Ciclesonide HPTLC Densitometric measurement Glucocorticoids Antiasthmatic
A selective high-performance thin-layer chromatographic (HPTLC) method has been established for the quantitative determination of oseltamivir phosphate (OST) without interference of ascorbic acid (ASC) added to some of its counterfeit pharmaceutical formulations. Chromatographic separation was performed on precoated silica gel 60 [GF.sub.254] plates with methanol-water-ammonia 6:4:0.05 (v/v) as mobile phase at ambient temperature. The developed plates were scanned and quantified at 254 nm. Experimental conditions such as band size, mobile phase volume, chamber saturation time, migration of solvent front, etc. were critically studied, and the optimum conditions were selected. A satisfactory resolution was obtained with [R.sub.F] 0.70 and 0.83 for OST and ASC, respectively. Also, HPTLC-band detection method has been established for rapid qualitative assay of OST using ninhydrin spray. On the other hand, a colorimetric method has been established using bromocresol green (BCG) as rapid, accurate, and selective comparative method. Both methods were validated for linearity, accuracy, precision, selectivity, and specificity. The calibration plots were linear between 5.00 and 14.00 [micro]g [band.sup.-1] and 6.00-18.00 [micro]g[mL.sup.-1] for the HPTLC and colorimetric methods, respectively. The detection limits were 1.80 [micro]g [band.sup.-1] and 2.00 [micro]g [mL.sup.-1], for the HPTLC and colorimetric methods, respectively. The simplicity of the proposed methods suggest its application in quality control analysis of OST in its capsules and granules for oral suspension.
Oseltamivir phosphate (OST) (ethyl(3R,4R,5S)-4-acetamido-5-amino-3-(1-ethylpropoxy)-1-cyclohexene-1-carboxylate phosphate; Figure 1a) is a prodrug of oseltamivir carboxylate, an inhibitor of the enzyme neuraminidase, which has a role in the infectivity and replication of influenza A and B viruses. It is used orally as capsules or suspension for the treatment and post-exposure prophylaxis of influenza A and B .
OST recently became official in the United States Pharmacopeia (USP) 2011  which describes high-performance liquid chromatography (HPLC) method for its assay in bulk powder as well as in capsules. Some spectrophotometric methods [3-5] were reported for the assay of OST. Some HPLC methods were described for the analysis of OST both in bulk and in commercial pharmaceuticals [6-8]. Also, a selective HPLC method was applied to evaluate potentially counterfeit OST capsules . Few HPLC methods were developed for the assay of OST in biological fluids using liquid chromatography coupled to tandem mass spectrometry [10-11]. Other methods were applied to its quantification in its capsules like spectrofluorimetry  and capillary electrophoresis . However, no high-performance thin-layer chromatography (HPTLC) method has been reported for the determination of OST.
The specter of an avian influenza pandemic has given OST much notoriety, and anticipation of the potential public health threat has prompted a demand for its pharmaceutical products. Consequently, criminal elements have already produced counterfeit OST preparations and specific cases of the seizure observed in the United Kingdom of 5000 counterfeit packets of the OST products . Also, ascorbic acid (ASC) (Figure 1b) was reported widely in counterfeit OST products which lacked the active ingredient. These products had been purchased through the internet and easily have gone unnoticed in the developing countries, where insufficient analytical...
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