Plasma Concentrations Of Protease Inhibitors Research Articles

Protease inhibitor plasma concentrations associate with COVID-19 infection.

Protease inhibitors influence a range of innate immunity and inflammatory pathways. We quantified plasma concentrations of key anti-inflammatory protease inhibitors in chronic haemodialysis patients with coronavirus disease 2019 (COVID-19). The samples were collected early in the disease course to determine whether plasma protease inhibitor levels associated with the presence and severity of COVID-19. We used antibody-based immunoassays to measure plasma concentrations of C1 esterase inhibitor, alpha2-macroglobulin, antithrombin and inter-alpha-inhibitor heavy chain 4 (ITIH4) in 100 serial samples from 27 haemodialysis patients with COVID-19. ITIH4 was tested in two assays, one measuring intact ITIH4 and another also detecting any fragmented ITIH4 (total ITIH4). Control cohorts were 32 haemodialysis patients without COVID-19 and 32 healthy controls. We compared protease inhibitor concentration based on current and future COVID-19 severity and with C-reactive protein. Results were adjusted for repeated measures and multiple comparisons. Analysis of all available samples demonstrated lower plasma C1 esterase inhibitor and α2M and higher total ITIH4 in COVID-19 compared with dialysis controls. These differences were also seen in the first sample collected after COVID-19 diagnosis, a median of 4 days from diagnostic swab. Plasma ITIH4 levels were higher in severe than the non-severe COVID-19. Serum C-reactive protein correlated positively with plasma levels of antithrombin, intact ITIH4 and total ITIH4. In conclusion, plasma protease inhibitor concentrations are altered in COVID-19.

Pharmacokinetic Parameters of HIV-1 Protease Inhibitors.

Since the beginning of the HIV epidemic, research has been carried out to control the virus. Understanding the mechanisms of replication has given access to the various classes of drugs that over time have transformed AIDS into a manageable chronic disease. The class of protease inhibitors (PIs) gained notice in anti-retroviral therapy, once it was found that peptidomimetic molecules act by blocking the active catalytic center of the aspartic protease, which is directly related to HIV maturation. However, mutations in enzymatic internal residues are the biggest issue for these drugs, because a small change in biochemical interaction can generate resistance. Low plasma concentrations of PIs favor viral natural selection; high concentrations can inhibit even partially resistant enzymes. Food-drug/drug-drug interactions can decrease the bioavailability of PIs and are related to many side effects. Therefore, this review summarizes the pharmacokinetic properties of current PIs, the changes when pharmacological boosters are used and also lists the major mutations to help understanding of how long the continuous treatment can ensure a low viral load in patients.

Clinical use of cobicistat as a pharmacoenhancer of human immunodeficiency virus therapy.

The pharmacoenhancement of plasma concentrations of protease inhibitors by coadministration of so-called boosters has been an integral part of antiretroviral therapy for human immunodeficiency virus (HIV) for 1.5 decades. Nearly all HIV protease inhibitors are combined with low-dose ritonavir or cobicistat, which are able to effectively inhibit the cytochrome-mediated metabolism of HIV protease inhibitors in the liver and thus enhance the plasma concentration and prolong the dosing interval of the antiretrovirally active combination partners. Therapies created in this way are clinically effective regimens, being convenient for patients and showing a high genetic barrier to viral resistance. In addition to ritonavir, which has been in use since 1996, cobicistat, a new pharmacoenhancer, has been approved and is widely used now. The outstanding property of cobicistat is its cytochrome P450 3A-selective inhibition of hepatic metabolism of antiretroviral drugs, in contrast with ritonavir, which not only inhibits but also induces a number of cytochrome P450 enzymes, UDP-glucuronosyltransferase, P-glycoprotein, and other cellular transporters. This article reviews the current literature, and compares the pharmacokinetics, pharmacodynamics, and safety of both pharmacoenhancers and discusses the clinical utility of cobicistat in up-to-date and future HIV therapy.

