ABT-378, a highly potent inhibitor of the human immunodeficiency virus protease

The Tablet Formulation of Lopinavir/Ritonavir Provides Similar Bioavailability to the Soft-Gelatin Capsule Formulation With Less Pharmacokinetic Variability and Diminished Food Effect

Lopinavir, an HIV protease inhibitor, is coformulated with ritonavir to enhance the bioavailability and pharmacokinetics of lopinavir. The original solid oral formulation of lopinavir/ritonavir, a soft-gelatin capsule (SGC), requires refrigerated storage, is taken as 6 capsules daily at the recommended adult dose, and is administered with food to maximize the bioavailability of lopinavir. Melt extrusion technology was used to produce a tablet formulation reducing the number of dosage units administered per day and simplifying storage requirements. Three studies assessed the bioavailability of tablet doses of lopinavir/ritonavir at 800/200 mg or 400/100 mg under different meal conditions compared with equal doses of the SGC after a moderate-fat meal. The tablet was bioequivalent to the SGC after a moderate-fat meal with respect to lopinavir and ritonavir areas under the concentration-time curve. Compared with the SGC formulation, the tablet formulation resulted in more consistent lopinavir and ritonavir exposures within and across studies and across meal conditions. The diminished food effect and decreased variability of the tablet are likely to result in more consistent lopinavir and ritonavir exposures, minimizing the likelihood of extreme high or low values compared with the SGC.

Lopinavir plus ritonavir: a novel protease inhibitor combination for HIV infections

Lopinavir is a protease inhibitor (PI) for the treatment of HIV infection that was specifically designed to overcome the shortcomings of earlier agents in this class. It is the only PI coformulated with ritonavir, whose pharmacological boosting effect results in a highly potent, well-tolerated, clinically effective antiretroviral agent with a high genetic barrier to resistance. Lopinavir/ritonavir is a recommended first-line option for antiretroviral-naive patients initiating PI-based therapy, and has an equally important role in the management of treatment-experienced individuals. Its favorable pharmacological and clinical characteristics have recently prompted investigators to explore its potential novel applications in HIV monotherapy and double-boosted regimens.

Directed reductive amination of beta-hydroxy-ketones: convergent assembly of the ritonavir/lopinavir core

An efficient procedure for the directed reductive amination of beta-hydroxy-ketones (3) for the stereoselective preparation of 1,3-syn-amino alcohols (6) is reported. The operationally simple protocol uses Ti(iOPr)4 for coordination of the intermediate imino alcohol (5) and PMHS as the reducing agent. The method was expanded to an asymmetric aldol reductive amination sequence to allow a highly convergent synthesis of the hydroxy-amine core of the HIV-protease inhibitors ritonavir and lopinavir. [reaction: see text].

A retrospective TDM database analysis of interpatient variability in the pharmacokinetics of lopinavir in HIV-infected adults

Lopinavir is one of the most-widely used protease inhibitors in the treatment of HIV-1 infected patients. Concentration-effect relationships have been described for both antiviral activity and toxicity. Less is known about patient characteristics that may determine interpatient variability in lopinavir plasma concentrations. A database was created containing all Therapeutic Drug Monitoring (TDM) results collected at our Department. Patients were included if they were using lopinavir twice daily for at least two weeks; subjects who were known to be nonadherent (based on either a lopinavir concentration <0.2 mg/L or suspected by the physician) were excluded. Demographic data were collected from TDM application forms and patient charts. Patients attending one of the 22 HIV treatment centers in The Netherlands. The Department of Clinical Pharmacy is a national referral center for TDM of antiretroviral agents. Lopinavir concentration ratios (CRs) were calculated for each patient by dividing the individual plasma concentration by the time-adjusted population value. Relationships with lopinavir CRs were tested using regression analysis and analysis of variance. A total of 802 patients were included (607 males; 150 females; 45 unknown). The age and body weight of the patients ranged from 18 to 74 years (mean 42) and 42 to 121 kg (mean 72), respectively. Race was known for 756 persons: Caucasian 76%, African 18% and Asian 6%. The median (+ interquartile range, IQR) lopinavir CR was 0.98 (IQR: 0.67-1.31). Body weight showed an inverse relationship with lopinavir CR (F = 23.1; P < 0.001). Age was not related with lopinavir CR (P = 0.99). Female patients had a significantly higher lopinavir CR than males: 1.18 vs. 1.03 (P = 0.005); race was not associated with differences in lopinavir CR. In a multivariate regression analysis body weight, but not gender, remained significantly related to lopinavir CR. Body weight is the only demographic factor that could be related to lopinavir exposure; clinicians should be alert for an increased risk of suboptimal antiviral efficacy in patients with high body weight, and for an increased risk of toxicity in patients with a low body weight.

Impact of EGFR point mutations on the sensitivity to gefitinib: insights from comparative structural analyses and molecular dynamics simulations

Emergence of resistant mutations in drug targets represents a serious problem in the targeted chemotherapy. One challenging issue is to understand the atomic-detailed effect of the mutation on the target. Another intriguing issue is how to predict specific mutations that would show up in the clinical setting, leading to drug resistance. By computational approaches, we have investigated structural, dynamics and energetic effects of a series of EGFR mutations identified from the lung cancer patients. We demonstrated mutation L858R caused gefitinib move closer to the hinge region, whereas T790M caused the ligand escape from the binding pocket. In particular, the T790M decreased the size of the hydrophobic slot formed by L718 and G796. This suggests that, to be effective against the T790M mutant, the inhibitors should avoid interactions with the hydrophobic slot. Mutations T790M, L858R, and their combinations are found to cause different conformational redistribution and to perturb the electrostatic potential at the ATP-binding pocket. Normal mode analysis revealed the mutations resulted in changes in the correlated movements in the protein. In an attempt to develop a computational descriptor for predicting the functional effect of EGFR mutations, we have developed a Plarm algorithm, and the Plarm score was found to be an excellent predictor of the functional impact of six clinical relevant mutations in EGFR tyrosine kinase domains, including T790M, L858R, G719C, L861Q, T790M + L858R double mutant, and delL747-P753insS. The Plarm algorithm could be readily extended to investigate other drug targets.

