Pharmacokinetic and other drug interactions in patients with AIDS

Drug-Drug Interactions and HIV Therapy: What Should Pharmacists Know?

Drug-interaction issues continue to present a major dilemma for the clinician caring for complex patients such as those infected with HIV. The inherent possibility of a drug interaction is magnified by the multitude of drugs being administered in highly-active antiretroviral therapy (HAART). In addition, other classes of medications are used to alleviate side effects, reduce toxicities associated with HAART, or treat concomitant diseases. The modification of one drug by another substance or drug-drug interaction is the main focus of this article. Drug-drug interactions may result in toxicity, treatment failure, or loss of effectiveness and can significantly affect a patient’s clinical outcome. An understanding of the fundamental mechanisms of HIV drug-drug interactions may allow for the early detection or avoidance of troublesome regimens and prudent management if they develop. Although HIV drug interactions are usually thought of as detrimental, resulting in a loss of therapeutic effect or toxicity, some drug interactions such as ritonavir boosted protease inhibitor–based antiretroviral treatments are beneficial and are commonly used in clinical practice. Therefore, pharmacists need to understand drug interaction mechanisms, remember key drug interactions, and vigilantly monitor patients for potential complications.

Drug Monitoring and Viral Response to Lopinavir/Ritonavir or Saquinavir/Ritonavir Containing Regimens in Individuals Infected with the Human Immunodeficiency Virus Type1

The aim of this study was to correlate results of therapeutic drug monitoring, genotypic resistance and viral response to lopinavir/ritonavir (LPV/r) or saquinavir/ritonavir (SQV/r) containing antiretroviral regimens. The retrospective short-term study included 20 patients with LPV/r and 20 patients with SQV/r containing highly active antiretroviral therapy (HAART). At baseline 7 LPV/r patients and 10 SQV/r patients had CD4+T cell counts above 410 cells/μl. After 6 months CD4+T cells had doubled in 5 LPV/r and 2 SQV/r patients. In LPV/r patients the mean serum concentration of lopinavir (LPV) was 2.6 ppm and 67% of all LPV/r samples had 50 or fewer viral copies/ml. In SQV/r patients the mean serum concentration of saquinavir (SQV) was 2.1 ppm. 79% of all SQV/r samples had 50 or fewer viruses/ml. Pharmacoenhanced regimens efficiently suppress human immunodeficiency virus type 1 (HIV-1) and the risk of developing resistance mutations is therefore reduced. The implementation of drug monitoring is an additional tool to determine optimal treatment conditions.

Prevalence and Pattern of Chronic Kidney Disease in Antiretroviral-Naïve Patients with HIV/AIDS

BACKGROUND

Chronic renal failure and HIV/AIDS are both prevalent in Nigeria. We performed a cross-sectional analysis of renal function in newly diagnosed, treatment-naive HIV-infected patients before initiating highly active antiretroviral therapy.

METHODS

Treatment-inexperienced individuals were recruited. Patients with diabetes mellitus and hypertension were excluded. Plasma creatinine level was used to measure the estimated glomerular filtration rate ([eGFR] by Modification of Diet in Renal Disease equation). Predictors of creatinine and eGFR were determined by univariate and multivariate analyses.

RESULTS

We evaluated 183 patients. In all, 44 (24%) patients had a GFR <60 mL/min/1.73 m(2), implying moderate chronic kidney disease (CKD). Considering the eGFR, 22 (12%) patients had stage 1, 117 (63.9%) stage 2, 13 (7.1%) stage 3, 27 (14.8%) stage 4, and 4 (2.2%) stage 5 CKD. Creatinine inversely correlated with CD4 (r = -.228, P = .025). CD4 predicts creatinine (odds ratio 1.6, 95% confidence interval 1.0-1.8, P = .003).

CONCLUSION

In ART-naive patients, CKD is common, and low eGFR was associated with lower CD4 counts.

