Quantification of nimesulide in human plasma by high-performance liquid chromatography/tandem mass spectrometry. Application to bioequivalence studies

A method based on liquid chromatography with negative ion electrospray ionization and tandem mass spectrometry is described for the determination of nimesulide in human plasma. Liquid-liquid extraction using a mixture of diethyl ether and dichloromethane was employed and celecoxib was used as an internal standard. The chromatographic run time was 4.5 min and the weighted (1/x) calibration curve was linear in the range 10.0-2000 ng x ml(-1). The limit of quantification was 10 ng x ml(-1), the intra-batch precision was 6.3, 2.1 and 2.1% and the intra-batch accuracy was 3.2, 0.3 and 0.1% for 30, 300 and 1200 ng x ml(-1) respectively. The inter-batch precision was 2.3, 2.8 and 2.7% and the accuracy was 3.3, 0.3 and 0.1% for 30, 300 and 1200 ng x ml(-1) respectively. This method was employed in a bioequivalence study of one nimesulide drop formulation (nimesulide 50 mg x ml(-1) drop, Medley S/A Indústria Farmacêutica, Brazil) against one standard nimesulide drop formulation (Nisulid, 50 mg x ml(-1) drop, Astra Médica, Brazil). Twenty-four healthy volunteers (both sexes) took part in the study and received a single oral dose of nimesulide (100 mg, equivalent to 2 ml of either formulation) in an open, randomized, two-period crossover way, with a 2-week washout interval between periods. The 90% confidence interval (CI) for geometric mean ratios between nimesulide and Nisulid were 93.1-109.6% for C(max), 87.7-99.8% for AUC(last) and 88.1-99.7% for AUC(0-infinity). Since the 90% CI for the above-mentioned parameters were included in the 80-125% interval proposed by the US Food and Drug Administration, the two formulations were considered bioequivalent in terms of both rate and extent of absorption.

Comparative bioavailability of 4 amoxicillin formulations in healthy human volunteers after a single dose administration

OBJECTIVE

To compare the bioavailability of two amoxicillin oral suspension (250 mg/5 ml) formulations and two amoxicillin capsule (500 mg) formulations (Amoxicilina from Medley S/A Indústria Farmaceûtica, Brazil, as test formulations and Amoxil from SmithKline Beecham Laboratórios Ltda., Brazil, as reference formulations) in 48 volunteers of both sexes.

MATERIAL AND METHODS

The study was conducted open with a randomized two-period crossover design and a one-week washout period. Plasma samples were obtained over a 12-hour interval. Amoxicillin concentrations were analyzed by combined reversed phase liquid chromatography and tandem mass spectrometry (LC-MS-MS) with positive ion electrospray ionization using the selected ion monitoring method. From the amoxicillin plasma concentration vs. time curves the following pharmacokinetic parameters were obtained: AUC(last), AUC(0-infinity) and Cmax.

RESULTS

Geometric mean of Amoxicilina/Amoxil 250 mg/5 ml individual percent ratio was 103.70% for AUC(last), 103.15% for AUC(0-infinity) and 106.79% for Cmax. The 90% confidence intervals were 97.82-109.94%, 97.40 to 109.24%, and 96.38-118.33%, respectively. Geometric mean of Amoxicilina/Amoxil 500 mg capsule individual percent ratio was 93.26% for AUC(last), 93.27% for AUC(0-infinity) and 90.74% for Cmax. The 90% confidence intervals were 85.0-102.33%, 85.12-102.31%, and 80.14-102.73%, respectively.

CONCLUSION

Since the 90% CI for both Cmax, AUC(last) and AUC(0-inifnity) were within the 80-125% interval proposed by the Food and Drug Administration, it was concluded that Amoxicilina 250 mg/5 ml oral suspension and Amoxicilina 500 mg capsule were bioequivalent to Amoxil 250 mg/5 ml oral suspension and to Amoxil capsule 500 mg, respectively, with regard to both the rate and extent of absorption.

Nitric oxide modulates Na+, K+-ATPase activity through cyclic GMP pathway in proximal rat trachea

The present work demonstrated that nitric oxide (NO) modulates Na+, K+-ATPase activity in the proximal rat trachea. Sodium nitroprusside induced concentration-dependent (10-100 microM) stimulation in proximal trachea Na+, K+-ATPase activity. The effect was specific for Na+, K+-ATPase since Mg-ATPase activity was unaffected. This NO-donor changed neither Na+, K+-ATPase nor Mg-ATPase activity in the distal segment. The modulatory action on Na+, K+-ATPase induced by sodium nitroprusside was linked to an increase in nitrates/nitrites and cyclic GMP levels in proximal segments. Modulation of proximal Na+, K+-ATPase activity by sodium nitroprusside was mimicked by S-nitroso-N-acetylpenicillamine (100 microM) and 8-bromo-cyclic GMP (100 microM). Both sodium nitroprusside and 8-bromo-cyclic GMP effects on Na+, K+-ATPase activity of proximal segments of trachea were blocked by 2 microM of KT 5823 (a cyclic GMP-dependent protein kinase inhibitor), but not by 0.5 microM of KT 5720 (a cyclic AMP-dependent protein kinase inhibitor). Both kinase inhibitors decreased proximal Na+, K+-ATPase activity, but did not change Mg-ATPase activity. Okadaic acid (1 microM), a phosphatase-1 inhibitor, increased proximal Na+, K+-ATPase but not Mg-ATPase activity. The effect of okadaic acid was non-additive with that of 8-bromo-cGMP on Na+, K+-ATPase activity. Our results suggest that NO modulates proximal rat trachea Na+, K+-ATPase activity through cyclic GMP and cyclic GMP-dependent protein kinase.