Validated specific HPLC method for determination of zidovudine during stability studies

The objective of the current study was to develop a validated stability-indicating assay method (SIAM) for zidovudine (3′-azido-3′-deoxythymidine) after subjecting it to forced decomposition under hydrolysis, oxidation, photolysis and thermal stress conditions. The drug decomposed under hydrolytic stress upon refluxing, and also on exposure to light. It was stable to oxidation and thermal stress. The same major decomposition product could be seen in all the decomposed solutions, which was identified as thymine through comparison with the standard. Separation of drug from major and minor degradation products was successfully achieved on a C-18 column utilising water–methanol in the ratio of 77:23. The detection wavelength was 265 nm. The method was validated and response was found to be linear in the drug concentration range of 25–500 μg ml⁻¹. The mean values (±R.S.D.) of slope and correlation coefficient were 21,859 (±0.213) and 0.9995 (±0.00578), respectively. The R.S.D. values for intra- and inter-day precision were <0.9 and <1.6%, respectively. The method was established to have sufficient intermediate precision as similar separation was achieved on another instrument handled by a different operator. The recovery of the drug from a mixture of degraded samples ranged between 100.6 and 100.9%. PDA peak purity test confirmed the specificity of the method. The method was also successful in analysis of drug in marketed tablets subjected to stability testing under accelerated conditions of temperature, humidity, and to thermal and photolytic stress.     

The ICH guidance in practice: stress degradation studies on ornidazole and development of a validated stability-indicating assay

The present study describes degradation of ornidazole under different ICH prescribed stress conditions (hydrolysis, oxidation and photolysis), and establishment of a stability-indicating reversed-phase HPLC assay. Degradation was found to occur in alkaline medium, under high acidic conditions, under oxidative stress, and also in the presence of light in acid conditions. Previously the drug is only known to decompose under alkaline conditions. Separation of drug and the degradation products under various conditions was successfully achieved on a C-18 column utilising water-acetonitrile in the ratio of 86:14. The detection wavelength was 310 nm. The method was validated with respect to linearity, precision, accuracy, selectivity, specificity and ruggedness. The response was linear in the drug concentration range of 5–500 μg ml⁻¹. The mean values (±RSD) of slope, intercept and correlation coefficient were 45251 (±1.59), 104418 (±2.49) and 0.9996 (±0.03), respectively. The RSD values for intra- and inter-day precision studies were <1 and <2.6%, respectively. The recovery of the drug ranged between 100–103% from a mixture of degradation products. The method was specific to drug and also selective to degradation products.     

Development and validation of a sensitive liquid chromatographic method for the analysis of a novel radioprotectant: ON 01210.Na

ON 01210.Na is a chlorobenzylsulfone derivative with potential property to mitigate the effects of accidental or intentional exposure to life threatening levels of radiation. A simple and sensitive HPLC method was developed and validated for the assay of ON 01210.Na. The isocratic system used a mobile phase consisting of acetonitrile:0.1% trifluroacetic acid in water (60:40, v/v) at a flow rate of 1 ml/min. The method used a C-18 Gemini column (250 mm × 4.6 mm) with column effluents monitored at 254 nm. Forced degradation of the drug was achieved by autoclaving ON 01210.Na with 0.05N HCl, 0.05N NaOH or 1.5% (v/v) hydrogen peroxide. The assay validation parameters evaluated include specificity, linearity, precision, accuracy and sensitivity. The retention time of the drug and the other effluents were well within 7 min. Standard curves were linear over the concentration range of 10–500 μg/ml. The R.S.D. values for the within-day and day-to-day precision ranged from 0.4 to 2.5 and 2.2 to 4.4%, respectively. The R.S.D. for accuracy measurement ranged from 0.85 to 1.7%. The critical level, the detection level and the determination level for this assay were 2.86 ± 0.67, 5.69 ± 0.67 and 15.6 ± 1.8 μg/ml, respectively. A simple, sensitive and stability indicating HPLC assay was developed and validated for the analysis of a novel radioprotectant. This method was used to evaluate the aqueous as well as solid-state stability of this drug during autoclaving.     