No evidence for induction of ABC transporters in peripheral blood mononuclear cells in humans after 14 days of efavirenz treatment

Intracellular concentrations of antiretroviral drugs in peripheral blood mononuclear cells (PBMCs) are an important determinant of therapeutic success. In vitro data indicate that efavirenz induces several ATP-binding cassette (ABC) transporters, and pharmacogenetic studies found an association between ABCB1(C3435T) and efavirenz exposure and between this polymorphism and improved virological outcomes. We therefore aimed to clarify whether efavirenz also induces ABC transporters in vivo in PBMCs and whether intracellular concentrations might be altered after induction. Twelve healthy individuals received multiple oral doses of efavirenz over 14 days (400 mg once daily). Blood samples were drawn on study days 1 (single dose) and 14 (multiple dose), and efavirenz concentrations were analyzed by liquid chromatography-tandem mass spectrometry. Expression of P glycoprotein (P-gp) and of the multidrug resistance-associated proteins 1 and 2 as well as P-gp activity was analyzed in PBMCs on day 1 and day 14 using real-time reverse transcription-PCR (RT-PCR) and rhodamine 123 efflux. Although a clear autoinduction could be confirmed by a significant decrease of efavirenz exposure from day 1 to day 14, efavirenz did not change expression of the ABC transporters or P-gp activity in PBMCs. Moreover, intracellular concentrations of efavirenz were 1.3- to 1.8-fold higher than the corresponding plasma concentrations, and the intracellular/plasma concentration ratio remained constant during the treatment and did not correlate with ABC transporter expression or function. In conclusion, our study confirmed that intracellular concentrations of efavirenz are independent from these efflux transporters and demonstrated for the first time that the transporters are not induced in PBMCs in vivo after 2 weeks of treatment with efavirenz.

Influence of the cytochrome P450 2B6 genotype on population pharmacokinetics of efavirenz in human immunodeficiency virus patients

A population pharmacokinetic model for efavirenz has been developed from therapeutic drug monitoring data in human immunodeficiency virus (HIV)-positive patients by using a nonlinear mixed-effect model. The efavirenz plasma concentrations (n = 375) of 131 patients were analyzed using high-performance liquid chromatography with UV detection. Pharmacokinetic parameters were estimated according to a one-compartment model. The effects of sex, age, total body weight, height, body mass index, and HIV treatment were analyzed. In a subgroup of 32 patients, genetic polymorphisms of the cytochrome P450 2B6 gene (CYP2B6), CYP3A4, and MDR1 were also investigated. Efavirenz oral clearance and the apparent volume of distribution were 9.50 liters/h and 311 liters, respectively. The model included only the effect of CYP2B6 polymorphisms on efavirenz clearance; this covariate reduced the intersubject variability of clearance by about 27%. Patients showing G/T and T/T CYP2B6 polymorphisms exhibited efavirenz clearances that were about 50% and 75% lower than those observed in the patients without these polymorphisms (G/G). Accordingly, to obtain EFV steady-state concentrations within the therapeutic range (1 to 4 mg/liter), it would be advisable to implement a gradual reduction in dose to 400 or 200 mg/day for patients that are intermediate or poor metabolizers, respectively. However, the remaining interindividual variability observed in the pharmacokinetic parameters of the model highlights the need for dose individualization to avoid inadequate exposure to efavirenz and suggests that these recommended doses be used with caution and confirmed by therapeutic drug monitoring and clinical efficacy. The population model can be implemented in pharmacokinetic clinical software for dosage optimization by using the Bayesian approach.

Comparison of the induction of P-glycoprotein activity by nucleotide, nucleoside, and non-nucleoside reverse transcriptase inhibitors

Combination therapy against human immunodeficiency virus (HIV)-infection is complicated by drug-drug interactions between antiretrovirals and also between anti-HIV drugs and drugs used to treat co-morbidity. P-glycoprotein represents one important site for drug interactions and induction of its function could reduce the effectiveness of drugs that are P-glycoprotein substrates. We therefore investigated induction of P-glycoprotein function in LS180 cells by non-nucleoside and nucleoside reverse transcriptase inhibitors (NNRTIs and NRTIs) and tenofovir as essential components of antiretroviral combination therapy. P-glycoprotein activity was increased by all NNRTIs and some NRTIs with delavirdine (5.3-fold at 100 muM) having the largest effect.

Effects of human immunodeficiency virus protease inhibitors on the intestinal absorption of tenofovir disoproxil fumarate in vitro

