Development and validation of an UPLC-MS/MS method for the simultaneous determination of fexofenadine and olmesartan in human serum: Application to in vivo pharmacokinetic studies.

A sensitive, reproducible, robust, high-throughput ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed and validated for the simultaneous quantification of fexofenadine and olmesartan in human serum. Samples (50 µL) undergo protein precipitation prior to UPLC-MS/MS analysis. The analytes were separated using an Acquity BEH C18 column (2.1 mm × 50 mm, 1.7 µm) at a flow rate of 0.5 mL/min using a gradient elution with a total run time of 4 min. The analytes were detected in positive ion mode and selected reaction monitoring (SRM) was used for quantitation. The standard curve concentration range was 1.0-500.0 ng/mL for both analytes and each analyte showed excellent linearity with correlation coefficients (R2 > 0.99). The intra- and inter-day accuracy and precision were ±15% for each analyte, and excellent recovery was demonstrated (93-98%) for both analytes. The method is well suited for high-throughput quantitative determination of fexofenadine and olmesartan simultaneously and was successfully applied to an in vivo pharmacokinetic and transporter phenotyping study in humans.

Effects of membrane transport activity and cell metabolism on the unbound drug concentrations in the skeletal muscle and liver of drugs: A microdialysis study in rats.

The unbound concentrations of 14 commercial drugs, including five non-efflux/uptake transporter substrates-Class I, five efflux transporter substrates-class II and four influx transporter substrates-Class III, were simultaneously measured in rat liver, muscle, and blood via microanalysis. Kpuu,liver and Kpuu,muscle were calculated to evaluate the membrane transport activity and cell metabolism on the unbound drug concentrations in the skeletal muscle and liver. For Class I compounds, represented by antipyrine, unbound concentrations among liver, muscle and blood are symmetrically distributed when compound hepatic clearance is low. And when compound hepatic clearance is high, unbound concentrations among liver, muscle and blood are asymmetrically distributed, such as Propranolol. For Class II and III compounds, overall, the unbound concentrations among liver, muscle, and blood are asymmetrically distributed due to a combination of hepatic metabolism and efflux and/or influx transporter activity.

Predicted values for human total clearance of a variety of typical compounds with differently humanized-liver mouse plasma data.

Prediction of human pharmacokinetics is important in the preclinical stage. Values for total clearance of compounds from plasma should be one of the most important pharmacokinetic parameters for predictions. Although several physiological and empirical methods including single-species allometry for prediction of values for human clearance of compounds using humanized-liver mice have been reported, further improvement of prediction accuracies would be still expected. To optimize these approaches, we proposed methods for unbound intrinsic clearance in virtually 100% humanized-liver mouse by incorporating unbound plasma fractions of compounds in differently humanized-liver mice. Comparisons of prediction accuracies of values for human clearance of 15 model compounds were performed among our current physiological and previously reported models and single-species allometry using humanized-liver mice. Incorporation of the actual unbound plasma fractions of compounds and correction of residual mice hepatocyte in humanized-liver mice showed comparable prediction accuracy to that by single-species allometry. After exclusion of 3 compounds with large species differences in values of clearance and unbound plasma fractions between mice and humans out of 15 compounds, prediction accuracies were improved in the methods investigated. The previously and present reported physiological methods could show the good prediction accuracy of values for clearance of drugs from plasma.

Chiral Discrimination of P-glycoprotein in Parturient Women: Effect of Fluoxetine on Maternal-Fetal Fexofenadine Pharmacokinetics.