Lopinavir/ritonavir: a review of its use in the management of HIV infection

Coformulated lopinavir/ritonavir (Kaletra) is a boosted protease inhibitor (PI) containing lopinavir and low-dose ritonavir. It is approved for use in combination with other antiretroviral drugs for the treatment of HIV infection in adults, adolescents and children aged >or=6 months (in the US) or >or=2 years (in the EU).Lopinavir/ritonavir-based antiretroviral therapy (ART) is generally well tolerated and has shown durable virological efficacy in clinical trials in ART-naive and -experienced patients with virological failure. Lopinavir/ritonavir is one of the preferred PIs for first-line treatment of HIV infection in adults, adolescents and children, according to US and British guidelines, reflecting its comparatively better virological efficacy than nelfinavir and low incidence of de novo resistance during long-term treatment. Lopinavir/ritonavir-based treatment may produce a more effective virological response than other PI-based regimens in single PI-experienced, non-nucleoside reverse transcriptase inhibitor (NNRTI)-naive patients. In PI- and NNRTI-experienced patients, atazanavir/saquinavir was inferior to lopinavir/ritonavir; further well designed trials are required to determine the comparative efficacy of lopinavir/ritonavir versus other PIs such as ritonavir-boosted atazanavir, or fosamprenavir or tipranavir in these patients. Lopinavir/ritonavir is more likely than atazanavir (alone or boosted) or nelfinavir to cause hypertriglyceridaemia and is associated with a higher incidence of hypercholesterolaemia than atazanavir (alone or boosted). The new lopinavir/ritonavir tablet coformulation offers a reduced pill count and lack of food interaction, and ART-naive patients in the US and Canada, who are not receiving efavirenz, nelfinavir, nevirapine or amprenavir, may benefit from convenient once-daily administration of lopinavir/ritonavir. Thus, lopinavir/ritonavir is a convenient, effective option for use in the treatment of HIV infection in ART-naive and -experienced adults, adolescents and children.

Screening and selecting for optimized antiretroviral drugs: rising to the challenge of drug resistance

BACKGROUND

Resistance to antiretroviral (ARV) drugs constitutes one of the greatest limitations to effective long-term therapy for human immunodeficiency virus (HIV) infection--a problem alleviated, but by no means overcome, by the application of carefully selected, sequential combination regimens. The rational development of novel therapeutics with the ability to suppress viraemia effectively and also address the complex problems of resistance offers a useful way forward for HIV therapy. The investigational drug TMC114 (darunavir) was designed to be active against both wild-type HIV and strains that are resistant to currently available protease inhibitors.

SCOPE

This review describes the challenges posed by HIV drug resistance and the novel approach taken in the design and selection of TMC114. Articles were identified by searching MEDLINE in September 2005 (search limits: 1995-2006) using the terms: TMC114, darunavir, resistance, screening, selection, ARV therapy, HIV and HAART. Additional data included bibliographies from identified articles.

FINDINGS

With the continuing problem of resistance, ARV drugs must be designed with broad-spectrum activity forming a central part of their development and screening. Drugs must not only be able to treat existing resistant strains, but must also possess more intrinsic resilience to the development of resistance. TMC114 was designed and selected with strong emphasis on potent activity across a range of both wild-type and resistant HIV strains and high binding affinity to HIV protease.

CONCLUSION

This review illustrates that future treatment strategies should include screening against multiple-resistant strains to optimize the identification of novel therapeutic agents for the treatment of HIV.

Long-term immunologic outcome in HAART-experienced subjects receiving lopinavir/ritonavir

The long-term immunological efficacy of regimens including lopinavir/ritonavir (LPV/r) has not been assessed in HIV-infected HAART-experienced subjects. The present study included 452 consecutive HIV-infected outpatients starting LPV/r before May 2003 after failing (HIV-RNA > 1000 copies/ml) HAART. Four groups were considered according to CD4 cell counts at LPV/r initiation: group 1 (G1, n = 115) < 100 cells/mm(3); group 2 (G2, n = 113) 100-199 cells/mm(3); group 3 (G3, n = 115) 200-349 cells/mm(3); group 4 (G4, n = 109) >/= 350 cells/mm(3). The majority of patients were males (n = 320, 70.8%), the median age was 38 years, and 180 (39.6%) were on CDC stage C. The median time of previous HAART was 51.1 months (12-81.7) and a median of 7 antiretroviral regimens and of 3 protease inhibitors was changed before LPV/r. The mean CD4 cell count increase was 105, 113, 128, and 144 cells/mm(3) after 12 months (p < 0.01 for each group) and 128, 106, 90, and 100 cells/mm(3) at month 48 (p < 0.01 for each group) in G1, G2, G3, and G4, respectively. The mean increase was comparable among the four groups. The on treatment analysis showed a better immunologic response among G1 and G2 patients from month 36. Forty-seven patients (10.4%), mainly in G1 and G2, maintained LPV/r despite persistent HIV-RNA > 1000 copies/ml. A mean increase of 64 and 65 cells/mm(3) and of 88 and 56 cells/mm(3) at month 12 and 48 was observed in G1 and G2, respectively. The use of LPV/r-based regimens also provided a durable immunologic recovery in highly pretreated HIV-infected subjects.

Population pharmacokinetics of lopinavir in combination with ritonavir in HIV-1-infected patients

AIMS

To develop a population pharmacokinetic model for lopinavir in combination with ritonavir, in which the interaction between both drugs was characterized, and in which relationships between patient characteristics and pharmacokinetics were identified.

METHODS

The pharmacokinetics of lopinavir in combination with ritonavir were described using NONMEM (version V, level 1.1). First, ritonavir data were fitted to a previously developed model to obtain individual Bayesian estimates of pharmacokinetic parameters. Hereafter, an integrated model for the description of the pharmacokinetics of lopinavir with ritonavir was designed.

RESULTS

From 122 outpatients 748 lopinavir and 748 ritonavir plasma concentrations were available for analysis. The interaction between the drugs was described by a time-independent inverse relationship between the exposure to ritonavir over a dosing-interval and the apparent clearance (CL/F) of lopinavir. The model parameters volume of distribution and absorption rate constant were 61.6 l (95% prediction interval (PI) 22.4, 83.7) and 0.564 h(-1) (95% PI 0.208, 0.947), respectively. The model yielded a theoretical value for the CL/F of lopinavir without ritonavir of 14.8 l h(-1) (95%PI 12.1, 20.1), which translates to a value of 5.73 l h(-1) in the presence of ritonavir. The only factor with significant effect on the pharmacokinetics was concurrent use of non-nucleoside reverse transcriptase inhibitors (NNRTI), which increased the CL/F of lopinavir by 39% (P < 0.001).

CONCLUSIONS

We have developed a model that has defined a time-independent inverse relationship between the exposure to ritonavir and the CL/F of lopinavir, and provided an adequate description of the pharmacokinetic parameters for the latter. Concomitant use of the NNRTIs efavirenz and nevirapine increased the CL/F of lopinavir.

Single-dose safety and pharmacokinetics of brecanavir, a novel human immunodeficiency virus protease inhibitor

Brecanavir (BCV, 640385) is a novel, potent protease inhibitor (PI) with low nanomolar 50% inhibitory concentrations against PI-resistant human immunodeficiency virus (HIV) in vitro. This phase I, double-blind, randomized, placebo-controlled, two-part single-dose study (first time with humans) was conducted to determine the safety, tolerability, and pharmacokinetics of BCV administered at 10 mg/ml in a tocopherol-polyethylene glycol succinate-polyethylene glycol 400-ethanol 50:40:10 solution. In part 1 of the study, single oral doses of BCV ranged from 25 mg to 800 mg. In part 2, single oral doses of BCV ranged from 10 mg to 300 mg and were coadministered with 100-mg oral ritonavir (RTV) soft gel capsules. Single doses of BCV and BCV/RTV were generally well tolerated. There were no severe adverse events (SAEs), and no subject was withdrawn due to BCV. The most commonly reported drug-related AEs during both parts of the study combined were gastrointestinal disturbances (similar to placebo) and headache. BCV was readily absorbed following oral administration with mean times to maximum concentration from >1 h to 2.5 h in part 1 and from 1.5 h to 3 h in part 2. Administration of BCV without RTV resulted in BCV exposures predicted to be insufficient to inhibit PI-resistant virus based on in vitro data. Coadministration of 300 mg BCV with 100 mg RTV, however, significantly increased the plasma BCV area under the concentration-time curve and maximum concentration 26-fold and 11-fold, respectively, achieving BCV concentrations predicted to inhibit PI-resistant HIV.