Validation and application of a stability-indicating HPLC method for the in vitro determination of gastric and intestinal stability of venlafaxine

Gastrointestinal stability of venlafaxine was evaluated in vitro in simulated gastric (SGF) and intestinal (SIF) fluids using a stability indicating HPLC method. The method was validated using a 5 μm Ascentis^® C₁₈ column (150 mm × 4.6 mm) and mobile phase consisting of 30% acetonitrile in 20 mM potassium phosphate buffer (pH 6.5) delivered isocratically at a flow rate of 1 mL/min with UV detection at 228 nm. Venlafaxine in USP simulated gastric and intestinal fluids (0.4 mg/mL) was incubated at 37 °C in a shaking water bath. The gastric stability study samples were assayed at 0, 15, 30 and 60 min intervals while sampling for the intestinal stability study was at 0, 1, 2 and 3 h. System suitability determinations gave R.S.D.s of 0.68, 0.5 and 3.9% for retention factor (k′), peak area and tailing factor, respectively. The method was shown to be accurate, precise, specific, and linear over the analytical range. Intra- and inter-day precision was <5.3%. Forced degradation studies of drug substance in basic media at 70 °C as well as in H₂O₂ for 1 h and ultra-violet photostability studies at 255 and 365 nm for 24 h did not produce any detectable degradation products. Forced degradation studies of drug substance in acidic media at 70 °C for 1 h produced the dehydro-venlafaxine degradant. Venlafaxine was stable in SGF (pH 1.2) for the 1-h incubation period and in SIF (pH 6.8) up to 3 h with <1.5% relative difference (RD) between the amount of drug added and that found for all time points. This stability experiment in simulated gastric and intestinal fluids suggests that drug loss in the gastrointestinal tract takes place by membrane permeation rather than a degradation process.     

Stability-indicating methods for the determination of piretanide in presence of the alkaline induced degradates

Stability-indicating high performance liquid chromatography (HPLC), thin-layer chromatography (TLC) and first-derivative of ratio spectra (1DD) methods are developed for the determination of piretanide in presence of its alkaline induced degradates. HPLC method depends on separation of piretanide from its degradates on μ-Bondapak C₁₈ column using methanol:water:acetic acid (70:30:1, v/v/v) as a mobile phase at flow rate 1.0 ml/min and UV detector at 275 nm. TLC densitometic method is based on the difference in Rf-values between the intact drug and its degradates on thin-layer silica gel. Iso-propanol:ammonia 33% (8:2, v/v) was used as a developing mobile phase and the chromatogram was scanned at 275 nm. The derivative of ratio spectra method (1DD) depends on the measurement of the absorbance at 288 nm in the first-derivative of ratio spectra for the determination of the cited drug in the presence of its degradates. Calibration graphs of the three suggested methods are linear in the concentration ranges 0.02–0.3 μg/20 μl, 0.5–10 μg/spot and 5–50 μg/ml, with mean percentage recovery 99.27 ± 0.52, 99,17 ± 1.01 and 99.65 ± 1.01%, respectively. The three proposed methods were successfully applied for the determination of piretanide in bulk powder, laboratory-prepared mixtures and pharmaceutical dosage form with good accuracy and precision. The results were statistically analyzed and compared with those obtained by the official method. Validation of the method was determined with favourable specificity, linearity, precision, and accuracy was assessed by applying the standard addition technique.     

A validated stability indicating LC method for oxcarbazepine

The present paper describes the development of a stability indicating reversed phase liquid chromatographic (RPLC) method for oxcarbazepine in the presence of its impurities and degradation products generated from forced decomposition studies. The drug substance was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. The degradation of oxcarbazepine was observed under base hydrolysis. The drug was found to be stable to other stress conditions attempted. Successful separation of the drug from the synthetic impurities and degradation product formed under stress conditions was achieved on a C18 column using mixture of aqueous 0.02 M potassium dihydrogen phosphate–acetonitrile–methanol (45:35:20, v/v/v) as mobile phase. The developed HPLC method was validated with respect to linearity, accuracy, precision, specificity and robustness. The developed HPLC method to determine the related substances and assay determination of oxcarbazepine can be used to evaluate the quality of regular production samples. It can be also used to test the stability samples of oxcarbazepine.     