BACKGROUND AND OBJECTIVE: Fluoxetine, antidepressant widely-used during pregnancy, is a selective inhibitor for P-glycoprotein (P-gp). Fexofenadine, an in vivo P-gp probe, is an antihistamine drug for seasonal allergic rhinitis and chronic urticaria treatment during pregnancy and it is available as a racemic mixture. This study evaluated the chiral discrimination of P-gp investigating the effect of fluoxetine on maternal-fetal pharmacokinetics of fexofenadine. METHODS: Healthy parturient women received either a single oral dose of 60 mg racemic fexofenadine (Control group; n = 8) or a single oral dose of 40 mg racemic fluoxetine 3 h before a single oral dose of 60 mg racemic fexofenadine (Interaction group; n = 8). Maternal blood and urine samples were collected up to 48 h after fexofenadine administration. At delivery, maternal-placental-fetal blood samples were collected. RESULTS: The maternal pharmacokinetics of fexofenadine was enantioselective (AUC0-∞R-(+)/S-(-) ~ 1.5) in both control and interaction groups. Fluoxetine increased AUC0-∞ (267.7 vs 376.1 ng.h/mL) and decreased oral total clearance (105.1 vs 74.4 L/h) only of S-(-)-fexofenadine, whereas the renal clearance were reduced for both enantiomers, suggesting that the intestinal P-gp-mediated transport of S-(-)-fexofenadine is influenced by fluoxetine to a greater extent that the R-(+)-fexofenadine. However, the transplacental transfer of fexofenadine is low (~16%), non-enantioselective and non-influenced by fluoxetine. CONCLUSIONS: A single oral dose of 40 mg fluoxetine inhibited the intestinal P-gp mediated transport of S-(-)-fexofenadine to a greater extent than R-(+)-fexofenadine in parturient women. However, the placental P-gp did not discriminate fexofenadine enantiomers and was not inhibited by fluoxetine.

Direct chiral LC-MS/MS analysis of fexofenadine enantiomers in plasma and urine with application in a maternal-fetal pharmacokinetic study.

This study shows the development and validation of two enantioselective LC-MS/MS methods for the determination of fexofenadine in biological matrices including the elution order determination. Plasma (200 µL) or urine (50 µL) aliquots were added to the internal standard solution [(S)-(-)-metoprolol] and extracted in the acid medium with chloroform. Resolution of the (R)-(+)- and (S)-(-)-fexofenadine enantiomers was performed in a Chirobiotic V column. The methods showed linearity at the range of 0.025-100 ng/mL plasma and 0.02-10 µg/mL urine for each fexofenadine enantiomer. These methods were applied to the maternal-fetal pharmacokinetics of fexofenadine enantiomers in plasma and urine of parturient women (n = 8) treated with a single oral 60 mg dose of racemic fexofenadine. Enantiomeric ratio in plasma (AUC0-∞(R)-(+)/(S)-(-)) was close to 1.5, nevertheless in urine was closed to unity. The transplacental transfer was approximately 18% for both fexofenadine enantiomers. The enantioselective methods can also be useful in future clinical studies of chiral discrimination of drug transporters.

Evaluation of potential herbal-drug interactions of a standardized propolis extract (EPP-AF®) using an in vivo cocktail approach.

ETHNOPHARMACOLOGICAL RELEVANCE: Propolis has been employed extensively in many cultures since ancient times as antiseptic, wound healing, anti-pyretic and others due to its biological and pharmacological properties, such as immunomodulatory, antitumor, anti-inflammatory, antioxidant, antibacterial, antiviral, antifungal, antiparasite activities. But despite its broad and traditional use, there is little knowledge about its potential interaction with prescription drugs. AIM OF THE STUDY: The main objective of this work was to study the potential herbal-drug interactions (HDIs) of EPP-AF® using an in vivo assay with a cocktail approach. MATERIALS AND METHODS: Subtherapeutic doses of caffeine, losartan, omeprazole, metoprolol, midazolam and fexofenadine were used. Sixteen healthy adult volunteers were investigated before and after exposure to orally administered 125 mg/8 h (375 mg/day) EPP-AF® for 15 days. Pharmacokinetic parameters were calculated based on plasma concentration versus time (AUC) curves. RESULTS: After exposure to EPP-AF®, it was observed decrease in the AUC0-∞ of fexofenadine, caffeine and losartan of approximately 18% (62.20 × 51.00 h.ng/mL), 8% (1085 × 999 h.ng/mL) and 13% (9.01 × 7.86 h.ng/mL), respectively, with all 90% CIs within the equivalence range of 0.80-1.25. On the other hand, omeprazole and midazolam exhibited an increase in AUC0-∞ of, respectively, approximately 18% (18.90 × 22.30 h.ng/mL) and 14% (1.25 × 1.43 h.ng/mL), with the upper bounds of 90% CIs slightly above 1.25. Changes in pharmacokinetics of metoprolol or its metabolite α-hydroxymetoprolol were not statistically significant and their 90% CIs were within the equivalence range of 0.80-1.25. CONCLUSIONS: In conclusion, our study shows that EPP-AF® does not clinically change CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A activities, once, despite statistical significant, the magnitude of the changes in AUC values after EPP-AF® were all below 20% and therefore may be considered safe regarding potential interactions involving these enzymes. Besides, to the best of our knowledge this is the first study to assess potential HDIs with propolis.