Discovery of imidazolidine-2,4-dione-linked HIV protease inhibitors with activity against lopinavir-resistant mutant HIV

A new series of HIV protease inhibitors has been designed and synthesized based on the combination of the (R)-(hydroxyethylamino)sulfonamide isostere and the cyclic urea component of lopinavir. The series was optimized by replacing the 6-membered cyclic urea linker with an imidazolidine-2,4-dione which readily underwent N-alkylation to incorporate various methylene-linked heterocycle groups that bind favorably in site 3 of HIV protease. Significant improvements compared to lopinavir were seen in cell culture activity versus wild-type virus (pNL4-3) and the lopinavir-resistant mutant virus A17 (generated by in vitro serial passage of HIV-1 (pNL4-3) in MT-4 cells). Select imidazolidine-2,4-dione containing PIs were also more effective at inhibiting highly resistant patient isolates Pt1 and Pt2 than lopinavir. Pharmacokinetic data collected for compounds in this series varied considerably when coadministered orally in the rat with an equal amount of ritonavir (5 mg/kg each). The AUC values ranged from 0.144 to 12.33 microg h/mL.

Lopinavir/ritonavir induces the hepatic activity of cytochrome P450 enzymes CYP2C9, CYP2C19, and CYP1A2 but inhibits the hepatic and intestinal activity of CYP3A as measured by a phenotyping drug cocktail in healthy volunteers

OBJECTIVE

The effect of lopinavir/ritonavir (LPV/r) administration on cytochrome P450 (CYP) enzyme activity was quantified using a phenotyping biomarker cocktail. Changes in CYP2C9, CYP2C19, CYP3A, CYP1A2, N-acetyltransferase-2 (NAT-2), and xanthine oxidase (XO) activities were evaluated using warfarin (WARF) + vitamin K, omeprazole (OMP), intravenous (IV) and oral (PO) midazolam (MDZ), and caffeine (CAF).

DESIGN

: Open-label, multiple-dose, pharmacokinetic study in healthy volunteers.

METHODS

Subjects (n = 14) simultaneously received PO WARF 10 mg, vitamin K 10 mg, OMP 40 mg, CAF 2 mg/kg, and IV MDZ 0.025 mg/kg on days (D) 1 and 14, and PO MDZ 5 mg on D2 and D15. LPV/r (400/100 mg twice daily) was administered on D4-17. CYP2C9 and CYP2C19 activities were quantified by S-WARF AUC0-inf and OMP/5-hydroxy OMP ratio, respectively. CYP1A2, NAT-2, and XO activities were quantified by urinary CAF metabolite ratios. Hepatic and intestinal + hepatic CYP3A activities were quantified by IV (CL) and PO (CL/F) MDZ clearance, respectively.

RESULTS

After LPV/r therapy, CYP2C9, CYP2C19, and CYP1A2 activity increased by 29%, 100%, and 43% (P = 0.001, 0.046, and 0.001), respectively. No changes were seen in NAT-2 or XO activity. Hepatic and intestinal + hepatic CYP3A activity decreased by 77% (P < 0.001) and 92% (P = 0.001), respectively.

CONCLUSION

LPV/r therapy results in modest induction of CYP1A2 and CYP2C9 and potent induction of CYP2C19 activity. Increasing doses of concomitant medications metabolized by these enzymes may be necessary. LPV/r inhibited intestinal CYP3A to a greater extent than hepatic CYP3A activity. Doses of concomitant CYP3A substrates should be reduced when combined with LPV/r, although intravenously administered compounds may require less of a relative dose reduction than orally administered compounds.

Structural biology and drug discovery

It has long been recognized that knowledge of the 3D structures of proteins has the potential to accelerate drug discovery, but recent developments in genome sequencing, robotics and bioinformatics have radically transformed the opportunities. Many new protein targets have been identified from genome analyses and studied by X-ray analysis or NMR spectroscopy. Structural biology has been instrumental in directing not only lead optimization and target identification, where it has well-established roles, but also lead discovery, now that high-throughput methods of structure determination can provide powerful approaches to screening.

Lopinavir/ritonavir: towards simplifying therapy in HIV infection

Combination antiretroviral therapy has greatly decreased the morbidity and mortality associated with HIV infection, although many agents currently available are limited by difficult dosing requirements, side-effect profiles and the development of resistance. Lopinavir/ritonavir is a coformulation of two protease inhibitors that exploit a favorable drug–drug interaction, yielding sustained increases in plasma levels of lopinavir. This agent has shown excellent therapeutic efficacy in both antiretroviral-naïve and –experienced patients, with a tolerable side-effect profile and without evidence of the development of primary resistance mutations in registrational trials. Once-daily dosing has been approved recently for use in antiretroviral-naïve patients, and US FDA approval was granted recently for a new tablet formulation that decreases the number of pills required for standard dosing.

Non-infectious fluorimetric assay for phenotyping of drug-resistant HIV proteinase mutants

BACKGROUND

The introduction of HIV proteinase inhibitors (PIs) as anti-AIDS drugs resulted in decreased mortality and prolonged life expectancy of HIV-positive patients. However, rapid selection of drug-resistant HIV variants is a common complication in patients undergoing highly active anti-retroviral therapy (HAART). Thus, monitoring of clinical resistance development is indispensable for rational pharmacotherapy.

OBJECTIVE

We present a non-infectious cell-based assay for drug resistance quantification of HIV proteinase (PR) - an important target of HAART.

STUDY DESIGN

Previously, we showed [Lindsten K, Uhlikova T, Konvalinka J, Masucci MG, Dantuma NP. Cell-based fluorescence assay for human immunodeficiency virus type 1 protease activity. Antimicrob Agents Chemother 2001;45:2616-22] that the expression of a fusion protein (GFP-PR), comprised of HIV-1 proteinase wild-type artificial precursor (PR) and green fluorescent protein (GFP), in transiently transfected tissue culture cells depends on the presence of PR-specific inhibitors (PIs). Here we show that in the GFP-PR reporter the HIV wild-type PR can be replaced by a drug-resistant HIV PR mutant, yielding a simple and biologically relevant tool for the quantitative analysis of drug-resistant HIV PR mutants susceptibility to HIV proteinase inhibitors.