HIV protease inhibitors are substrates for OATP1A2, OATP1B1 and OATP1B3 and lopinavir plasma concentrations are influenced by SLCO1B1 polymorphisms

OATP1B1 and OATP1B3 are major hepatic drug transporters whilst OATP1A2 is mainly located in the brain but is also located in liver and several other organs. These transporters affect the distribution and clearance of many endobiotics and xenobiotics and have been reported to have functional single nucleotide polymorphisms (SNPs). We have assessed the substrate specificities of these transporters for a panel of antiretrovirals and investigated the effects of SNPs within these transporters on the pharmacokinetics of lopinavir. SLCO1A2, SLCO1B1 and SLCO1B3 were cloned, verified and used to generate cRNA for use in the Xenopuslaevis oocyte transport system. Using the oocyte system, antiretrovirals were tested for their substrate specificities. Plasma samples (n=349) from the Liverpool therapeutic drug monitoring registry were genotyped for SNPs in SLCO1A2, SLCO1B1 and SLCO1B3 and associations between SNPs and lopinavir plasma concentrations were analysed. Antiretroviral protease inhibitors, but not non-nucleoside reverse transcriptase inhibitors, are substrates for OATP1A2, OATP1B1 and OATP1B3. Furthermore, ritonavir was not an inhibitor of OATP1B1. The 521T>C polymorphism in SLCO1B1 was significantly associated with higher lopinavir plasma concentrations. No associations were observed with functional variants of SLCO1A2 and SLCO1B3. These data add to our understanding of the factors that contribute to variability in plasma concentrations of protease inhibitors. Further studies are now required to confirm the association of SLCO1B1 521T>C with lopinavir plasma concentrations and to assess the influence of other polymorphisms in the SLCO family.

Pregnancy Does Not Increase CYP3A or P-Glycoprotein Activity in the Non-Human Primate, Macaca nemestrina

Plasma concentrations of protease inhibitors are lower in pregnant women than in nonpregnant women or men. Using nelfinavir as a model protease inhibitor, we have shown that this phenomenon can be reproduced in a representative non-human primate model, Macaca nemestrina (J Pharmacol Exp Ther 329:1016-1022, 2009). Nelfinavir is cleared from the body predominantly by CYP3A metabolism and P-glycoprotein (P-gp) efflux. Therefore, using midazolam (MDZ) as a CYP3A probe and digoxin (DIG) as a P-gp probe, we determined the antepartum (73-118 days) and postpartum (61-130 days) in vivo intestinal and hepatic CYP3A or P-gp activity in the macaque. Although the systemic clearance of MDZ was significantly increased ( approximately 70%) during pregnancy after intra-arterial (IA) administration of the drug ((15)N-labeled MDZ; 40 microg/kg), pregnancy did not affect the oral clearance of the drug administered simultaneously (1 mg/kg p.o.) with the IA dose. In vitro studies in hepatic and intestinal S-9 fractions indicated no effect of pregnancy on CYP3A activity or protein expression in the small intestine or liver. In contrast, neither the oral (100 microg/kg) nor the IA (10 microg/kg) clearance of DIG was significantly altered by pregnancy, indicating no effect of pregnancy on P-gp activity. Assuming that MDZ and DIG are selective substrates of the macaque CYP3A enzymes and P-gp, respectively, these results suggest that factors other than increased CYP3A or P-gp activity contribute to the increased clearance of protease inhibitors during M. nemestrina pregnancy.