LC/ESI-MS method for the determination of trimetazidine in human plasma: application to a bioequivalence study on Chinese volunteers

A rapid liquid chromatography electrospray ionization mass spectrometry (LC/ESI-MS) method with good sensitivity and specificity has been developed and validated for the identification and quantification of trimetazidine in human plasma. Trimetazidine and lidocaine (internal standard) were isolated from plasma samples by protein precipitation with methanol. The chromatographic separation was accomplished on a Xterra MS C₁₈ Column (150 mm × 4.6 mm, 5 μm particle size) with the mobile phase consisting of methanol and water (40:60, v/v) (pH 2.0, adjusted with trifluoroacetic acid), and the flow rate was set at 0.6 mL/min. Detection was performed on a single quadruple mass spectrometer by selected ion monitoring (SIM) mode (m/z 267.0 for trimetazidine and m/z 235.0 for lidocaine) with the retention time at about 3.47 and 5.05 min, respectively. The calibration curve for trimetazidine was satisfactory with regression coefficient 0.9995 over the range of 2.5–100 ng/mL in the plasma. The LOQ (S/N = 10) was accordingly 2.5 ng/mL. The intra-day and inter-day precision expressed as relative standard deviation was 2.83–6.10% and 4.83–5.82%. The method was successfully applied to investigate the bioequivalence between two kinds of tablets (test versus reference product) in 19 healthy male Chinese volunteers. After a single 20 mg dose for the test and reference product, the resulting mean of major pharmacokinetic parameters such as AUC_0–24, AUC_0−∞, C_max, T_max and t_1/2 of trimetazidine were (673.1 ± 117.6 ng h mL⁻¹ versus 652.3 ± 121.9 ng h mL⁻¹), (717.1 ± 120.9 ng h mL⁻¹ versus 692 ± 128.6 ng h mL⁻¹), (74.85 ± 12.13 ng mL⁻¹ versus 71.93 ± 14.32 ng mL⁻¹), (2.312 ± 0.663 h versus 2.211 ± 0.608 h) and (4.785 ± 0.919 h versus 4.740 ± 0.823 h), respectively, indicating that these two kinds of tablets were bioequivalent in the Chinese population.     

Intrapulmonary pharmacokinetics and pharmacodynamics of meropenem

The objective of this study was to determine the plasma and intrapulmonary pharmacokinetic parameters of intravenously administered meropenem in healthy volunteers. Four doses of 0.5 g, 1.0 g or 2.0 g meropenem were administered intravenously to 20, 20 and 8 healthy adult subjects, respectively. Standardised bronchoscopy and timed bronchoalveolar lavage (BAL) were performed following administration of the last dose. Blood was obtained for drug assay prior to drug administration and at the time of BAL. Meropenem was measured in plasma, BAL fluid and alveolar cells (ACs) using a combined high pressure liquid chromatographic–mass spectrometric technique. Plasma, epithelial lining fluid (ELF) and AC pharmacokinetics were derived using non-compartmental methods. C_max/MIC₉₀ (where C_max is the maximum plasma concentration and MIC₉₀ is the minimum inhibitory concentration required to inhibit 90% of the pathogen), AUC/MIC₉₀ (where AUC is the area under the curve for the mean concentration–time data), intrapulmonary drug exposure ratios and percent time above MIC₉₀ during the dosing interval (%T > MIC₉₀) were calculated for common respiratory pathogens with MIC₉₀ values of 0.12–4 μg/mL. In the 0.5 g dose group, the C_max (mean ± S.D.), AUC_0–8 h and half-life for plasma were, respectively, 25.8 ± 5.8 μg/mL, 28.57 μg h/mL and 0.77 h; for ELF the values were 5.3 ± 2.5 μg/mL, 12.27 μg h/mL and 1.51 h; and for ACs the values were 1.0 ± 0.5 μg/mL, 4.30 μg h/mL and 2.61 h. In the 1.0 g dose group, the C_max, AUC_0–8 h and half-life for plasma were, respectively, 53.5 ± 19.7 μg/mL, 55.49 μg h/mL and 1.31 h; for ELF the values were 7.7 ± 3.1 μg/mL, 15.34 μg h/mL and 0.95 h; and for ACs the values were 5.0 ± 3.4 μg/mL, 14.07 μg h/mL and 2.17 h. In the 2.0 g dose group, the C_max, AUC_0–8 h and half-life for plasma were, respectively 131.7 ± 18.2 μg/mL, 156.7 μg h/mL and 0.89 h. The time above MIC in plasma ranged between 28% and 78% for the 0.5 g dose and between 45% and 100% for the 1.0 g and 2.0 g doses. In ELF, the time above MIC ranged from 18% to 100% for the 0.5 g dose and from 25% to 88% for the 1.0 g dose. In ACs, the time above MIC ranged from 0% to 100% for the 0.5 g dose and from 24% to 100% for the 1.0 g dose. Time above MIC in ELF and ACs for the 2.0 g dose was not calculated because of sample degradation. The prolonged T > MIC₉₀ and high intrapulmonary drug concentrations following every 8 h administration of 0.5–2.0 g doses of meropenem are favourable for the treatment of common respiratory pathogens.     