RESULTS

We cloned a set of GFP-PR reporters, some of which possess a simple, well-defined drug-resistant PR mutant (G48V L90M, V82A, A71V V82T I84V, D30N, K45I); another four complex PR mutants were obtained from patients undergoing HAART. The results were compared with genotyping and enzyme kinetics data. Furthermore, we designed a single inhibitor concentration experiment setup for easy evaluation of drug resistance profiles for mutants of interest. The resistance profiles clearly demonstrate the importance of succession of individual drugs during the treatment for drug resistance development.

CONCLUSION

We show that the GFP-PR assay might serve as a non-infectious, rapid, cheap, and reliable alternative to the currently used phenotypic assays.

Prevalence of the HIV-1 protease mutation I47A in clinical practice and association with lopinavir resistance

Mutation proI47A has recently been associated with lopinavir/ritonavir (LPV/r) resistance. Only four out of 1859 specimens (0.2%) sent for drug resistance testing (219 drug-naive and 1650 antiretroviral-experienced) showed I47A. All belonged to patients failing LPV/r. The prevalence among protease inhibitor-experienced patients was 0.6%. Phenotypic testing showed that proI47A caused high-level lopinavir resistance (> 100-fold) and cross-resistance to amprenavir, whereas it caused hypersusceptibility to saquinavir. ProI47A should thus be considered the primary lopinavir resistance mutation.

Minimizing resistance consequences after virologic failure on initial combination therapy: a systematic overview

OBJECTIVE

To identify optimal first-line therapies based on the rate of virologic success (VS) and the preservation of future treatment options in antiretroviral therapy (ART)-naive subjects.

DESIGN

Systematic overview of genotypic resistance mutations from clinical trials of combination ART.

METHODS

Various sources were searched for studies in ART-naive subjects providing virologic response rates and genotypes from subjects with virologic failure. The International AIDS Society-USA genotypic resistance guidelines were used to calculate regimen resistance cost (RCreg) and number of active drug (AD) scores for each regimen and to rank the regimens.

RESULTS

Intra- and interstudy comparisons showed higher VS rates for nonnucleoside reverse transcriptase inhibitor (NNRTI) regimens (range: 51%-76%) and boosted protease inhibitor (boosted PI) regimens (range: 55%-79%). Boosted PI failures had the lowest RCreg (range: 0.12-0.21) and the highest AD (range: 19.80-20.18) scores. NNRTI failures had higher RCreg (range: 0.00-1.22) and lower AD (range: 16.83-21) scores.

CONCLUSIONS

NNRTI and boosted PI regimens provide the highest rates of VS in treatment-naive HIV-infected persons. Treatment option scores were higher in subjects who failed boosted PI- containing regimens versus NNRTI-containing regimens, however.

Potencies of human immunodeficiency virus protease inhibitors in vitro against Plasmodium falciparum and in vivo against murine malaria

Parasite resistance to antimalarial drugs is a serious threat to human health, and novel agents that act on enzymes essential for parasite metabolism, such as proteases, are attractive targets for drug development. Recent studies have shown that clinically utilized human immunodeficiency virus (HIV) protease inhibitors can inhibit the in vitro growth of Plasmodium falciparum at or below concentrations found in human plasma after oral drug administration. The most potent in vitro antimalarial effects have been obtained for parasites treated with saquinavir, ritonavir, or lopinavir, findings confirmed in this study for a genetically distinct P. falciparum line (3D7). To investigate the potential in vivo activity of antiretroviral protease inhibitors (ARPIs) against malaria, we examined the effect of ARPI combinations in a murine model of malaria. In mice infected with Plasmodium chabaudi AS and treated orally with ritonavir-saquinavir or ritonavir-lopinavir, a delay in patency and a significant attenuation of parasitemia were observed. Using modeling and ligand docking studies we examined putative ligand binding sites of ARPIs in aspartyl proteases of P. falciparum (plasmepsins II and IV) and P. chabaudi (plasmepsin) and found that these in silico analyses support the antimalarial activity hypothesized to be mediated through inhibition of these enzymes. In addition, in vitro enzyme assays demonstrated that P. falciparum plasmepsins II and IV are both inhibited by the ARPIs saquinavir, ritonavir, and lopinavir. The combined results suggest that ARPIs have useful antimalarial activity that may be especially relevant in geographical regions where HIV and P. falciparum infections are both endemic.

Low Genetic Barrier to Large Increases in HIV-1 Cross-Resistance to Protease Inhibitors during Salvage Therapy

HIV-1 resistance to protease inhibitors (PIs) is characterized by extensive cross-resistance within this drug class. Some PIs, however, appear less affected by cross-resistance and are often prescribed in salvage therapy regimens for patients who have failed previous PI treatment. To examine the capacity of HIV-1 to adapt to these treatment changes, we have followed the evolution of HIV-1 protease genotypes and phenotypes in 21 protease-inhibitor-experienced patients in whom 26 weeks of an aggressive salvage regimen associating lopinavir, amprenavir and ritonavir failed to suppress viral replication. Baseline genotypes exhibited a median of seven resistance mutations in the protease. After 26 weeks of treatment, changes in protease genotypes were seen in 13/21 patients. The evolution of these protease genotypes was rapid, with more than one-third of the changes occurring during the first 6 weeks. Although the mean number of additional mutations was small (2.15 new mutations at week 26) these mutations were sufficient to promote remarkable changes in resistance phenotype. In several patients, some of the new mutations were found to exist before salvage treatment as part of minority quasi-species. Thus, in the face of the strong pharmacological pressure exerted by combinations of PIs to which it has never been exposed, and in spite of limited cross-resistance to these drugs before salvage therapy, HIV-1 can rapidly adapt its resistance genotype and phenotype at a minimal evolutionary cost.

Predictive factors of hyperlipidemia in HIV-infected subjects receiving lopinavir/ritonavir

We studied 382 multiexperienced HIV-infected patients followed up for > or =3 months after starting lopinavir/ritonavir (LPV/r) to identify the factors predicting hypertriglyceridemia and high non-HDL cholesterol levels (triglycerides > or =200 mg/dl and/or non-HDL cholesterol > or =190 mg/dl) after 6 and 12 months of LPV/r exposure. The predictors of hypertriglyceridemia were higher baseline triglyceride levels [OR: 2.28 (95% CI: 1.67-3.12) for each additional 100 mg/dl; p = 0.001], the total duration of antiretroviral treatment [OR: 1.26 (95% CI: 1.12-1.41) for each additional year; p = 0.01], CDC stage C (OR: 2.06; 95% CI: 1.24-3.88; p = 0.02), and male gender (OR: 2.52; 95% CI: 1.42-4.74; p = 0.02); intravenous drug abusers seem less likely to develop the event (OR: 0.52; 95% CI: 0.37-0.92; p = 0.03). The predictors of high non-HDL cholesterol levels were higher baseline levels [OR: 3.92 (95% CI: 1.92-6.24) for each additional 100 mg/dl; p = 0.001) and the combination of NRTIs and NNRTIs with LPV/r (OR: 1.83; 95% CI: 1.10-3.69; p = 0.03). The 75 patients stopping LPV/r showed a significant reduction in median triglyceride and non-HDL cholesterol levels after 3 months of 39 mg/dl and 20 mg/dl (p = 0.01 for both), respectively. Patients with high triglyceride and non- HDL cholesterol levels at the start of LPV/r treatment are at higher risk of developing hyperlipidemia.

