their use in novel paediatric treatment strategies. This review examines the role of efavirenz and nevirapine in paediatric antiretroviral therapy in children within different treatment settings. In addition, this review also outlines available clinical data on etravirine and rilpivirine in the context of how these antiretrovirals may address some of the limitations of efavirenz and nevirapine in paediatric patients.

Influence of CYP2B6 516G>T polymorphism and interoccasion variability (IOV) on the population pharmacokinetics of efavirenz in HIV-infected South African children

OBJECTIVE

To investigate the influence of CYP2B6 516G>T polymorphism, as a covariate, and of interoccasion variability (IOV) on the oral clearance (CL/F) of efavirenz (EFV) in treatment-naïve black South African children over a period of 24 months post-antiretroviral therapy (ART) initiation.

METHODS

HIV-infected black children (n = 60, aged 3-16 years), with no prior exposure to ART, eligible to commence ART and attending an outpatient clinic were enrolled into this study. Blood samples were taken at mid-dose interval at 1, 3, 6, 12, 18 and 24 months post-ART initiation. EFV plasma samples were determined with an adapted and validated LC/MS/MS method. Genotyping of the CYP2B6 G516T single nucleotide polymorphism (SNP) was performed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). NONMEM was used for the population pharmacokinetic modelling.

RESULTS

EFV concentrations below 1 μg/mL accounted for 18% (116/649), EFV concentrations >4 μg/mL accounted for 29.5% (192/649) and concentrations within the therapeutic range (1-4 μg/mL) represented 52.5% (341/649) of all the samples determined. The covariates age, weight and CYP2B6 G516Tgenotype were included in the final model with population estimates for CL/F determined as 2.46, 4.60 and 7.33 L/h for the T/T, G/T and G/G genotype groups respectively.

CONCLUSIONS

The inclusion of both age and weight to predict accurate EFV CL values for the respective genotype groups within this paediatric population was required, whereas the addition of gender and body surface area did not improve the predictions. The importance of introducing IOV in a PK model for a longitudinal study with sparsely collected data was again highlighted by this investigation.

Pediatric antiretroviral therapy

The rate of perinatal HIV transmission has decreased significantly in developed countries. However, worldwide, it remains the main source of HIV infection within the pediatric population. Recent advances as a result of findings from clinical trials, viral resistance testing and the advent of new drugs have increased the options for initial treatment regimens. This article provides an overview of antiretroviral therapy in treatment-naive children, including recent pediatric data and updated guidelines from the NIH. It also provides information on new drugs approved for the pediatric age group, dosage information, drug resistance testing and monitoring suggestions for children and adolescents receiving antiretroviral therapy. Special issues pertaining to adherence, disclosure and contraception are also highlighted.

Efavirenz in the therapy of HIV infection

IMPORTANCE OF THE FIELD

The use of the first generation non-nucleoside reverse transcriptase inhibitor efavirenz (EFV) as a component of first-line antiretroviral therapy has been accepted worldwide. EFV is the only antiretroviral agent currently on the market that has been combined with emtricitabine and tenofovir disoproxil fumarate in a single tablet and administered once daily.

AREAS COVERED IN THIS REVIEW

This article reviews efficacy and safety data on EFV and the role of pharmacogenetics in EFV exposure. Published articles and conference presentations on EFV are reviewed.

WHAT THE READER WILL GAIN

CYP2B6 genetic polymorphisms influence the metabolism of EFV. The CYP2B6 G to T polymorphism at position 516 is shown to be associated with elevated plasma concentrations and an increase in neurotoxicity of EFV, while the wild-type genotype has been associated with sub-therapeutic concentrations of EFV, potentially leading to the development of viral resistance. This polymorphism is significantly higher in sub-Saharan Africans and African Americans as compared to Hispanic, European and Asian populations.

TAKE HOME MESSAGE

The significance of CYP2B6 polymorphism in EFV exposure indicates the need for prospective clinical studies to evaluate the utility of genotype-driven dose adjustments in populations of diverse descent.

