Simultaneous quantitation of abiraterone, enzalutamide, N-desmethyl enzalutamide, and bicalutamide in human plasma by LC-MS/MS.

Inhibiting the androgen receptor (AR) pathway is an important clinical strategy in metastatic prostate cancer. Novel agents including abiraterone acetate and enzalutamide have been shown to prolong life in men with metastatic, castration-resistant prostate cancer (mCRPC). To evaluate the pharmacokinetics of AR-targeted agents, we developed and validated an LC-MS/MS assay for the quantitation of enzalutamide, N-desmethyl enzalutamide, abiraterone and bicalutamide in 0.05mL human plasma. After protein precipitation, chromatographic separation was achieved with a Phenomenex Synergi Polar-RP column and a linear gradient of 0.1% formic acid in methanol and water. Detection with an ABI 4000Q mass spectrometer utilized electrospray ionization in positive multiple reaction monitoring mode. The assay was linear over the ranges of 1-1000ng/mL for abiraterone and bicalutamide and 100-30,000ng/mL for N-desmethyl enzalutamide and enzalutamide and proved to be accurate (92.8-107.7%) and precise (largest was 15.3% CV at LLOQ for bicalutamide), and fulfilled FDA criteria for bioanalytical method validation. We demonstrated the suitability of this assay in plasma from patients who were administered enzalutamide 160mg, abiraterone 1000mg and bicalutamide 50mg once a day as monotherapy or in combination. The LC-MS/MS assay that has been developed will be an essential tool that further defines the pharmacology of the combinations of androgen synthesis or AR-receptor targeted agents.

Rapid determination of canagliflozin in rat plasma by UHPLC-MS/MS using negative ionization mode to avoid adduct-ions formation.

Canagliflozin is the first sodium-glucose co-transporter-2 inhibitor, approved by the US Food and Drug Administration for the treatment of type 2 diabetes mellitus. In this study, a sensitive UHPLC-MS/MS assay for rapid determination of canagliflozin in rat plasma was developed and validated for the first time. Chromatographic separation of canagliflozin and zafirlukast (IS) was carried out on Acquity BEH C18 column (100×2.1 mm, i.d. 1.7 µm) using acetonitrile-water (80:20, v/v) as mobile phase at a flow rate of 0.3 mL min(-1). Canagliflozin and IS were extracted from plasma by protein precipitation method using acetonitrile. The mass spectrometric detection was performed using electrospray ionization source in negative mode to avoid canagliflozin adduct ions formation. Multiple reaction monitoring were used for quantitation of precursor to product ion at m/z 443.16 >364.96 for canagliflozin and m/z 574.11>462.07 for IS, respectively. The assay was fully validated in terms of selectivity, linearity, accuracy, precision, recovery, matrix effects and stability. The validated method was successfully applied to the characterization of oral pharmacokinetic profiles of canagliflozin in rats. The mean maximum plasma concentration of canagliflozin of 1616.79 ng mL(-1) was achieved in 1.5 h after oral administration of 20 mg kg(-1) in rats.

Simple and rapid determination of zafirlukast in plasma by ultra-performance liquid chromatography tandem mass spectrometric method: application into pharmacokinetic study in rabbits.

Zafirlukast is a selective leukotriene receptor antagonist used for the prophylaxis and chronic treatment of asthma. The aim of the present study was to develop a simple sensitive ultra-performance liquid chromatography tandem mass spectroscopy method for rapid determination of zafirlukast in plasma. After a simple one step protein precipitation by acetonitrile, zafirlukast and montelukast (IS) were separated on Acquity UPLC BEH(TM) C18 column (50 × 2.1 mm, i.d. 1.7 µm, Waters, USA) using a mobile phase of acetonitrile:water containing 10 mM acetic acid (80:20, v/v) at a flow rate of 0.3 mL/min. Zafirlukast and IS were eluted at 0.51 and 1.1 min, respectively with a total run time of only 1.5 min. The mass spectrometric determination was carried out using an electrospray interface operated in the negative mode with multiple reactions monitoring mode. The precursor to product ion transitions of m/z 574.11>462.07 and m/z 584.2>472.1 were used to quantify zafirlukast and IS, respectively. The method was linear in the concentration range of 0.17-600 ng/mL with coefficients of determination greater than 0.996 and lower limit of quantitation of 0.17 ng/mL. Intra-day and inter-day accuracies were 88.3-113.9% and the precisions were ≤ 12.6%. Zafirlukast was found to stable under various storage and sample processing conditions as per guidelines of bio-analytical method validation. The method developed herein is simple and rapid, and was successfully applied for the pharmacokinetic study in rabbits.