Atazanavir/ritonavir: A review of its use in HIV therapy

Recommendations for a highly active antiretroviral therapy (HAART) in either pretreated patients or symptomatic patients with an AIDS-defining event are based on a combination of three or more agents from different antiretroviral classes including two nucleoside reverse transcriptase inhibitors with at least one protease inhibitor. The majority of currently available protease inhibitors are coadministered with low-dose ritonavir as a pharmacoenhancer that significantly increases protease inhibitor plasma concentrations. Atazanavir is a highly active azapeptide inhibitor of the HIV protease. It was the first, and to date the only, protease inhibitor designed to be applied once daily (q.d.) and is expected to overcome the problems of earlier agents of this class of drugs, such as unfavorable adverse events like hyperlipidemia, diarrhea and lipodystrophy. Atazanavir, formerly known as BMS-232632, can be dosed either at 400 mg q.d. without a pharmacoenhancer as first-line HIV therapy or combined with ritonavir as atazanavir/ritonavir 300/100 mg q.d. for therapy-experienced patients. The pharmacoenhancing effect of ritonavir on atazanavir resulted in a potent, clinically effective and well-tolerated antiretroviral drug with high plasma concentrations and a sufficient genetic barrier to viral resistance. Nevertheless, noninferiority to lopinavir/ritonavir-containing HAART could not be shown when atazanavir was given unboosted in pretreated patients in the AI424-043 study. When atazanavir was boosted with low-dose ritonavir its efficacy was comparable to that of lopinavir/ritonavir in non-naive patients (AI424-045 study). Additionally, specific side effects were identified during clinical practice, such as an increased rate of patients with jaundice, and, more recently, genetic risk factors causing hyperbilirubinemia. Atazanavir inhibits glucuronyltransferase, an enzyme responsible for the metabolism of bilirubin in liver, thus increasing unconjugated bilirubin levels in blood. However, atazanavir itself also enhances plasma concentrations of other coadministered HIV-1 protease inhibitors, so that its use as a combination partner in boosted double protease inhibitor combinations, with or without the addition of nucleoside reverse transcriptase inhibitors, is being evaluated. Unboosted atazanavir is approved for first-line HIV therapy in adults in the United States, and atazanavir/ritonavir is recommended for the second-line therapy of HIV-1 infection in adult HIV-1-infected patients in the United States and the European Union. More recently, data from the CASTLE study (AI424-138) have been reported at the 15th Conference on Retroviruses and Opportunistic Infections by Molina et al., where boosted atazanavir-containing HAART was compared to a regimen with lopinavir/ritonavir in therapy-naive patients.

Pharmacokinetics of Two Randomized Trials Evaluating the Safety and Efficacy of Indinavir, Saquinavir and Lopinavir in Combination with Low‐Dose Ritonavir: The MaxCmin1 and 2 Trials*

Our objective was to identify possible differences in protease inhibitor plasma concentrations between and within three protease inhibitor regimens (indinavir, saquinavir and lopinavir all in combination with low-dose ritonavir) and to relate these differences to safety and efficacy. Data originated from pre-defined pharmacokinetic substudies within two randomized 48-week trials evaluating the safety and efficacy of three protease inhibitor regimens. At weeks 4 and 48, plasma was collected and minimum drug plasma concentrations, C(min), were obtained. Out of 656 randomized patients, 283 patients had available C(min) at week 4. Indinavir, saquinavir and lopinavir C(min) were high when combined with low-dose ritonavir. No significant difference in the proportion of patients experiencing treatment failure could be found according to the C(min) within any treatment arm. A saquinavir C(min) > 2000 ng/ml was associated with an increased risk of gastrointestinal grade 3 or 4 adverse events and higher total cholesterol. Overall, there were no changes in C(min) from week 4 to week 48 in patients who remained on therapy. No association between treatment failure and the C(min) could be demonstrated. Associations between high C(min) and toxicity were identified in the saquinavir arm; therefore, dose reductions may be appropriate in certain patients with C(min) several times above the minimum effective concentration.

