First Selective 12-LOX Inhibitor, ML355, Impairs Thrombus Formation and Vessel Occlusion In Vivo With Minimal Effects on Hemostasis.

OBJECTIVE: Adequate platelet reactivity is required for maintaining hemostasis. However, excessive platelet reactivity can also lead to the formation of occlusive thrombi. Platelet 12(S)-lipoxygenase (12-LOX), an oxygenase highly expressed in the platelet, has been demonstrated to regulate platelet function and thrombosis ex vivo, supporting a key role for 12-LOX in the regulation of in vivo thrombosis. However, the ability to pharmacologically target 12-LOX in vivo has not been established to date. Here, we studied the effect of the first highly selective 12-LOX inhibitor, ML355, on in vivo thrombosis and hemostasis. APPROACH AND RESULTS: ML355 dose-dependently inhibited human platelet aggregation and 12-LOX oxylipin production, as confirmed by mass spectrometry. Interestingly, the antiplatelet effects of ML355 were reversed after exposure to high concentrations of thrombin in vitro. Ex vivo flow chamber assays confirmed that human platelet adhesion and thrombus formation at arterial shear over collagen were attenuated in whole blood treated with ML355 comparable to aspirin. Oral administration of ML355 in mice showed reasonable plasma drug levels by pharmacokinetic assessment. ML355 treatment impaired thrombus growth and vessel occlusion in FeCl3-induced mesenteric and laser-induced cremaster arteriole thrombosis models in mice. Importantly, hemostatic plug formation and bleeding after treatment with ML355 was minimal in mice in response to laser ablation on the saphenous vein or in a cremaster microvasculature laser-induced rupture model. CONCLUSIONS: Our data strongly support 12-LOX as a key determinant of platelet reactivity in vivo, and inhibition of platelet 12-LOX with ML355 may represent a new class of antiplatelet therapy.

Gastrointestinal Motility Variation and Implications for Plasma Level Variation: Oral Drug Products.

The oral route of administration is still by far the most ubiquitous method of drug delivery. Development in this area still faces many challenges due to the complexity and inhomogeneity of the gastrointestinal environment. In particular, dosing unpredictably relative to motility phase means the gastrointestinal environment is a random variable within a defined range. Here, we present a mass balance analysis that captures this variation and highlights the effects of gastrointestinal motility, exploring what impacts it ultimately has on plasma levels and the relationship to bioequivalence for high solubility products with both high and low permeability (BCS I and III). Motility-dependent compartmental absorption and transit (MDCAT) mechanistic analysis is developed to describe the underlying fasted state cyclical motility and how the contents of the gastrointestinal tract are propelled.

Efecto in vitro del policosanol (alcoholes de la cera de Saccharum officinarum L) sobre la enzima 5-lipooxigenasa / In vitro effects of policosanol (Saccharum officinarum L wax alcohols) on the 5-lipooxygenase enzyme

INTRODUCTION: policosanol, a mixture of high molecular weight aliphatic alcohols purified from sugarcane with octacosanol as the main component, shows cholesterol-lowering and antiplatelet effects in addition to an inhibitory effect on type I cicloxygenase. OBJECTIVE: to determine whether policosanol may inhibit 5-LOX enzyme activity in vitro. METHODS: effects on 5-LOX enzyme activities were assessed in rat blood polymorphonuclear leukocytes. Vehicle or Policosanol suspensions (0.6 to 6 000 µg/mL) were added to tubes containing the reaction mix and then absorbance changes at 234 nm were measured. RESULTS: added Policosanol inhibited in vitro 5-LOX activity by 30 percent, which was not a significant figure but depended on the concentration(r= 0.992; p< 0.05); it was 1 250 µg/mL. CONCLUSIONS: policosanol did not significantly inhibit 5-LOX enzyme activity in rat PMNL preparations, so that it does not seem to be a dual inhibitor of COX and-LOX enzymes. This result differs from that found for beeswax alcohols and underlines the different effects of the mixtures of long-chain fatty alcohols purified from the sugarcane and the beeswax(AU).

