Discovery of Novel Oral Protein Synthesis Inhibitors of Mycobacterium tuberculosis That Target Leucyl-tRNA Synthetase.

The recent development and spread of extensively drug-resistant and totally drug-resistant resistant (TDR) strains of Mycobacterium tuberculosis highlight the need for new antitubercular drugs. Protein synthesis inhibitors have played an important role in the treatment of tuberculosis (TB) starting with the inclusion of streptomycin in the first combination therapies. Although parenteral aminoglycosides are a key component of therapy for multidrug-resistant TB, the oxazolidinone linezolid is the only orally available protein synthesis inhibitor that is effective against TB. Here, we show that small-molecule inhibitors of aminoacyl-tRNA synthetases (AARSs), which are known to be excellent antibacterial protein synthesis targets, are orally bioavailable and effective against M. tuberculosis in TB mouse infection models. We applied the oxaborole tRNA-trapping (OBORT) mechanism, which was first developed to target fungal cytoplasmic leucyl-tRNA synthetase (LeuRS), to M. tuberculosis LeuRS. X-ray crystallography was used to guide the design of LeuRS inhibitors that have good biochemical potency and excellent whole-cell activity against M. tuberculosis Importantly, their good oral bioavailability translates into in vivo efficacy in both the acute and chronic mouse models of TB with potency comparable to that of the frontline drug isoniazid.

Macrolones Are a Novel Class of Macrolide Antibiotics Active against Key Resistant Respiratory Pathogens In Vitro and In Vivo.

As we face an alarming increase in bacterial resistance to current antibacterial chemotherapeutics, expanding the available therapeutic arsenal in the fight against resistant bacterial pathogens causing respiratory tract infections is of high importance. The antibacterial potency of macrolones, a novel class of macrolide antibiotics, against key respiratory pathogens was evaluated in vitro and in vivo MIC values against Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, and Haemophilus influenzae strains sensitive to macrolide antibiotics and with defined macrolide resistance mechanisms were determined. The propensity of macrolones to induce the expression of inducible erm genes was tested by the triple-disk method and incubation in the presence of subinhibitory concentrations of compounds. In vivo efficacy was assessed in a murine model of S. pneumoniae-induced pneumonia, and pharmacokinetic (PK) profiles in mice were determined. The in vitro antibacterial profiles of macrolones were superior to those of marketed macrolide antibiotics, including the ketolide telithromycin, and the compounds did not induce the expression of inducible erm genes. They acted as typical protein synthesis inhibitors in an Escherichia coli transcription/translation assay. Macrolones were characterized by low to moderate systemic clearance, a large volume of distribution, a long half-life, and low oral bioavailability. They were highly efficacious in a murine model of pneumonia after intraperitoneal application even against an S. pneumoniae strain with constitutive resistance to macrolide-lincosamide-streptogramin B antibiotics. Macrolones are the class of macrolide antibiotics with an outstanding antibacterial profile and reasonable PK parameters resulting in good in vivo efficacy.

Observed Antagonistic Effect of Linezolid on Daptomycin or Vancomycin Activity against Biofilm-Forming Methicillin-Resistant Staphylococcus aureus in an In Vitro Pharmacodynamic Model.

Pharmacodynamic activity in antibiotic combinations of daptomycin, vancomycin, and linezolid was investigated in a 48-h in vitro pharmacodynamic model. Using human-simulated free drug concentrations, activity against clinical biofilm-forming methicillin-resistant Staphylococcus aureus isolates was evaluated. Linezolid antagonized vancomycin activity at 24 and 48 h. Linezolid antagonized daptomycin at 24 and 48 h depending on dose and strain. Adding daptomycin increased vancomycin activity at 48 h (P < 0.03). These results may be strain dependent and require further clinical investigation.

A novel ketolide, RBx 14255, with activity against multidrug-resistant Streptococcus pneumoniae.