Multidrug Resistance 1 Polymorphisms and Trough Concentrations of Atazanavir and Lopinavir in Patients with HIV

HIV-infected patients receiving protease inhibitors may benefit from therapeutic drug monitoring-assisted dose adjustment to achieve target plasma concentrations. However, efflux pumps such as permeability-glycoprotein, which is encoded by the multidrug resistance (MDR)1 gene, may decrease intracellular drug concentrations, thus reducing the amount of drug at the site of action. Plasma concentrations of protease inhibitors and CD4 cell count response have been associated with the T allele at the MDR1 C3435T locus. We examined MDR1 single nucleotide polymorphisms in a cohort of patients in whom therapeutic drug monitoring is ongoing through a research protocol. In a multicenter study, genotypic analyses at two MDR1 loci, C3435T and G2677T, were performed by a real-time polymerase chain reaction method using DNA from 103 patients categorized as substance users or nonusers on atazanavir or lopinavir as the primary antiretrovirals. Allelic frequencies were determined as a function of racial/ethnic background, substance use status and trough concentrations of atazanavir and lopinavir. The C/T and G/T alleles at the MDR1 C3435T and G2677T loci were equally frequent in the Caucasian population, but the wild-type alleles were more prevalent in the African-American population (59% homozygous [CC] and 32% heterozygous [CT] for C3435T; 80% homozygous [GG] and 16% heterozygous [GT] for G2677T). The frequencies in the Hispanic population were 46% CC and 38% CT for C3435T, and 58% GG and 38% GT for G2677T. No significant differences were seen in allele frequencies for MDR1 polymorphisms in substance user versus nonuser groups. Trough plasma concentrations of atazanavir or lopinavir were not correlated with the variant T allele. These data confirm the higher prevalence of wild-type alleles of the MDR1 gene in African-Americans and the linkage disequilibrium between C3435T and G2677T loci. The T allele at the MDR1 C3435T and G2677T loci was not associated with higher atazanavir or lopinavir trough concentrations.

Lopinavir/rotinavir: Appraisal of its use in HIV therapy

Recommendations for a highly active antiretroviral therapy in either pretreated patients or symptomatic patients with an AIDS-defining event include at least one protease inhibitor. The majority of currently available protease inhibitors are coadministrated with low-dose ritonavir, a pharmacoenhancer that significantly increases protease inhibitor plasma concentrations. In the class of protease inhibitors lopinavir plus ritonavir is the only coformulation. This coformulation was designed to overcome the problems of earlier agents of this class of drugs concerning unfavorable pharmacokinetics with a higher frequency of dosing and therapy failure. The pharmacoenhancing effect of ritonavir on lopinavir resulted in a highly potent, clinically effective antiretroviral drug with a high genetic barrier to viral resistance. Safety concerns have taken a backseat, focusing instead on the favorable efficacy of lopinavir, which recently led to the evaluation of its use in boosted double-protease-inhibitor regimens, as a once-daily application and even in HIV monotherapy. Nevertheless, since HIV infection became a chronic but controllable disease, side effects like metabolic disorders and cardiovascular disease have begun to draw increased attention in the long-term treatment with protease inhibitors. Coformulated lopinavir/ritonavir is available as a soft gelatin capsule (133.33/33.33 mg), liquid formulation (80/20 mg/ml) and recently approved melt-extrusion tablet (200/50 mg). Lopinavir/ritonavir is recommended for first- and second-line therapy in HIV-1 infection, in children as well as adolescents and adults.

530 ALT increase after initiation of protease inhibitor (PI) containing antiretroviral therapy in HIV-HCV coinfected patients is not related to high PI plasma concentrations. ANRSCO-08 cohort

530 ALT increase after initiation of protease inhibitor (PI) containing antiretroviral therapy in HIV-HCV coinfected patients is not related to high PI plasma concentrations. ANRSCO-08 cohort

Elevated Plasma Concentrations of Protease Inhibitors and Nonnucleoside Reverse Transcriptase Inhibitors in Patients Coinfected with Human Immunodeficiency Virus and Hepatitis B or C: Case Series and Literature Review