Telemetered common marmosets is useful for the assessment of electrocardiogram parameters changes induced by multiple cardiac ion channel inhibitors.

The objective of this study is to assess the response of telemetered common marmosets to multiple cardiac ion channel inhibitors and to clarify the usefulness of this animal model in evaluating the effects of drug candidates on electrocardiogram (ECG). Six multiple cardiac ion channel inhibitors (sotalol, astemizole, flecainide, quinidine, verapamil and terfenadine) were orally administered to telemetered common marmosets and changes in QTc, PR interval and QRS duration were evaluated. Drugs plasma levels were determined to compare the sensitivity in common marmosets to that in humans. QTc prolongation was observed in the marmosets dosed with sotalol, astemizole, flecainide, quinidine, verapamil and terfenadine. PR prolongation was noted after flecainide and verapamil administration, and QRS widening occurred following treatment with flecainide and quinidine. Drugs plasma levels associated with ECG changes in marmosets were similar to those in humans, except for verapamil-induced QTc prolongation. Verapamil-induced change is suggested due to body temperature decrease. These results indicate that telemetered common marmoset is a useful animal for evaluation of the ECG effects of multiple cardiac ion channel inhibitors and the influence of body temperature change should be considered in the assessment.

Modulation of Fexofenadine Pharmacokinetics by Osimertinib in Patients With Advanced EGFR-Mutated Non-Small Cell Lung Cancer.

Osimertinib is a potent, third-generation, irreversible, central nervous system active epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI) that selectively inhibits EGFR-TKI sensitizing and EGFR T790M resistance mutations. It is approved for first-line treatment of patients with advanced non-small cell lung cancer (NSCLC) whose tumors have EGFR exon 19 deletions or exon 21 L858R mutations, and for patients with T790M-positive advanced NSCLC whose disease has progressed on or after EGFR-TKI therapy. This study investigated the pharmacokinetics (PK) of fexofenadine (P-glycoprotein substrate) following single- and multiple-dose osimertinib in patients with advanced NSCLC who have progressed on prior EGFR-TKI therapy. This open-label, phase 1 study (NCT02908750) comprised the PK phase and continued access phase. The former comprised 2 distinct periods with a 3- to 7-day washout: treatment period 1 (n = 24, fexofenadine 120 mg, day 1) and treatment period 2 (fexofenadine 120 mg + osimertinib 80 mg single dose on days 1 and 39 and osimertinib 80 mg once daily from days 4 to 41). Patients could continue osimertinib 80 mg once daily based on investigator's discretion in the continued access phase. Fexofenadine area under the plasma concentration-time curve and maximum concentration increased by 56% (90% confidence interval [CI], 35.4-78.6) and 76% (90%CI, 49.3-108.3) following coadministration with osimertinib single dose, and by 27% (90%CI, 11.2-45.8) and 25% (90%CI, 5.6-48.1) when given with osimertinib at steady state, respectively. Following osimertinib coadministration, median fexofenadine time to maximum concentration increased by approximately 30 minutes compared with time to maximum concentration following fexofenadine alone. No new osimertinib safety findings were observed. The increase in fexofenadine exposure following osimertinib coadministration shows osimertinib as a weak P-glycoprotein inhibitor.

Impact of ABCB1 genotype in Collies on the pharmacokinetics of R- and S-fexofenadine.

