Enhancement and in vitro evaluation of amifostine permeation through artificial membrane (PAMPA) via ion pairing approach and mechanistic selection of its optimal counter ion.

This study presents the results of in vitro evaluation of a series of organic counter ions that form ion pairs with amifostine. The selected counter ions have different lipophilicity, shape and flexibility. Intrinsic octanol buffer partition coefficient and binding constant of the ion pairs were calculated using quasi-equilibrium analysis. Permeation through hydrophobic PAMPA membranes of amifostine and its ion pairs with different counter ions was studied. Three counter ions, succinic acid, benzoic acid and phthalic acid demonstrated an increase in the apparent partition coefficient of amifostine in n-octanol. These counter ions were selected for permeability experiments in PAMPA membranes and an increase of the apparent permeability value Papp (cm/s) was also observed as a function of the counter ion concentration. Phthalic acid produced 1.6-fold increase of log PAB while for benzoic acid and succinic acid the values were 1.2 and 0.75-fold respectively. PAMPA permeability of amifostine significantly increased in the presence of phthalic acid (42-fold), benzoic acid (37-fold) and succinic acid (10.5-fold). This study showed that the permeability of amifostine across a lipophilic membrane was enhanced in the presence of counter-ions resulting ion pair formation.

Ion-pair strategy for enabling amifostine oral absorption: rat in situ and in vivo experiments.

This study shows the effect of ion pair formation on intestinal absorption and oral bioavailability of amifostine. Amifostine is a prodrug used as a highly potent and selective radiotherapy and chemotherapy protectant but due to its low lipophilicity and charge at physiological pH range, its trans epithelial transport and its potential for oral drug delivery is very low. Ion pair formation with negatively charged counter ions was evaluated by in situ rat perfusion studies as a possible strategy to enhance intestinal absorption of amifostine. Succinic acid, phthalic acid and benzoic acid were used as counter ions. Rat intestinal perfusion studies confirmed a statistically significant increase in amifostine permeability in the presence of the counter ions in the order of succinic>phthalic>benzoic. Rat pharmacokinetic studies in vivo were performed to calculate oral absolute bioavailability of amifostine alone and with ion pairs in order to confirm the in situ perfusion results and the applicability of the ion pair approach. Intravenous and intraduodenal administrations were done in rats using a permanent jugular vein cannulation technique and a duodenal cannulation method to avoid drug degradation in stomach. In vivo oral bioavailability studies demonstrated a 20-30-fold increase in amifostine bioavailability with succinic acid depending on counter ion ratio and 10-fold increase with phthalic acid as ion pair. In summary ion pair strategy with succinic acid could enable amifostine oral administration on enteric coated formulations.

Quantification of carvedilol in human plasma by liquid chromatography using fluorescence detection: application in pharmacokinetic studies.

A simple, rapid and sensitive isocratic reversed-phase HPLC method with fluorescence detection using a monolithic column has been developed and validated for the determination of carvedilol in human plasma. The separation was performed on a Chromolith Performance (RP-18e, 100mm x 4.6mm) column with an isocratic mobile phase consisting of 0.01 M disodium hydrogen phosphate buffer-acetonitrile (40:60, v/v) adjusted to pH 3.5. The sample preparation involves protein precipitation procedure and analytical recovery was complete. Letrozole was used as internal standard. The assay enables the measurement of carvedilol for therapeutic drug monitoring with a minimum quantification limit (LOQ) of 1 ng ml(-1). The excitation and emission wavelengths were set at 240 and 340 nm, respectively. The calibration curve was linear over the concentration range 1-80 ng ml(-1). The coefficients of variation for inter-day and intra-day assay were found to be less than 8.0%.

Application of monolithic column in quantification of gliclazide in human plasma by liquid chromatography.

A simple, rapid and sensitive isocratic reversed phase HPLC method with UV detection using a monolithic column has been developed and validated for the determination of gliclazide in human plasma. The assay enables the measurement of gliclazide for therapeutic drug monitoring with a minimum quantification limit of 10ngml(-1). The method involves simple, one-step extraction procedure and analytical recovery was complete. The separation was carried out in reversed-phase conditions using a Chromolith Performance (RP-18e, 100mmx4.6mm) column with an isocratic mobile phase consisting of 0.01M disodium hydrogen phosphate buffer-acetonitrile (52:48, v/v) adjusted to pH 4.0. The wavelength was set at 230nm. The calibration curve was linear over the concentration range 10-5000ngml(-1). The coefficients of variation for inter-day and intra-day assay were found to be less than 6.0%.