To evaluate antiretroviral pharmacokinetics in patients who are coinfected with human immunodeficiency virus (HIV) and hepatitis B and/or C virus. Specifically, we sought to determine whether coinfection results in higher than expected concentrations of protease inhibitors and nonnucleoside reverse transcriptase inhibitors (NNRTIs). Case series. Human immunodeficiency virus clinic. Twenty-six patients infected with HIV and hepatitis B and/or C virus. Patients' plasma trough concentrations (Cmeasured) of protease inhibitors and NNRTIs were compared with population average trough concentrations reported in the literature (Cpredicted). Trough concentrations were obtained irrespective of the patients' liver function. A concentration ratio of Cmeasured: Cpredicted was determined for each patient. The mean concentration ratio of the 26 patients was 1.43 (95% confidence interval 1.08-1.78). For the six patients taking nelfinavir, the ratio of nelfinavir's active metabolite (M8): parent drug was calculated. The median M8:nelfinavir ratio for these six patients was 69% lower than what has been reported in a general HIV population. These preliminary findings suggest that trough concentrations of protease inhibitors and NNRTIs may be elevated in patients with HIV infection who are coinfected with hepatitis B and/or C, compared with a general population of patients with HIV infection. Until further investigation defines the relationship between coinfection, metabolic dysfunction, and increased antiretroviral exposure, therapeutic drug monitoring may be helpful to identify coinfected patients at risk for antiretroviral toxicity secondary to elevated plasma drug concentrations.

Maternal-fetal transfer and amniotic fluid accumulation of protease inhibitors in pregnant women who are infected with human immunodeficiency virus

ObjectiveThe purpose of this study was to investigate placental transfer and amniotic fluid concentrations of protease inhibitors when they are given to pregnant women who are infected with human immunodeficiency virus. Study designFifty-eight mothers who received antiretroviral therapy that included ≥1 protease inhibitors for clinical indications at the time of delivery were enrolled in the study. Maternal blood samples and amniotic fluid were obtained during delivery or cesarean delivery, and paired cord blood samples were obtained by venopuncture immediately after the delivery. Drug concentrations were measured with high performance liquid chromatography. ResultsMost maternal protease inhibitor plasma concentrations (38/66 concentrations) were below the trough concentrations that are recommended for therapeutic drug monitoring. Cord blood concentrations were below the assay limit of detection in 10 of 40 samples for nelfinavir and 25 of 40 samples for its metabolite M8, 9 of 11 samples for ritonavir, 4 of 6 samples for indinavir, 5 of 6 samples for saquinavir but were detectable in 3 of 3 samples for amprenavir. Among the 24 amniotic fluid samples that were available, the concentrations below the detection limit were 10 of 16 samples for nelfinavir, 11 of 16 samples for M8, 1 of 3 samples for indinavir, 4 of 4 samples for ritonavir, and 0 of 1 samples for amprenavir. There were significant correlations between cord blood and maternal concentrations of nelfinavir and its metabolite M8. ConclusionPlacental transfer of the human immunodeficiency virus protease inhibitors is generally low; however, it may differ greatly according to the molecule.

The Correlation between Plasma Concentrations of Protease Inhibitors, Medication Adherence and Virological Outcome in HIV-Infected Patients

Although adherence clearly influences response to antiretroviral therapy (ART), accurate assessment of adherence is problematic. The objective of this analysis was to assess the independent predictive value of protease inhibitor (PI) concentrations as a supplement to self-report as markers of medication adherence. This retrospective analysis was conducted from a prospective clinical trial designed to compare the outcomes of frequent versus infrequent HIV RNA measurement used to manage antiretroviral therapy. For 131 patients, self-reported medication adherence, HIV RNA levels, CD4 counts and PI concentrations (unannounced, random samples) were measured at baseline (when patients changed to a new regimen) and every 2 months thereafter. The change in HIV RNA from baseline to month 6 (area-based measure) was used to evaluate overall response. The proportion of measured PI concentrations below the detection limit was used as an alternative marker of adherence. An undetectable concentration would be expected after missing a single dose. The mean baseline CD4 count was 125 cells/mm3 and the mean HIV RNA level was 4.7 log10 copies/ml. The mean change in log10 HIV RNA was -0.73 copies/ml. The mean percentage of self-reported adherence was 91% (range: 15-100%) and the mean proportion of undetectable PI concentrations was 27% (range: 0-100%, mean 2.5 samples/patient). The correlation between the two measures was -0.23 (P=0.009). In a multivariate model, percentage of visits with undetectable PI concentrations (P=0.02), percentage of medication adherence (P=0.02), baseline HIV RNA level (P=0.005), prior PI use (P=0.0004), prior lamivudine (3TC) use (P=0.0009) and randomization to the frequent HIV RNA measurement group (P<0.0001) were all related to change in HIV RNA. After accounting for adherence, patients who always had detectable PI concentrations had an average of 0.4 log10 additional HIV RNA reduction compared with those who had no detectable concentrations. Repeated, random PI concentration values are independently predictive of virological response and may add to self-report of adherence in understanding the response to ART.