Possible mechanism of adaptogenic activity of seabuckthorn (Hippophae rhamnoides) during exposure to cold, hypoxia and restraint (C–H–R) stress induced hypothermia and post stress recovery in rats

The present study was carried out to investigate mechanism of adaptogenic activity of seabuckthorn dry leaves aqueous lyophilized extract, administered in rats at a dose of 100 mg/kg body weight prior to cold (5 °C)–hypoxia (428 mm Hg)–restraint (C–H–R) exposure up to fall of T_rec 23 °C and recovery (T_rec 37 °C) from C–H–R induced hypothermia. The effect of extract treatment was studied on key metabolic regulatory enzymes in blood, liver and muscle and tissue glycogen in rats on attaining T_rec 23 °C and post stress recovery of T_rec 37 °C. In control rats during C–H–R exposure on attaining T_rec 23 °C there was significant decrease in enzyme activities of blood hexokinase (HK), citrate synthase (CS) and glucose-6-phosphate dehydrogenase (G-6-PD); liver CS; and in muscle glycogen, and CS and G-6-PD activities. In control rats on recovery of T_rec 37 °C there was also a significant decrease in liver and muscle glycogen levels along with decreased enzyme activities of blood G-6-PD; liver CS; and liver and muscle G-6-PD. This suggested that during severe stressful exposure to C–H–R and post stress recovery the aerobic metabolism as well as hexose monophosphate (HMP) pathway is suppressed. The single and five doses extract treatment restricted the decrease or better maintained tissue glycogen and enzyme activities, viz. HK, phosphofructokinase (PFK), CS and G-6-PD, in blood, liver and muscle, during C–H–R exposure (T_rec 23 °C) and recovery of T_rec 37 °C. The results suggest that seabuckthorn extract treatment caused a trend for shifting anaerobic metabolism to aerobic during C–H–R exposure and post stress recovery.     

High performance liquid chromatographic and thin layer densitometric methods for the determination of risperidone in the presence of its degradation products in bulk powder and in tablets

Two reproducible stability indicating methods were developed for the determination of risperidone (RISP) in presence of its degradation products in pure form and in tablets. The first method was based on reversed phase high performance liquid chromatography (HPLC), on Lichrosorb RP C 18 column (250 mm i.d., 4 mm, 10 μm), using methanol:0.05 M potassium dihydrogen phosphate pH 7 (65:35 (v/v)) as the mobile phase at a flow rate of 1 ml min⁻¹ at ambient temperature. Quantification was achieved with UV detection at 280 nm over a concentration range of 25–500 μg ml⁻¹ with mean percentage recovery of 99.87 ± 1.049. The method retained its accuracy in the presence of up to 90% of RISP degradation products. The second method was based on TLC separation of RISP from its degradation products followed by densitometric measurement of the intact drug spot at 280 nm. The separation was carried out on aluminum sheet of silica gel 60F₂₅₄ using acetonitrile:methanol:propanol:triethanolamine (8.5:1.2:0.6:0.2 (v/v/v/v)), as the mobile phase, over a concentration range of 2–10 μg per spot and mean percentage recovery of 100.1 ± 1.18. The two methods were simple, precise, sensitive and could be successfully applied for the determination of pure, laboratory prepared mixtures and tablets. The results obtained were compared with the manufacturer's method.     

