Selective determination of naproxen in the presence of nonsteroidal anti-inflammatory drugs in serum and urine samples using room temperature liquid phosphorimetry

Binding of naproxen enantiomers to human serum albumin studied by fluorescence and room-temperature phosphorescence

The interaction of the enantiomers of the non-steroidal anti-inflammatory drug naproxen (NPX) with human serum albumin (HSA) has been investigated using fluorescence and phosphorescence spectroscopy in the steady-state and time-resolved mode. The absorption, fluorescence excitation, and fluorescence emission spectra of (S)-NPX and (R)-NPX differ in shape in the presence of HSA, indicating that these enantiomers experience a different environment when bound. In solutions containing 0.2M KI, complexation with HSA results in a strongly increased NPX fluorescence intensity and a decreased NPX phosphorescence intensity due to the inhibition of the collisional interaction with the heavy atom iodide. Fluorescence intensity curves obtained upon selective excitation of NPX show 8-fold different slopes for bound and free NPX. No significant difference in the binding constants of (3.8±0.6)×10(5) M(-1) for (S)-NPX and (3.9±0.6)×10(5) M(-1) for (R)-NPX was found. Furthermore, the addition of NPX quenches the phosphorescence of the single tryptophan in HSA (Trp-214) based on Dexter energy transfer. The short-range nature of this mechanism explains the upward curvature of the Stern-Volmer plot observed for HSA: At low concentrations NPX binds to HSA at a distance from Trp-214 and no quenching occurs, whereas at high NPX concentrations the phosphorescence intensity decreases due to dynamic quenching by NPX diffusing into site I from the bulk solution. The dynamic quenching observed in the Stern-Volmer plots based on the longest phosphorescence lifetime indicates an overall binding constant to HSA of about 3×10(5) M(-1) for both enantiomers.

Novel Validated Stability-Indicating UPLC Method for the Estimation of Naproxen and its Impurities in Bulk Drugs and Pharmaceutical Dosage Form

A novel, reversed-phase ultra-performance liquid chromatographic method was developed and validated for the determination of related substances in Naproxen (NAP) bulk drugs and dosage forms. The related substances included degradation and process-related impurities. The method was developed using the Waters Acquity BEH C18 column using the gradient program with mobile phase A of a pH 7.0 phosphate buffer and methanol in the ratio of 90: 10 (v/v) and mobile phase B as methanol and acetonitrile in the ratio of 50:50 (v/v). Naproxen and its impurities were monitored at 260 nm. Naproxen was subjected to the stress conditions of oxidative, acid, base, hydrolytic, thermal, humidity, and photolytic degradations. The degradation products were well-resolved from the main peak and its impurities, proving the stability-indicating power of the method. The performance of the method was validated according to the present ICH guidelines for specificity, limit of detection, limit of quantification, linearity, accuracy, precision, ruggedness, and robustness.

Combined liquid and solid-surface room temperature fluorimetric determination of naproxen and salicylate in serum

A rapid and sensitive method for the determination of naproxen and salicylate in serum is presented. The employed strategy combines solid-phase extraction on a reverse-phase membrane with spectrofluorimetry. Solid-phase extraction under optimum pH conditions makes NX to be retained over the solid surface (where it is directly determined by a fluorimetric technique). Salicylate passes through the disk and is also fluorimetrically determined, but in solution. The linear calibration ranges for NX in the membrane and salicylate in solution were 0.014-0.250 and 0.010-0.250 microg ml(-1), respectively. The lowest value, in each case, is the corresponding limit of quantitation. The performance of the method is demonstrated with the successful determination of both drugs in spiked and real human serum samples.

Simultaneous determination of naproxen and related compounds by HPLC using porous graphitic carbon column

A simple, selective and sensitive high performance liquid chromatographic (HPLC) method has been developed for the simultaneous determination of naproxen and its main degradation products such as 1-(6-methoxy-2-naphthyl) ethanol (MNE), 2-methoxy-6-ethyl naphthalene (MEN) and 2-acetyl-6-methoxy naphthalene (AMN). The separation of these compounds was achieved on porous graphitic carbon (PGC) column using tetrahydrofuran-methanol as the mobile phase, and the effluent from the column was monitored at 272 nm. At a flow rate of 1 ml min(-1), the retention time of the last eluting compound was less than 10 min. Correlation coefficient for calibration curves in the ranges 2-25 microg ml(-1) for all compounds studied were greater than 0.999. The sensitivity of detection is 0.05 microg l(-1) for naproxen, MNE and MEN and 0.20 microg ml(-1) for AMN. The reproducibility of the peak area of these compounds using isocratic elution were quite high, and the standard deviations (S.D.) were below 2% (n=5). The reproducibility of retention times of these compounds was within 1% (n=5). The proposed liquid chromatographic method was successfully applied to the analysis of commercially available naproxen sodium (NS) dosage forms with recoveries of 98.8-102%. A comparative study shows that the selectivity of these compounds on PGC column was different to that obtained with octadecyl silica (ODS) columns.

Spectrofluorometric determination of naproxen in tablets

A rapid, selective, sensitive and simple fluorescence method was developed for the direct determination of naproxen in tablets. The tablets were triturated, dissolved in either NH(3) or NaOH solution, sonicated, filtered and then direct fluorescence emission was read at 353 nm (exciting at 271 nm). In order to validate the method the results were compared with those obtained by the USP XXIV NF 19 Pharmacopeia reference method (high performance liquid chromatography). The slope, intercept and variances which are associated with the regression coefficient calculated with bivariate least square (BLS) regression indicate that both methods are statistically comparable. The recoveries were excellent, except in tablets containing the antibiotic tetracycline. In this latter case a correction procedure is necessary.