IINTRODUCCIÓN: el policosanol es una mezcla de alcoholes alifáticos aislados y purificados de la caña de azúcar cuyo componente mayoritario es el octacosanol, con efecto sobre la reducción de colesterol y antiagregante plaquetario, además inhibe la ciclooxigenasa (COX) tipo 1. OBJETIVO: determinar el poder de inhibición del policosanol en la actividad de la enzima 5-LOX in vitro. MÉTODOS: el efecto sobre la actividad de la enzima 5-LOX se determinó en leucocitos polimorfonucleares obtenidos de sangre de ratas. Se añadieron vehículo o suspensiones de policosanol (0,6 a 6 000 µg/mL) a tubos que contenían la mezcla de reacción y se medió el cambio de absorbancia a 234 nm. RESULTADOS: la adición de policosanol inhibió in vitro la actividad de la 5-LOX en un 30 por ciento que no fue significativo pero sí dependiente de la concentración (r= 0,992; p< 0,05), inhibición esta que alcanzó 1 250 µg/mL. CONCLUSIÓN: el policosanol no inhibió significativamente la actividad de la enzima 5-LOX en preparación de polimorfonucleares de ratas, por lo que no es un inhibidor dual de las enzimas. Este resultado difiere del encontrado para los alcoholes de la cera de abeja y subraya la diferencia de los efectos hallados entre las mezclas de alcoholes alifáticos de cadenas largas purificados de la caña de azúcar y la cera de abeja(AU)

Efecto in vitro del policosanol (alcoholes de la cera de Saccharum officinarum L) sobre la enzima 5-lipooxigenasa / In vitro effects of policosanol (Saccharum officinarum L wax alcohols) on the 5-lipooxygenase enzyme

Introducción: el policosanol es una mezcla de alcoholes alifáticos aislados y purificados de la caña de azúcar cuyo componente mayoritario es el octacosanol, con efecto sobre la reducción de colesterol y antiagregante plaquetario, además inhibe la ciclooxigenasa (COX) tipo 1. Objetivo: determinar el poder de inhibición del policosanol en la actividad de la enzima 5-LOX in vitro. Métodos: el efecto sobre la actividad de la enzima 5-LOX se determinó en leucocitos polimorfonucleares obtenidos de sangre de ratas. Se añadieron vehículo o suspensiones de policosanol (0,6 a 6 000 µg/mL) a tubos que contenían la mezcla de reacción y se medió el cambio de absorbancia a 234 nm. Resultados: la adición de policosanol inhibió in vitro la actividad de la 5-LOX en un 30 por ciento que no fue significativo pero sí dependiente de la concentración (r= 0,992; p< 0,05), inhibición esta que alcanzó 1 250 µg/mL. Conclusión: el policosanol no inhibió significativamente la actividad de la enzima 5-LOX en preparación de polimorfonucleares de ratas, por lo que no es un inhibidor dual de las enzimas. Este resultado difiere del encontrado para los alcoholes de la cera de abeja y subraya la diferencia de los efectos hallados entre las mezclas de alcoholes alifáticos de cadenas largas purificados de la caña de azúcar y la cera de abeja(AU)

Introduction: policosanol, a mixture of high molecular weight aliphatic alcohols purified from sugarcane with octacosanol as the main component, shows cholesterol-lowering and antiplatelet effects in addition to an inhibitory effect on type I cicloxygenase. Objective: to determine whether policosanol may inhibit 5-LOX enzyme activity in vitro. Methods: effects on 5-LOX enzyme activities were assessed in rat blood polymorphonuclear leukocytes. Vehicle or Policosanol suspensions (0.6 to 6 000 µg/mL) were added to tubes containing the reaction mix and then absorbance changes at 234 nm were measured. Results: added Policosanol inhibited in vitro 5-LOX activity by 30 percent, which was not a significant figure but depended on the concentration(r= 0.992; p< 0.05); it was 1 250 µg/mL. Conclusions: policosanol did not significantly inhibit 5-LOX enzyme activity in rat PMNL preparations, so that it does not seem to be a dual inhibitor of COX and-LOX enzymes. This result differs from that found for beeswax alcohols and underlines the different effects of the mixtures of long-chain fatty alcohols purified from the sugarcane and the beeswax(AU)

Quantification of the 5-lipoxygenase inhibitor zileuton in human plasma using high performance liquid chromatography-tandem mass spectrometry.

