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AIM
A randomized, two-way, crossover, bioequivalence study was conducted in 25 fasting, healthy, male volunteers to compare two brands of fexofenadine 180 mg tablets, FEXOFENADINE 180 mg Film Tablet (Drogsan A.S., Ankara, Turkey) as test and Telfast 180 mg Tablet (Aventis Pharma, Frankfurt am Main, Germany) as a reference product.


METHOD
One tablet of either formulation was administered after 10 h of overnight fasting. After dosing, serial blood samples were collected during a period of 48 hours. Plasma samples were analysed for fexofenadine by a validated HPLC method. The pharmacokinetic parameters AUC(0-48), AUC(0-alpha), C(max), T(max), K(el), T(1/2), and CL were determined from plasma concentration-time profiles for both formulations and were compared statistically.


RESULTS AND CONCLUSIONS
The analysis of variance (ANOVA) did not show any significant difference between the two formulations and 90% confidence intervals (CI) fell within the acceptable range, satisfying the bioequivalence criteria of the FDA. Based on these statistical inferences it was concluded that the two brands exhibited comparable pharmacokinetics profiles and that Drogsan's Fexofenadine is equivalent to Telfast of Aventis Pharma, Frankfurt am Main, Germany.


INTRODUCTION
Fexofenadine is a selective and peripherally acting H 1 -receptor antagonist.In clinical studies this nonsedating antihistamine has been found to relieve symptoms associated with allergic conditions such as seasonal allergic rhinitis 1,2 .Results of clinical safety and effi cacy trials with fexofenadine HCl doses up to 240 mg twice daily in patients with seasonal rhinitis have further demonstrated its safety, indicating a large therapeutic window for this drug 3 .The drug eff ect is seen within 1 hr, achieving maximum eff ect at 6 hr, and lasting a minimum of 12 hr after medication 4,5 , and the drug can be used for long periods without evidence of intolerance 6 .
The objective of this study was to evaluate, in healthy volunteers, the bioequivalence (BE) of a test formulation of the 180 mg (tablets) of fexofenadine HCl manufactured by Drogsan A.S., Ankara, Turkey (FEXOFENADINE 180 mg Film Tablet) and a commercial formulation of 180 mg (tablets) of fexofenadine HCl (Telfast ® produced by Aventis Pharma, Frankfurt am Main, Germany) used as a reference formulation.

Study design and healthy volunteers
Twenty-fi ve healthy adult male volunteers aged between 18 and 50 years (26.3 ± 6.2 years, mean ± S.D.) and within 15% of the ideal body weight, weight between 67.0 and 111.0 kg (80.8 ± 10.1), and height between 170 and 198 cm (184.0 ± 7.4), were selected for the study.
All subjects gave written informed consent and the Local Ethics Committee (Hospital and Polyclinic in Mělník) approved the clinical protocol.All volunteers were assessed as healthy based on medical history, clinical examination, blood pressure, ECG and laboratory investigation (hematology, blood biochemistry and urine).
The study was conducted in a randomized, single-dose, two-way, cross-over design with a two-week wash-out period between two doses.During each period, the volunteers were admitted to hospital and after overnight fasting they received a single reference or test 180 mg fexofenadine tablet.Low-carbonate water (240 mL) was given immediately after drug administration.All volunteers fasted 4 h after the drug administration, and then they received a snack.Standardized meals (lunch, afternoon snack, dinner and breakfast) were provided to volunteers 6, 9, 12 and 24 hr after dosing.
The study was performed in accordance with the guidelines of the revised Declaration of Helsinki on biomedical research involving subjects and the requirements of Good Clinical Practice.
Blood (9 ml) was sampled from antecubital or cubital veins and collected into sodium citrate-containing tubes before and 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 6, 8, 10, 12, 16, 24, 36 and 48 hours after the administration of each fexofenadine tablet formulation (180 mg).The blood samples were centrifuged at 2500 g for 10 min at 4 °C and the separated plasma was collected and stored at -20 °C until drug analysis.After a wash-out period of 14 days, the study was repeated in the same manner to complete the cross-over design.

