Apixaban and clopidogrel in a fixed-dose combination: Formulation and in vitro evaluation.

Fixed-dose combination (FDC) products represent a novel, safe, and cost-effective formulation. Combined use of anticoagulant and antiplatelet medications is common among comorbid cardiovascular patients. This study aimed to formulate FDC tablets for Apixaban and Clopidogrel, as prophylaxis and treatment of thrombo-embolic events. FDC tablets were developed by combining small tablets of Immediate-Release Clopidogrel 75 mg and Extend-Release Apixaban 5 mg through direct compression and wet granulation. Particularly, Apixaban tablets were developed using design expert software, and various types and concentrations of polymers were entered. For Clopidogrel tablets, various diluents were used to develop the formulation. Then, the dissolution profile for each formula was studied. Finally, the optimized formulations were encapsulated within hard gelatin capsules. Apixaban formulation followed zero-order with super case Ⅱ transport mechanism as the dominant mechanism of drug release. The Apixaban drug release rate was affected by the type and concentration of the polymers in the formulation (P < 0.05). As the HPMC concentration was increased, Apixaban release was retarded. For, Clopidogrel, the formulated tablets with spray-dried lactose filler and sodium stearyl fumarate lubricant were found to be stable with good properties. In conclusion, the optimum formulation yielded Clopidogrel and extended-release Apixaban for 24 h with the desired in vitro drug dissolution.

Development of Gabapentin Expandable Gastroretentive Controlled Drug Delivery System.

Expandable drug delivery systems are one of many gastroretentive delivery systems which have emerged during the last few years. Expandable systems are usually folded in a capsule and expand to dimensions greater than the pyloric sphincter upon contact with gastric fluid. This prevents them from being evacuated by gastric emptying. The main objective of developing such systems is to increase the residence time of a specific drug in stomach; controlling its release, increasing its bioavailability and decreasing its side effects and dosing frequency. An expandable gastroretentive drug delivery system containing Gabapentin was developed using experimental design (D-optimal reduced quadratic design). This system was able to unfold at stomach pH in less than 15 minutes and obtain a controlled release of 78.1 ± 4.7% in 6 hours following zero-order release kinetic model. It is rigid in stomach and its rigidity decreases at intestinal pH. FTIR analysis indicated the occurrence of hydrogen bonding in Gabapentin when present in the developed system, which might be responsible for the drug's controlled release. XRD analysis indicated that Gabapentin physical properties changed from crystalline in the typical state to amorphous in the developed system.

Artificial neural networks in the optimization of a nimodipine controlled release tablet formulation.

Artificial neural networks (ANNs) were employed in the optimization of a nimodipine zero-order release matrix tablet formulation, and their efficiency was compared to that of multiple linear regression (MLR) on an external validation set. The amounts of PEG-4000, PVP K30, HPMC K100 and HPMC E50LV were used as independent variables following a statistical experimental design, and three dissolution parameters (time at which the 90% of the drug was dissolved, t(90%), percentage of nimodipine released in 2 and 8h, Y(2h), and Y(8h), respectively) were chosen as response variables. It was found that a feed-forward back-propagation ANN with eight hidden units showed better fit for all responses (R(2) of 0.96, 0.90 and 0.98 for t(90%), Y(2h) and Y(8h), respectively) compared to the MLR models (0.92, 0.87 and 0.92 for t(90%), Y(2h) and Y(8h), respectively). The ANN was further simplified by pruning, which preserved only PEG-4000 and HPMC K100 as inputs. Optimal formulations based on ANN and MLR predictions were identified by minimizing the standardized Euclidian distance between measured and theoretical (zero order) release parameters. The estimation of the similarity factor, f(2), confirmed ANNs increased prediction efficiency (81.98 and 79.46 for the original and pruned ANN, respectively, and 76.25 for the MLR).

Developing and optimizing a validated isocratic reversed-phase high-performance liquid chromatography separation of nimodipine and impurities in tablets using experimental design methodology.

In the present study an isocratic reversed-phase high-performance liquid chromatography was investigated for the separation of nimodipine and impurities (A, B and C) using statistical experimental design. Initially, a full factorial design was used in order to screen five independent factors: type of the organic modifier - methanol or acetonitrile - and concentration, column temperature, mobile phase flow rate and pH. Except pH, the rest examined factors were identified as significant, using ANOVA analysis. The optimum conditions of separation (optimum values of significant factors) determined with the aid of central composite design were: (1) mobile phase: acetonitrile/H(2)O (67.5/32.5, v/v), (2) column temperature 40 degrees C and (3) mobile phase flow rate 0.9 ml/min. The proposed method showed good prediction ability (observed-predicted correlation). The analysis was found to be linear, specific, precise, sensitive and accurate. The method was also studied for robustness and intermediate precision using experimental design methodology. Three commercially available nimodipine tablets were analyzed showing good % recovery and %RSD. No traceable amounts of impurities were found in all products.

Tailoring the release rates of fluconazole using solid dispersions in polymer blends.