Zileuton is an orally active, selective inhibitor of 5-lipoxygenase, which catalyzes the first step in the conversion of arachadonic acid into leukotrienes. Given the important role of leukotrienes in inflammation and cell signaling, multiple studies have investigated the efficacy of zileuton in the treatment of human disease. Examples of disease targets include asthma, ulcerative colitis, rheumatoid arthritis, and more recently, acne, ischemic/reperfusion injury, inflammatory pain, and sickle cell anemia. Zileuton is currently approved for the prophylaxis and chronic treatment of asthma. We report the development and validation of a sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for the quantification of zileuton in human EDTA plasma. The range of reliable response was 3.05-20,000ng/mL in human plasma. The calibration curves had a correlation coefficient of r(2)>0.99. The intra-day precision was 3.4-5.3%. The inter-day precision ranged from 4.5% to 7.3% and inter-day accuracy from 100% to 107%. No matrix interferences, ion suppression/enhancement, or carry-over was observed. The assay met all predefined acceptance criteria and was subsequently employed to measure plasma zileuton concentrations in a clinical trial.

Pharmacokinetic, distribution, metabolism, and excretion of (Z)-2-amino-1,5-dihydro-1-methyl-5-[4-(mesyl)benzylidene]-4H-imidazol-4-one mesilate (ZLJ-601) in Sprague-Dawley rats.

(Z)-2-amino-1,5-dihydro-1-methyl-5-[4-(mesyl)benzylidene]-4H-imidazol-4-one mesilate (ZLJ-601) is an imidazolone COX/5-LOX inhibitor, which has excellent anti-inflammatory activity with an improved gastrointestinal safety profile. The purpose of this study was to evaluate the in vivo absorption, distribution, metabolism, and excretion of ZLJ-601 in Sprague-Dawley rats. After intravenous or intragastric administration to rats, the concentration of ZLJ-601 in plasma, bile, urine, feces and various types of tissues was detected by LC-MS. We also conducted the identification of metabolites using tandem mass spectrometry. After the intravenous administration, the t(1/2) ranged from 38.71 to 42.62 min and the AUC increased in a dose-proportional manner. After oral dosing, the plasma level of ZLJ-601 peaked at 28.33 min, having a C(max) value of 0.26 mg/l, and the bioavailability was only 4.92%. The highest tissue concentration of ZLJ-601 was observed in lung and kidney, but it was not found in brain. The majority of unchanged ZLJ-601 was excreted in urine (∼35.87%) within 36 h. Two main metabolites are the hydroxylation product and the glucuronide conjugate of the hydroxylation product.

Discovery of (2-fluoro-benzyl)-(2-methyl-2-phenethyl-2H-chromen-6-yl)-amine (KRH-102140) as an orally active 5-lipoxygenase inhibitor with activity in murine inflammation models.

OBJECTIVE AND DESIGN: We investigated anti-inflammatory properties of a novel 5-lipoxygenase (5-LO) inhibitor, KRH-102140, in vitro and in vivo. 5-LO enzyme activity was assayed using insect cell lysates overexpressing rat 5-LO. The leukotriene B(4) (LTB(4)) level was assayed in rat basophilic leukemia (RBL-1) cell line. ICR (Institute of Cancer Research) mice were used for in vivo assays. Mouse ear edema was induced by topical application of arachidonic acid. An air pouch was induced by subcutaneous injection of sterile air into mice, followed by zymosan treatment. Sprague-Dawley rats were used for pharmacokinetic studies. RESULTS: KRH-102140 inhibited 5-LO activity with an IC(50) value of 160 ± 23 nmol/l in parallel with LTB(4) inhibition in RBL-1 cells. Oral administration of KRH-102140 (10-100 mg/kg) reduced ear edema, myeloperoxidase activity and LTB(4) production in murine inflammation models. Oral bioavailability as determined in rats was 66%. CONCLUSIONS: Our results show that KRH-102140, a new 5-LO inhibitor, exhibits potent anti-inflammatory activities in vitro as well as in vivo.

Improvement of dissolution and oral absorption of ER-34122, a poorly water-soluble dual 5-lipoxygenase/cyclooxygenase inhibitor with anti-inflammatory activity by preparing solid dispersion.