Bicalutamide nanocrystals with improved oral bioavailability: in vitro and in vivo evaluation.

CONTEXT: Bicalutamide (BCT) is an antiandrogenic compound belonging to Biopharmaceutics Classification System (BCS) class II drug. Thus it has limited aqueous solubility and hence limited oral bioavailability. OBJECTIVE: The purpose of the present investigation was to obtain stable nanocrystals of BCT with improved kinetic solubility, dissolution and pharmacokinetic profiling. MATERIALS AND METHODS: BCT nanocrystals were prepared by antisolvent precipitation method using Soluplus, a novel amphiphilic polymer. Nanocrystals were characterized for particle size, powder X-ray diffraction analysis (PXRD), in vitro dissolution, in vivo pharmacokinetic profile and stability. RESULTS AND DISCUSSION: The obtained nanocrystals had particle size of 168 nm and were spherical in shape. The nanocrystals exhibited fivefold increase in kinetic solubility as compared to pure drug and 85% dissolution in 60 min. PXRD studies established the retention of crystalline polymorphic form II. The in vivo pharmacokinetic study demonstrated that the Cmax and AUC of nanosized BCT were about 3.5 times higher as compared to pure drug. CONCLUSION: Nanosizing of BCT significantly improved the pharmacokinetic profile of the drug administered to rats. Prepared nanocrystals were found to be stable over the entire stability period. Thus the use of amphiphilic polymer like Soluplus singularly helped in efficient size reduction and stabilization of the drug.

A study of plasma bicalutamide concentrations in hemodialysis patients.

Bicalutamide is an anti-androgen that is used worldwide to treat prostate cancer (CaP). However, there are no data on blood bicalutamide concentrations in hemodialysis (HD) patients with CaP. Therefore, we investigated the plasma levels of bicalutamide during the peridialysis period in this population. The study group included 5 HD patients with CaP who had been treated with bicalutamide (80 mg/day) for at least 3 months. Blood samples were taken during and between HD sessions and the plasma concentrations of the active R enantiomer (R-bicalutamide) were assessed using an HPLC assay. The plasma R-bicalutamide levels on the non-dialysis day were measured in 2 patients (patients 1 and 2) immediately before dosing and 8 and 24 h after dosing. These levels were 18,730, 19,090 and 19,420 ng/ml (patient 1), and 4,522, 4,581, and 5,296 ng/ml (patient 2), respectively. The mean plasma levels of R-bicalutamide in all 5 subjects just before HD, and 2 and 4 h after the start of HD were 8,726, 9,354 and 10,068 ng/ml, respectively. These results show that bicalutamide does not accumulate and is not diluted in the blood circulation of HD patients when given at the normal dosage used in the general population.

Confirmation of no impact from different anticoagulant counter ions on bioanalytical method.

BACKGROUND: In the past several years, the impact of changing counter ions while keeping the same anticoagulant in bioanalytical LC-MS/MS methods has become a highly discussed topic. In order to confirm that there is no impact from counter ions, matrix effect and stability evaluations were performed on bicalutamide LC-MS/MS bioanalytical methods. RESULTS: Independently from the anticoagulant counter ion used, the matrix effect evaluation met acceptance criteria, even when using conditions expected to increase matrix effect, such as protein precipitation with an analog internal standard. Freeze-thaw along with storage stabilities, namely short- and long-term, demonstrated less than 8% deviation regardless of the counter ion used. CONCLUSION: Differences in the anticoagulant counter ion used has no impact on the bicalutamide bioanalytical LC-MS/MS method.