Efavirenz-loaded polymeric micelles for pediatric anti-HIV pharmacotherapy with significantly higher oral bioavailability

Children constitute the most challenging population in anti-HIV/AIDS pharmacotherapy. Efavirenz (EFV; aqueous solubility 4 µg/ml, bioavailability 40–45%) is a first-line agent in the pediatric therapeutic cocktail. The liquid formulation of EFV is not available worldwide, preventing appropriate dose adjustment and more convenient administration. The bioavailability of liquid EFV is lower than that of the solid formulation. Improving the bioavailability of the drug would reduce the cost of treatment and enable less affluent patients to access this drug. Aim: To encapsulate EFV in polymeric micelles to improve the aqueous solubility and the the oral bioavailability of the drug. Methods: EFV was incorporated into the core of linear and branched poly(ethylene oxide)–poly(propylene oxide) block copolymer micelles. The size and size distribution of the drug-loaded aggregates were characterized by dynamic light scattering and the morphology by transmission electron microscopy. The bioavailability of the EFV-loaded micellar system (20 mg/ml) was assessed in male Wistar rats (40 mg/kg) and compared to that of a suspension prepared with the content of EFV capsules in 1.5% carboxymethylcellulose PBS solution (pH 5.0), and an EFV solution in a medium-chain triglyceride (Miglyol® 812). Results: This work demonstrates that the encapsulation of EFV, which is poorly water soluble, into polymeric micelles of different poly(ethylene oxide)–poly(propylene oxide) block copolymers significantly improves the oral bioavailability of the drug, and reduces the interindividual variability. Conclusion: This strategy appears a very promising one towards the development of a liquid aqueous EFV formulation for the improved pediatric HIV pharmacotherapy.

Clinical practice treatment of HIV infection in children

Perinatal transmission remains the main cause of HIV infection in the pediatric population. Treatment of HIV-infected children has become less of a problem in resource-rich countries with a remarkable decrease of perinatal infections, resulting in an effective prevention of mother-to-child transmission and antiretroviral treatment of HIV infection in pediatrics because of differences in drug pharmacokinetics, the lack of available licensed drugs, the use of different immunologic markers and age-related adherence issues. This review, for the general pediatrician, summarizes the most recent pediatric data and guidelines for treatment of HIV. Recommendations for when to initiate therapy are more aggressive in children than in adults, particularly in infants because disease progression in children is more rapid. The indications to start therapy differ by age and are based on international immunologic and clinical classification system for HIV infection. At present, combination regimens of at least three drugs are recommended. Moreover, therapies must also consider the potential complications in these children currently treated for a long time.

Practical therapeutic drug management in HIV-infected patients: use of population pharmacokinetic models supplemented by individualized Bayesian dose optimization

Individualized, model-based, target-oriented optimal concentration-controlled dosing of HIV medications can be beneficial to patients for whom there are limited dosing guidelines, such as children, adolescents, or patients with altered physiologic function. Barriers to this approach include lack of training, expertise, and access to appropriate software to assist the clinician. The authors present 4 illustrative clinical cases of HIV-infected patients whose therapy was optimized using population pharmacokinetic models (here generated from published studies) and supplemented by individualized Bayesian adaptive control of dosage regimens as implemented in the MM-USCPACK software. These 4 cases illustrate how clinicians can maximize therapeutic success in (1) patients with reduced drug clearance, (2) young adolescents transitioning to adult physiology, (3) patients with dose-dependent toxicity, and (4) adolescents with limited therapeutic options.

High prevalence of subtherapeutic plasma concentrations of efavirenz in children

OBJECTIVE

Efavirenz-containing regimens using concentration-controlled dosing have been shown to provide potent antiretroviral activity in children. In many settings, concentration-controlled dosing is not available. In this study, efavirenz plasma concentrations were evaluated in South African HIV-infected children receiving efavirenz-based antiretroviral treatment.

METHODS

Three consecutive blood samples were drawn between 12 and 24 hours after dosing in 15 HIV-infected children receiving the recommended daily doses of efavirenz. Validated liquid chromatography tandem mass spectrometry methods were used to determine plasma levels of efavirenz. The trough concentration (Cmin) of efavirenz was estimated by extrapolation of the log-linear regression line of the 3 concentration versus time points to 24 hours.

RESULTS

The estimated Cmin was <1 mg/L in 6 (40%) of the children. Three of the 5 children with detectable viral loads had low efavirenz concentrations. Marked bimodality in efavirenz concentrations was observed.