We present here the novel ketolide RBx 14255, a semisynthetic macrolide derivative obtained by the derivatization of clarithromycin, for its in vitro and in vivo activities against sensitive and macrolide-resistant Streptococcus pneumoniae. RBx 14255 showed excellent in vitro activity against macrolide-resistant S. pneumoniae, including an in-house-generated telithromycin-resistant strain (S. pneumoniae 3390 NDDR). RBx 14255 also showed potent protein synthesis inhibition against telithromycin-resistant S. pneumoniae 3390 NDDR. The binding affinity of RBx 14255 toward ribosomes was found to be more than that for other tested drugs. The in vivo efficacy of RBx 14255 was determined in murine pulmonary infection induced by intranasal inoculation of S. pneumoniae ATCC 6303 and systemic infection with S. pneumoniae 3390 NDDR strains. The 50% effective dose (ED50) of RBx 14255 against S. pneumoniae ATCC 6303 in a murine pulmonary infection model was 3.12 mg/kg of body weight. In addition, RBx 14255 resulted in 100% survival of mice with systemic infection caused by macrolide-resistant S. pneumoniae 3390 NDDR at 100 mg/kg four times daily (QID) and at 50 mg/kg QID. RBx 14255 showed favorable pharmacokinetic properties that were comparable to those of telithromycin.

Reductive activation of type 2 ribosome-inactivating proteins is promoted by transmembrane thioredoxin-related protein.

Members of the type 2 ribosome-inactivating proteins (RIPs) family (e.g. ricin, abrin) are potent cytotoxins showing a strong lethal activity toward eukaryotic cells. Type 2 RIPs contain two polypeptide chains (usually named A, for "activity", and B, for "binding") linked by a disulfide bond. The intoxication of the cell is a consequence of a reductive process in which the toxic domain is cleaved from the binding domain by oxidoreductases located in the lumen of the endoplasmic reticulum (ER). The best known example of type 2 RIPs is ricin. Protein disulfide isomerase (PDI) was demonstrated to be involved in the process of ricin reduction; however, when PDI is depleted from cell fraction preparations ricin reduction can still take place, indicating that also other oxidoreductases might be implicated in this process. We have investigated the role of TMX, a transmembrane thioredoxin-related protein member of the PDI family, in the cell intoxication operated by type 2 RIPs ricin and abrin. Overexpressing TMX in A549 cells resulted in a dramatic increase of ricin or abrin cytotoxicity compared with control mock-treated cells. Conversely, no difference in cytotoxicity was observed after treatment of A549 cells or control cells with saporin or Pseudomonas exotoxin A whose intracellular mechanism of activation is not dependent upon reduction (saporin) or only partially dependent upon it (Pseudomonas exotoxin A). Moreover, the silencing of TMX in the prostatic cell line DU145 reduced the sensitivity of the cells to ricin intoxication further confirming a role for this enzyme in intracellular ricin activation.

Pharmacokinetics of intravenous linezolid in moderately to morbidly obese adults.

The pharmacokinetics of linezolid was assessed in 20 adult volunteers with body mass indices (BMI) of 30 to 54.9 kg/m(2) receiving 5 intravenous doses of 600 mg every 12 h. Pharmacokinetic analyses were conducted using compartmental and noncompartmental methods. The mean (±standard deviation) age, height, and weight were 42.2 ± 12.2 years, 64.8 ± 3.5 in, and 109.5 ± 18.2 kg (range, 78.2 to 143.1 kg), respectively. Linezolid pharmacokinetics in this population were best described by a 2-compartment model with nonlinear clearance (original value, 7.6 ± 1.9 liters/h), which could be inhibited to 85.5% ± 12.2% of its original value depending on the concentration in an empirical inhibition compartment, the volume of the central compartment (24.4 ± 9.6 liters), and the intercompartment transfer constants (K(12) and K(21)) of 8.04 ± 6.22 and 7.99 ± 5.46 h(-1), respectively. The areas under the curve for the 12-h dosing interval (AUCτ) were similar between moderately obese and morbidly obese groups: 130.3 ± 60.1 versus 109.2 ± 25.5 µg · h/ml (P = 0.32), and there was no significant relationship between the AUC or clearance and any body size descriptors. A significant positive relationship was observed for the total volume of distribution with total body weight (r(2) = 0.524), adjusted body weight (r(2) = 0.587), lean body weight (r(2) = 0.495), and ideal body weight (r(2) = 0.398), but not with BMI (r(2) = 0.171). Linezolid exposure in these obese participants was similar overall to that of nonobese patients, implying that dosage adjustments based on BMI alone are not required, and standard doses for patients with body weights up to approximately 150 kg should provide AUCτ values similar to those seen in nonobese participants.

[Protective effect of selank on the model of mnestic function violation induced by pharmacological blockade of protein synthesis].