Development an ion-pair liquid chromatographic method for determination of sotalol in plasma using a monolithic column.

A rapid and sensitive ion-pair HPLC method using a monolithic column and fluorescence detection has been developed for quantification of sotalol in plasma. The assay enables the measurement of sotalol for therapeutic drug monitoring with a minimum quantification limit of 10 ng ml(-1). The analytical method involves simple, one-step protein precipitation and no extraction procedure is needed. Sample preparation is fast and the analytical recovery was complete. The separation was carried out in reversed-phase conditions using a Chromolith Performance (RP-18e, 100 mm x 4.6 mm) column at ambient temperature. The mobile phase was 10% acetonitrile, 0.001 M heptane sulfonic acid, 0.02 M sodium dihydrogen phosphate, and distilled water to 100%, adjusted to pH 5.5 at a flow rate of 1.8 ml/min. The excitation wavelength was set at 235 nm, emission at 300 nm. The calibration curve was linear over the concentration range 20-1500 ng ml(-1). The coefficients of variation for inter-day and intra-day assay were found to be less than 7%. The method has been applied to the determination of sotalol in plasma from 12 subjects dosed with racemic sotalol.

Simple and rapid high-performance liquid chromatographic method for determination of celecoxib in plasma using UV detection: application in pharmacokinetic studies.

A rapid, sensitive and reproducible HPLC method was developed and validated for the analysis of celecoxib in human plasma. The analysis was carried out on a monolithic silica column using UV detection at 254 nm. The assay enables the measurement of celecoxib for therapeutic drug monitoring with a minimum quantification limit of 10 ng ml(-1). The method involves simple, one-step extraction procedure, and analytical recovery was 100.5 +/- 1.3%. The calibration curve was linear over the concentration range of 10-800 ng ml(-1). The coefficients of variation for inter-day and intra-day assay were found to be less than 8%. We also demonstrate the applicability of this method for pharmacokinetic studies in humans.

Validated HPLC method for determination of amlodipine in human plasma and its application to pharmacokinetic studies.

A rapid, simple and sensitive high-performance liquid chromatography (HPLC) method has been developed for quantification of amlodipine in plasma. The assay enables the measurement of amlodipine for therapeutic drug monitoring with a minimum detectable limit of 0.2 ng ml(-1). The method involves simple, one-step extraction procedure and analytical recovery was about 97%. The separation was performed on an analytical 125 x 4.6 mm i.d. Nucleosil C8 column. The wavelength was set at 239 nm. The mobile phase was a mixture of 0.01 M sodium dihydrogen phosphate buffer and acetonitrile (63:37, v/v) adjusted to pH 3.5 at a flow rate of 1.5 ml min(-1). The calibration curve was linear over the concentration range 0.5-16 ng ml(-1). The coefficients of variation for inter-day and intra-day assay were found to be less than 10%.

Development of a rapid HPLC method for determination of famotidine in human plasma using a monolithic column.

A rapid and sensitive HPLC method using a monolithic column has been developed for quantification of famotidine in plasma. The assay enables the measurement of famotidine for therapeutic drug monitoring with a minimum detectable limit of 5 ngml(-1). The method involves simple, one-step extraction procedure and analytical recovery was complete. The separation was carried out in reversed-phase conditions using a Chromolith Performance (RP-18e, 100 mm x 4.6 mm) column with an isocratic mobile phase consisting of 0.03 M disodium hydrogen phosphate buffer-acetonitrile (93:7, v/v) adjusted to pH 6.5. The wavelength was set at 267 nm. The calibration curve was linear over the concentration range 20-400 ngml(-1). The coefficients of variation for inter-day and intra-day assay were found to be less than 8%.

Rapid determination of minoxidil in human plasma using ion-pair HPLC.

A rapid, simple and sensitive ion-pair high-performance liquid chromatography (HPLC) method has been developed for quantification of minoxidil in plasma. The assay enables the measurement of minoxidil for therapeutic drug monitoring with a minimum detectable limit of 0.5 ng ml(-1). The method involves simple, one-step extraction procedure and analytical recovery was complete. The separation was performed on an analytical 150 x 4.6 mm i.d. microbondapak C18 column. The wavelength was set at 281 nm. The mobile phase was a mixture of 0.01 M sodium dihydrogen phosphate buffer and acetonitrile (60:40, v/v) containing 2.5 mM sodium dodecyl sulphate adjusted to pH 3.5 at a flow rate of 1 ml/min. The column temperature was set at 50 degrees C. The calibration curve was linear over the concentration range 2-100 ng ml(-1). The coefficients of variation for inter-day and intra-day assay were found to be less than 8%.