Stability-indicating methods for the determination of sumatriptan succinate

Four stability-indicating methods were developed for the determination of sumatriptan succinate in the presence of its degradation products. The first method depends on the quantitative densitometric evaluation of thin-layer chromatography of sumatriptan succinate in the presence of its degradation products without any interference. Cyclohexane–dichloromethane–diethylamine (50:40:10 v/v/v) was used as a mobile phase and the chromatogram was scanned at 228 nm. This method determines sumatriptan succinate in the concentration range l–8 μg per spot with mean percentage recovery 100.52±1.23%. The second and third methods depend on the use of first-derivative (D₁) and second-derivative (D₂) spectrophotometry at 234 and 238 nm, respectively. These methods determine the drug in the concentration range 1.25–10 μg ml⁻¹ with mean percentage recovery 99.91±1.01% and 99.96±1.13% for (D₁) and (D₂), respectively. The fourth method depends on the use of ratio derivative spectrophotometric technique. The amplitude in the first derivative of the ratio spectra at 235 nm was selected to determine the cited drug in the presence of its degradation products. Calibration graph is linear in the concentration range 1.25–10 μg ml⁻¹ with mean percentage recovery 100.19±1.19%. The suggested methods were successfully applied for determining sumatriptan succinate in bulk powder, laboratory-prepared mixtures and pharmaceutical dosage forms (Imigran tablet) with good accuracy and precision. The results obtained by applying the proposed methods were statistically analyzed and compared with those obtained by the reported method.     

Comparison of the stability of split and intact gabapentin tablets

The purpose of this study was to determine the stability differences between split and intact gabapentin tablets. Gabapentin tablets from three different manufacturers (G1, G2 and G3) were tested for a period of 9 weeks under long-term (25 °C/60% RH) and intermediate stability (30 °C/60% RH) storage conditions after storage in closed amber pharmacy dispensing containers. Samples were analyzed for dissolution and potency using validated HPLC methods. Potency test also included the quantitation of gabapentin's main degradation product. Tablets from all manufacturers and at all time points had potency >90%. At 9 weeks, a statistically significant decrease (p < 0.02) in gabapentin potency was observed for the whole and split G2 and G3 tablets under the intermediate storage conditions. At the end of 9 weeks, all samples also showed slightly higher levels of degradation product which was statistically significant (p < 0.01) for samples stored under intermediate stability storage conditions and exceeded the proposed USP (PF, 2006) limit for the G3 split and intact tablets. No difference was observed between the potency and dissolution of the intact and the split tablets from the same manufacturer and the three products tested remained stable throughout the study period. The results suggest that splitting of gabapentin tablets did not affect the stability of these particular drug products tested as part of this study when stored under normal storage conditions for a period of up to 9 weeks. However, the results should not be extrapolated to other gabapentin drug products and to other tablet dosage forms.     

Rapid quantification of nebivolol in human plasma by liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A simple, sensitive and rapid liquid chromatographic/electrospray ionization tandem mass spectrometric method was developed and validated for the quantitation of nebivolol in human plasma. The method involved a simple single-step liquid–liquid extraction with diethyl ether/dichloromethane (70/30). The analyte was chromatographed on Waters symmetry^® C₁₈ reversed-phase chromatographic column by isocratic elution with water:acetonitrile:formic acid (30:70:0.03, v/v) and analyzed by mass spectrometry in the multiple reaction monitoring mode. The precursor to product ion transitions of m/z 406.4–151.5 and m/z 409.1–228.1 were used to measure the analyte and the internal standard (I.S.), respectively. The chromatographic runtime was 2 min and the weighted (1/x²) calibration curves were linear over the range 50–10,000 pg/mL. The method was validated in terms of accuracy, precision, absolute recovery, freeze-thaw stability, bench-top stability and re-injection reproducibility. The limit of detection and lower limit of quantification in human plasma were 10 and 50 pg/mL, respectively. The within- and between-batch accuracy and precision were found to be well within acceptable limits (<10%). The analyte was stable after three freeze-thaw cycles (deviation <10%). The average absolute recoveries of nebivolol and tamsulosin, used as an internal standard, from spiked plasma samples were 73.4 ± 3.7 and 72.1 ± 2.0%, respectively. The assay method described here was applied to study the pharmacokinetics of nebivolol.     

Ordered mesoporous silica induces pH-independent supersaturation of the basic low solubility compound itraconazole resulting in enhanced transepithelial transport