Human immunodeficiency virus protease inhibitors (PIs) modestly affect the plasma pharmacokinetics of tenofovir (TFV; -15% to +37% change in exposure) following coadministration with the oral prodrug TFV disoproxil fumarate (TDF) by a previously undefined mechanism. TDF permeation was found to be reduced by the combined action of ester cleavage and efflux transport in vitro. Saturable TDF efflux observed in Caco-2 cells suggests that at pharmacologically relevant intestinal concentrations, transport has only a limited effect on TDF absorption, thus minimizing the magnitude of potential intestinal drug interactions. Most tested PIs increased apical-to-basolateral TDF permeation and decreased secretory transport in MDCKII cells overexpressing P-glycoprotein (Pgp; MDCKII-MDR1 cells) and Caco-2 cells. PIs were found to cause a multifactorial effect on the barriers to TDF absorption. All PIs showed similar levels of inhibition of esterase-dependent degradation of TDF in an intestinal subcellular fraction, except for amprenavir, which was found to be a weaker inhibitor. All PIs caused a dose-dependent increase in the accumulation of a model Pgp substrate in MDCKII-MDR1 cells. Pgp inhibition constants ranged from 10.3 microM (lopinavir) to >100 microM (amprenavir, indinavir, and darunavir). Analogous to hepatic cytochrome P450-mediated drug interactions, we propose that the relative differences in perturbations in TFV plasma levels when TDF is coadministered with PIs are based in part on the net effect of inhibition and induction of intestinal Pgp by PIs. Combined with prior studies, these findings indicate that intestinal absorption is the mechanism for changes in TFV plasma levels when TDF is coadministered with PIs.

Therapeutic drug monitoring

PURPOSE OF REVIEW

Traditionally, therapeutic drug monitoring has been used for the management of epilepsy, cardiac arrhythmias, asthma and depression. This review provides an update, particularly for the newer clinical applications, and how therapeutic drug monitoring (including use of analytical and interpretation tools) can improve clinical outcomes.

RECENT FINDINGS

Improved drug assay methodologies and a greater understanding of pharmacokinetic and pharmacodynamic mechanisms has allowed the use of therapeutic drug monitoring for immunosuppressant drugs in organ transplant recipients, antiretroviral agents for HIV/AIDS and antimetabolite drugs for leukaemia. In addition, new computer software to analyse drug concentrations in complex populations is being developed and introduced into routine clinical applications to allow increasingly patient-specific assay interpretation.

SUMMARY

Therapeutic drug monitoring assists in improving clinical success rates and minimizing toxicity. The use of therapeutic drug monitoring is therefore likely to become more widespread as new modalities are adopted.

Comparison of the inhibitory activity of anti-HIV drugs on P-glycoprotein

Human immunodeficiency virus 1 (HIV-1) infections are treated with HIV-protease inhibitors (PIs), nucleoside (NRTIs), non-nucleoside (NNRTIs), and nucleotide reverse transcriptase inhibitors (NtRTIs). The combined administration of antiretrovirals improves patient outcomes while increasing the likelihood of drug interactions. Indeed, as substrates, inhibitors, and occasionally also inducers of P-glycoprotein (P-gp) PIs may substantially alter the pharmacokinetics of co-administered drugs. However, the P-gp inhibitory potencies specified in the numerous publications are not comparable, because they were determined with different assays and cell lines. Moreover, data on the interaction of other anti-HIV drugs with P-gp are sparse and conflicting. We therefore aimed to clarify, which anti-HIV drugs inhibit P-gp and to compare the inhibitory potencies using two independent standard methods (calcein uptake assay, flow cytometric rhodamine123 efflux assay). In the calcein assay, all PIs, all NNRTIs, abacavir, and tenofovir disoproxil fumarate acted as P-gp inhibitors with largely differing potencies between compounds. In P388/dx cells the ranking order of inhibition was: nelfinavir>ritonavir>tipranavir>lopinavir>quinidine (positive control)>delavirdine>saquinavir>amprenavir>atazanavir>efavirenz>nevirapine>abacavir>tenofovir disoproxil fumarate. In conclusion this is the first study to provide comprehensive information on the P-gp interaction profile of anti-HIV drugs under identical assay conditions. Our study reveals that many compounds may indeed inhibit P-gp substantially and further indicates that of the various systems tested, the calcein assay in P388/dx/P388 cells is the most suitable and reliable in vitro model for the quantification of P-gp inhibition.

Inhibition of MRP1/ABCC1, MRP2/ABCC2, and MRP3/ABCC3 by Nucleoside, Nucleotide, and Non-Nucleoside Reverse Transcriptase Inhibitors