CONCLUSIONS

Our findings, together with those of previous studies, indicate that many children dosed according to the current guidelines do not achieve adequate efavirenz exposure. Because low efavirenz concentrations are associated with the rapid emergence of efavirenz-resistant mutations and treatment failure, the current recommended efavirenz doses should be re-evaluated, especially in developing countries, where therapeutic drug monitoring is seldom available.

Efavirenz/emtricitabine/tenofovir disoproxil fumarate fixed-dose combination: first-line therapy for all?

ATRIPLA (Bristol-Myers Squibb and Gilead Sciences) is a complete regimen in a single, fixed-dose combination tablet that contains: efavirenz 600 mg, emtricitabine 200 mg and tenofovir disoproxil fumarate 300 mg. Current treatment guidelines recommend this triple combination for initial therapy because of its excellent potency, tolerability and favorable safety profile. Individually, these agents have long half-lifes that allow for once-daily dosing and may provide a pharmacologic bridge for the occasional missed dose. Although several options for once-daily regimens are available, comparative clinical trials are still in progress. This article reviews relevant efficacy and safety data of efavirenz, emtricitabine and tenofovir disoproxil fumarate, compared with other once-daily agents or certain common alternate drugs presently used as initial therapy in treatment-naive patients.

Recommendations in pediatric antiretroviral therapy

The pathogenesis of HIV infection and the general principles of therapy are the same for HIV-infected adults, adolescents, children and infants. However, antiretroviral treatment of HIV infection in pediatrics requires the consideration of a number of factors specific to its population, including differences in drug pharmacokinetics and the use of virologic and immunologic markers, as well as age-related adherence issues. This review summarizes the text of the Guidelines for the Use of Antiretroviral Agents in Pediatric HIV Infection, which was updated in October 2006. The guidelines are the work of the Working Group on Antiretroviral Therapy and Medical Management of HIV-Infected Children, a group of the Office of AIDS Research Advisory Council of the National Institutes of Health, which reviews new data on an ongoing basis and provides regular updates to the guidelines. As these guidelines were developed for the US, they may not be applicable in other countries. This summary does not attempt to place the Working Group guidelines in the context of international guidelines, nor does it attempt to detail the use of antiretroviral medication in the prevention of perinatal transmission of HIV, such as addressing the use of zidovudine versus single-dose nevirapine.

Nelfinavir: a review of its use in the management of HIV infection

Nelfinavir (Viracept) is an orally administered protease inhibitor. In combination with other antiretroviral drugs (usually nucleoside reverse transcriptase inhibitors [NRTIs]), nelfinavir produces substantial and sustained reductions in viral load in patients with HIV infection. Nelfinavir may be used in the treatment of adults, adolescents and children aged >or=2 years with HIV infection. It can also be used in pregnancy. Resistance to nelfinavir may develop, but the most common mutation (D30N, appearing mainly in HIV-1 subtype B) does not confer resistance to other protease inhibitors, thereby conserving these agents for later use. Although less effective than lopinavir/ritonavir, the preferred first-line treatment in US guidelines, nelfinavir is positioned as an alternative agent for the treatment of adults and adolescents with HIV infection and is an option for those unable to tolerate other protease inhibitors. Nelfinavir also has a role in the management of pregnant patients as well as paediatric patients with HIV infection.

Pharmacokinetics of antiretroviral therapy in HIV-1-infected children

The initiation of antiretroviral therapy has resulted in an impressive reduction in the rate of disease progression in AIDS and HIV-1-related deaths in children; however, there are still several major challenges to be faced in order to improve therapy. A major topic that needs to be dealt with is the establishment of the optimal dosage of antiretroviral therapy for children. This review presents the currently available peer-reviewed data on the pharmacokinetics of nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), protease inhibitors (PIs) and fusion inhibitors (FIs) in children. In addition, the data are discussed in relation to the currently available European and US guidelines and the US FDA-approved drug labels. High intra- and interpatient variability in pharmacokinetics are often observed for all antiretroviral drugs. The number of children included in the pharmacokinetic studies is often small and children are often divided into divergent groups using different dosage levels and/or drug formulations. For a substantial number of antiretroviral drugs, dosage recommendations, especially for young children, are still absent in the European and US guidelines. The recommended drug dosages in the guidelines are often different from that in the officially approved drug product label. In addition, the recommended drug dosages may deviate between the European and US guidelines. Thus, while practioners aim to meet the recommendations in the official guidelines, patients may receive highly divergent dosages of medication. The high intra- and interpatient variability in pharmacokinetics of antiretroviral drugs in children hampers the application of fixed dosages of antiretroviral drugs. For PIs and NNRTIs, plasma drug levels correlate with viral suppression and drug toxicity. NRTIs are prodrugs that are intracellularly converted to their active triphosphate form and, therefore, plasma NRTI levels correlate poorly with viral suppression. Therapeutic drug monitoring of PIs and NNRTIs should be considered to optimise HIV therapy in children.