The potential impact of structural genomics on tuberculosis drug discovery

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB) in humans, is a devastating infectious organism that kills approximately two million people annually. The current suite of antibiotics used to treat TB faces two main difficulties: (i) the emergence of multidrug-resistant (MDR) strains of M. tuberculosis, and (ii) the persistent state of the bacterium, which is less susceptible to antibiotics and causes very long antibiotic treatment regimes. The complete genome sequences of a laboratory strain (H37Rv) and a clinical strain (CDC1551) of M. tuberculosis and the concurrent identification of all the open reading frames that encode proteins within this organism, present structural biologists with a wide array of protein targets for structure determination. Comparative genomics of the species that make up the M. tuberculosis complex has also added an array of genomic information to our understanding of these organisms. In response to this, structural genomics consortia have been established for targeting proteins from M. tuberculosis. This review looks at the progress of these major initiatives and the potential impact of large scale structure determination efforts on the development of inhibitors to many proteins. Increasing sophistication in structure-based drug design approaches, in combination with increasing numbers of protein structures and inhibitors for TB proteins, will have a significant impact on the downstream development of TB antibiotics.

Pharmacoenhancement of Protease Inhibitors

Toxicity, adherence problems, and virological failure may limit treatment by protease inhibitor-containing regimens at standard doses. Addition of low-dose ritonavir results in a high plasma concentration of coadministered protease inhibitor resulting in decreased pill burden, a reduction in the number of doses, fewer food and/or fluid restrictions, and a higher rate of virological suppression. These effects are due to improved pharmacokinetics of coadministered protease inhibitors.

Therapeutic Drug Monitoring and Human Immunodeficiency Virus (HIV) Antiretroviral Therapy

Treatment with antiretroviral drugs such as the HIV protease inhibitors and non-nucleoside reverse transcriptase inhibitors have contributed to the improvement of life of many HIV-infected patients in recent years, but antiretroviral therapy is not without problems. In some patients, treatment is not effective and suppression of viral replication is not achieved. Other patients experience toxicity and have to stop treatment or change to a less effective treatment. Several studies have demonstrated a relationship between plasma concentrations of the protease inhibitors and non-nucleoside reverse transcriptase inhibitors and viral suppression and toxicity. Therapeutic drug monitoring uses drug concentrations to individualize and optimise therapy by dosage adjustments and many clinicians have advocated for the use of therapeutic drug monitoring in HIV antiretroviral therapy. Evidence from a number of randomized clinical trials supports the use of therapeutic drug monitoring, but the studies have limitations and might not apply to all the antiretroviral drugs. However, the consensus is that certain patients are very likely to benefit from therapeutic drug monitoring. Additionally, the combination of therapeutic drug monitoring and genotypic or phenotypic resistance testing might further improve antiretroviral therapy.

[Progress in antiretroviral drugs]

HIV-1, causative agent of acquired immunodeficiency syndrome, was identified in the early 1980s . The plague quickly spread throughout the world and today 40 million people are living with HIV/AIDS. The first anti-HIV drug "zidovudine", was discovered in 1985, and many other inhibitory compounds have been developed successfully in the last decade. Today, three classes 17 antiretroviral drugs are available in Japan. This article overviews the history of anti-HIV drug discovery, present HIV-1 treatment, and on-going drug discovery.

Synthesis and antiviral activities of novel N-alkoxy-arylsulfonamide-based HIV protease inhibitors

A series of novel N-alkoxy-arylsulfonamide HIV protease inhibitors with low picomolar enzyme activity and single digit nanomolar antiviral activity is disclosed.

Absence of circadian variation in the pharmacokinetics of lopinavir/ritonavir given as a once daily dosing regimen in HIV-1-infected patients

AIMS

To compare the pharmacokinetics of lopinavir/ritonavir (LPV/r) 800/200 mg administered once daily in the morning compared with the evening.

METHODS

This was a randomized, two-way, cross-over study in HIV+ subjects. In each subject the pharmacokinetics of each drug were characterized after 2 weeks of LPV/r 800/200 mg administered once daily at 08.00 h and 19.00 h. On study days, LPV/r was taken with a standardized meal (800 kCal, 25% from fat) after fasting for at least 5 h. LPV/r concentrations were measured by LC-MS/MS, and the data were analyzed by noncompartmental pharmacokinetic analysis.

RESULTS

Fourteen subjects completed the study (all men, mean age/weight 44 year/81 kg). The median (interquartile range) LPV AUC(0,24 h), maximum plasma concentration (C(max)) and concentration at the end of the dosing interval (C(24 h)) after am and pm dosing was, respectively, 143 (116-214) mg l(-1) h, 12.8 (10.3-17.2) mg l(-1), 1.34 (0.58-3.25) mg l(-1), and 171 (120-232) mg l(-1) h, 12.9 (8.22-16.3) mg l(-1), 1.15 (0.59-1.98) mg l(-1). The geometric mean ratio (GMR, am : pm) and 95% CI of the LPV AUC(0,24 h), C(max), and C(24 h) was 0.91 (0.79, 1.06), 1.11 (0.94, 1.32), and 1.19 (0.72, 1.96), respectively. The median ritonavir C(max) after am and pm dosing was 1.05 and 0.90 mg l(-1), respectively. The GMR (95% CI) of the RTV AUC(0,24 h), C(max), and C(24 h) was 0.93 (0.80, 1.08), 1.27 (1.00, 1.63), and 1.04 (0.68, 1.60), respectively. Administration of LPV/r in a once-daily regimen was generally well tolerated.

CONCLUSIONS

No differences were observed in the pharmacokinetics of LPV/r after am or pm dosing with food, which suggests that this once daily combination, can be taken in the morning or evening. Such flexibility in dosing may improve adherence.