The majority of innovative drug candidates are poorly water soluble and exhibit basic properties. This makes them highly dependent on the in vivo encountered acid–neutral pH sequence to achieve a sufficient dissolution and thus absorption. In this study, we evaluated the pH-independent generation of intraluminally induced supersaturation of the model compound itraconazole and its beneficial effect on the extent of absorption in the Caco-2 system and the rat in situ perfusion system. Local supersaturation was obtained by means of a solvent shift method and a novel formulation strategy based on ordered mesoporous silica (OMS) as a carrier. In vitro results evidenced that both methods were capable of creating a supersaturated state of itraconazole in fasted state simulated intestinal fluid (FaSSIF) when no preceding acidic dissolution was simulated. The extent of supersaturation exceeded 21.9 and 9.6 during at least 4 h for the solvent shift method and OMS as a carrier, respectively. As compared to saturation conditions (0.09 ± 0.01 μg), supersaturation induced by the solvent shift method as well as by the use of OMS increased transport across a Caco-2 cell monolayer more than 16-fold, resulting in the basolateral appearance of 2.20 ± 0.29 μg and 1.46 ± 0.03 μg itraconazole after 90 min, respectively. In the absence of an acid–neutral pH sequence, the performance of the marketed product Sporanox^® was inferior with total transport amounting to 0.12 ± 0.03 μg after 90 min. Enhanced absorption was confirmed in the in situ perfusion model where OMS was able to boost total transport of itraconazole after 60 min from 0.03 ± 0.01 nmol cm⁻¹ to 0.70 ± 0.09 nmol cm⁻¹ compared to saturated equilibrium conditions in FaSSIF. The solid dosage form Sporanox^® again failed to achieve a similar extent of absorption enhancement (0.29 ± 0.01 nmol cm⁻¹). These findings suggest that intraluminal supersaturation can be created by the use of OMS and that preceding dissolution of basic compounds in the acidic medium of the stomach is not required to allow for efficient intestinal absorption. The use of OMS appears to be a promising strategy for the delivery of especially basic low solubility compounds in patients suffering from hypochlorhydria; the pH independency may also result in a more reproducible systemic exposure.     

Fortum stability in different disposable infusion devices by pyridine assay

The stability of ceftazidime in 5% dextrose injection and 0.9% sodium chloride injection when stored in a different disposable infusion device was determined. Solutions of ceftazidime 40 mg/ml were used to fill the drug administration devices. Stability was determined for both 5% dextrose injection and 0.9% sodium chloride injection solutions at 37 °C in four disposable infusion devices. Ceftazidime and its mean degradation product, pyridine, were simultaneously assayed in triplicate by a stability-indicating high-performance liquid chromatographic (HPLC) method. This method was simple, sensitive (limit of quantitation (LOQ), 2 ng injected for both compounds), rapid (run time was 7 min) and precise (mean recovery was 100.5±2.9 and 103.6±1.9% for pyridine and ceftazidime, respectively). The ceftazidime stability in the 5% dextrose solution was lower than in the 0.9% sodium chloride solution. When stored at 37 °C in a disposable infusion device, the stability of the ceftazidime is included in large hourly range, depending strongly on the manufacturer. The stability of ceftazidime exceed 19 h in none studied cases. The pyridine formed in 24 h was in the range of 100–400 mg depending on devices and infusions.     

Stability of ramipril in the solvents of different pH

The stability of ramipril in the buffer solution with different pH and the influence of acid, alkaline and oxidative medium on ramipril stability were studied. The ramipril degradation products were determined by high-performance liquid chromatography (HPLC) method. Acetonitrile:sodium perchlorate was used as the mobile phase, at a flow rate of 1.0 ml/min (linear gradient elution). A Nucleosil 100-S 5 μm C18, 250 mm × 4.6 mm i.d. was utilized as stationary phase. Detection was affected spectrophotometrically at 210 nm. The drug substance was dissolved in the ammonium phosphate buffer (pH 3, 5 and 8) and these solutions were stored at 90 °C for 1 h. The other series of test solutions were prepared from stock solution (drug substance dissolved in solvent A of the mobile phase) by dilution in acid (0.1 M HCl), alkaline (0.1 M NaOH) and oxidative (hydrogen peroxide solution) medium. More then 0.2% of impurity D (ramipril–diketopiperazine) was detected in the buffer of pH 3 and pH 5. In the buffer of pH 8 there was detected more then 1% of impurity E (ramipril–diacid). No peaks for degradation products appeared in the chromatograms above limit of quantification. The alkaline medium has the greatest effect on degradation of ramipril into impurity E (more than 50%).     