Development and validation of a highly sensitive LC-MS/MS-ESI method for the determination of bicalutamide in mouse plasma: application to a pharmacokinetic study.

A highly sensitive, rapid assay method has been developed and validated for the estimation of bicalutamide in mouse plasma using liquid chromatography coupled to tandem mass spectrometry with electrospray ionization in the negative-ion mode. The assay procedure involves extraction of bicalutamide and tolbutamide (internal standard, IS) from mouse plasma with a simple protein precipitation method. Chromatographic separation was achieved using an isocratic mobile phase (0.2% formic acid:acetonitrile, 35:65, v/v) at a flow rate of 0.5 mL/min on an Atlantis dC18 column (maintained at 40 ± 1°C) with a total run time of 3.0 min. The MS/MS ion transitions monitored were m/z 428.9 → 254.7 for bicalutamide and m/z 269.0 → 169.6 for IS. Method validation was performed as per FDA guidelines and the results met the acceptance criteria. The lower limit of quantitation achieved was 1.04 ng/mL and the linearity range extended from 1.04 to 1877 ng/mL. The intra- and inter-day precisions were in the ranges of 0.49-4.68 and 2.62-4.15, respectively.

Fluconazole but not the CYP3A4 inhibitor, itraconazole, increases zafirlukast plasma concentrations.

PURPOSE: Zafirlukast is a substrate of cytochrome P450 2C9 (CYP2C9) and cytochrome P450 3A4 (CYP3A4) in vitro, but the role of these enzymes in its metabolism in vivo is unknown. To investigate the contribution of CYP2C9 and CYP3A4 to zafirlukast metabolism, we studied the effects of fluconazole and itraconazole on its pharmacokinetics (PK). METHODS: In a randomized crossover study, 12 healthy volunteers ingested fluconazole 200 mg (first dose 400 mg) once daily, itraconazole 100 mg (first dose 200 mg) twice daily, or placebo twice daily for 5 days, and on day 3, 20 mg zafirlukast. Plasma concentrations of zafirlukast and the antimycotics were measured up to 72 h. RESULTS: Fluconazole increased the total area under the plasma concentration-time curve (AUC) of zafirlukast 1.6-fold [95% confidence interval (CI) 1.3-2.0-fold, P < 0.001), and its peak plasma concentration 1.5-fold (95% CI 1.2-2.0-fold, P < 0.05). Fluconazole did not affect the time of peak plasma concentration or elimination half-life of zafirlukast. None of the zafirlukast PK variables differed significantly from the control in the itraconazole phase; e.g., the ratio to control of the total AUC of zafirlukast was 1.0 (95% CI 0.82-1.2) during the itraconazole phase. CONCLUSIONS: Fluconazole, but not itraconazole, increases zafirlukast plasma concentrations, strongly suggesting that CYP2C9 but not CYP3A4 participates in zafirlukast metabolism in humans.

The CYP2C8 inhibitor gemfibrozil does not affect the pharmacokinetics of zafirlukast.

PURPOSE: Gemfibrozil, a strong inhibitor of cytochrome P450 (CYP) 2C8 in vivo, was recently found to markedly increase the plasma concentrations of montelukast in humans. Like montelukast, zafirlukast is a substrate of CYP2C9 and CYP3A4 and a potent inhibitor of CYP2C8 in vitro. To investigate the contribution of CYP2C8 to the metabolism of zafirlukast in vivo, we studied the effect of gemfibrozil on the pharmacokinetics of zafirlukast. METHODS: Ten healthy subjects in a randomized cross-over study took gemfibrozil 600 mg or placebo twice daily for 5 days, and on day 3, a single oral dose of 20 mg zafirlukast. The plasma concentrations of zafirlukast were measured for 72 h postdose. RESULTS: The mean total area under the plasma concentration-time curve of zafirlukast during the gemfibrozil phase was 102% (geometric mean ratio; 95% confidence interval 89-116%) of that during the placebo phase. Furthermore, there were no statistically significant differences in the peak plasma concentration, time of peak concentration, or elimination half-life of zafirlukast between the phases. CONCLUSIONS: Gemfibrozil has no effect on the pharmacokinetics of zafirlukast, indicating that CYP2C8 does not play a significant role in the elimination of zafirlukast.