Mechanism-based inhibition of cytochrome P450 3A4 by therapeutic drugs

Consistent with its highest abundance in humans, cytochrome P450 (CYP) 3A is responsible for the metabolism of about 60% of currently known drugs. However, this unusual low substrate specificity also makes CYP3A4 susceptible to reversible or irreversible inhibition by a variety of drugs. Mechanism-based inhibition of CYP3A4 is characterised by nicotinamide adenine dinucleotide phosphate hydrogen (NADPH)-, time- and concentration-dependent enzyme inactivation, occurring when some drugs are converted by CYP isoenzymes to reactive metabolites capable of irreversibly binding covalently to CYP3A4. Approaches using in vitro, in silico and in vivo models can be used to study CYP3A4 inactivation by drugs. Human liver microsomes are always used to estimate inactivation kinetic parameters including the concentration required for half-maximal inactivation (K(I)) and the maximal rate of inactivation at saturation (k(inact)). Clinically important mechanism-based CYP3A4 inhibitors include antibacterials (e.g. clarithromycin, erythromycin and isoniazid), anticancer agents (e.g. tamoxifen and irinotecan), anti-HIV agents (e.g. ritonavir and delavirdine), antihypertensives (e.g. dihydralazine, verapamil and diltiazem), sex steroids and their receptor modulators (e.g. gestodene and raloxifene), and several herbal constituents (e.g. bergamottin and glabridin). Drugs inactivating CYP3A4 often possess several common moieties such as a tertiary amine function, furan ring, and acetylene function. It appears that the chemical properties of a drug critical to CYP3A4 inactivation include formation of reactive metabolites by CYP isoenzymes, preponderance of CYP inducers and P-glycoprotein (P-gp) substrate, and occurrence of clinically significant pharmacokinetic interactions with coadministered drugs. Compared with reversible inhibition of CYP3A4, mechanism-based inhibition of CYP3A4 more frequently cause pharmacokinetic-pharmacodynamic drug-drug interactions, as the inactivated CYP3A4 has to be replaced by newly synthesised CYP3A4 protein. The resultant drug interactions may lead to adverse drug effects, including some fatal events. For example, when aforementioned CYP3A4 inhibitors are coadministered with terfenadine, cisapride or astemizole (all CYP3A4 substrates), torsades de pointes (a life-threatening ventricular arrhythmia associated with QT prolongation) may occur.However, predicting drug-drug interactions involving CYP3A4 inactivation is difficult, since the clinical outcomes depend on a number of factors that are associated with drugs and patients. The apparent pharmacokinetic effect of a mechanism-based inhibitor of CYP3A4 would be a function of its K(I), k(inact) and partition ratio and the zero-order synthesis rate of new or replacement enzyme. The inactivators for CYP3A4 can be inducers and P-gp substrates/inhibitors, confounding in vitro-in vivo extrapolation. The clinical significance of CYP3A inhibition for drug safety and efficacy warrants closer understanding of the mechanisms for each inhibitor. Furthermore, such inactivation may be exploited for therapeutic gain in certain circumstances.

Safety of lopinavir/ritonavir for the treatment of HIV-infection

Kaletra, a fixed-dose co-formulation of lopinavir/ritonavir, was the first boosted protease inhibitor developed for the treatment of HIV-infection. In September 2000, the US FDA granted Kaletra fast-track approval as data showed a higher efficacy in the treatment of HIV-infection than standard protease inhibitors of that time. Although potency was of major concern in the early years of highly active antiretroviral therapy (HAART), presently, with the perspective of HIV-infection becoming a chronic but well controllable disease, other issues begin to draw increased attention in the long-term management of HIV-infected patients. Among general health issues such as cardiovascular disease, metabolic disorders or hepatitis co-infection, the long-term toxicity and safety of HAART is an important concern when choosing antiretroviral drugs for each individual patient. In this review, the authors report on the safety of lopinavir/ritonavir in the treatment of HIV-infected patients, and focus on special patient groups and relevant safety issues.

Use of lopinavir/ritonavir in HIV-infected patients failing a first-line protease-inhibitor-containing HAART

OBJECTIVES

The long-term virological efficacy of lopinavir/ritonavir-containing highly active antiretroviral therapy (HAART) in HIV-infected patients failing a first-line protease inhibitor (PI)-based regimen is still unclear.

METHODS

An observational study was carried out from December 2000-December 2002 on 111 consecutive patients starting lopinavir/ritonavir. The primary end-point was virological success (HIV RNA <50 copies/mL in two consecutive determinations). CD4 outcome, lipid levels and adverse events were recorded. The Kaplan-Meier method and log-rank test were used to estimate the time-dependent probability of reaching the end-point using intention-to-treat and on-treatment approaches.

RESULTS

Ninety-six patients obtained virological success during follow-up; Kaplan-Meier analysis showed that the time-dependent probability of obtaining this end-point was 78.4% at month 12 and 85.8% at month 24. The median CD4+cell count increased by 118 cells/mm(3) from baseline to month 12 and by 153 cells/mm(3) to month 24. Thirty-one patients discontinued lopinavir/ritonavir: 16 because of drug-related toxicities, six for simplification, five because of virological failure, one patient was lost at follow-up and three died. An elevation in lipid parameters was observed, but only a minority of patients developed a grade 3 or higher hypertriglyceridaemia and/or hypercholesterolaemia. Among the 15 patients not reaching virological success, five had < or =5 mutations in the protease region known to reduce susceptibility to lopinavir/ritonavir (one discontinued lopinavir/ritonavir because of gastrointestinal intolerance), five had no mutations (two discontinued lopinavir/ritonavir because of gastrointestinal intolerance) and five showed > or =6 mutations (all discontinued lopinavir/ritonavir); however, of the patients who discontinued lopinavir/ritonavir none achieved HIV RNA <50 copies/mL on subsequent regimens.

CONCLUSIONS

Lopinavir/ritonavir was highly effective and well tolerated in HIV-infected patients failing a first-line PI-based HAART.

Monitoring processed, mature Human Immunodeficiency Virus type 1 particles immediately following treatment with a protease inhibitor-containing treatment regimen

Protease inhibitors (PIs) block HIV-1 maturation into an infectious virus particle by inhibiting the protease processing of gag and gag-pol precursor proteins. We have used a simple anti-HIV-1 p24 Western blot to monitor the processing of p55gag precursor into the mature p24 capsid immediately following the first dosage of a PI-containing treatment regimen. Evidence of PI activity was observed in plasma virus as early as 72 hours post treatment-initiation and was predictive of plasma viral RNA decrease at 4 weeks.

Metabolism and disposition of the HIV-1 protease inhibitor lopinavir (ABT-378) given in combination with ritonavir in rats, dogs, and humans

PURPOSE

The objective of this study was to examine the metabolism and disposition of the HIV protease inhibitor lopinavir in humans and animal models.

METHODS

The plasma protein binding of [14C]lopinavir was examined in vitro via equilibrium dialysis technique. The tissue distribution of radioactivity was examined in rats dosed with [14C]lopinavir in combination with ritonavir. The metabolism and disposition of [14C]lopinavir was examined in rats, dogs, and humans given alone (in rats only) or in combination with ritonavir.

RESULTS

The plasma protein binding of lopinavir was high in all species (97.4-99.7% in human plasma), with a concentration-dependent decrease in binding. Radioactivity was extensively distributed into tissues, except brain, in rats. On oral dosing to rats, ritonavir was found to increase the exposure of lopinavir-derived radioactivity 13-fold. Radioactivity was primarily cleared via the hepato-biliary route in all species (>82% of radioactive dose excreted via fecal route), with urinary route of elimination being significant only in humans (10.4% of radioactive dose). Oxidative metabolites were the predominant components of excreted radioactivity. The predominant site of metabolism was found to be the carbon-4 of the cyclic urea moiety, with subsequent secondary metabolism occurring on the diphenyl core moiety. In all the three species examined, the primary component of plasma radioactivity was unchanged lopinavir (>88%) with small amounts of oxidative metabolites.

