Richard C. Brundage

COMBINATION THERAPY WITH EFAVIRENZ, NELFINAVIR, AND NUCLEOSIDE REVERSE-TRANSCRIPTASE INHIBITORS IN CHILDREN INFECTED WITH HUMAN IMMUNODEFICIENCY VIRUS TYPE 1

BACKGROUND Consistent long-term viral suppression has been difficult to achieve in children with human immunodeficiency virus type 1 (HIV-1) infection. We tested the safety and antiviral efficacy of a novel combination consisting of efavirenz, nelfinavir, and one or more nucleoside reverse-transcriptase inhibitors in 57 children previously treated with only nucleoside reverse-transcriptase inhibitors. METHODS The children were monitored for 48 weeks after the initiation of therapy. We assessed plasma concentrations of efavirenz and nelfinavir, plasma HIV-1 RNA levels, and lymphocyte subpopulations. RESULTS At base line, the 57 HIV-1-infected children (age range, 3.8 to 16.8 years) had a median of 699 CD4 cells per cubic millimeter and 10,000 copies of HIV-1 RNA per milliliter of plasma. The most common treatment-related effects of at least moderate severity were rash (in 30 percent of children), diarrhea (in 18 percent), neutropenia (in 12 percent), and biochemical abnormalities (in 12 percent). Serious side effects were uncommon. The mean values for the area under the curve for efavirenz and nelfinavir corresponded to expected values. In an intention-to-treat analysis, 76 percent of children had plasma HIV-1 RNA levels of less than 400 copies per milliliter after 48 weeks of therapy and 63 percent had levels of less than 50 copies per milliliter. A high plasma HIV-1 RNA level at base line significantly decreased the likelihood that plasma levels of HIV-1 RNA would become undetectable during treatment. CONCLUSIONS In HIV-1-infected children who were previously treated with nucleoside reverse-transcriptase inhibitors, the combination of efavirenz, nelfinavir, and nucleoside reverse-transcriptase inhibitors was generally well tolerated and had a potent and sustained antiviral effect.

A Prospective Clinical Study of Epstein‐Barr Virus and Host Interactions during Acute Infectious Mononucleosis

BACKGROUND Characterizing virus-host interactions during self-limited infectious mononucleosis could explain how Epstein-Barr virus (EBV) replication is normally controlled and provide insight into why certain immunocompromised patients fail to contain it. METHODS University students had an average of 7 clinical and virologic evaluations during acute infectious mononucleosis. EBV was quantified in 697 samples of oral wash fluid, whole blood, peripheral blood mononuclear cells (PBMCs), and plasma by a real-time (TaqMan) polymerase chain reaction (qEBV) assay developed in our laboratory. RESULTS Twenty of 25 subjects had serologically confirmed primary EBV infection. EBV was cleared from whole blood by a first-order process with a median half-life of 3 days, and its quantity was associated with severity of illness (r2=0.82). Oral shedding persisted at a median of >or=1x104 copies/mL for 32 weeks and was unrelated to severity of illness. Subjects with nonprimary EBV infection shed virus intermittently, and median quantities for all samples became undetectable within 4 weeks. CONCLUSIONS Using a novel qEBV assay, we demonstrated that young adults with primary EBV infection rapidly cleared virus from blood but not from the oropharynx. High oral concentrations of EBV in asymptomatic persons who have resumed normal activities support the concept that infectious mononucleosis is most likely acquired by kissing.

Population Pharmacokinetic and Concentration—QTc Models for Moxifloxacin: Pooled Analysis of 20 Thorough QT Studies

To increase our understanding of important subject characteristics and design variables affecting the performance of oral moxifloxacin in thorough QT studies, population pharmacokinetic and concentration—QTc models were developed by pooling data from 20 studies. A 1‐compartment model with first‐order elimination described the pharmacokinetics. Absorption delay was modeled using 8 transit compartments. Mean (95% confidence interval) values for oral clearance, apparent volume of distribution, the first‐order absorption rate constant, and mean transit time were 11.7 (11.5–11.9) L/h, 147 (144–150) L, 1.9 (1.7–2.1) 1/h, and 0.3 (0.28–0.34) hours, respectively. Overencapsulating the moxifloxacin tablet increased mean transit time by 138% and delayed time to maximum concentration by 0.5 hours but had a minimal effect on overall exposure. Administration with food decreased absorption rate constant by 27%. Women had higher moxifloxacin exposure compared with men, which was explained by lower body weights. A linear model described the concentration—QTc relationship with a mean slope of 3.1 (2.8–3.3) milliseconds per μg/mL moxifloxacin. Mean slopes for individual studies ranged from 1.6 to 4.8 milliseconds per μg/mL. Hysteresis between moxifloxacin plasma concentrations and QTc was modest, and incorporating this delay did not result in a different slope (3.3 milliseconds per μg/mL). There were no differences in slope estimates between men and women or among race categories.

An MDR1-3435 variant is associated with higher plasma nelfinavir levels and more rapid virologic response in HIV-1 infected children.