Thirty-two Collies were used to determine the impact of ABCB1 genotype and phenotype on the plasma pharmacokinetics of fexofenadine's (Fex) R- and S-enantiomers after bolus Fex administration, as human P-gp exhibits stereoselectivity. Each Collie's ABCB1 genotype and ivermectin (IVM) sensitivity (phenotype) was determined prior to study enrolment. Wild-type (WT) Collies had lower plasma concentrations of the individual enantiomers as compared to heterozygous IVM nonsensitive (HNS), heterozygous IVM-sensitive (HS) and homozygous mutant (MUT) Collies. Based on pairwise statistical comparison, WT Collies had statistically significantly lower (AUC0-last ) and peak (Cmax ) values compared to HS, HNS and MUT Collies. Tmax was not influenced by genotype/phenotype. Inter-individual variability in PK metrics tended to be largest for WT Collies. Although the influence of genotype/phenotype on Fex PK occurred with the individual isomers, impairment of S-Fex absorption, particularly in the MUT dogs, exceeded that associated with R-Fex. Since Fex elimination occurs primarily via biliary excretion via a transporter other than P-glycoprotein, and based upon our understanding of Fex absorption kinetics, we attributed these differences primarily to the absorption portion of the profile. These differences are expressed in a stereo-specific manner. These results demonstrate the potential negative impact on estimates of drug effectiveness and toxicity, especially for P-gp substrates that do not exhibit Central Nervous System toxicities.

A sensitive method for the quantitation of the peptide-based glucagon-like peptide-1 receptor agonist liraglutide in plasma using microfluidics chromatography tandem MS.

AIM: An LC-MS/MS assay for the quantitation of liraglutide, a peptide-based injectable glucagon-like peptide-1 receptor agonist, has been developed as a convenient alternative to the enzyme-linked immunosorbent assay, and used to characterize liraglutide pharmacokinetics in cynomolgus monkeys. RESULTS: Assay calibration curves exhibited a linear dynamic range of 10-5000 ng/ml and correlation coefficient ≥0.98. Following a 30 µg/kg intravenous dose, liraglutide demonstrated low plasma clearance and distribution volume, which led to a terminal half-life of 6.59 h in monkeys. CONCLUSION: The dynamic range of our LC-MS/MS assay provides sufficient coverage of the average efficacious liraglutide concentrations in human plasma, and can be used for pharmacokinetics/pharmacodynamics studies in animals and potentially in humans.

Sensitivity and Reliability of Halothane-anaesthetized Microminipigs to Assess Risk of Drug-induced Long QT Syndrome.

Using moxifloxacin and terfenadine, which are known to induce benign and malignant QT interval prolongation, respectively, we analysed whether halothane-anaesthetized microminipigs are an appropriate model for assessing the risk of drug-induced long QT syndrome. Moxifloxacin (0.03, 0.3 and 3 mg/kg) and terfenadine (0.03, 0.3 and 3 mg/kg) were intravenously infused over 10 min. with a pause of 20 min. to the halothane-anaesthetized microminipigs (n = 4 for each drug). Moxifloxacin decreased the heart rate, whereas it increased the blood pressure in a dose-related manner. It also prolonged the PR interval and QT/QTc in a dose-related manner without altering the QRS width. Terfenadine decreased the heart rate and blood pressure, whereas it prolonged the PR interval, QRS width and QT/QTc in a dose-related manner. Terfenadine significantly prolonged the beat-to-beat variability of QT interval reflecting its pro-arrhythmic potential, which was not observed with moxifloxacin. The peak plasma concentrations of moxifloxacin and terfenadine after doses of 3 mg/kg were 4.81 and 10.15 µg/mL, respectively, which were both 1.5 times less in microminipigs than those previously reported in dogs. These results indicate that halothane-anaesthetized microminipigs would be useful for detecting drug-induced cardiovascular responses as well as differentiating benign from malignant QT interval prolongation like dogs, although there may be some differences in pharmacokinetic profile between these animals.

Effect of Garlic, Gingko, and St. John's Wort Extracts on the Pharmacokinetics of Fexofenadine: A Mechanistic Study.