CONCLUSIONS

Lopinavir was subject to extensive metabolism in vivo. Co-administered ritonavir markedly enhanced the pharmacokinetics of lopinavir-derived radioactivity in rats, probably due to inhibition of presystemic and systemic metabolism, leading to an increased exposure to this potent HIV protease inhibitor.

Boosted saquinavir hard gel formulation exposure in HIV-infected subjects: ritonavir 100 mg once daily versus twice daily

OBJECTIVES

The amount of ritonavir needed to enhance saquinavir hard gel (hg) plasma concentrations is unclear. Reduced ritonavir dosing may help to reduce ritonavir-related side effects and costs. This study examined the pharmacokinetics of twice-daily saquinavir-hg (1000 mg) in the presence of ritonavir 100 mg, dosed twice-daily and once-daily on one single occasion.

METHODS

Eighteen HIV-infected adults taking saquinavir/ritonavir 1000/100 mg twice-daily underwent pharmacokinetic (PK) assessment of saquinavir/ritonavir on day 1 following a morning saquinavir/ritonavir dose. On day 2, PK assessment was repeated when subjects took saquinavir without ritonavir. Drug intake (with a standard meal containing 20 g of fat) was timed on days -1, 1 and 2. Geometric mean ratios (GMR) and 95% confidence intervals (CI) were calculated to assess changes in saquinavir PK parameters.

RESULTS

Geometric mean saquinavir AUC(0-12), C(trough), C(max) and elimination half-life on days 1 and 2 were 14 389 and 9590 ng.h/mL, 331 and 234 ng/mL, 2503 and 1893 ng/mL and 2.80 and 2.82 h, respectively. The GMR (95% CI) for these parameters were 0.67 (0.53-0.84), 0.71 (0.48-1.04), 0.76 (0.58-0.98) and 1.01 (0.86-1.18), respectively.

CONCLUSIONS

Withholding a ritonavir dose significantly reduces overall saquinavir exposure and C(max), but had no impact on the elimination half-life. These data establish the need to administer saquinavir and ritonavir simultaneously.

Low-dose fluvoxamine as an adjunct to reduce olanzapine therapeutic dose requirements: a prospective dose-adjusted drug interaction strategy

Despite the advances in antipsychotic pharmacotherapy over the past decade, many atypical antipsychotic agents are not readily accessible by patients with major psychosis or in developing countries where the acquisition costs may be prohibitive. Olanzapine is an efficacious and widely prescribed atypical antipsychotic agent. In theory, olanzapine therapeutic dose requirement may be reduced during concurrent treatment with inhibitors of drug metabolism. In vitro studies suggest that smoking-inducible cytochrome P450 (CYP) 1A2 contributes to formation of the metabolite 4'-N-desmethylolanzapine. The present prospective study tested the hypothesis that olanzapine steady-state doses can be significantly decreased by coadministration of a low subclinical dose of fluvoxamine, a potent inhibitor of cytochrome P450 1A2. The study design followed a targeted "at-risk" population approach with a focus on smokers who were likely to exhibit increased cytochrome P450 1A2 expression. Patients with stable psychotic illness (N = 10 men, all smokers) and receiving chronic olanzapine treatment were evaluated for steady-state plasma concentrations of olanzapine and 4'-N-desmethylolanzapine. Subsequently, olanzapine dose was reduced from 17.5 +/- 4.2 mg/d (mean +/- SD) to 13.0 +/- 3.3 mg/d, and a nontherapeutic dose of fluvoxamine (25 mg/d, PO) was added to regimen. Patients were reevaluated at 2, 4, and 6 weeks during olanzapine-fluvoxamine cotreatment. There was no significant change in olanzapine plasma concentration, antipsychotic response, or metabolic indices (eg, serum glucose and lipids) after dose reduction in the presence of fluvoxamine (P > 0.05). 4'-N-desmethylolanzapine/olanzapine metabolic ratio decreased from 0.45 +/- 0.20 at baseline to 0.25 +/- 0.11 at week 6, suggesting inhibition of the cytochrome P450 1A2-mediated olanzapine 4'-N-demethylation by fluvoxamine (P < 0.05). In conclusion, this prospective pilot study suggests that a 26% reduction in olanzapine therapeutic dose requirement may be achieved by coadministration of a nontherapeutic oral dose of fluvoxamine.

Novel nonpeptidic inhibitors of HIV-1 protease obtained via a new multicomponent chemistry strategy

Using a newly developed multicomponent chemistry strategy in combination with structure based drug design, a new class of HIV-1 protease inhibitors has been obtained.

Symmetric fluoro-substituted diol-based HIV protease inhibitors. Ortho-fluorinated and meta-fluorinated P1/P1'-benzyloxy side groups significantly improve the antiviral activity and preserve binding efficacy

HIV-1 protease is a pivotal enzyme in the later stages of the viral life cycle which is responsible for the processing and maturation of the virus particle into an infectious virion. As such, HIV-1 protease has become an important target for the treatment of AIDS, and efficient drugs have been developed. However, negative side effects and fast emerging resistance to the current drugs have necessitated the development of novel chemical entities in order to exploit different pharmacokinetic properties as well as new interaction patterns. We have used X-ray crystallography to decipher the structure-activity relationship of fluoro-substitution as a strategy to improve the antiviral activity and the protease inhibition of C2-symmetric diol-based inhibitors. In total we present six protease-inhibitor complexes at 1.8-2.3 A resolution, which have been structurally characterized with respect to their antiviral and inhibitory activities, in order to evaluate the effects of different fluoro-substitutions. These C2-symmetric inhibitors comprise mono- and difluoro-substituted benzyloxy side groups in P1/P1' and indanoleamine side groups in P2/P2'. The ortho- and meta-fluorinated P1/P1'-benzyloxy side groups proved to have the most cytopathogenic effects compared with the nonsubstituted analog and related C2-symmetric diol-based inhibitors. The different fluoro-substitutions are well accommodated in the protease S1/S1' subsites, as observed by an increase in favorable Van der Waals contacts and surface area buried by the inhibitors. These data will be used in the development of potent inhibitors with different pharmacokinetic profiles towards resistant protease mutants.

Estimation of serum-free 50-percent inhibitory concentrations for human immunodeficiency virus protease inhibitors lopinavir and ritonavir

Using measured free fraction and 50% inhibitory concentration (IC50) values for the human immunodeficiency virus protease inhibitors lopinavir (LPV) and ritonavir (RTV) in tissue culture media with various protein concentrations ranging from 5 to 50%, we estimated serum-free IC50 values for each drug. The range of serum-free IC50 values (0.64 to 0.77 ng/ml for LPV and 3.0 to 5.0 ng/ml for RTV) did not exhibit a trend with increasing protein concentrations, despite a 10-fold difference in the free fraction value (0.006 to 0.063) for LPV and a 5-fold difference in the free fraction value (0.013 to 0.057) for RTV. The mean serum-free IC50 by the MTT-MT4 assay (0.69 ng/ml for LPV and 4.0 ng/ml for RTV) may be the most accurate parameter for the estimation of the inhibitory quotient (IQ), a relative measure of in vivo potency defined as the ratio of the minimal free drug concentration in plasma (C(trough,free)) for a specific patient population and the serum-free IC50. Using this approach, we calculated the average IQs for protease inhibitor-naïve patients for LPV and RTV to be 67 and 5.6, respectively.