Several formulation approaches were attempted to improve the dissolution and the oral absorption of ER-34122, which is a novel dual 5-lipoxygenase/cyclooxygenase inhibitor with potent anti-inflammatory activity. The solid dispersion of ER-34122 with hydroxypropylmethylcellulose (TC-5RW), which is an inert solid carrier, resulted in a significant improvement in the dissolution rate of ER-34122. The solid dispersion was prepared by a solvent evaporation method using ethanol and water. The solid-state characteristics of the solid dispersion, the corresponding physical mixture, and ER-34122 alone were investigated by X-ray powder diffraction, Fourier transform infrared spectroscopy (FTIR), and an automated controlled-atmosphere microbalance. The X-ray powder diffraction patterns suggest that the solid dispersion exists in a totally amorphous state and the others exist in a crystalline state. The FTIR spectra results suggest that ER-34122 can interact with TC-5RW through intermolecular hydrogen bonding in the solid dispersion. This interaction may cause a stabilization of ER-34122 in the higher-energy, faster-dissolving amorphous state. The dissolution rate of ER-34122 from the solid dispersion was significantly greater than that from the physical mixture or the pure drug. Furthermore, when orally administrated to beagle dogs, ER-34122 showed about a 100-fold increase in both maximum concentration (C(max)) and area under the curve of concentration versus time (AUC) compared with the pure drug. Consequently, it was determined that the solid dispersion technique with TC-5RW provides a promising way to increase the dissolution rate and the oral absorption of poorly water-soluble drugs such as ER-34122.

Age-related alteration of carbamazepine-serum protein binding in man.

To determine whether biological maturation influences the kinetics of carbamazepine-serum protein binding, the carbamazepine free fraction (%) was investigated in the serum of 66 patients, ranging from 4 to 83 years, with epilepsy or trigeminal neuralgia, treated with carbamazepine alone or carbamazepine in combination with phenytoin, phenobarbital, and/or valproic acid, over a relatively long period. Biochemical parameters such as levels of albumin and non-glycated albumin showed a significant relationship with carbamazepine free fraction (r = -0.521, P < 0.001 for albumin; r = -0.700, P < 0.001 for non-glycated albumin). Non-glycated albumin was more strongly correlated with carbamazepine free fraction. The biochemical parameters showed a significant relationship with age (r =-0.243, P < 0.1 for albumin; r =0.666, P < 0.001 for glycated albumin; r = -0.459, P < 0.001 for non-glycated albumin; r = 0.640, P < 0.001 for carbamazepine free fraction). Glycated albumin (%), non-glycated albumin and carbamazepine free fraction (%) were strongly correlated with age, whereas albumin showed only a weak correlation with age. To evaluate the effects of ageing on carbamazepine-serum protein binding, the patients were divided into three groups according to age: children, 4-15 years; adults, 16-64 years; elderly, 65-83 years. Albumin and non-glycated albumin were much lower, and glycated albumin (%) and carbamazepine free fraction (%) much higher in the elderly group than in the other two groups. The results of this study showed that the major ligand of carbamazepine in the serum was non-glycated albumin, which decreased with age. These observations suggested that in elderly patients, the elevation of free carbamazepine concentrations in the serum caused by reduced non-glycated albumin levels, induces increases in the sensitivity of the pharmacological effects of carbamazepine and the risk of drug interactions.

Inhibition of allergen-induced airway obstruction and leukotriene generation in atopic asthmatic subjects by the leukotriene biosynthesis inhibitor BAYx 1005.

BACKGROUND: Leukotriene receptor antagonists significantly blunt allergen-induced bronchoconstriction in asthmatic subjects. Inhibitors of leukotriene synthesis should theoretically provide similar protection, but conflicting results have been obtained when synthesis inhibitors have been tested in allergen challenge. BAYx 1005, a new inhibitor of leukotriene synthesis, was therefore evaluated in an allergen bronchoprovocation study. METHODS: Ten men with mild allergic asthma and bronchial hyperresponsiveness to histamine were recruited. On two different occasions each subject inhaled a single dose of allergen, previously determined to cause at least a 20% fall in forced expiratory volume in one second (FEV1) four hours after ingestion of 750 mg BAYx 1005 or placebo in a double blind crossover design. Urinary excretion of leukotriene E4 was measured before and during the challenges. RESULTS: The mean (SE) maximal fall in FEV1 was 7.1 (1.7)% after BAYx 1005 and 21.0 (3.0)% after placebo (p < 0.001). The mean difference between treatments was 13.9 (95% CI 7.0 to 20.8) for the maximal fall in FEV1. All subjects were protected by BAYx 1005, the mean inhibition of the fall in FEV1 being 70.0 (7.0)%. The mean area under the curve (AUC) for urinary excretion of leukotriene E4 in the first two hours after the challenge was 1.7 (0.9) after placebo and 0.4 (0.6) after BAYx 1005 (difference = 1.3 (95% CI-0.1 to 2.7); p < 0.05). CONCLUSIONS: These results indicate that BAYx 1005 is a potent inhibitor of allergen-provoked leukotriene synthesis in asthmatic subjects and lend further support to the suggestion that leukotrienes are important mediators of allergen-induced bronchoconstriction.