Determination of indinavir and nelfinavir trough plasma concentration efficacy thresholds according to virological response in HIV-infected patients.

There is evidence to suggest a pharmacokinetic-pharmacodynamic relationship in HIV-infected patients receiving protease inhibitor (PI)-containing highly active antiretroviral therapy (HAART); however, the effective trough PI plasma concentrations achieved have not been precisely determined. The relationship between HIV viral load and concomitant PI trough plasma concentration (C(trough)) was evaluated in 101 patients receiving at least 4 months of thrice daily indinavir (IDV)-containing (n=68) or nelfinavir (NFV)-containing (n=33) HAART. The more discriminating C(trough) efficacy thresholds were determined statistically for each PI by using the raw C(trough) and the time-corrected C(trough), using the precise delay since the last PI intake and the half-life of each PI. For IDV (P=0.002) and NFV (P=0.019) median C(trough) levels were higher in patients with undetectable viral load [0.23 mg/L (n=30) and 2.3 mg/L (n=16) respectively] than in patients with detectable viral load [0.11 mg/L (n=38) and 0.6 mg/L (n=17) respectively]. C(trough) levels of IDV (r=-0.45; P<0.0001) and NFV (r=-0.43; P=0.011) were correlated with the concomitant viral load. The more discriminating C(trough) efficacy thresholds were estimated statistically as 0.12 mg/L for IDV and 0.5 mg/L for NFV. When C(trough) values were time-corrected, the C(trough) efficacy thresholds, 8 h after the last intake, were 0.15 mg/L for IDV and 0.65 mg/L for NFV. These results support the importance of achieving minimal effective C(trough) to improve the virological efficacy of PI-containing HAART, and specify the target concentrations for IDV and NFV.

Updated clinical pharmacologic considerations for HIV-1 protease inhibitors

Many data associate low protease inhibitor plasma concentrations with suboptimal virologic responses, whereas fewer data associate high plasma concentrations with toxicity. Knowledge of relationships between concentrations and virologic response is important because significant variability in concentrations exists among patients. For antiretroviral-naïve patients, target trough concentrations have been suggested on the basis of retrospective associations with virologic responses. Two prospective studies demonstrated improved virologic responses when indinavir and nelfinavir doses were managed based on these troughs. Investigations among antiretroviral-experienced patients have identified a relationship between the trough concentration and the in-vitro susceptibility of the patient's virus with virologic outcome. However, differences in virologic response may further depend on other pharmacologic factors, such as protein binding, intracellular kinetics, function of drug transporters, and the activity of other drugs in the regimen. In the future, dosing strategies that accommodate the variability in pharmacokinetics and pharmacodynamics may improve virologic outcomes.

HIV and antiretroviral drug distribution in plasma and fat tissue of HIV-infected patients with lipodystrophy.