Many drug interactions with drugs used for the therapy of human immunodeficiency virus (HIV) occur at the level of different cytochrome P450 isozymes. Increasing evidence suggests that antiretrovirals may also modify activity and expression of active drug transport systems. Such interactions may alter drug absorption, elimination, and also drug distribution and reach clinical importance if thereby access to the target site is affected. Beyond P-glycoprotein, the family of multidrug resistance-related proteins (MRP/ABCC) substantially contributes to the elimination of numerous drugs and their metabolites. Because the interaction of MRPs with non-HIV protease inhibitor antiretrovirals has not been studied thoroughly, we investigated whether important non-nucleoside reverse transcriptase inhibitors (NNRTI) (delavirdine, efavirenz, and nevirapine), nucleoside reverse transcriptase inhibitors (NRTI) (abacavir, emtricitabine, and lamivudine), and tenofovir as a nonnucleotide reverse transcriptase inhibitor can interact with MRP1, MRP2, and MRP3 in vitro. Inhibition of these ABC transporters was quantified by confocal laser-scanning microscopy using the 5-chloromethylfluorescein diacetate assay. With the exception of abacavir, which had no effect on MRP3, all the test compounds increased intracellular 5-chloromethylfluorescein fluorescence in a concentration-dependent manner, and this effect was observed in all the overexpressing cell lines but not in the parental cell line, indicating inhibition of MRP1, MRP2, and MRP3. In conclusion, the present study provides the first evidence for a significant and concentration-dependent inhibition of MRPs by NNRTI, NRTI, and tenofovir, which was most pronounced for delavirdine, efavirenz, and emtricitabine, suggesting that this might contribute to some of the known drug interactions impairing HIV therapy and also to the superior effectiveness of combination pharmacotherapy.

Highly active antiretroviral therapy and the kidney: an update on antiretroviral medications for nephrologists

Highly active antiretroviral therapy has dramatically altered the treatment and life expectancy of individuals who are infected with HIV. More than 20 antiretroviral drugs and drug combinations now are available in the United States. Nephrologists need to have an understanding of the pharmacokinetics of antiretroviral medications and the proper dosing of these medications in patients with impaired kidney function. It is also important for nephrologists to be aware of drug-drug interactions that can occur between antiretroviral medications and other medications that they may prescribe, including immunosuppressive medications that are used for renal transplantation, as this becomes more common in HIV-infected patients. Adverse reactions that affect the kidneys and cause fluid-electrolyte complications occur with certain antiretroviral agents, although most are relatively free of nephrotoxicity. This article reviews the clinical pharmacology and dosing modifications of the newer antiretroviral medications in patients with reduced kidney function; important drug-drug interactions involving these medications, particularly with other medications that are likely to be prescribed by nephrologists; and renal toxicities of antiretroviral agents.

Luminometric method for screening retroviral protease inhibitors

We have developed a sensitive luminometric assay for determining the activity of retroviral proteases that uses proteolytic cleavage of polypeptide substrate immobilized on Ni-NTA HisSorb Strips microplates. The protease substrate derived from the Gag precursor protein of Mason-Pfizer monkey virus (M-PMV) was conjugated with horseradish peroxidase (HRP), which catalyzes oxidation of luminol in the assay. The cleavage of the substrate was monitored as a decrease in luminescent signal caused by the release of the cleavage product conjugated to HRP. Testing of a set of M-PMV protease inhibitors confirmed that this method is sufficiently sensitive and specific for high-throughput screening of retroviral protease inhibitors.

Application and impact of population pharmacokinetics in the assessment of antiretroviral pharmacotherapy

Population pharmacokinetics has been an important technique used to explore and define relevant sources of variation in drug exposure and response in patient populations. This has been especially true in the area of antiretroviral therapy where the assurance of adequate and sustained drug exposure of multiple agents is highly correlated with therapeutic success. Population pharmacokinetic analyses across the four drug classes and 20 US FDA-approved products used to treat HIV have been published to date. The published reports were predominantly based on actual clinical trials conducted in HIV-infected patients with one or more agents administered. Modelling and simulation approaches have been used in the evaluation of antiretroviral agent outcomes incorporating problematic design and analysis factors such as sparse plasma sampling, data imbalance and censored data. Additional benefits of population modelling approaches applied to the investigation of antiretroviral agents include the ability to assess dosing compliance, understanding and quantifying drug-drug interactions in order to select dosing regimens and the screening of new drug candidates. Pharmacokinetic/pharmacodynamic models have been used to characterise the relationship between drug exposure and virological and immunological response, and to predict clinical outcome. These models offer the best opportunity for individualising and optimising patient therapy, particularly when adjusted for adherence/compliance. The impact of population pharmacokinetics in the area of antiretroviral therapy can be directly assessed by its role in the validation of surrogate markers such as viral RNA load, therapeutic drug monitoring and the management of individual patient outcomes via exposure-toxicity relationships. Each of these population pharmacokinetic outcomes has contributed to the current regulatory environment, specifically in the area of accelerated approval of new antiretroviral agents.