Positive virological outcome after lopinavir/ritonavir salvage therapy in protease inhibitor-experienced HIV-1-infected children: a prospective cohort study

BACKGROUND

Lopinavir/ritonavir has demonstrated antiviral activity in the HIV-infected patient.

OBJECTIVE

To analyse virological response to lopinavir/ritonavir therapy in previously protease inhibitor (PI)-experienced HIV-1-infected children.

MATERIALS AND METHODS

Sixty-seven HIV-1-children on lopinavir/ritonavir were studied in a multicentre prospective cohort observational study. The outcome variables were undetectable viral load (uVL; VL < or =400 copies/mL) and virological failure after uVL with a rebound of VL >400 copies/mL. VL and genotype of HIV-1-isolates were measured using standard assays.

RESULTS

83.5% of children had a 1 log10 VL decrease including 65.6% who reached uVL. Children with >2 changes of antiretroviral therapy (ART) or >5 drugs needed a median time of 3-4 months higher than children with < or =2 changes of ART or < or =5 drugs previous to lopinavir/ritonavir, to reach those values, and the relative proportions (RP) were 2.2 (P =0.038) and 1.9 (P=0.050), respectively. Children with CD4+>15% (P=0.122), VL < or =30,000 (P < 0.001) copies/mL, and age >12 years (P=0.096) achieved an earlier control of VL during the follow-up. The children with virological failure or rebound of VL had higher baseline VL and lower CD4+ T-lymphocytes/mm3 and had taken a greater number of drugs previous to lopinavir/ritonavir. HIV-children with a new nucleoside reverse transcriptase inhibitor (NRTI), or protease inhibitor (PI) or PI plus non-nucleoside reverse transcriptase inhibitors (NNRTI) in the current regimen had a better virological response than children without these new drugs. Also, children with <6 protease mutations had an RP of 2.31 of achieving uVL.

CONCLUSIONS

Highly active antiretroviral therapy (HAART) including lopinavir/ritonavir induces beneficial effects in terms of virological outcome responses, and it is an effective option for salvage therapy in PI-experienced HIV-1-infected children.

Management of Antiretroviral Therapy in Neonates, Children, and Adolescents

There have been tremendous advances in the prevention of mother-to-child transmission of HIV and treatment of HIV-infected children and adolescents. Although multiple classes of anti-HIV drugs are available that can control viral replication and stabilize immune function when used in combination, patients and their providers also must manage complex and frequently toxic regimens. This article summarizes official National Institutes of Health guidelines for the prevention of perinatal HIV infection and the management of pediatric and adolescent HIV infection, and provides the most current updates on indications for therapy, recommended first-line therapy, criteria for changing therapy, salvage therapy, and novel management strategies.

Pharmacology considerations for antiretroviral therapy in human immunodeficiency virus (HIV)-infected children

The contemporary treatment of the child infected with human immunodeficiency virus (HIV) unavoidably requires combination therapy with antiretroviral agents and may include additional drugs for the prevention and treatment of opportunistic infections or other disease states. The current guidelines for the treatment of the HIV-infected child recommend that the same principles of treatment for adults should apply to children. However, the pharmacokinetic and pharmacodynamic characteristics of many agents and regimens used in adults have not been defined adequately in children, and large-scale clinical trials to establish safety and show efficacy have not been completed. Therefore, the clinician will be required to use agents with incomplete knowledge about their pharmacologic properties. The purpose of this article is to provide an overview of the pediatric pharmacologic principles, a review of the pharmacologic characteristics of selected antiretroviral agents in children, and a prospectus on the design of drug dosing regimens in children.