To determine HIV and antiretroviral drug distribution in plasma and fat tissue of HIV-infected patients with lipodystrophy. Twenty-three consecutive HIV-infected patients (median age, 43 years; male:female ratio, 18:5; median CD4 cell count, 419 x 10(6)/l) undergoing Coleman's lipostructure were enrolled prospectively in this study. HIV-1 RNA and plasma concentration of antiretroviral drugs were determined blindly in plasma and adipocyte lysate samples. HIV-1 proviral DNA was detected by nested PCR in fresh frozen adipocytes. Mean plasma HIV-1 RNA was significantly higher than that in adipocyte lysate samples (this was below the limit of detection in all patients tested). HIV-1 proviral DNA was positive in two out of 18 adipocyte samples with a level between 2 and 5 copies; the distribution seemed to be specific and comparable within each therapeutic class--protease inhibitors (PI) or non-nucleoside reverse transcriptase inhibitors (NNRTI). NNRTI concentrations in adipocyte lysates were approximately 100-fold higher than those of PI. Efavirenz may accumulate in fat tissue as a function of treatment duration. Our results suggest that HIV does not replicate and does not integrate its genome in fat tissue in patients with fat redistribution abnormalities. In patients with effective nadir plasma concentrations of PI and NNRTI, determination of concentration in adipocyte lysates suggests that PI may diffuse in fat tissue with the same pattern of distribution for all structurally related components tested. NNRTI present a high affinity for fat tissue and may accumulate in this compartment.

Pharmacokinetics of amprenavir and lopinavir in combination with nevirapine in highly pretreated HIV-infected patients.

A pharmacokinetic study was performed in five patients treated with the combination of amprenavir, lopinavir and nevirapine. Although the concentrations of amprenavir were within the expected range, lopinavir concentrations varied widely and tended to be lower than predicted by the manufacturer. We concluded that therapeutic drug monitoring should be performed when this combination is applied. In patients failing multiple antiretroviral regimens few options are currently available. The recently licensed protease inhibitors amprenavir and lopinavir have shown substantial virological efficacy in those individuals. When amprenavir is combined with ritonavir 100 mg twice a day, the daily dose can be reduced from 1200 to 450–600 mg twice a day, resulting in sustained or even increased minimal plasma concentrations [1]. Lopinavir is already being co-formulated with ritonavir to achieve sufficient bioavailability. Therefore, the combination of both drugs may be an interesting option for a salvage regimen from both clinical and pharmacokinetics aspects. We studied five severely immunocompromised HIV-infected individuals with virological failure after several treatment regimens including all antiretroviral classes. All patients were treated with at least one nucleoside reverse transcriptase inhibitor (NRTI) and nevirapine (200 mg twice a day) in addition to lopinavir (400/100 mg twice a day) and amprenavir (600 mg twice a day). Baseline characteristics and NRTI as well as HIV-RNA levels and CD4 cell counts after 12 weeks are given in Table 1.Table 1: Baseline and week 12 data in five patients. After 12 weeks only one subject experienced a decline in the HIV-RNA level of more than 1 log10. However, three patients showed a substantial increase in CD4 cell counts. All patients had a complete pharmacokinetic evaluation 2–4 weeks after the start of the combination. Plasma samples were drawn at time points 0, 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8, and 10 h after dosing. They were stored at −80°C until shipping to the laboratory. A method of the simultaneous determination of protease inhibitors was applied, as described previously [2]. The results of the pharmacokinetics are given in Table 2.Table 2: Pharmacokinetic data in five patients. Whereas amprenavir concentrations were within the expected range [3], lopinavir concentrations were quite variable and 40–60% lower than has been reported by the manufacturer [4]. The reason for this effect is unclear from our data. Possible explanations include the co-medication of nevirapine, which may decrease lopinavir concentrations by induction of the cytochrome P450 system, and the interaction of amprenavir with lopinavir. Decreased plasma concentrations of lopinavir when combined with efavirenz have been described in the Abbott study M98-957 [5]. This effect has not been observed with nevirapine [4]. Recently, the combination of amprenavir and lopinavir has been studied by French investigators. In contrast to our data, they found reduced minimal concentrations of amprenavir in the presence of lopinavir. However, no pharmacokinetics were performed, and data were analysed retrospectively [6]. Therefore, confounding factors cannot be excluded in this study. We concluded that the combination of amprenavir, lopinavir and nevirapine may result in unpredictable plasma concentrations of lopinavir. As in the scenario of salvage therapy with multiple underlying resistance mutations, plasma concentrations of protease inhibitors should be as high as possible, and pharmacological monitoring is advisable in patients treated with such combinations. Gerd Fätkenheuera Katja Römera Robert Kampsa Bernd Salzbergera David Burgerb

Limited patient adherence to highly active antiretroviral therapy for HIV-1 infection in an observational cohort study.