Drug interactions in the management of HIV infection

The availability of antiretroviral therapy has significantly reduced the morbidity and mortality of HIV infection. In addition, improved treatment of opportunistic infections and comorbidities common to patients with HIV is further prolonging the lives of patients. Improvement in the treatment of HIV has led to a significant increase in the number of medications which caregivers are able to utilise to manage HIV/AIDS. Antiretroviral medications, as well as many of the drugs used in the management of opportunistic infections and primary care (e.g., macrolide antibiotics, azole antifungals, cholesterol-lowering medications), are particularly prone to drug interactions. The interpretation of clinically significant interactions is complicated by the rate at which new information on drug metabolism and transport is becoming available. Management of drug interactions in HIV is further confounded by conflicting study results and differences between documented and theoretical inter-actions. The mechanisms and significance of interactions involving antiretrovirals, drugs used for opportunistic infections, and other medications commonly used in HIV patients will be reviewed.

Quantification of antiretroviral drugs in dried blood spot samples by means of liquid chromatography/tandem mass spectrometry

For the first time approved antiretroviral drugs, i.e. protease inhibitors (PI) and non-nucleoside reverse transcriptase inhibitors (NNRTI), were quantified in dried blood spots (DBS) from HIV/AIDS patient whole blood samples as the basis for therapeutic drug monitoring (TDM) by a robust simultaneous liquid chromatography/tandem mass spectrometry (LC/MS/MS) method. This study included seven PI (amprenavir, nelfinavir, indinavir, lopinavir, saquinavir, ritonavir, atazanavir) and two NNRTI (nevirapine, efavirenz). LC/MS/MS coupling was realized using a Phenomenex Synergy Max RP LC column (150 x 2 mm, 4 micro) in combination with a tandem mass spectrometer (API 2000, Applied Biosystems/MDS Sciex Concord) operating in positive and negative multiple reaction monitoring (MRM) mode with reserpine as internal standard. DBS samples were punched out and extracted with 50:50 MeOH/0.2 M ZnSO4 (v/v) as extraction reagent. The method performance data for the drugs in DBS like limits of detection (LOD, 8-70 ng/mL), lower limits of quantification (LLOQ, 41-102 ng/mL), linearity (R2, 0.9981-0.9999), linear concentration ranges (41-10.000 ng/mL), accuracies (92-113%), recoveries (62-94%), and ion suppression were investigated and are comparable to data obtained from human plasma, which is the current standard matrix for TDM of PI and NNRTI. In this case, off-line plasma sample preparation was performed by means of simple protein precipitation with 80:20 methanol/0.2 M ZnSO4 (v/v) as precipitation reagent. Significant correlations between real patient plasma and DBS were obtained for samples containing lopinavir, atazanavir, ritonavir, saquinavir, and efavirenz. DBS preparation as sampling alternative is well suited and practicable for TDM minimizing the high infection risk of HIV/AIDS samples and may facilitate sample mailing.

Therapeutic drug monitoring for patients with HIV infection: Children's National Medical Center, Washington DC experience

This paper provides a brief overview of therapeutic drug monitoring (TDM) in patients with HIV infection. The manuscipt not only focuses on an update on TDM in HIV infection but also provides the latest information on tandem mass spectrometric methods for antiretroviral drug quantification. Also discussed are the preliminary new and original data on free antiretroviral drug measurement in both plasma and saliva.

Role of purine nucleoside phosphorylase in interactions between 2',3'-dideoxyinosine and allopurinol, ganciclovir, or tenofovir

The level of systemic exposure to 2',3'-dideoxyinosine (ddI) is increased 40 to 300% when it is coadministered with allopurinol (Allo), ganciclovir (GCV), or tenofovir. However, the mechanism for these drug interactions remains undefined. A metabolic route for ddI clearance is its breakdown by purine nucleoside phosphorylase (PNP). Consistent with previous reports, enzymatic inhibition assays showed that acyclic nucleotide analogs can inhibit the phosphorolysis of inosine. It was further established that the mono- and diphosphate forms of tenofovir were inhibitors of PNP-dependent degradation of ddI (K(i)s, 38 nM and 1.3 microM, respectively). Allo and its metabolites were found to be relatively weak inhibitors of PNP (K(i)s, >100 microM). Coadministration of tenofovir, GCV, or Allo decreased the amounts of intracellular ddI breakdown products in CEM cells, while they increased the ddI concentrations (twofold increase with each drug at approximately 20 microM). While inhibition of the physiological function of PNP is unlikely due to the ubiquitous presence of high levels of enzymatic activity, phosphorylated metabolites of GCV and tenofovir may cause the increased level of exposure to ddI by direct inhibition of its phosphorolysis by PNP. The discrepancy between the cellular activity of Allo and the weak enzyme inhibition by Allo and its metabolites may be explained by an indirect mechanism of PNP inhibition. This mechanism may be facilitated by the unfavorable equilibrium of PNP and the buildup of one of its products (hypoxanthine) through the inhibition of xanthine oxidase by Allo. These findings support the inhibition of PNP-dependent ddI degradation as the molecular mechanism of these drug interactions.