A 42-Week Open-Label Study to Assess the Pharmacokinetics, Antiretroviral Activity, and Safety of Amprenavir or Amprenavir plus Ritonavir in Combination with Abacavir and Lamivudine for Treatment of HIV-Infected Patients

The pharmacokinetics, antiviral activity, and safety of an amprenavir-ritonavir (APV-RTV) 600/100 mg b.i.d. regimen and an APV-RTV 1200/200 mg q.d. regimen were studied in a human immunodeficiency virus (HIV)-infected population. The geometric least-square mean ratio (90% confidence interval) of steady-state trough concentrations, compared with that of the amprenavir 1200 mg b.i.d. regimen, was 6.08 (4.94-7.49) for the twice-daily APV-RTV regimen, and it was 4.19 (2.90-6.08) for the daily APV-RTV regimen. The regimens were well tolerated, which supports APV-RTV as an option for twice-daily or daily therapy for HIV.

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 therapy to treat salvage patients. Potency of these combination regimens is increased while pill burden, food restrictions and often, side effects are decreased. These clinical 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 200 mg to saquinavir 1200-1800 mg 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 (C(min)) 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 (IC(50)). Yet, when low doses of ritonavir were added, C(min) values were 50- to 100-fold greater than the concentration required to produce 50% of the maximum effect for wild-type HIV (EC(50)). The following manuscript will discuss the rationale for combining protease inhibitors and will review pertinent pharmacokinetic and clinical data on these combination regimens.

Therapeutic drug monitoring of lopinavir/ritonavir given alone or with a non-nucleoside reverse transcriptase inhibitor

AIMS

To evaluate the interindividual variability in the plasma concentrations of lopinavir in the context of routine monitoring with or without treatment with a non-nucleoside reverse transcriptase inhibitor and to assess the interaction between the coformulation of lopinavir/ritonavir and efavirenz or nevirapine.

METHODS

Plasma trough and peak concentrations (C(trough), C(max)) of lopinavir from 182 HIV-1-infected patients were analysed by high-performace liquid chromatography. Three lopinavir/ritonavir regimens were assessed, namely (A) 400 mg lopinavir/100 mg ritonavir twice daily given alone (n = 125), (B) 400/100 mg twice daily together with a non-nucleoside reverse transcriptase inhibitor (n = 25), and (C) 533/133 mg twice daily together with a non-nucleoside reverse transcriptase inhibitor (n = 32).

RESULTS

Median (ng ml(-1)) C(trough) and C(max) lopinavir (interquartile range, CV) were: (A) 4852 (3198-6891, 56%) and 8501 (6333-11 584, 41%), (B) 2979 (1704-5186, 74%) and 5612 (3362-11 704, 76%) and (C) 5082 (2696-7226, 74%) and 9757 (4883-12 963, 60%). Median C(trough) of lopinavir was lower in patients taking both efavirenz [P = 0.01, 95% confidence interval (CI) for difference between medians 343, 2713] and nevirapine (P = 0.019, 95% CI for difference between medians 354, 3681) compared with those taking lopinavir/ritonavir alone. A higher interindividual variability was observed when lopinavir/ritonavir was given with a non-nucleoside reverse transcriptase inhibitor. The risk of achieving a 'suboptimal'C(trough) of lopinavir (below a threshold of 3000 ng ml(-1)) was statistically higher in patients treated with a non-nucleoside reverse transcriptase inhibitor (P < 0.001, 95% CI for difference between percentages 8.8, 43.1%) compared with those receiving lopinavir/ritonavir alone.

CONCLUSIONS

Our results confirmed the interaction between lopinavir and efavirenz, and also demonstrated a significant interaction between the former drug and nevirapine, resulting in lower C(trough) of lopinavir. The wide interpatient variability in this interaction suggests that therapeutic drug monitoring may be useful in optimizing the dose of lopinavir.

The Plasma and Intracellular Steady-State Pharmacokinetics of Lopinavir/Ritonavir in HIV-1-Infected Patients

Therapeutic drug monitoring of protease inhibitors (PIs) is usually performed on plasma samples although their antiretroviral effect takes place inside cells. Little is known, however, about the intracellular accumulation and related plasma pharmacokinetics of PIs such as lopinavir/ritonavir (LPV/RTV). Therefore, we studied the plasma and intracellular (cell-associated) steady-state pharmacokinetics of this PI combination in a dosage of 400/100 mg twice daily in a non-randomized cohort of HIV-1-infected individuals. Plasma (0–12 h) and peripheral blood mononuclear cell (PBMC; 0–8 h) samples were drawn during a 12-h dosing interval in 11 subjects.

The plasma concentrations versus time curves of LPV and RTV were characterized by an irregular absorption phase showing double-peaks (Cmax) in most subjects and single-peaks in the remaining patients between 1 and 3 h after drug intake. Pre-dose concentrations of both agents in plasma were significantly higher than the concentrations at the end of the dosing interval indicating the presence of a circadian rhythm in their pharmacokinetics. The course of the intracellular concentrations versus time curves appeared to be similar to the plasma concentration curves, with the highest intracellular concentration measured 3 h after drug intake. The intracellular RTV concentrations were higher than reported in vitro EC50 values and might therefore contribute to the antiretroviral effect of LPV/RTV. The median intracellular-to-plasma concentration ratios (interquartile range) were 1.18 (0.74–2.06) and 4.59 (3.20–7.70) for LPV and RTV, respectively.

In conclusion, both LPV and RTV accumulate to potential therapeutic concentrations in PBMCs. Irregular absorption and circadian plasma clearance patterns were observed for the PI combination LPV/RTV.

Dynamics of HIV replication in lymphocytes and the efficacy of protease inhibitors

Using a system that allows transfection of resting peripheral blood lymphocytes (PBLs) two questions were addressed: the kinetics of HIV replication from the state of proviral latency, and the impact of different parameters on the efficacy of protease inhibitors to control HIV replication. PBLs were transfected with an infectious full length HIV-DNA harboring a luciferase reporter gene and activated thereafter. Ritonavir was added at different times at doses ranging from to 0.06 to 1 microM. Viral expression was assessed by quantifying luciferase activity in cell extracts and levels of p24 HIV antigen in culture supernatants. After transfection and cell activation, intracellular expression of HIV proteins, as assessed by luciferase detection, occurred within 2 hr. HIV-gag p24 antigen was detected in culture supernatants between 6 and 8 hr post-activation. Ritonavir was effective in blocking viral replication when given within 4 hr following HIV reactivation, but a delay in ritonavir administration or breaches in ritonavir levels after 6 hr from transfection resulted in viral escape. HIV reactivation from proviral latency in PBLs is an extremely rapid process, faster than estimated from previous models. These data stress the need for maintaining effective antiretroviral concentrations to block completely viral replication.