Involvement of leukotrienes in allergic pleurisy in actively sensitized rats: inhibition by the lipoxygenase inhibitor T-0757 of the increase in vascular permeability and leukotriene E4 production.

The relative contributions of inflammatory mediators to the increase in vascular permeability in antigen-induced pleurisy were examined in rats actively sensitized with ovalbumin. The effects of various inhibitors were assessed on the exudate volume and plasma exudation rate in the pleural cavity. Two peaks were observed in plasma exudation rate at 0.5 and 3 h after antigen challenge. At 0.5 h, there was a marked decrease in the histamine content of the pleural cells and also a sharp increase in the LTE4 level in the exudate, which was inhibited dose-dependently by the lipoxygenase inhibitor T-0757. Indomethacin and cyproheptadine both depressed exudate volume and exudation rate, whereas T-0757 only reduced the exudation rate. At 3 h, a substantial LTE4 concentration was still detected in the exudate, and the exudation rate was depressed by T-0757 and indomethacin, but not by cyproheptadine. These results suggest that histamine is involved mainly in the early phase, and leukotrienes predominantly contribute to the later phase of exudation. Prostaglandins appear to be involved in both phases. Allergic pleurisy of rats, therefore, may be a suitable model to examine the roles of these inflammatory mediators.

Different biliary excretion systems for glucuronide and sulfate of a model compound; study using Eisai hyperbilirubinemic rats.

The disposition of conjugated metabolites (sulfate and glucuronide) was investigated in Eisai hyperbilirubinemic rats (EHBR) and normal Sprague-Dawley (SD) rats by in vivo and liver perfusion methods. EHBR are mutant rats that have conjugated hyperbilirubinemia as an autosomal recessive trait inheritance, and they show impaired excretion of organic anions into the bile. 6-Hydroxy-5,7-dimethyl-2-methylamino-4-(3-pyridylmethyl) benzothiazole (E3040), a novel dual inhibitor of 5-lipoxygenase and thromboxane A2 synthetase, was used as a model compound, because the major metabolites of E3040 are glucuronide and sulfate. After the i.v. injection of [14C]E3040 to EHBR and SD rats, the plasma AUC for glucuronide was greater in EHBR than in SD rats. The cumulative biliary excretion of the glucuronide was impaired to a great extent in EHBR, and the urinary excretion was enhanced. There was no significant difference in the cumulative biliary and urinary excretion of sulfate between EHBR and SD rats. The influx, efflux and sequestration rates of E3040, measured by a multiple indicator dilution method in the perfused rat liver, were similar in EHBR and SD rats. The biliary excretion of the glucuronide formed in the liver, measured by the liver perfusion method, was also severely impaired in EHBR, so the recovery of the glucuronide in the outflow specimens was markedly enhanced. The disposition of the sulfate did not change in either type of rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of a new 5-lipoxygenase inhibitor, zileuton, and its inactive N-dehydroxylated metabolite in plasma by high performance liquid chromatography.

A rapid and sensitive assay was developed for the measurement of plasma concentrations of zileuton racemate, a potent inhibitor of 5-lipoxygenase. Zileuton and its inactive N-dehydroxylated metabolite were extracted from human, monkey, and rat plasma by use of a solid-phase extraction column (Analytichem Bond Elut). The compounds were then separated by reverse-phase high performance liquid chromatography (HPLC) on a Supelcosil LC-18 column and quantified on the basis of ultraviolet absorption at 260nm relative to an internal standard. The extraction recovery of zileuton, as determined by HPLC assay, was 77.9 +/- 1.7%. Recovery of the metabolite was 85.8 +/- 0.7%. Calibration curves for both compounds were linear over the zileuton concentration range 0.01 to 10.0 mg/L (correlation coefficients > 0.987), while the intra- and interassay coefficients of variation were < 15.6%. In practice, > 97% of blinded daily spiked control samples for zileuton and > 90% of those for the metabolite were within 10% of their target concentrations.