We have studied the ability of peptide anxiolytic selank (Thr-Lyz-Pro-Arg-Pro-Gly-Pro) to compensate for mnestic dysfunction caused by the administration of actinomycin D, which inhibits protein synthesis by blocking DNA-dependent RNA polymerase. The experiments were performed on white rats with acquired adaptive ability of spatial visual orientation in a 16-door labyrinth. The learning was based on the avoidance of electric skin irritation at alternating sites of escape reaction (site reflex). Selank (0.5 mg/kg, i.p.) prevented or compensated for actinomycin D (250 mg/kg, i.p.) induced violation of the process of acquisition, improvement, and consolidation of memory trace during the development of a complex site reflex. The drug administration also reduced the time required for acquisition of the adaptive ability of spatial visual orientation in the labyrinth and restored the actinomycin D violated process of re-learning upon a change in the alternation of escape sites under free-choice conditions.

Resistance emergence mechanism and mechanism of resistance suppression by tobramycin for cefepime for Pseudomonas aeruginosa.

The panoply of resistance mechanisms in Pseudomonas aeruginosa makes resistance suppression difficult. Defining optimal regimens is critical. Cefepime is a cephalosporin whose 3' side chain provides some stability against AmpC ß-lactamases. We examined the activity of cefepime against P. aeruginosa wild-type strain PAO1 and its isogenic AmpC stably derepressed mutant in our hollow-fiber infection model. Dose-ranging studies demonstrated complete failure with resistance emergence (both isolates). Inoculum range studies demonstrated ultimate failure for all inocula. Lower inocula failed last (10 days to 2 weeks). Addition of a ß-lactamase inhibitor suppressed resistance even with the stably derepressed isolate. Tobramycin combination studies demonstrated resistance suppression in both the wild-type and the stably derepressed isolates. Quantitating the RNA message by quantitative PCR demonstrated that tobramycin decreased the message relative to that in cefepime-alone experiments. Western blotting with AmpC-specific antibody for P. aeruginosa demonstrated decreased expression. We concluded that suppression of ß-lactamase expression by tobramycin (a protein synthesis inhibitor) was at least part of the mechanism behind resistance suppression. Monte Carlo simulation demonstrated that a regimen of 2 g of cefepime every 8 h plus 7 mg/kg of body weight of tobramycin daily would provide robust resistance suppression for Pseudomonas isolates with cefepime MIC values up to 8 mg/liter and tobramycin MIC values up to 1 mg/liter. For P. aeruginosa resistance suppression, combination therapy is critical.

Endocytosis and intracellular localisation of type 1 ribosome-inactivating protein saporin-s6.

Saporin-S6 is a single-chain ribosome-inactivating protein (RIP) that has low toxicity in cells and animals. When the protein is bound to a carrier that facilitates cellular uptake, the protein becomes highly and selectively toxic to the cellular target of the carrier. Thus, saporin-S6 is one of the most widely used RIPs in the preparation of immunoconjugates for anti-cancer therapy. The endocytosis of saporin-S6 by the neoplastic HeLa cells and the subsequent intracellular trafficking were investigated by confocal microscopy that utilises indirect immunofluorescence analysis and transmission electron microscopy that utilises a direct assay with gold-conjugated saporin-S6 and an indirect immunoelectron microscopy assay. Our results indicate that saporin-S6 was taken up by cells mainly through receptor-independent endocytosis. Confocal microscopy analysis showed around 30% co-localisation of saporin-S6 with the endosomal compartment and less than 10% co-localisation with the Golgi apparatus. The pathway identified by the immunofluorescence assay and transmission electron microscopy displayed a progressive accumulation of saporin-S6 in perinuclear vesicular structures. The main findings of this work are the following: i) the nuclear localisation of saporin-S6 and ii) the presence of DNA gaps resulting from abasic sites in HeLa nuclei after intoxication with saporin-S6.

Pharmacological enhancement of ex vivo gene therapy neuroprotection in a rodent model of retinal degeneration.

AIMS: We have previously shown the benefits of cell-based delivery of neuroprotection in a rodent model of retinitis pigmentosa (RP). In order to maximise the effectiveness of this approach, we hypothesised that this could be augmented by combination with an aminoglycoside known to limit the abnormal RNA translation seen in this model. METHODS: A rhodopsin TgN S334ter-4 rat model of RP underwent daily subcutaneous injection of 12.5 µg/g gentamicin from postnatal day 5 (P5). At P21, selected rats also underwent intravitreal injection of cells genetically engineered to oversecrete glial cell-derived neurotrophic factor. Histological imaging was undertaken to evaluate photoreceptor survival at P70 and compared with images from untreated TgN S334ter-4 rats and control Sprague-Dawley rats. RESULTS: Statistically significant (p < 0.05) improvements in outer retinal indices were seen with this combination strategy when compared with results in rats treated with individual therapies alone. This improvement was most apparent in the peripheral retina, where the greatest degeneration was observed. CONCLUSIONS: We have shown that the combination of neuroprotection plus aminoglycoside read-through in an animal model of retinal degeneration improved the histological appearance of the retina such that it was statistically indistinguishable from unaffected controls. Further functional and longitudinal studies of this approach are warranted.