Objective:The multidrug-resistance transporter gene (MDR1) encoding for P-glycoprotein (P-gp) and genes encoding for isoenzymes of cytochrome P450 (CYP) have an important role in transport and metabolism of antiretroviral agents. This research examined the impact of single nucleotide polymorphisms (SNP) of MDR1 and CYP genes on nelfinavir and efavirenz pharmacokinetics and the response to highly active antiretroviral therapy (HAART) in HIV-1 infected children. Methods:Seventy-one HIV-1-infected children from PACTG 382 receiving nelfinavir, efavirenz and one or two nucleoside reverse transcriptase inhibitors had genomic DNA from PBMC evaluated for MDR1 and CYP SNP by real-time PCR. Plasma drug concentrations, CD4 lymphocyte counts and HIV-1 RNA were measured during HAART. Results:The frequencies of C/C, C/T and T/T genotypes in the MDR1-3435-C→T polymorphisms were 44% (n = 31), 46% (n = 33) and 10% (n = 7), respectively. Ninety-one percent of children with the C/T genotype reached plasma HIV-1 RNA < 400 copies/ml by week 8 compared to 59% of children with the C/C genotype (P = 0.01). Children with the C/T genotypes had higher 8 h postdose concentration (P = 0.02) and lower clearance rate (P = 0.04) for nelfinavir compared to those with the C/C genotype. The seven children with the T/T genotype had nelfinavir pharmacokinetics and virologic response similar to those with the C/C genotype. No compensatory polymorphisms were observed between MDR1 and CYP genotypes. Conclusions:HIV-1 infected children with the MDR1-3435-C/T genotype had more rapid virologic responses to HAART at week 8 with higher plasma nelfinavir concentrations compared to those with the C/C genotype. These findings suggest that P-gp may play an important role in the pharmacokinetics and virologic response to HAART containing nelfinavir.

Zidovudine triphosphate and lamivudine triphosphate concentration-response relationships in HIV-infected persons.

ObjectiveTo quantitate intracellular concentrations of zidovudine and lamivudine triphosphate and explore relationships with virologic and immunologic responses to antiretroviral therapy. DesignEight antiretroviral-naive, HIV-infected persons with CD4 T cell counts > 100 × 106 cells/l, and HIV RNA in plasma > 5000 copies/ml participating in a prospective, randomized, open-label study of standard dose versus concentration-controlled therapy with zidovudine, lamivudine, and indinavir. MethodsPeripheral blood mononuclear cells and plasma were collected frequently throughout the study for quantitation of intracellular zidovudine triphosphate and lamivudine triphosphate concentrations, and zidovudine and lamivudine concentrations in plasma. CD4 T cells and HIV RNA in plasma (Roche Amplicor Ultrasensitive Assay) were measured at baseline and every 4 weeks throughout the study. Relationships among intracellular and plasma concentrations, and CD4 T cells and HIV RNA in plasma were investigated with regression analyses. ResultsSignificant relationships were observed between the intracellular concentrations of zidovudine triphosphate and lamivudine triphosphate and the baseline level of CD4 cells. Lamivudine triphosphate concentrations were related in a linear manner to the apparent oral clearance of lamivudine from plasma. A direct linear relationship was found between the intracellular concentrations of zidovudine triphosphate and lamivudine triphosphate. The percent change in CD4 cells during therapy and the rate of decline in HIV RNA in plasma were related to the intracellular concentrations of zidovudine triphosphate and lamivudine triphosphate. ConclusionThese studies into the intracellular clinical pharmacology of nucleoside reverse transcriptase inhibitors illustrate potential clinical implications as determinants of therapeutic success. Moreover, these findings provide several leads and a strong impetus for future investigations with nucleoside reverse transcriptase inhibitors particularly when given in combination and sequentially.

Pharmacodynamics of Human Immunodeficiency Virus Type 1 Protease Inhibitors

Many factors are involved in the success or failure of antiretroviral therapy. Recent data suggest that there are significant differences in drug absorption and disposition for the protease inhibitor class of antiretroviral drugs, and relationships between plasma concentrations and their antiviral effect have been described. Consequently, the issue of whether therapeutic drug monitoring should be employed for patients receiving treatment with these drugs has arisen. Several criteria must be met before a drug is considered a candidate for therapeutic drug monitoring. These criteria include pharmacological, clinical, and analytic components. Although not all the necessary criteria have yet been met, some of these components have been defined, and additional data are being generated. However, prospectively designed clinical trials must be completed to determine if monitoring protease inhibitor plasma concentrations provides additional clinical benefit to the patient.

Clinical Implications of CNS Penetration of Antiretroviral Drugs

The CNS serves as an important sanctuary site for HIV replication. The presence of HIV in this compartment may contribute to neurological complications in individuals infected with HIV. Understanding the CNS penetration capabilities of available antiretroviral agents may help clinicians to design treatment regimens with neuroprotective effects. Although numerous clinical studies and anecdotal reports have examined CSF antiretroviral drug exposure as a marker of CNS penetration, understanding the clinical relevance of these findings is difficult. Challenges with study design and subject recruitment often limit the investigator’s ability to collect comprehensive data. Upon review of available data, the antiretroviral agents zidovudine, stavudine, lamivudine, nevirapine, efavirenz and indinavir demonstrate consistent penetration into the CSF. Zidovudine-, stavudine-, lamivudine-, didanosine- and protease inhibitor-based regimens also appear to suppress CSF viraemia or improve HIV neurological disease. These agents may be appropriate candidates for neuroprotective antiretroviral treatment regimens. Despite these data, several unanswered questions about the CSF antiretroviral drug exposure-response relationship still remain. Prospective, controlled studies examining this relationship are needed before absolute clinical recommendations are founded.