The aim of this study was to determine the effects of garlic and ginkgo herbal extracts on the pharmacokinetics of the P-glycoprotein (P-gp)/organic anion-transporting polypeptides (Oatps) substrate fexofenadine. Male rats were dosed orally with garlic (120 mg/kg), ginkgo (17 mg/kg), St. John's wort (SJW; 1000 mg/kg; positive control), or Milli-Q water for 14 days. On day 15, rats either were administered fexofenadine (orally or i.v.), had their livers isolated and perfused with fexofenadine, or had their small intestines divided into four segments (SI-SIV) and analyzed for P-gp and Oatp1a5. In vivo, SJW increased the clearance of i.v. administered fexofenadine by 28%. Garlic increased the area under the curve0-∞ and maximum plasma concentration of orally administered fexofenadine by 47% and 85%, respectively. Ginkgo and SJW had no effect on the oral absorption of fexofenadine. In the perfused liver, garlic, ginkgo, and SJW increased the biliary clearance of fexofenadine with respect to perfusate by 71%, 121%, and 234%, respectively. SJW increased the biliary clearance relative to the liver concentration by 64%. The ratio of liver to perfusate concentrations significantly increased in all treated groups. The expression of Oatp1a5 in SI was increased by garlic (88%) and SJW (63%). There were no significant changes in the expression of P-gp. Induction of intestinal Oatp1a5 by garlic may explain the increased absorption of orally administered fexofenadine. Ginkgo had no effect on the expression of intestinal P-gp or Oatp1a5. A dual inductive effect by SJW on opposing intestinal epithelial transport by Oatp1a5 and P-gp remains a possibility.

Influence of P-glycoprotein on the disposition of fexofenadine and its enantiomers.

OBJECTIVES: P-glycoprotein (P-gp) is responsible for the efflux of a broad variety of human and veterinary drugs. Canine P-gp polymorphisms alter drug disposition and toxicity, but their impact on the disposition of enantiomeric drugs is unknown. Using fexofenadine as a model compound, we developed and validated HPLC-fluorescence methods to determine the effect of P-gp on the disposition of fexofenadine and its enantiomers. METHODS: A chiral CD-Ph column was used for the separation of (R) and (S)-fexofenadine. Determination of racemic fexofenadine was achieved on an XDB-CN column. Fexofenadine and its enantiomers were detected by fluorescence at the excitation wavelength of 220 nm and emission wavelength of 300 nm. These methods were used to measure concentrations of fexofenadine and its enantiomers in Collie plasma after oral administration. KEY FINDINGS: This study demonstrates that P-gp prefers to transport (S)-fexofenadine, and P-gp deficiency causes the increase in both (R)-fexofenadine and (S)-fexofenadine in plasma. Racemic fexofenadine, (R)-fexofenadine and (S)-fexofenadine were increased in ABCB1-1Δ Collies (118.7, 72.0 and 48.3 ng/ml) compared to wild-type Collies (25.0, 16.5 and 7.7 ng/ml) at 1 h postadministration. The results demonstrate that the stereoselectivity of P-gp plays a key role in the disposition of fexofenadine enantiomers. CONCLUSIONS: The information derived from this drug model will be used to determine whether additional safety or efficacy requirements are necessary for enantiomeric drugs that would be used in dogs or humans.

D-Optimal mixture design optimization of an HPLC method for simultaneous determination of commonly used antihistaminic parent molecules and their active metabolites in human serum and urine.

This study describes a specific, precise, sensitive and accurate method for simultaneous determination of hydroxyzine, loratadine, terfenadine, rupatadine and their main active metabolites cetirizine, desloratadine and fexofenadine, in serum and urine using meclizine as an internal standard. Solid-phase extraction method for sample clean-up and preconcentration of analytes was carried out using Phenomenex Strata-X-C and Strata X polymeric cartridges. Chromatographic analysis was performed on a Phenomenex cyano (150 × 4.6 mm i.d., 5 µm) analytical column. A D-optimal mixture design methodology was used to evaluate the effect of changes in mobile phase compositions on dependent variables and optimization of the response of interest. The mixture design experiments were performed and results were analyzed. The region of ideal mobile phase composition consisting of acetonitrile-methanol-ammonium acetate buffer (40 mm; pH 3.8 adjusted with acetic acid): 18:36:46% v/v/v was identified by a graphical optimization technique using an overlay plot. While using this optimized condition all analytes were baseline resolved in <10 min. Solvent mixtures were delivered at 1.5 mL/min flow rate and analytes peaks were detected at 222 nm. The proposed bioanalytical method was validated according to US Food and Drug Administration guidelines. The proposed method was sensitive with detection limits of 0.06-0.15 µg/mL in serum and urine samples. Relative standard deviation for inter- and intra-day precision data was found to be <7%. The proposed method may find application in the determination of selected antihistaminic drugs in biological fluids.

