Digoxin bioequivalence study: determination in human plasma by microparticle enzyme immunoassay.

OBJECTIVE: In this study a bioanalytical method for digoxin quantification was developed using Abbott AxSYM Digoxin II with fluorescence detection to assess the bioequivalence of two digoxin tablet formulations (Digox 0.25 mg tablet from Pharlab Ind. Ltd., Brazil as test formulation and Digoxin 0.25 mg tablet from Laboratório Glaxo SmithKline, Brazil as reference formulation). MATERIAL AND METHODS: 30 healthy volunteers (both sexes) received a single oral dose of digoxin in an open, randomized, two-period crossover study with a seven half-life washout interval of at least (21 days). Plasma samples were obtained over a 288-h interval after each oral administration of digoxin. The present method utilizes microenzyme particle immunoassay technology, in which the digoxin in the sample binds to anti-digoxin-coated microparticles and after separation; digoxin-alkaline phosphatase conjugate binds to the available sites remaining. Digoxin concentrations are calculated from the fluorescent products generated as a result of substrate (4-methylumbelliferyl) passage through the matrix cell. RESULTS: The method was shown to be specific and sensitive with good accuracy and precision. The geometric mean and 90% confidence intervals (CI) for the Digox/Digoxin ratio were 107.62% (96.71 - 119.80%) for AUC0-t, 97.15% (80.54 - 117.19%) for AUC0-inf, and 91.23% (83.55 - 99.62%) for Cmax. CONCLUSION: Since the 90% CI for the parameters were all within the 80 - 125% interval proposed by the US Food and Drug Administration Agency, the two formulations were considered bioequivalent in terms of rate and extent of absorption.

Meloxicam determination in human plasma by high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS-MS) in Brazilian bioequivalence studies.

OBJECTIVE: In this study, the bioavailability of 2 meloxicam 15 mg tablet formulations was compared. A single dose of each formulation was administered to 24 healthy volunteers (12 males and 12 females). MATERIAL AND METHODS: The study was conducted using an open, randomized and crossover design with a 2-week washout interval. The plasma samples were obtained over a 96-hour interval and meloxicam concentrations were analyzed by high-performance liquid chromatography (an agilent) coupled to an API 2000 turboionspray tandem mass spectrometry (LC-MS-MS). An electrospray ionization (ESI) source operating in the positive ion mode, using a cross flow counter electrode and set for the multiple reaction monitoring (MRM) was employed. The plasma protein precipitate was reconstituted with acetonitrile/water + 10 mM acetic acid (20/80, v/v) and injected in a Prevail C8 5 microm (150 mm x 4.6 mm i.d.) analytical column with reverse-phase liquid chromatography. The retention time observed for meloxicam and tenoxicam (internal standard) was 1.8 and 1.4 minutes, respectively. The mean recovery of meloxicam was 95.9% and the limit ofquantification was 0.02 microg/ml. RESULTS: The geometric mean of meloxicam/movatec 15 mg individual % ratio was 101.3% for AUC(last), 99.9% for AUC(0-infinity) and 107.7% for C(max). The 90% confidence intervals were 97.3 - 105.4%, 96.0 - 104.0% and 98.8 - 117.4%, respectively. CONCLUSION: Since the 90% CI for both AUC(Iast), AUC(0-infinity) and C(max), ratios were all inside the 80 - 125% interval proposed by the US Food and Drug Administration Agency and accepted by Brazilian ANVISA (Sanitary Surveillance Agency), it was concluded that the meloxicam formulation produced by Merck S.A. lndústrias Químicas is bioequivalent to the movatec formulation regarding both the rate and extent of absorption. This assay method was faster, more simple, specific, precise and accurate in determining the bioequivalence of meloxicam than any method previously described.

A bioequivalence study of citalopram based on quantification by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry.

OBJECTIVE: The aim of this study was to compare the bioavailability of two citalopram formulations (citalopram from Eurofarma Laboratórios Ltda., as the test formulation, and cipramil from Schering-Plough, Brazil, as the reference formulation) in healthy volunteers. METHODS: The study had an open, randomized, two-period crossover design with a two-week washout interval between doses. The samples were obtained over a 168-hour interval after each oral administration of citalopram (one 20 mg tablet of each formulation). The analyte and the internal standard were extracted from plasma using diethylether: dichloromethane (70 : 30, v/v) and the extracts were analyzed by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry. Chromatography was done isocratically using a Genesis C8 analytical column (4 microm, 2.1 mm i.d. x 100 mm). The method had a chromatographic run time of three minutes and a linear calibration curve over the range of 0.5 - 200 ng x ml(-1) (r2 > 0.999887). The limit of quantification was 0.5 ng x ml(-1). RESULTS: The geometric mean and 90% confidence intervals (CI) for the citalopram/cipramil ratio were 98.28% (94.24 - 102.49%) for AUClast, 96.44% (90.20 - 103.11%) for AUCinf, and 98.54% (94.70 - 102.54%) for Cmax. CONCLUSION: Since the 90% CI for Cmax, AUClast and AUC(0-infinity) ratios were all within the 80 - 125% interval proposed by the US Food and Drug Administration, we concluded that the citalopram formulation elaborated by Eurofarma Laboratórios Ltda. was bioequivalent to the cipramil formulation in its rate and extent of absorption.