Iodine status of pregnant women from central Poland ten years after introduction of iodine prophylaxis programme.

INTRODUCTION: Until 1997, Poland was one of the European countries suffering from mild/moderate iodine deficiency. In 1997, a national iodine prophylaxis programme was implemented based on mandatory iodisation of household salt with 30 ± 10 mg KI/kg salt, obligatory iodisation of neonatal formula with 10 µg KI/100 mL and voluntary supplementation of pregnant and breast-feeding women with additional 100-150 µg of iodine. Our aim in this study was to evaluate the iodine status of pregnant women ten years after iodine prophylaxis was introduced. MATERIAL AND METHODS: A cross-sectional study was undertaken in 100 healthy pregnant women between the fifth and the 38th week of gestation with normal thyroid function, singleton pregnancy, normal course of gestation, without drugs known to influence thyroid function except iodine. Serum TSH, fT(4), fT(3), thyroglobulin (TG), anti-peroxidase antibodies (TPO-Ab), anti-thyroglobulin antibodies (TGAb) and urinary iodine concentration (UIC) were determined. Thyroid volume and structure were evaluated by ultrasonography. RESULTS: Fifty nine per cent of studied pregnant women had a diet rich with iodine carriers and 35% obtained iodine supplements. Twenty eight per cent appeared to have a goitre: 11 diffuse and 17 a nodular one, median goitre volume was 18.7 mL (range 6.8-29.0 mL). Median UIC was 112.6 µg/L (range 36.3-290.3 µg/L), only 28% of women had UIC ≥ 150 µg/L. Median UIC was significantly higher in the group receiving iodine supplements than in the group without iodine supplements: 146.9 µg/L v. 97.3 µg/L respectively, p 〈 0.001. Serum TSH, fT(3) and fT(3)/fT(4) molar ratio increased significantly during pregnancy while fT(4) declined. Median serum TG was normal: 18.3 ng/mL (range 0.4-300.0 ng/mL) and did not differ between trimesters. Neonatal TSH performed on the third day of life as a neonatal screening test for hypothyroidism was normal in each case: median value was 1.49 mIU/L (range 0.01-7.2 mIU/L). Less than 3% (2 out of 68) of results were 〉 5 mIU/L. CONCLUSION: Iodine supplements with 150 µg of iodine should be prescribed for each healthy pregnant woman according to the assumptions of Polish iodine prophylaxis programme to obtain adequate iodine supply. (Pol J Endocrinol 2010; 61 (6): 646-651).

Age disrupts androgen receptor-modulated negative feedback in the gonadal axis in healthy men.

Testosterone (T) exerts negative feedback on the hypothalamo-pituitary (GnRH-LH) unit, but the relative roles of the CNS and pituitary are not established. We postulated that relatively greater LH responses to flutamide (brain-permeant antiandrogen) than bicalutamide (brain-impermeant antiandrogen) should reflect greater feedback via CNS than pituitary/peripheral androgen receptor-dependent pathways. To this end, 24 healthy men ages 20-73 yr, BMI 21-32 kg/m2, participated in a prospective, placebo-controlled, randomized, double-blind crossover study of the effects of antiandrogen control of pulsatile, basal, and entropic (pattern regularity) measurements of LH secretion. Analysis of covariance revealed that flutamide but not bicalutamide 1) increased pulsatile LH secretion (P = 0.003), 2) potentiated the age-related abbreviation of LH secretory bursts (P = 0.025), 3) suppressed incremental GnRH-induced LH release (P = 0.015), and 4) decreased the regularity of GnRH-stimulated LH release (P = 0.012). Furthermore, the effect of flutamide exceeded that of bicalutamide in 1) raising mean LH (P = 0.002) and T (P = 0.017) concentrations, 2) accelerating LH pulse frequency (P = 0.013), 3) amplifying total (basal plus pulsatile) LH (P = 0.002) and T (P < 0.001) secretion, 4) shortening LH secretory bursts (P = 0.032), and 5) reducing LH secretory regularity (P < 0.001). Both flutamide and bicalutamide elevated basal (nonpulsatile) LH secretion (P < 0.001). These data suggest the hypothesis that topographically selective androgen receptor pathways mediate brain-predominant and pituitary-dependent feedback mechanisms in healthy men.