Therapeutic drug monitoring of antiretroviral therapy

The concept of managing pharmacotherapy based on plasma drug concentrations has been used for decades in a variety of clinical settings. The interest in therapeutic drug monitoring (TDM) of antiretroviral drugs has grown significantly since highly active antiretroviral therapy (HAART) became a standard of care in clinical practice. A primary characteristic of TDM of antiretroviral drugs is that multiple agents are concomitantly used in HAART regimens. Inadequate drug concentrations may lead to evolution of drug resistance mutations and endanger present and future treatment options. A number of clinical trials have demonstrated that drug serum concentrations are an important factor in response to therapy for HIV, but whether TDM will become a tool for the routine management of HIV infection remains to be determined. This review includes an illustrative case report of measuring concentrations of antiretroviral drugs in a pediatric patient.

Clinical use of a simultaneous HPLC assay for indinavir, saquinavir, ritonavir and nelfinavir in children and adults

PROTEASE INHIBITOR TDM: This study examines the importance of therapeutic drug monitoring (TDM) of protease inhibitors (PI) in adults and children infected with the human immunodeficiency virus (HIV). Pediatric patients were included because information in this population is limited. A high performance liquid chromatographic (HPLC) assay measured indinavir, saquinavir, ritonavir and nelfinavir simultaneously in 0.2 mL of plasma. Initially, the reliability, sensitivity and specificity of the assay were verified in stored samples of plasma from adult patients who had been receiving PIs. Non-detectable concentrations (ND) were <25-50 ng/mL. In 96 out of 293 stored samples from adult patients, selected randomly, concentrations of PIs were ND. In a second prospective study of 10 adults (9 mothers and one father, aged 24-42 years) and 15 children (2.9-18 years) ND levels of PI were observed frequently (27% or 4 out of 15 pediatric subjects). In the latter study, drug-drug interactions, dosing errors, noncompliance and other important problems were identified and corrected. Routine monitoring and interpretation of PI concentrations (TDM) may improve the management of adult and pediatric patients infected with HIV, especially in those who fail to respond, develop adverse effects or viral resistance, or lack compliance.

Therapeutic Drug Monitoring of the HIV/AIDS Drugs Abacavir, Zidovudine, Efavirenz, Nevirapine, Indinavir, Lopinavir, and Nelfinavir

Combination therapy with antiretroviral drugs is used for the treatment of patients infected with the human immunodeficiency virus. To achieve optimal drug concentrations for viral suppression and avoidance of drug toxicity, monitoring of drug levels has been considered essential. We set up an analytical procedure for monitoring the plasma concentrations of a total of seven drugs: abacavir, zidovudine, efavirenz, nevirapine, indinavir, lopinavir, and nelfinavir. The plasma samples were liquid/liquid extracted and subjected to high-performance liquid chromatography (HPLC) analysis. The compounds were monitored by ultraviolet detection: indinavir, lopinavir, and nelfinavir at 215 nm; efavirenz at 254 nm, and abacavir, zidovudine, and nevirapine at 266 nm. Two different extraction procedures and two different HPLC eluents on a C(8) reversed-phase HPLC column were used to monitor all seven compounds. Under steady state conditions, the plasma concentrations of antiviral drugs in 175 patients were correlated with the time after the last dosing to define the peak or trough levels. Due to the short plasma elimination half-life of abacavir and zidovudine, only peak levels could be determined for these compounds, whereas both peak and trough levels could be assessed for the other compounds because of a longer plasma elimination half-life. The mean peak concentrations (microg/ml) were 0.69 for abacavir and 0.57 for zidovudine; the mean peak/trough concentrations (microg/ml) were 2.07/1.32 for efavirenz, 2.43/2.23 for nevirapine, 5.48/1.08 for indinavir, 4.69/3.51 for lopinavir, and 3.54/1.45 for nelfinavir. The described analytical method offers a broad-spectrum monitoring of plasma levels of antiretroviral drugs.