Pharmacokinetic interactions between zileuton and prednisone.

A randomized double-blind placebo-controlled crossover study evaluated the effects of zileuton 600mg 4 time daily on the pharmacokinetics of prednisolone after a single 400mg oral dose of prednisone. the effects of the single prednisone dose on the steady-state pharmacokinetics of zileuton were also evaluated. Multiple doses of zileuton had no significant effects on mean peak plasma concentration (Cmax), time to Cmax(tmax), or area under the plasma concentration-time curve from 0 to infinity (AUC0-infinity) values for prednisolone after oral administration of prednisone 40mg. A slight but statistically significant increase in the mean half-life (t1/2) of prednisolone was detected with zileuton + prednisone administration compared with prednisone + placebo (from 2.8 to 2.9 hours); however, this change was of no clinical relevance. Mean Cmax values of zileuton after coadministration with prednisone were similar to those of zileuton alone. While the single 40mg dose of prednisone resulted in a slight but statistically significant decrease in the mean zileuton AUC value from 0 to 6 hours (AUC0-6) [from 23 to 20 mg/L/h] and a reduction in tMAX (from 2.3 to 1.7 hours), these results were not considered to be clinically significant. Therefore, it is considered that zileuton and prednisone may be coadministered with minimal risk of a clinically significant pharmacokinetic interaction.

The pharmacokinetic and pharmacodynamic interactions between the 5-lipoxygenase inhibitor zileuton and the cyclo-oxygenase inhibitor naproxen in human volunteers.

The potential pharmacokinetic and pharmacodynamic interactions between zileuton, a 5-lipoxygenase inhibitor, and naproxen, a nonsteroidal anti-inflammatory drug that acts as a cyclo-oxygenase inhibitor, have been investigated in 24 healthy volunteers. Coadministration of these 2 drugs had no effect upon the plasma concentration-time curves of either zileuton (800mg) or naproxen (500mg) when compared with each drug administered alone. Both naproxen plasma concentrations during the elimination phase and area under the plasma concentration-time curve values were statistically significantly raised upon coadministration with zileuton, when compared with naproxen alone. However, these differences in these 2 values were sufficiently small to be of no clinical significance. There is no evidence that the combination of zileuton and naproxen had an effect on leukotriene B4 levels that was different from the inhibitory effect of zileuton alone, or had an effect on serum thromboxane B2 levels that was different from the effect of naproxen alone. Moreover, inhibition of the 5-lipoxygenase pathway by zileuton did not appear to aggravate the gastrointestinal adverse events commonly associated with naproxen administration. It is concluded that zileuton and naproxen may be coadministered with minimal risk of a clinically significant interaction.

In vitro plasma protein binding of zileuton and its N-dehydroxylated metabolite.

An ultrafiltration technique or equilibrium dialysis has been used to study the in vitro human plasma protein binding of racemic zileuton, its individual enantiomers, and its pharmacologically inactive metabolite N-dehydroxyzileuton. The plasma protein binding of zileuton and N-dehydroxyzileuton over the concentration range of 0.1 to 100 mg/L averaged 93.1 +/- 0.22 and 92.0 +/- 0.12%, respectively. However, there appeared to be a stereoselective effect, with the R(+) enantiomer of zileuton demonstrating greater binding to plasma proteins than the S(-) enantiomer (96 vs 88%, respectively). Zileuton was bound to both human serum albumin (40 g/L) and alpha 1-acid glycoprotein (1 g/L), although binding affinity to albumin was approximately 3-fold greater. Displacement interactions of zileuton with warfarin, salicylate, theophylline, naproxen, ibuprofen, prednisone, and terfenadine were minimal. The blood to plasma concentration ratio for zileuton and N-dehydroxyzileuton ranged from 0.65 to 0.68, indicating that these compounds were mainly distributed in the plasma. Thus, zileuton is approximately 93% bound to plasma proteins at expected therapeutic concentrations in vitro, and this figure is largely unaffected by several commonly prescribed agents with which the drug may be coadministered.

The pharmacokinetics of zileuton in healthy young and elderly volunteers.