Kinetic Target-Guided Synthesis: Reaching the Age of Maturity.

Kinetic target-guided synthesis (KTGS) is an original discovery strategy allowing a target to catalyze the irreversible synthesis of its own ligands from a pool of reagents. Although pioneered almost two decades ago, it only recently proved its usefulness in medicinal chemistry, as exemplified by the increasing number of protein targets used, the wider range of target and pocket types, and the diversity of therapeutic areas explored. In recent years, two new leads for in vivo studies were released. Amidations and multicomponent reactions expanded the armamentarium of reactions beyond triazole formation and two new examples of in cellulo KTGS were also disclosed. Herein, we analyze the origins and the chemical space of both KTGS ligands and warhead-bearing reagents. We review the KTGS timeline focusing on recent cases in order to give medicinal chemists the full scope of this strategy which has great potential for hit discovery and hit or lead optimization.

Role of Erythromycin-Regulated Histone Deacetylase-2 in Benign Tracheal Stenosis.

Objective: This study aims to explore the role of erythromycin-regulated histone deacetylase-2 in benign tracheal stenosis. Methods: The rabbit model of tracheal stenosis was established. The rabbits were randomly divided into 8 groups. Histone deacetylase-2 (HDAC2) expression was detected by immunofluorescence. The expression of type I collagen and type III collagen was detected by immunohistochemical method. The expression of TGF-ß1, VEGF and IL-8 in serum and alveolar lavage fluid was detected by ELISA. The expression of HDAC2, TGF-ß1, VEGF and IL-8 in serum and alveolar lavage fluid was detected by ELISA. The expression of HDAC2, TGF. Results: In Erythromycin (ERY) group, ERY + Budesonide group, ERY + Vorinostat group and ERY + Budesonide + Vorinostat group, the degree of bronchial stenosis was alleviated, and the mucosal epithelium was still slightly proliferated. The effect of ERY combined with other drugs was more obvious. The HDAC2 protein expression increased significantly in ERY group, ERY + Budesonide group and ERY + Budesonide + Vorinostat group and decreased significantly in Vorinostat group, the expression of collagen I and III decreased significantly in ERY group, ERY + Budesonide group and ERY + Budesonide + Vorinostat group (P < 0.05). The TGF-ß1, VEGF and IL-8 in serum and alveolar lavage fluid was detected by ELISA. The expression of HDAC2, TGF-P < 0.05). The TGF. Conclusions: Erythromycin inhibited inflammation and excessive proliferation of granulation tissue after tracheobronchial mucosal injury by up-regulating the expression of HDAC2, it promoted wound healing and alleviated tracheobronchial stenosis. When combined with budesonide, penicillin and other glucocorticoids and antibiotics, it had a good synergistic effect. However, vorinostat could attenuate erythromycin's effect by down-regulating the expression of HDAC2. It may have good clinical application prospects in the treatment of tracheal stenosis.

Shiga-like toxins and HIV-1 'go through' glycosphingolipids and lipid rafts in renal cells.

The binding of Shiga-like toxins (Stx) to globotriaosyl ceramide (Gb(3)) in renal cells plays a central role in Stx-induced hemolytic uremic syndrome (Stx-HUS). Khan et al. show that the presence of Gb(3) within lipid raft microdomains in glomerular but not tubular cells may be the basis for the glomerular- and age-restricted pathology of Stx-HUS. They also propose that the binding of the HIV-1 glycoprotein gp120 to Gb(3) in renal tubules may play a role in HIV nephropathy.

Time course and efficiency of protein synthesis inhibition following intracerebral and systemic anisomycin treatment.