Relative bioavailability and tolerability of two formulations of bicalutamide 50-mg tablets: a randomized-sequence, open-label, two-period crossover study in healthy Korean male subjects.

BACKGROUND: Bicalutamide is an oral nonsteroidal antiandrogenic drug used in the treatment of prostate cancer. A new generic 50-mg tablet formulation of bicalutamide has recently been developed. OBJECTIVE: This study evaluated the relative bioavailability and tolerability of the new generic formulation of bicalutamide 50-mg tablets (test) and the currently marketed formulation (reference) in healthy Korean male subjects. The study was conducted to meet Korean regulatory requirements for authorization to market the generic formulation. METHODS: This was a randomized-sequence, open-label study in which healthy Korean male subjects (aged 20-55 years) received single doses of the test and reference formulations in a 2-period crossover fashion, with a 6-week washout period between doses. Blood samples for the determination of plasma bicalutamide concentrations were obtained at regular intervals over 672 hours after dose administration. Pharmacokinetic parameters were determined using noncompartmental methods. Relative bioavailability was evaluated by comparing the log-transformed C(max) and AUC(0-672) of the 2 formulations; Korean regulatory requirements for the assumption of bioequivalence were met if the 90% CIs fell within the range of 0.80 to 1.25. Tolerability was assessed based on physical examinations, vital signs, clinical laboratory tests, electrocardiograms (ECGs), and adverse events (AEs) (spontaneously reported or observed by investigators). RESULTS: Of 47 volunteers screened for inclusion, 38 were enrolled and 32 completed the study (mean [SD] age, 24.9 [3.7] years; mean height, 173.8 [6.2] cm; mean weight, 66.1 [7.1] kg). Median T(max) was 24 hours for both formulations. The C(max) of the test and reference formulations was 1176.2 (191.6) and 1118.9 (209.5) µg/L, respectively. The corresponding values for AUC(0-672) were 277,503 (66,865) and 271,961 (75,597) µg · h/L. The 90% CIs for the geometric mean ratios of log-transformed C(max) and AUC(0-672) were 1.00 to 1.11 and 0.99 to 1.07, respectively. Thirty-three AEs were reported, including 17 events in 9 subjects who received the test formulation and 16 events in 12 subjects who received the reference formulation. All AEs were mild, and no subjects discontinued the study because of AEs. CONCLUSIONS: In this single-dose study in healthy Korean male subjects, the pharmacokinetic parameters of the new generic formulation of bicalutamide 50-mg tablets did not differ significantly from those of the reference formulation. The new generic formulation met Korean regulatory criteria for the assumption of bioequivalence to the currently marketed formulation. Both formulations were well tolerated. Korea Food and Drug Administration registration number: PSPD 3057.

High performance liquid chromatography method for the pharmacokinetic study of bicalutamide SMEDDS and suspension formulations after oral administration to rats.

Bicalutamide is a non-steroidal antiandrogen and is an oral medication that is used for treating prostate cancer. To evaluate the bioavailability of bicalutamide from bicalutamide self-microemulsifying drug delivery systems (SMEDDS) and bicalutamide suspension formulations, a sensitive, specific reversed-phase high performance liquid chromatographic (HPLC) method using ultraviolet detection was developed and validated for the analysis of bicalutamide (BCT) in rat blood plasma. Letrozole (LZ) was used as the internal standard. The chromatographic separation was achieved on C18 column at 35 degrees C, with a mobile phase consisting of water: acetonitrile (adjusted to pH 3.0 with 20% o-phosphoric acid) (60:40), at a flow rate of 1.0 mL min(-1). Bicalutamide and letrozole were well separated with retention times of 10.9+/-0.2 and 5.7+/-0.2 min, respectively. The method was successfully used to determine pharmacokinetics of bicalutamide, following oral administration of bicalutamide suspension and bicalutamide SMEDDS to wistar rats. Significant difference was observed in main pharmacokinetic parameters of tmax, Cmax and AUC(0 --> infinity) between SMEDDS and suspension, and a two fold increase in the relative bioavailability of bicalutamide was observed with the SMEDDS compared with suspension formulation. It was concluded that the absorption of bicalutamide from SMEDDS was enhanced.