The association between pro-arrhythmic agents and aortic stenosis in young adults: is it sufficient to clarify the sudden unexpected deaths?

Most young patients with mild-to-moderate aortic stenosis show no symptoms, and sudden death appears only occasionally. We hypothesised that malignant ventricular arrhythmias could be responsible for the high incidence of sudden death in such patients. If multiple factors such as asymptomatic aortic stenosis in association with arrhythmia-provoking agents are involved, could it be sufficient to account for sudden unexpected death? In this study, eight cases of sudden death in young adults, with ages ranging from 22 to 36 years, who had never reported any symptoms that could be related to aortic stenosis, were investigated. Full autopsies were performed, and congenital aortic stenosis in all eight cases was confirmed. DNA testing for channelopathies was negative. Comprehensive toxicological analyses found an electrolyte imbalance, or non-toxic concentrations of amitriptyline, terfenadine, caffeine, and ethanol. Collectively, these results suggest that congenital asymptomatic aortic stenosis without cardiac hypertrophy in young adults is not sufficient to cause sudden death merely on its own; rather, an additional provoking factor is necessary. According to our findings, the provoking factor may be a state of physical or emotional stress, a state of electrolyte imbalance, or even taking a therapeutic dose of a particular drug.

The Pharmacokinetic Exposure to Fexofenadine is Volume-Dependently Reduced in Healthy Subjects Following Oral Administration With Apple Juice.

Pharmacokinetic exposures to fexofenadine (FEX) are reduced by apple juice (AJ); however, the relationship between the AJ volume and the degree of AJ-FEX interaction has not been understood. In this crossover study, 10 healthy subjects received single doses of FEX 60 mg with different volumes (150, 300, and 600 mL) of AJ or water (control). To identify an AJ volume lacking clinically meaningful interaction, we tested a hypothesis that the 90% confidence interval (CI) for geometric mean ratio (GMR) of FEX AUCAJ /AUCwater is contained within a biocomparability bound of 0.5-2.0, with at least one tested volume of AJ. GMR (90% CI) of AUCAJ 150mL /AUCwater , AUCAJ 300mL /AUCwater , and AUCAJ 600mL /AUCwater were 0.903 (0.752-1.085), 0.593 (0.494-0.712), and 0.385 (0.321-0.462), respectively. While a moderate to large AJ-FEX interaction is caused by a larger volumes of AJ (e.g., 300 to 600 mL), the effect of a small volume (e.g., 150 mL) appears to be not meaningful.

No major effects of vitamin D3 (1,25 dihydroxyvitamin D3) on absorption and pharmacokinetics of folic acid and fexofenadine in healthy volunteers.

PURPOSE: In Caco-2 cells, folate uptake via the proton-coupled folate transporter (PCFT) increases significantly by a 3-day treatment with 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Additionally, mRNA content and protein expression of the transporter OATP1A2 were increased up to ninefold with 1,25(OH)2D3. We investigated whether these in vitro findings can be confirmed in humans in vivo. METHODS: Ten healthy volunteers (six women) received 5 mg folic acid orally once before and once together with the last intake of a 10-day course of 0.5 µg 1,25(OH)2D3 orally. One hundred twenty milligrams fexofenadine, an OATP1A2 substrate, was taken in 1 day before the first folic acid intake, and again on the ninth day of 1,25(OH)2D3 intake. Duodenal biopsies were taken for transporter mRNA assessments once before and once on the ninth or tenth day of the vitamin D3 course. Serum folic acid and fexofenadine concentrations were quantified with a chemiluminescence immunoassay and LC-MS/MS, respectively. Pharmacokinetics were compared between periods with standard bioequivalence approaches. RESULTS: While geometric mean folic acid AUC0-2h, which mainly reflects absorption, was 0.403 and 0.414 mg/L·h before and after the vitamin D3 course (geometric mean ratio (GMR), 1.027; 90 % confidence interval (90 % CI), 0.788-1.340), the geometric mean fexofenadine AUC0-2h was 1.932 and 2.761 mg/L·h, respectively (GMR, 1.429; 90 % CI, 0.890-2.294). PCFT- and OATP1A2-mRNA expressions in duodenal biopsies were essentially unchanged. CONCLUSIONS: No significant changes in folic acid and fexofenadine absorption were observed after a 10-day course of 1,25(OH)2D3 in humans in vivo. This study underlines the importance of confirming in vitro findings in vivo in humans.