Clinical Use of a Simultaneous HPLC Assay for Indinavir, Saquinavir, Ritonavir, and Nelfinavir in Children and Adults

Protease inhibitor (PI) monitoring may improve the care of human immunodeficiency virus (HIV)-infected patients; however, pediatric data are limited. A high-performance liquid chromatographic (HPLC) assay developed for the simultaneous determination of indinavir, ritonavir, saquinavir, and nelfinavir in 0.2 mL of plasma was used to quantify PI concentrations in HIV patients. The reliability, sensitivity, and specificity of the assay were first verified in stored adult samples. Later, blood collected prospectively from patients aged 2.9 to 42 years of age (10 adults aged 24 to 42 and 15 children aged 2.9 to 18 years) was tested. Nondetectable (below 25-50 ng/mL) concentrations (ND) were found in 33% of adult samples and 24% of pediatric samples. Four patients taking from 13.7 to 28 mg/kg/d of ritonavir (mean of 21.3) had concentrations ranging from ND to 11.4 microg/mL, quite different from predicted values. Correctable, important clinical problems including drug-drug interactions, drug administration problems, and confirmed noncompliance were identified and corrected using modern therapeutic drug monitoring (TDM) techniques. Routine PI monitoring and interpretation (TDM) could improve the care of adult and pediatric HIV patients; especially in patients who do not respond as expected to treatment, develop viral resistance or toxicity, and have questionable compliance.

Drugs and the liver: advances in metabolism, toxicity, and therapeutics

Biotransformation of drugs is one of the major functions of liver. Hepatic drug metabolism develops early in organogenesis and continues in postnatal life through puberty. Genetic and developmental studies on hepatic drug metabolism show that immaturity, polymorphisms, and altered balance of different hepatic enzymatic activities affect pharmacologic inactivation and alter the risk of toxic effects of drugs on the hepatic parenchyma. Although drug-induced liver disease is less common in children, several reports of hepatotoxicity are published every year. Furthermore, the increasing use of nonregulated remedies (eg, herbal preparations or recreational drugs) increases the risk of unpredictable and potentially severe reactions. Many significant advances in the treatment of hepatic diseases have been achieved recently. However, differences in clinical features, natural history, and response to treatment between children and adults require evaluation of new therapeutic options in focused pediatric clinical trials.

Nelfinavir, a protease inhibitor, increases sirolimus levels in a liver transplantation patient: a case report

With the increasing success of liver transplantation and the proven effectiveness of highly active retroviral therapy in HIV-positive patients, liver transplantation has been performed successfully in selected HIV-positive recipients with CD4 and an HIV viral load response to highly active antiretroviral therapy. In these patients, an interaction between a protease inhibitor (nelfinavir) and tacrolimus has been shown. The effect of nelfinavir on the pharmacokinetics of sirolimus, a newer immunosuppressive drug, is currently not known. The goal of the present case report is to document the interaction between sirolimus and nelfinavir in a liver transplantation patient. A 40-year-old woman who was HIV positive underwent a cadaveric liver transplantation for acute fulminant liver failure secondary to nevirapine (a nonnucleoside reverse transcriptase inhibitor). Postoperatively, she was treated with tacrolimus and steroids. She experienced steroid-resistant rejection and was started on sirolimus on the 17th postoperative day. Kinetic parameters were determined after a 2-mg oral dose of sirolimus and 250 mg of nelfinavir by collecting multiple peripheral venous blood samples before and after sirolimus administration. The kinetic parameters were compared with parameters from three liver transplantation patients on sirolimus who were not on nelfinavir. After normalizing the kinetic parameters to sirolimus dose of 1 mg/d, 0-hour and 24-hour trough sirolimus concentrations were nine-fold and five-fold higher for the patient who was on nelfinavir, compared with those who were not on nelfinavir. The maximum concentration was 3.2 times higher, the area under the concentration curve was 1.6 times higher, and the terminal disposition half-life was prolonged by 60%. The time to reach the peak concentration was 1 hour in all patients. Increase in trough concentration, peak concentration area under the curve concentration, and prolongation of half-life of sirolimus has been shown in a patient who was on a low dose (one fifth the recommended dose) of nelfinavir.