The effects of age and gender on the single and multiple dose pharmacokinetics of zileuton have been examined in a phase I nonblinded study. A total of 27 healthy volunteers were evaluable, 9 in the young group (age range 20 to 40 years; 5 males and 4 females) and 18 in the elderly group (range 65 to 81 years; 9 males and 9 females). A single oral dose of zileuton 600mg was given to all volunteers on day 1 of the study and at 6-hour intervals from days 3 to 7. Analysis of variance showed slight but significant decreases in the mean apparent clearance of total and free drug in the healthy elderly population after a single zileuton dose, but no significant age-related differences after multiple 6-hourly doses. Similarly, zileuton peak and trough plasma concentrations, and values for half-life, volume of distribution and protein binding were not significantly affected by age after either a single dose or multiple administration. Moreover, gender effects on the pharmacokinetics were also absent after correction for bodyweight differences. From the results of the present study, it is concluded that there is no pharmacokinetic basis for alteration of zileuton dosage schedules in elderly patients.

The effect of mild or moderate hepatic impairment (cirrhosis) on the pharmacokinetics of zileuton.

The pharmacokinetics of zileuton and its R(+) and S(-) glucuronide metabolites were determined after single and multiple (400mg every 8 hours) oral dose administration in healthy subjects (n = 5) and patients with mild or moderate hepatic impairment (cirrhosis; n = 8). The clearance of total zileuton (unbound plus bound to plasma proteins) in patients with hepatic impairment (approximately 350 ml/min) was approximately half than in healthy subjects (approximately 670 ml/min), with similar values in patients with mild or moderate cirrhosis. However, the clearance of unbound zileuton in patients with moderate hepatic impairment was nearly half that in patients with mild hepatic impairment, and one quarter that in healthy subjects. On the basis of these findings, it may be necessary to reduce the dose in patients with impaired hepatic function to maintain levels similar to those in healthy subjects.

The effect of food on the pharmacokinetics of zileuton.

The present study was undertaken to assess the effect of food on the pharmacokinetic parameters of zileuton. In a nonblinded crossover study, 18 healthy male volunteers who had fasted overnight were randomised to receive a single oral dose of zileuton 600mg in the presence or absence of food consisting of a standardised breakfast on the following morning. The mean zileuton peak plasma concentration (Cmax) increased significantly by 27% after food intake, while the mean area under the plasma concentration versus time curve increased by only 1.4%, a difference that was not statistically significant. The mean time to Cmax was unaffected by the presence of food, as were the other pharmacokinetic parameters assessed. Overall, the results suggest that food has a relatively small effect on the rate of zileuton absorption compared with the fasting state, while the bioavailability of the drug appears to be unaffected. Thus, it is concluded that it is appropriate to administer zileuton with or without food.

Effect of zileuton on theophylline pharmacokinetics.

In controlled trials involving asthma patients, zileuton - a selective 5-lipoxygenase inhibitor - has significantly improved pulmonary function and reduced symptoms. Since theophylline is frequently prescribed for asthma, we designed a placebo-controlled randomised crossover trial to examine the influence of zileuton on theophylline pharmacokinetics. 16 healthy adult males were given theophylline (Slo-Phyllin) 200mg 4 times daily for 5 days and either zileuton 800mg twice daily or a matching placebo. After a 15-day washout period, theophylline was resumed and the other study drugs reversed. During coadministration with zileuton, mean peak theophylline levels rose from 12.14 to 20.99 mg/L (p < 0.001), while the apparent plasma clearance dropped from 3.74 to 1.91 L/h (p < 0.001). The time to the peak theophylline concentration was delayed by 0.5 hours and the half-life was significantly prolonged by 1.5 hours. 14 volunteers reported 44 mild or moderately severe adverse events, possibly or probably related to coadministration of zileuton, and 8 volunteers reported 8 such events with placebo coadministration. Three volunteers receiving theophylline plus zileuton withdrew from the trial prematurely. Thus, a pharmacokinetic interaction that may produce theophylline toxicity exists between zileuton and theophylline. Accordingly, theophylline dosages in patients receiving zileuton should be adjusted to maintain levels within the therapeutic range. Upon initiation of zileuton, the typical asthma patient may require dosage reductions of one-half, and monitoring of plasma theophylline concentrations is recommended.