Adherence to highly active antiretroviral therapy (HAART) for human immunodeficiency syndrome type 1 (HIV-1) infection is essential to sustain viral suppression and prevent drug resistance. We investigated adherence to HAART among patients in a clinical cohort study. Patients receiving HAART had their plasma concentrations of protease inhibitors or nevirapine measured and completed a questionnaire on adherence. We determined the percentage of patients who reported taking all antiretroviral medication on time and according to dietary instructions in the past week. Drug exposure was compared between patients reporting deviation from their regimen and fully adherent patients. Among patients who received HAART for at least 24 weeks, we assessed the association between adherence and virologic outcome. A total of 224 of 261 eligible patients completed a questionnaire. Forty-seven percent reported taking all antiretroviral medication on time and according to dietary instructions. Patients who reported deviation from their regimen showed lower drug exposure compared with fully adherent patients (median concentration ratio, 0.81 vs 1.07; P =.001). Among those receiving HAART for at least 24 weeks, patients reporting deviation from their regimen were less likely to have plasma HIV-1 RNA levels below 500 copies/mL (adjusted odds ratio, 4.0; 95% confidence interval, 1.4-11.6) compared with fully adherent patients. Only half of the patients took all antiretroviral medication in accordance with time and dietary instructions in the preceding week. Deviation from the antiretroviral regimen was associated with decreased drug exposure and a decreased likelihood of having suppressed plasma HIV-1 RNA loads. Patient adherence should remain a prime concern in the management of HIV-1 infection.

Clinical Pharmacologic Considerations for HIV-1 Protease Inhibitors.

Many data associate low protease inhibitor plasma concentrations with suboptimal virologic responses, whereas relatively few data associate high plasma concentrations with increased likelihood of toxicity. Knowledge of relationships between concentrations and virologic response is important because significant variability in plasma concentrations exists among HIV-infected persons. Unfortunately, a prospectively confirmed therapeutic range that reduces the risk of virologic failure has not been established for the protease inhibitors. Recent investigations have identified a relationship between the measured minimum plasma concentration, the in vitro susceptibility of the subject's virus, and virologic outcome. However, differences in virologic response may further depend on other pharmacologic factors such as protein binding, intracellular kinetics, expression of drug transporters, and drug synergies or antagonisms. In the future, dosing strategies that accommodate the variability in both pharmacokinetics and pharmacodynamics may improve virologic outcomes. In summary, clinical pharmacologic considerations for protease inhibitors can be used to promote their optimal use.

Therapeutic drug monitoring as a tool in treating HIV infection.

Despite its success antiretroviral therapy (ART) is still associated with a significant risk of toxicity and subsequent virological failure. Pending the introduction of drugs with greater potency and durability one of the most pressing priorities in HIV treatment is to identify ways in which to maximize the efficacy of existing therapeutic options while minimizing its toxicity. Resistance testing has been shown to be one such strategy. Therapeutic drug monitoring (TDM) for HIV drugs has been widely proposed as another tool by which treatment may be optimized. There are some parallels with resistance testing not least the potential difficulties or pitfalls in interpreting test results and the understandable pressure for provision of this service in the face of increasingly limited treatment options notwithstanding the current lack of data from controlled clinical studies. In this reviews we shall discuss the value of TDM in the context of a ‘monitoring service (in other words drug concentrations are provided in conjunction with interpretation and advice) rather than a facility for ‘measuring drug concentrations. This distinction is important since the interpretation of drug concentrations is fraught with complexity. (excerpt)