Sex-Based Differences in Saquinavir Pharmacology and Virologic Response in AIDS Clinical Trials Group Study 359

AIDS Clinical Trials Group study 359 was a controlled study of saquinavir with either ritonavir or nelfinavir, together with delavirdine, adefovir, or both, in indinavir-experienced persons. Saquinavir was common in all study arms, and the study investigated relationships among characteristics of patients, saquinavir area under the curve (AUC) and trough concentrations (C(min)), and virologic response. Concentrations of saquinavir were higher when it was combined with ritonavir than when it was combined with nelfinavir and were lower with adefovir-containing regimens. Females had higher AUC and C(min) values than did males. Higher saquinavir AUC and C(min) values were associated with a greater likelihood of human immunodeficiency virus (HIV) RNA levels </=500 copies/mL (P=.008) and were better predictors of response than was the saquinavir inhibitory quotient. Males had a lower probability of having HIV RNA levels </=500 copies/mL at week 16 than did females (28% vs. 42%; adjusted odds ratio, 0.43). In this study, a greater proportion of females had HIV RNA levels </=500 copies/mL than did males, which can be attributed to higher concentrations of saquinavir in females than in males.

Dosing equation for tacrolimus using genetic variants and clinical factors

AIM To develop a dosing equation for tacrolimus, using genetic and clinical factors from a large cohort of kidney transplant recipients. Clinical factors and six genetic variants were screened for importance towards tacrolimus clearance (CL/F). METHODS Clinical data, tacrolimus troughs and corresponding doses were collected from 681 kidney transplant recipients in a multicentre observational study in the USA and Canada for the first 6 months post transplant. The patients were genotyped for 2,724 single nucleotide polymorphisms using a customized Affymetrix SNP chip. Clinical factors and the most important SNPs (rs776746, rs12114000, rs3734354, rs4926, rs3135506 and rs2608555) were analysed for their influence on tacrolimus CL/F. RESULTS The CYP3A5*1 genotype, days post transplant, age, transplant at a steroid sparing centre and calcium channel blocker (CCB) use significantly influenced tacrolimus CL/F. The final model describing CL/F (l h(-1)) was: 38.4 ×[(0.86, if days 6-10) or (0.71, if days 11-180)]×[(1.69, if CYP3A5*1/*3 genotype) or (2.00, if CYP3A5*1/*1 genotype)]× (0.70, if receiving a transplant at a steroid sparing centre) × ([age in years/50](-0.4)) × (0.94, if CCB is present). The dose to achieve the desired trough is then prospectively determined using the individuals CL/F estimate. CONCLUSIONS The CYP3A5*1 genotype and four clinical factors were important for tacrolimus CL/F. An individualized dose is easily determined from the predicted CL/F. This study is important towards individualization of dosing in the clinical setting and may increase the number of patients achieving the target concentration. This equation requires validation in an independent cohort of kidney transplant recipients.

Pharmacokinetic Enhancement of Protease Inhibitor Therapy

Combination antiretroviral therapy with two or more protease inhibitors has become the standard of care in the treatment of HIV infection. Dual protein inhibitor (PI) regimens, such as lopinavir/ritonavir, are commonly used as initial PI therapy. As viral resistance increases and the development of mechanistically novel protease inhibitors decreases, clinicians turn to ritonavir-enhanced dual PI therpay to treat salvage patients. Potency of these combination regimens is increased while pill burden, food restrictions and often, side effects are decreased. These clincial advantages result from the enhancement of their pharmacological properties, including alterations in the absorption and metabolism process. Alterations in the absorption and metabolism of protease inhibitors when co-administered with a cytochrome P450 (CYP) enzyme inhibitor, such as low dose ritonavir, are reflected by impressive changes in pharmacokinetic parameters. For example, the addition of ritonavir 100 or 200mg to saquinavir 1200–1800mg has been shown to increase saquinavir area under the concentration-time curve (AUC) by approximately 300–800% compared with saquinavir alone. The ability of ritonavir to increase plasma trough concentrations (Cmin) of concomitantly administered PIs is perhaps the greatest clinical benefit of dual or ritonavir-enhanced dual PI therapy since inadequate concentrations of antiretrovirals may support long term antiretroviral resistance. For example, lopinavir 400mg alone in healthy volunteers produced plasma concentrations that briefly exceeded the concentration required to inhibit 50% of viral replication (IC50). Yet, when low doses of ritonavir were added, Cmin values were 50- to 100-fold greater than the concentration required to produce 50% of the maximum effect for wild-type HIV (EC50). The following manuscript will discuss the rationale for combining protease inhibitors and will review pertinent pharmacokinetic and clinical data on these combination regimens.