Increasing the oral bioavailability of the poorly water soluble drug itraconazole with ordered mesoporous silica

This study aims to evaluate the in vivo performance of ordered mesoporous silica (OMS) as a carrier for poorly water soluble drugs. Itraconazole was selected as model compound. Physicochemical characterization was carried out by SEM, TEM, nitrogen adsorption, DSC, TGA and in vitro dissolution. After loading itraconazole into OMS, its oral bioavailability was compared with the crystalline drug and the marketed product Sporanox^® in rabbits and dogs. Plasma concentrations of itraconazole and OH–itraconazole were determined by HPLC-UV. After administration of crystalline itraconazole in dogs (20 mg), no systemic itraconazole could be detected. Using OMS as a carrier, the AUC_0–8 was boosted to 681 ± 566 nM h. In rabbits, the AUC_0–24 increased significantly from 521 ± 159 nM h after oral administration of crystalline itraconazole (8 mg) to 1069 ± 278 nM h when this dose was loaded into OMS. T_max decreased from 9.8 ± 1.8 to 4.2 ± 1.8 h. No significant differences (AUC, C_max, and T_max) could be determined when comparing OMS with Sporanox^® in both species. The oral bioavailability of itraconazole formulated with OMS as a carrier compares well with the marketed product Sporanox^®, in rabbits as well as in dogs. OMS can therefore be considered as a promising carrier to achieve enhanced oral bioavailability for drugs with extremely low water solubility.     

Determination of meloxicam in bulk and pharmaceutical formulations

Three sensitive and reproducible methods for quantitative determination of meloxicam (mel) in pure form and in pharmaceutical formulations are presented. The first method is high performance liquid chromatography by which the drug is determined in the presence of its degradation products over concentration range 100–500 μg ml⁻¹ with mean percentage accuracy 100.13±0.53. The second method is based on measuring the absorbance of the formed neutral complex between basic methylene blue and mel in phosphate buffer (pH 8) at λ=653.5 nm over concentration range 1–5 μg ml⁻¹ with mean percentage accuracy 99.12±1.18. The third method is based on reaction between 2,3-dichloro-5,6-dicyano-p-benzoquinone resulting in the formation of an intense orange red coloured product after heating in a boiling water bath for 5 min. The coloured product exhibits an absorption maximum at 455 nm, over concentration range 40–160 μg ml⁻¹ with mean percentage accuracy 100.53±1.04.     

Degradation studies of pentoxifylline: Isolation and characterization of a novel gem-dihydroperoxide derivative as major oxidative degradation product

Pentoxifylline was subjected to various stress conditions and degradation profile was studied with conventional LCMS. Interestingly, under oxidative stress conditions the drug substance underwent distinct transformation to give rise to a single major degradation product. The structure of this product was elucidated using 1D, 2D NMR spectroscopy, high resolution mass spectrometry (Q-TOF LC/MS) and found to be a novel gem-dihydroperoxide, namely 1-(5,5-Bis-hydroperoxy-hexyl)-3,7-dimethyl-3,7-dihydro-purine-2,6-dione. An efficient stability indicating liquid chromatographic separation method was developed for pentoxifylline and its three degradation products (including two from base hydrolysis) using 1.8 μm, C18 reverse phase column and UHPLC. Baseline separation was achieved with a run time of 4 min. The analytical assay method was validated with respect to system suitability, specificity, linearity, range, precision, accuracy and robustness.     

Stability indicating HPTLC determination of timolol maleate as bulk drug and in pharmaceutical preparations

Timolol was the first β blocker to be used as an anti-glaucoma agent and to date remains as the standard because none of the newer β blockers were found to be more effective. The high performance thin layer chromatographic method of analysis of timolol maleate is reported. The mobile phase selected was ethyl acetate–methanol–isopropyl alcohol–ammonia (25%) (80:20:2:1, v/v/v/v). The calibration curve of the drug was linear in the range of 100–600 ng. The spectrodensitometric analysis was carried out at 294 nm. The mean (±RSD) values of slope, correlation coefficient and intercept were 2487.5 (±0.9), 0.996 (±0.081) and 90463 (±1.1), respectively. The system precision and the method precision were excellent with an RSD of 2.8 and 1.004, respectively. The limits of detection and quantitation were 10 and 40 ng, respectively. The mean percent recovery was found to be 98.6. Timolol maleate was degraded by exposing the drug to heat, acid and base. The degraded products were found to be well separated from the pure drug with significantly different R_f values suggesting a stability indicating analysis method for quantification of timolol maleate in pharmaceutical preparations and as bulk drug. The method was utilized to analyze timolol maleate from conventional eye drops and novel sustained release solid polymeric ocular inserts and oral preparations. The reported method is simple, selective, precise, accurate, time saving and economic as compared to reported HPLC methods.