Since its discovery in the 1960s, anisomycin has been used for studying the impact of protein synthesis for manifold cerebral processes such as long-term plastic changes after learning. The common limitation of nearly all pharmacological experiments, including anisomycin treatment, is to precisely verify the affected brain regions. Here we illustrate anisomycin effects on protein synthesis in distinct brain regions of mice (C57BL/6JOlaHsd), revealing differences between three modes of anisomycin application (subcutaneous, s.c.; intraperitoneal, i.p.; local microinfusions into the hippocampus). Our method is based on inhibition of the incorporation of the radioactively-labelled amino acids [(35)S]-Methionine/Cysteine into newly synthesised proteins. Washing the brain slices before autoradiography removes pools of amino acids, which have not been incorporated into newly synthesised proteins, thus, illustrating pure protein synthesis. By comparing different routes of systemic anisomycin application (i.p. versus s.c.; 150 mg/kg) it became evident that the effect of i.p. injection of anisomycin is fully reversed after 6 h, whereas s.c. injection is inhibiting protein synthesis in the hippocampus even 9 h after application. Local microinfusions of anisomycin into the hippocampus were shown to have long-lasting effects as well, which reversed as late as 9 h after injection. The diffusion of anisomycin was maximal at 3 h after injection and more precisely confined to the intended area using a lower dose (20 microg/site) instead of the commonly used dose of 62.5 microg/site. The broad time window of anisomycin action, as revealed in our study, has to be considered, if it comes to the interpretation of time course studies within the context of protein synthesis-dependent processes.

Linezolid: a review of its properties, function, and use in critical care.

Linezolid can be considered as the first member of the class of oxazolidinone antibiotics. The compound is a synthetic antibiotic that inhibits bacterial protein synthesis through binding to rRNA. It also inhibits the creation of the initiation complex during protein synthesis which can reduce the length of the developed peptide chains, and decrease the rate of reaction of translation elongation. Linezolid has been approved for the treatment of infections caused by vancomycin-resistant Enterococcus faecium, hospital-acquired pneumonia caused by Staphylococcus aureus, complicated skin and skin structure infections (SSSIs), uncomplicated SSSIs caused by methicillin-susceptible S. aureus or Streptococcus pyogenes, and community-acquired pneumonia caused by Streptococcus pneumoniae. Analysis of high-resolution structures of linezolid has demonstrated that it binds a deep cleft of the 50S ribosomal subunit that is surrounded by 23S rRNA nucleotides. Mutation of 23S rRNA was shown to be a linezolid resistance mechanism. Besides, mutations in specific regions of ribosomal proteins uL3 and uL4 are increasingly associated with linezolid resistance. However, these proteins are located further away from the bound drug. The methicillin-resistant S. aureus and vancomycin-resistant enterococci are considered the most common Gram-positive bacteria found in intensive care units (ICUs), and linezolid, as an antimicrobial drug, is commonly utilized to treat infected ICU patients. The drug has favorable in vitro and in vivo activity against the mentioned organisms and is considered as a useful antibiotic to treat infections in the ICU.

Drug evaluation: PTC-124--a potential treatment of cystic fibrosis and Duchenne muscular dystrophy.

PTC-124, a 1,2,4-oxadiazole compound, is in development by PTC Therapeutics Inc as an orally active small molecule that can override nonsense stop translation signals to produce full-length proteins. PTC-124 is currently being evaluated in phase II clinical trials against cystic fibrosis (CF) and Duchenne muscular dystrophy (DMD). The functional properties of PTC-124 are similar to the aminoglycoside antibiotic gentamicin, but the two compounds are chemically distinct and PTC-124 does not exhibit any antibiotic characteristics. In vitro experiments showed PTC-124 to be superior to gentamicin at ribosomal read-through of nonsense mutations. In vivo investigations revealed that PTC-124 was effective in restoring the production of full-length protein in animal models of CF and DMD. Phase I clinical trials reported that PTC-124 was well tolerated in healthy patients. The author concludes that the encouraging results observed to date make PTC-124 an attractive option for further well-designed, long-term human studies on larger sample populations. The author also predicts that if results continue to be positive, PTC-124 could also be trialed in other single gene disorders with nonsense mutations such as hemophilia, neurofibromatosis, retinitis pigmentosa, bullous skin diseases and lysosomal storage disorders.

Antibiotics and pregnancy.