Comparative pharmacokinetic evaluation of two formulations of bicalutamide 50-mg tablets: an open-label, randomized-sequence, single-dose, two-period crossover study in healthy Korean male volunteers.

BACKGROUND: Bicalutamide is an oral nonsteroidal antiandrogen drug used during hormone ablation therapy for prostate cancer. A new generic formulation of bicalutamide has been developed. OBJECTIVES: This study was conducted to meet Korean and US regulatory requirements for the marketing of the generic 50-mg tablet formulation of bicalutamide. To this end, the pharmacokinetic properties of the new (test) formulation were compared with those of the currently marketed (reference) formulation. Tolerability was also evaluated. METHODS: An open-label, randomized-sequence, single-dose, 2-period crossover study was conducted in healthy Korean male volunteers. Subjects received either the test or reference formulation of bicalutamide 50-mg tablets in the first period and crossed over to the alternative formulation in the second period. Serial blood samples for pharmacokinetic analysis were taken over 672 hours after dosing. Plasma concentrations of bicalutamide were measured by HPLC-MS/MS. Pharmacokinetic parameters, including AUC(0-672h), were determined by noncompartmental analysis. Log-transformed C(max) and AUC(0-672h) for the 2 formulations were compared. Tolerability was monitored based on laboratory tests, ECGs, vital signs, and physical examinations. RESULTS: Of the 34 subjects initially enrolled, 33 completed the study. The mean (SD) age, height, and weight of participants were 25.8 (4.1) years, 173.6 (5.7) cm, and 68.9 (7.8) kg, respectively. The median T(max) was 36.0 hours for both formulations. The mean (SD) t(1/2), C(max), and AUC(0-672h) for the reference formulation were 135.4 (28.6) hours, 933.2 (169.2) microg/L, and 215,680.1 (48,753.4) microg x h/L, respectively. Corresponding values for the test formulation were 134.3 (30.7) hours, 946.7 (179.9) microg/L, and 221,708.8 (54,935.1) microg x h/L. The 90% CIs for the mean ratios (test/reference) of log-transformed C(max) and AUC(0-672h) were 0.97 to 1.06 and 0.98 to 1.07, respectively. Twelve adverse events were reported for each formulation, none of which were considered drug related in the test-formulation group and 4 of which were considered drug related in the reference-formulation group (3 cases of headache, 1 case of erythematous rash). CONCLUSIONS: In this single-dose study in healthy Korean male subjects, the new formulation of bicalutamide 50-mg tablets met Korean and US regulatory criteria for assumption of bioequivalence with the currently marketed formulation. Both formulations were generally well tolerated, with no clinically relevant safety concerns.

Development and validation of a sensitive LC-MS/MS method with electrospray ionization for quantitation of zafirlukast, a selective leukotriene antagonist in human plasma: application to a clinical pharmacokinetic study.

A highly sensitive and specific LC-MS/MS method has been developed and validated for the estimation of zafirlukast (ZFK) with 500 microL human plasma using valdecoxib as an internal standard (IS). The API-4,000 LC-MS/MS was operated under multiple reaction-monitoring mode using the electrospray ionization technique. The assay procedure involved extraction of ZFK and IS from human plasma with ethyl acetate. The resolution of peaks was achieved with 10 mm ammonium acetate (pH 6.4):acetonitrile (20:80, v/v) on a Hypersil BDS C(18) column. The total chromatographic run time was 2.0 min and the elution of ZFK and IS occurred at approximately 1.11 and 1.58 min, respectively. The MS/MS ion transitions monitored were 574.2 --> 462.1 for ZFK and 313.3 --> 118.1 for IS. The method was proved to be accurate and precise at a linearity range of 0.15-600 ng/mL with a correlation coefficient (r) of >or=0.999. The method was rugged with 0.15 ng/mL as lower limit of quantitation. The intra- and inter-day precision and accuracy values were found to be within the assay variability limits as per the FDA guidelines. The developed assay method was applied to a pharmacokinetic study in human volunteers following oral administration of 20 mg ZFK tablet.