The interaction between antiretroviral agents and tacrolimus in liver and kidney transplant patients

Solid organ transplantations have been performed successfully in selected HIV-positive patients with highly active antiretrovirus therapy (HAART). However, some of the medications in the HAART regimen require metabolism via the cytochrome P4503A, the same enzyme complex responsible for clearance of the calcineurin inhibitors cyclosporine and tacrolimus. Several case reports have described significant interactions between the agents used in HAART and immunosuppressive drugs. The goal of this report is to examine the extent of potential drug interactions between antiretroviral agents and tacrolimus after liver and kidney transplantation. Seven liver transplant (LTx) patients (M = 6, F = 1) and four kidney transplant (KTx) patients (M = 4) infected with HIV underwent surgery between September 1997 and January 2001. Initial immunosuppression consisted of tacrolimus and steroids for LTx patients or tacrolimus, steroids, and mycophenolate mofetil for KTx recipients. Their current baseline immunosuppression and HAART regimen were examined retrospectively. Of the seven liver recipients, one (case 4) died 2 weeks after LTx and never received HAART therapy posttransplantation. The remaining six patients were placed on a regimen consisting of two nucleoside reverse transcriptase inhibitors (NRTI) and one protease inhibitor (PI) (nelfinavir in 5, indinavir in 1) based on known viral sensitivities or history of a previous clinical response. Kidney recipients received NRTI and nonnucleoside reverse transcriptase inhibitors (NNRTI). The mean dose of tacrolimus in liver recipients was 0.6 mg/d, with mean trough concentration of 9.7 mg/mL. Compared with historic controls (liver transplant patients not on HAART), the average tacrolimus dose was 16-fold lower in patients on HAART. In contrast to liver recipients, HIV-positive kidney recipients not on PI therapy required a mean tacrolimus dose of 9.5 mg/d to maintain a mean trough concentration of 9.6 ng/mL. Of the two protease inhibitors used, nelfinavir seems to have a more profound effect than indinavir. When patients on nelfinavir alone (n = 5) were compared with a control group not on antiretroviral therapy, the need for a tacrolimus dose was 38 times lower (mean dose, 0.26 mg/d). Profound drug interactions between PI and tacrolimus have been observed requiring up to 50-fold reductions in dosage. This effect seems to be most pronounced with the use of nelfinavir as opposed to indinavir, although further experience is required to confirm this observation. In contrast, HAART using NRTI and NNRTI without the use of PI, as shown in kidney recipients, produces less significant effects on tacrolimus metabolism. Great caution and frequent drug level monitoring are necessary when HAART is introduced or withdrawn in HIV-positive recipients of organ transplants.

[Recommendations of the Spanish AIDS Study Group (GESIDA) and the National Aids Plan (PNS) for antiretroviral treatment in adult patients with human immunodeficiency virus infection in 2002]

OBJECTIVE

To provide an update of recommendation on antiretroviral treatment (ART) in HIV-infected adults.Methods. These recommendations have been agreed by consensus by a committee of the spanish AIDS Study Group (GESIDA) and the National AIDS Plan. To do so, advances in the physiopathology of AIDS and the results on efficacy and safety in clinical trials, cohort and pharmacokinetics studies published in biomedical journals or presented at congresses in the last few years have been reviewed. Three levels of evidence have been defined according to the data source: randomized studies (level A), case-control or cohort studies (level B) and expert opinion (level C). Whether to recommend, consider, or not to recommend ART has been established for each situation.

RESULTS

Currently, ART with combinations of at least three drugs constitutes the treatment of choice in chronic HIV infection. In patients with symptomatic HIV infection, initiation of ART is recommended. In asymptomatic patients initiation of ART should be based on the CD41/mL lymphocyte count and on the plasma viral load (PVL): a) in patients with CD41 lymphocytes < 200 cells/mL, initiation of ART is recommended; b) in patients with CD41 lymphocytes between 200 and 300 cells/mL, initiation of ART should, in most cases, be recommended; however, it could be delayed when the CD41 lymphocyte count remains close to 350 cells/mL and the PVL is low, and c) in patients with CD41 lymphocytes > 350 cells/mL, initiation of ART can be delayed. The aim of ART is to achieve an undetectable PVL. Adherence to ART plays a role in the durability of the antiviral response. Because of the development of cross-resistance, the therapeutic options in treatment failure are limited. In these cases, genotypic analysis is useful. Toxicity limits ART. The criteria for ART in acute infection, pregnancy and postexposure prophylaxis and in the management of coinfection with HIV and hepatitis C and B virus are controversial.

CONCLUSIONS

The current approach to initiating ART is more conservative than in previous recommendations. In asymptomatic patients, the CD41 lymphocyte count is the most important reference factor for initiating ART. Because of the considerable number of drugs available, more sensitive monitoring methods (PVL) and the possibility of determining resistance, therapeutic strategies have become much more individualized.