Simple high-performance liquid chromatographic determination of buspirone in human plasma.

A simple, rapid and sensitive high-performance liquid chromatographic method for the determination of buspirone in plasma was developed. Buspirone was isolated from plasma using protein precipitation by acetonitrile and the recovery was complete. Citalopram was used as internal standard. The chromatographic conditions were as follows: analytical 125 x 4 mm, i.d. Nucleosil C18 column (5 microm particle size), mobile phase consisting of sodium dihydrogen phosphate buffer/acetonitrile (60:40, v/v) adjusted to pH 5.5 at a flow rate of 1.0 ml min(-1), UV detection at 235 nm. The quantification limit for buspirone in plasma was 0.5 ng ml(-1). The calibration curve was linear over the concentration range 0.5-10 ng ml(-1). The inter- and intra-day assay coefficients of variation were found to be less than 8%. The present validated method was successfully used for bioequivalence studies of buspirone in human subjects.

Rapid determination of metformin in human plasma using ion-pair HPLC.

A rapid, simple and sensitive ion-pair HPLC method has been developed for quantification of metformin in plasma. The assay enables the measurement of metformin for therapeutic drug monitoring with a minimum detectable limit of 20 ng/ml. The method involves simple, one-step extraction procedure and analytical recovery was complete. The separation was performed on an analytical 150 x 4.6 mm i.d. mubondapak C(18) column. The wavelength was set at 235 nm. The mobile phase was 40% acetonitrile, 0.01 M sodium dodecyl sulphate, 0.01 M sodium dihydrogen phosphate, and distilled water to 100%, adjusted to pH 5.1 at a flow rate of 1.5 ml/min. The calibration curve was linear over the concentration range 0.2-2.5 microg/ml. The coefficients of variation for inter-day and intra-day assay were within the range of clinical usefulness.

Fumonisin B(1) in maize harvested in Iran during 1999.

The fumonisin B(1) (FB(1)) contamination of maize collected in two areas of Iran during 1999 was determined. The 20 maize samples from Mazandaran Province, situated on the Caspian littoral of Iran, consisted of random samples of farmers' lots and were all contaminated with FB(1) at a mean level of 3.18 mg kg(-1) (range 0.68-7.66 mg kg(-1)). The 10 samples (of the same maize cultivar) from Isfahan Province in central Iran were purchased as maize cobs in local retail markets and had mean FB levels of 0.22 mg kg(-1) (mean of all samples, 6/10 samples positive, range <0.01-0.88 mg kg(-1)). The FB levels in Mazandaran, an area of high oesophageal cancer, were significantly (p < 0.0001) higher than the FB levels found in maize from Isfahan, an area of low oesophageal cancer in Iran.

Determination of azathioprine and its related substances by capillary zone electrophoresis and its application to pharmaceutical dosage forms assay.

The development of a stability-indicating capillary zone electrophoresis (CZE) method for the determination of the drug azathioprine (AZA) and its related substances in bulk and dosage forms is described. Theophylline was used as an internal standard to improve quantitative results. The method was fully validated in terms of repeatability (n = 10, RSD for migration time and peak area ratio were 0.15% and 0.60%, respectively), reproducibility (n = 5, RSD of peak area ratio was 0.84%), linearity at two ranges of the azathioprine concentration, limits of detection (LOD) and quantitation (LOQ), and robustness. The method was applied for determination of the drug in bulk and a commercial tablet dosage form (recovery 98.3-101.3%) and in powder for injection (recovery 98.7-100.6%). The method was fast and reliable for the analysis of AZA and its related substances in bulk and dosage forms.

Development and validation of a capillary zone electrophoretic method for the determination of atenolol in presence of its related substances in bulk and tablet dosage form.

The development of a capillary zone electrophoresis method for determination of the drug atenolol in the presence of its related substances in bulk and in a tablet dosage form is described. The method was fully validated in terms of repeatability (RSDs for migration time and peak area of atenolol at 0.05 mg ml-1 were 0.25% and 0.52%, n = 10, respectively), reproducibility (RSD of peak area 0.84%, n = 5), linearity at two ranges of atenolol concentration, limits of detection and quantitation, ruggedness and robustness. The method was applied to the determination of the drug in a commercial tablet preparation (recovery 99.4%, m/m). The method proved to be fast and reliable for the quantitative analysis of atenolol in the presence of its related substances in bulk and pharmaceutical forms.