Montelukast and zafirlukast do not affect the pharmacokinetics of the CYP2C8 substrate pioglitazone.

OBJECTIVE: Pioglitazone, a thiazolidinedione antidiabetic drug, is metabolised mainly by the cytochrome P450 (CYP) 2C8 enzyme. The leukotriene receptor antagonists montelukast and zafirlukast have potently inhibited CYP2C8 activity and the metabolism of pioglitazone in vitro. Our objective was to determine whether montelukast and zafirlukast increase the plasma concentrations of pioglitazone in humans. METHODS: In a randomised, double-blind crossover study with three phases and a washout period of 3 weeks, 12 healthy volunteers took either 10 mg montelukast once daily and placebo once daily, or 20 mg zafirlukast twice daily, or placebo twice daily, for 6 days. On day 3, they received a single oral dose of 15 mg pioglitazone. The plasma concentrations of pioglitazone and its metabolites M-IV, M-III, M-V and M-XI were measured for 96 h. RESULTS: The total area under the plasma concentration-time curve of pioglitazone during the montelukast and zafirlukast phases was 101% (range 71-143%) and 103% (range 78-146%), respectively, of that during the placebo phase. Also, the peak plasma concentration and elimination half-life of pioglitazone remained unaffected by montelukast and zafirlukast. There were no statistically significant differences in the pharmacokinetics of any of the metabolites of pioglitazone between the phases. CONCLUSIONS: Montelukast and zafirlukast do not increase the plasma concentrations of pioglitazone, indicating that their inhibitory effect on CYP2C8 is negligible in vivo, despite their strong inhibitory effect on CYP2C8 in vitro. The results highlight the importance of in vivo interaction studies and of the incorporation of relevant pharmacokinetic properties of drugs, including plasma protein binding data, to in vitro-in vivo interaction predictions.

A reversed-phase high-performance liquid chromatographic method for the determination of zafirlukast in pharmaceutical formulations and human plasma.

Zafirlukast (ZAF) is a leukotriene receptor antagonist used in the treatment of chronic asthma. In this study, a simple and sensitive reversed-phase, high-performance liquid chromatographic method was developed for the determination of ZAF in pharmaceutical formulations and human plasma. Piribedil was used as an internal standard. Analysis was carried out on a Nucleosil C18 100 A (150 mm x 4.6 mm id, 5 Vm) column with acetonitrile-pH 3.0 acetate buffer (70 + 30, v/v) as the mobile phase at a flow rate of 0.8 mL/min. The peak was detected by an ultraviolet detector set at a wavelength of 240 nm. The retention times were about 3.9 min for piribedil and 5.8 min for ZAF. The developed method was applied to the determination of ZAF in its pharmaceutical formulation and spiked human plasma. For quantification of ZAF in spiked plasma, proteins were precipitated with ethanol before chromatographic analysis. The calibration range was linear from 49.69-437.50 ng/mL in spiked plasma. The absolute recovery from spiked plasma was 98.73 +/- 0.42% at a concentration of 254.78 ng/mL of ZAF. No endogenous substances from plasma were found to interfere.

Role of metallothionein in regulating the abundance of histochemically reactive zinc in rat tissues.