Like anybody else, pregnant women are susceptible to infections. The correct treatment of these women, however, must consider along with pathogens, the infection site and antibiotic pharmacokinetics, the fetus and possible side effects to the child. When prescribing over this special condition, the physician must remember that the prescription will affect two organism and the drug must treat the mother without affecting the fetus. Beta-lactams having a long history of use without significant deleterious effects on the fetuses still are the safest choice during pregnancy. However, considering the constant increase of multi-resistant microorganisms, the physician has been forced to use different antimicrobial agents. Usually, data regarding safety during pregnancy are very limited, which causes serious doubts during prescription. In addition, many studies regarding the safe use of antibiotics during pregnancy are inconclusive or demand more evidence. The present study is a wide revision regarding the use of antibiotics during pregnancy, considering their pharmacokinetics and the clinical experience in recent years. It also intends to assist the physician during prescription and to give information to the pharmacists to help pregnant women.

[Linezolid, the first oxazolidinone antibiotic]. / Le linézolide, premier antibiotique de la famille des oxazolidinones.

The spread of multiresistant Staphylococcus and Enterococcus strains required the development of new drugs. Linezolid is the first molecule of a new antibiotic family, oxazolidinones, with an original mechanism of action. In this general review, the authors first present its antibacterial activity, its pharmacokinetic properties, its therapeutic uses in serious Gram-positive infections, pneumonia, skin and soft tissue infections, and also in other indications. They then explain the rules for administration and tolerability.

Troglitazone induces CYP3A4 activity leading to falsely abnormal dexamethasone suppression test.

After evaluating a patient who appeared to have a falsely abnormal response to the dexamethasone suppression test while taking troglitazone, we examined the effects of troglitazone on the activity of hepatic CYP3A4 and the screening tests for Cushing's syndrome. We studied five healthy women and three healthy men, aged 25 +/- 2 yr, before and after treatment with troglitazone (600 mg daily) for 28 d. Baseline 0800 h cortisol and corticosterone were similar before and after troglitazone treatment. Before troglitazone treatment, all subjects suppressed 0800 h cortisol below 1.8 micro g/dl (mean, 0.66 +/- 0.08 micro g/dl) during the 1-mg overnight dexamethasone suppression test (DST), whereas during troglitazone treatment none of the subjects suppressed 0800 h cortisol below 1.8 micro g/dl (mean, 9.0 +/- 1.8 micro g/dl). Serum dexamethasone levels decreased by 66 +/- 4%, and the erythromycin breath test measurements increased by 27 +/- 8%, indicating increased CYP3A4 activity during troglitazone treatment. The hydrocortisone suppression test (HST) was performed by administering 50 mg hydrocortisone at 2300 h. Using the criterion of suppression of 0800 h plasma corticosterone by more than 50%, the specificity of the HST was 100% both before and after troglitazone treatment. In conclusion, troglitazone induced the activity of CYP3A4 leading to falsely abnormal DST. HST is a useful alternative to the DST in patients taking medications that increase the activity of CYP3A4.

Steady-state pharmacokinetics of delavirdine in HIV-positive patients: effect on erythromycin breath test.

OBJECTIVE: The steady-state kinetics of delavirdine and desisopropyldelavirdine were evaluated in human immunodeficiency virus-positive patients after escalating oral doses and after repeated oral administrations at the same dose level. STUDY DESIGN: Patients (n = 8 males) were given escalating oral doses of delavirdine mesylate, in a sequential fashion, over 14 days for phases 1 (200 mg every 8 hours), 2 (300 mg every 8 hours), and 3 (400 mg every 8 hours). Control patients (n = 4 males) were given 300 mg oral doses of drug every 8 hours for all three phases. Hepatic CYP3A activity was evaluated with the erythromycin breath test (ERMBT). RESULTS: In the escalating-dose group, delavirdine displayed nonlinear kinetics as indicated by the decreasing oral clearance, maximum steady-state plasma concentration/minimum steady-state plasma concentration ratio, and log-linear terminal rate constant, as well as by increasing half-life at higher doses; the ratio of desisopropyl-delavirdine formation clearance to elimination clearance was also reduced. In the control group, the kinetics of delavirdine and desisopropyl-delavirdine were unchanged. Plasma protein binding was linear for delavirdine in the escalating-dose and control groups; on average, the fraction unbound was about 2.3% and 2.0%, respectively. Hepatic CYP3A activity was markedly reduced after short- and long-term exposure to all doses of delavirdine mesylate. Delavirdine could maximally inhibit 70% to 75% of predose ERMBT values, with an IC50 of about 0.9 mumol/L. CONCLUSION: Delavirdine is a potent and reversible inhibitor of hepatic CYP3A; it is also a substrate for this CYP450 isoform. It is likely that delavirdine will exhibit drug-drug interactions when coadministered with other CYP3A substrates.