HPLC Determination of Fexofenadine in Human Plasma For Therapeutic Drug Monitoring and Pharmacokinetic Studies.

A simple and sensitive method was developed for fexofenadine determination in human plasma by liquid chromatography with ultraviolet detection. Satisfactory separation was achieved on a Hypersil® BDS C18 column (250 × 4.6 mm, 5µm) using a mobile phase comprising 20 mm sodium dihydrogen phosphate-2 hydrate (pH adjusted to 3 with phosphoric acid)-acetonitrile at a ratio of 52:48, v/v. The elution was isocratic at ambient temperature with a flow rate of 1.0 mL/min. The UV detector was set at 215 nm for the drug and 330 nm for the internal standared (tinidazole). The total time for a chromatographic separation was ~6.5 min. Linearity was demonstrated over the concentration range 0.01-4 µg/mL. The observed within- and between-day assay precision ranged from 0.346 to 13.6%; accuracy varied between 100.4 and 111.2%. This method was successfully applied for therapeutic drug monitoring in patients treated with clinical doses of fexofenadine and for pharmacokinetic studies. Copyright © 2015 John Wiley & Sons, Ltd.

Effects of Cremophor EL on the absorption of orally administered saquinavir and fexofenadine in healthy subjects.

Modulation of CYP3A and/or P-gp function by several excipients has been reported. However, relatively few studies have investigated their effects in humans. Therefore, the aim of this clinical study was to clarify the effects of Cremophor EL on the inhibition of CYP3A and P-gp in the human small intestine. Eight healthy Japanese subjects received an oral dose of saquinavir (2 mg, substrate of P-gp/CYP3A) or fexofenadine (50 µg, substrate of P-gp) without or with Cremophor EL (720 mg and 1440 mg). Significant increases in Cmax (1.3-fold) and AUC0-24 (1.6-fold) were observed for fexofenadine when administered with 1440 mg of Cremophor EL. In contrast, a significant decrease was observed for saquinavir when administered with 720 mg of Cremophor EL. The equilibrium dialysis experiment was performed to investigate the micellar interaction between Cremophor EL and drugs. The equilibrium dialysis study showed that saquinavir was far extensively entrapped into the micelles. The reduced concentration of free saquinavir by entrapping in micelles was considered to cause the reduction of systemic exposure for saquinavir. In conclusion, this clinical study suggests that Cremophor EL at least inhibits P-gp in the human small intestine.

Effect of diosmin on the intestinal absorption and pharmacokinetics of fexofenadine in rats.

BACKGROUND: Diosmin is a natural flavone glycoside, a potent P-glycoprotein (P-gp) inhibitor in cultured cells and have the potential to alter the bioavailability of P-gp substrate drugs. However, the interaction between diosmin and fexofenadine is unreported. Hence, the present study was performed to investigate the effect of diosmin on the intestinal absorption and pharmacokinetics of fexofenadine, a P-gp substrate in rats. METHODS: Fexofenadine intestinal transport and permeability were evaluated by in vitro non-everted sac and in situ single pass intestinal perfusion (SPIP) studies. These results were confirmed by an in vivo pharmacokinetic study of oral administered fexofenadine (10mg/kg) in rats. RESULTS: The intestinal transport and apparent permeability (Papp) of fexofenadine were significantly increased in duodenum, jejunum and ileum of diosmin pretreated group as compared with the control. Similarly effective permeability (Peff) of fexofenadine was increased significantly in ileum of diosmin pretreated group as compared with control. In comparison with control, pretreatment with diosmin significantly increased peak plasma concentration (Cmax) and area under the concentration-time curve (AUC), while there was no significant change was observed in half life (T1/2), time to reach peak plasma concentration (Tmax) and elimination rate constant (Kel) of fexofenadine. CONCLUSIONS: Diosmin significantly enhanced the oral bioavailability of fexofenadine by the inhibition of P-gp mediated drug efflux during the intestinal absorption. Co-administration of diosmin with fexofenadine can reduce the dosage and results in reduced side effects of fexofenadine. The clinical relevance of this interaction should be further evaluated in human subjects.