The objectives of this study were (i) to investigate the modulating effects of zinc nutrition on histochemically reactive zinc in the rat intestine and liver and (ii) to assess the relationship between histochemically reactive zinc and metallothionein-bound zinc in these tissues under varying zinc nutrition. Male Wistar rats were fed a zinc-deficient (3 mg zinc/kg), adequate-zinc (30 mg zinc/kg, ad libitum or pair-fed), or zinc-supplemented (155 mg zinc/kg) diet for 2 or 6 weeks. Plasma N-(6-methoxy-8-quinolyl)-para-toluenesulfonamide-reactive zinc reflected dietary zinc intake. Abundance of the intestine histochemically reactive zinc was correlated with dietary zinc intake after 2 weeks of dietary treatment. Dietary zinc intake had no effect on the abundance of the intestine histochemically reactive zinc after 6 weeks of dietary treatment and the hepatic histochemically reactive zinc after both 2 and 6 weeks of dietary treatment. This lack of effect of dietary zinc intake on the abundance of histochemically reactive zinc was associated with a higher level of metallothionein. The molecular-mass distribution profile revealed that N-(6-methoxy-8-quinolyl)-para-toluenesulfonamide-reactive zinc and metallothionein-bound zinc represented two different, but interrelated, pools of zinc. Overall, these results suggested that the abundance of histochemically reactive zinc was homeostatically regulated, which was partially achieved through the regulation of metallothionein levels in rats.

A single dose of zafirlukast reduces LTD4-induced bronchoconstriction in patients on maintenance inhaled corticosteroid therapy.

BACKGROUND: Previous studies demonstrated that leukotriene receptor antagonists (LTRAs) are effective in reducing asthma symptoms and the airway response to inhaled leukotriene D4 (LTD4) in asthmatic patients receiving inhaled beta2-agonists alone. OBJECTIVE: To investigate the efficacy of a single 20-mg dose of the oral LTRA zafirlukast in reducing the airway response to inhaled LTD4 in mild-to-moderate asthmatic patients receiving inhaled beta2-agonists and inhaled corticosteroids (ICS). METHODS: In this double-blind, crossover trial, six patients on maintenance ICS (median dose 800 microg/day; range 336 to 1600 microg/day), who had a 20% decrease in FEV1 following inhalation of a maximal concentration of 50 microg/mL LTD4, received either zafirlukast or placebo on each of two study days. Two hours after dosing, patients underwent bronchoprovocation challenges with increasing concentrations of LTD4 (0.1 to 1000 microg/mL) at 10-minute intervals until either the patient's FEV1 decreased by 20% or the maximum concentration of LTD4 was given. Spirometric tests were done just before (baseline) and throughout the challenge phase until the patient's FEV1 returned to within 5% of baseline. Blood samples were collected two hours after dosing to determine plasma concentrations of zafirlukast. RESULTS: Compared with placebo, zafirlukast produced a 1.82-unit increase in logPC20FEV1 and a 1.88-unit increase in logPD20FEV1, representing a 66-fold higher concentration and a 76-fold higher dose of LTD4, respectively, to produce a 20% decrease in FEV1 (P < .001). Mean time to recovery after challenge was 36.7 versus 51.7 minutes when patients received zafirlukast and placebo, respectively. No correlation between clinical effects and plasma drug levels was observed. CONCLUSIONS: This trial demonstrated that asthmatic patients on maintenance ICS can respond to exogenously administered LTD4 and that zafirlukast reduced the airway response to LTD4 in these patients.

Determination of zafirlukast, a selective leukotriene antagonist, human plasma by normal-phase high-performance liquid chromatography with fluorescence detection.

A high-performance liquid chromatographic (HPLC) method was developed for the determination of zafirlukast, a selective peptide leukotriene receptor antagonist, in human plasma. Zafirlukast and the internal standard, ICI 198 707, were extracted from deproteinated plasma samples using large reservoir C18 solid-phase extraction columns and analyzed by normal-phase liquid chromatography with fluorescence detection. The method had a lower limit of quantitation of 0.75 ng/ml and a linear calibration curve in the range of 0.75 to 200 ng/ml. The absolute recovery of zafirlukast was > 90%, and the within-day and between-day relative standard deviations were < 9%. The utility of the method in the characterization of the plasma concentration-time profiles of zafirlukast in clinical studies was demonstrated.