Drug analysis
All plasma samples were analysed for fexofenadine concentration according to a sensitive, selective, and accurate high-performance liquid chromatography (HLPC) method, which was developed and validated before the study at the laboratories of I.Q.A..
The chromatographic separations and quantitative determination were performed using a high-performance liquid chromatograph from Agilent Technologies (HPST, Prague, Czech Republic): Model 1100 series, equipped with a degassing unit, quaternary pump, autoinjector, UV detector, and controlled by Agilent Chem.Station software.Chromatographic separation was performed using an Eclipse XDB-C 18 (150 × 4.6 mm id.; 5 μm particle size) HPLC column from Agilent Technologies (HPST, Prague, Czech Republic).The mobile phase consisted of acetonitrile and potassium dihydrogen phosphate (0.05 mol/l, pH 5.0).The mobile phase was eluted at a fl ow rate of 1.5 ml/min at 50 °C.UV detection of fexofenadine and the internal standard (cetirizine) was performed at 195 nm.Each analysis required a maximum of 12 min.The calibration curves were linear over a range of 10-1000 ng/ml using 1.0 ml plasma samples.All samples from each volunteer were measured on the same day in order to avoid inter-assay variation.

Pharmacokinetic and statistical analysis
Pharmacokinetic analysis was performed by means of a model-independent method using the GraphPad Prism (rev.2.01), Lotus Approach and Lotus 1-2-3 (rev.9) computer programs.The maximum fexofenadine plasma concentration (C max ) and the corresponding time of peak plasma concentration (T max ) were taken directly from the individual plasma data.The elimination rate constant (K el ) was estimated from the slope of the semilogarithmic plot of the terminal phase of the plasma concentrati ontime curve calculated by linear regression, and the elimination half-life (T 1/2 ) was generated by dividing ln2 by the elimination rate constant K el.The area under the plasma concentration-time curve AUC 0-48 and the area to the infi nity AUC 0-α were calculated using the linear trapezoidal method.Extrapolation of these areas to infi nity (AUC 0-α ) was done by adding the value C last /k el to the calculated AUC 0-48 (where C last = the last detectable concentration).The clearance (CL) was calculated using the following equation (dose/body wt)/AUC 0-α .
For the purpose of bioequivalence analysis, a two-way analysis of variance (ANOVA, GLM procedure) was used to assess the eff ect of formulations, periods, sequences, and subjects on AUC 0-48 , AUC 0-α and C max.The diff erence of two related parameters was considered statistically signifi cant for p < 0.05.

RESULTS AND DISCUSSION
Both fexofenadine formulations (FEXOFENADINE and Telfast 180 mg tablets) were well tolerated in all subjects; unexpected serious adverse events that could  There was no drop-out and all subjects who started the study continued to the end and were discharged in good health.
Both medications were readily absorbed from the gastrointestinal tract and fexofenadine was already measurable at the fi rst sampling time (0.5 hr) in all the volunteers.The plasma drug concentration-time curves show that the mean concentrations of fexofenadine were similar for the two formulations over the 48-hr sampling period (Fig. 1).
The results after statistical analysis of the main pharmacokinetic parameters are shown in Table 1.The parametric 90 % confi dence intervals for the main pharma cokinetic parameter values of C max , AUC 0-48 and AUC 0-α lie entirely within the BE acceptance limits approved by EMEA and FDA (i.e.80 % to 125 %).The mean fexofenadine values were T max 1.84 ± 0.87 hr; K el 0.2368 ± 0.0290 1/hr; T 1/2 2.97 ± 0.32 hr and CL 76.55 ± 40.01 L/hr for the test formulation, and T max 1.86 ± 0.77 hr; K el 0.2382 ± 0.0223 1/hr; T 1/2 2.94 ± 0.29 hr and CL 76.64 ± L42.7 1/hr for the reference formulation.Based on the nonparametric Wilcoxon test and the paired t-test, there were no signifi cant diff erences (at p > 0.05) in T max , K el, T 1/2 , and CL values for either formulation.

CONCLUSION
The mean bioequivalence of 180 mg fexofenadine tablets of the test formulation compared to the reference formulation was confi rmed.Ninety % CI of AUC 0-48 , AUC 0-α and C max ratios of fexofenadine of these two prepa-rations fell within the 80-125 % interval proposed by the US FDA 7 .Both formulations were equivalent in terms of rate and extent of absorption.Consequently, bioequivalence between the two formulations can be concluded.

Fig. 1 .
Fig. 1.Fexofenadine plasma mean concentrations versus time profi le obtained aftersingle oral administration of 180 mg of fexofenadine tablet formulation.

Table 1 .
Arithmetic and geometric means and 90 % confi dence intervals (90 % CI) of Cmax, AUC 0-48 and AUC 0-α (log transformed) of fexofenadine during single dose administration of 180 mg test and reference formulations in 25 healthy male subjects.Bioequivalence of two fexofenadine formulations in healthy human volunteers after single oral administration have infl uenced the outcome of the study did not occur.