Formulations of the drug Fluconazole with different release characteristics were prepared by dispersing the active pharmaceutical ingredient (API) in various polymeric carriers, and especially in polymer blends. Fluconazole was tested as a model drug with low solubility in water. First solid dispersions in pure polymers were studied. Use of pure polyvinylpyrrolidone (PVP) as carrier even for high drug load (30 wt%) resulted in rapid release. The drug release rates decreased by increasing the API content. The dissolution rate enhancement was attributed to drug amorphization, particle size reduction, and possible improvement of the drug wetting characteristics. Hydroxypropyl methylcellulose (HPMC) gave solid dispersions, from which the release rates of the drug varied from immediate to sustaining. As the drug amount increased, the rates became higher. Similar behavior also was found when Chitosan was used as carrier, with much more controlled rates close to those for sustained release. These differences were mainly attributed to the limited solubility and swelling of HPMC and Chitosan in aquatic media. To study the effectiveness of polymer blends in adjusting the release rates of the drug, solid dispersions in PVP/HPMC and PVP/Chitosan miscible blends were studied. The release rates of Fluconazole were adequately adjusted by differentiating the weight ratio of the polymers in the blends. PVP/HPMC blends with high PVP content can be used for immediate release formulations but PVP/Chitosan blends are inappropriate for such formulations and can only be used for controlled release.

Development and validation of a high performance liquid chromatographic method for the determination of oxcarbazepine and its main metabolites in human plasma and cerebrospinal fluid and its application to pharmacokinetic study.

An isocratic reversed-phase HPLC-UV procedure for the determination of oxcarbazepine and its main metabolites 10-hydroxy-10,11-dihydrocarbamazepine and 10,11-dihydroxy-trans-10,11-dihydrocarbamazepine in human plasma and cerebrospinal fluid has been developed and validated. After addition of bromazepam as internal standard, the analytes were isolated from plasma and cerebrospinal fluid by liquid-liquid extraction. Separation was achieved on a X-TERRA C18 column using a mobile phase composed of 20 mM KH(2)PO(4), acetonitrile, and n-octylamine (76:24:0.05, v/v/v) at 40 degrees C and detected at 237 nm. The described assay was validated in terms of linearity, accuracy, precision, recovery and lower limit of quantification according to the FDA validation guidelines. Calibration curves were linear with a coefficient of variation (r) greater than 0.998. Accuracy ranged from 92.3% to 106.0% and precision was between 2.3% and 8.2%. The method has been applied to plasma and cerebrospinal fluid samples obtained from patients treated with oxcarbazepine, both in monotherapy and adjunctive therapy.

A validated solid-phase extraction HPLC method for the simultaneous determination of the citrus flavanone aglycones hesperetin and naringenin in urine.

A simple, specific, precise, accurate, and robust HPLC assay for the simultaneous analysis of hesperetin and naringenin in human urine was developed and validated. Urine samples were incubated with beta-glucuronidase/sulphatase and the analytes were isolated by solid-phase extraction using C18 cartridges and separated on a C8 reversed phase column using a mixture of methanol/water/acetic acid (40:58:2, v/v/v) at 45 degrees C. The method was found to be linear in the 50-1200 ng/ml concentration range for both hesperetin and naringenin (r > 0.999). The accuracy of the method was greater than 94.8%, while the intra- and inter-day precision for hesperetin was better than 4.9 and 8.2%, respectively and for naringenin was better than 5.3 and 7.8%, respectively. Recovery for hesperetin, naringenin and internal standard 7-ethoxycoumarin was greater than 70.9%. The method has been applied for the determination of hesperetin and naringenin in urine samples obtained from a male volunteer following a single 300 mg oral dose of each of the corresponding flavanone glycosides hesperidin and naringin. The intra- and inter-day reproducibility through enzyme hydrolysis was less than 3.9% for both total (free + conjugated) hesperetin and naringenin. Stability studies showed urine quality control samples to be stable for both hesperetin and naringenin through three freeze-thaw cycles and at room temperature for 24 h (error < or = 3.6%).

A validated HPLC determination of the flavone aglycone diosmetin in human plasma.

Diosmetin, 3',5,7-trihydroxy-4'-methoxy flavone, is the aglycone of the flavonoid glycoside diosmin that occurs naturally in foods of plant origin. Diosmin exhibits antioxidant and anti-inflammatory activities, improves venous tone and it is used for the treatment of chronic venous insufficiency. Diosmin is hydrolyzed by enzymes of intestinal micro flora before absorption of its aglycone diosmetin. A specific, sensitive, precise, accurate and robust HPLC assay for the determination of diosmetin in human plasma was developed and validated. Diosmetin and the internal standard 7-ethoxycoumarin were isolated from plasma by liquid-liquid extraction and separated on a C8 reversed-phase column with methanol-water-acetic acid (55:43:2, v/v/v) as the mobile phase at 43 degrees C. Peaks were monitored at 344 nm. The method was linear in the 10-300 ng/mL concentration range (r > 0.999). Recovery for diosmetin and internal standard was greater than 89.7 and 86.8%, respectively. Intra-day and inter-day precision for diosmetin ranged from 1.6 to 4.6 and from 2.2 to 5.3%, respectively, and accuracy was better than 97.9%.

Validated high-performance liquid chromatographic method utilizing solid-phase extraction for the simultaneous determination of naringenin and hesperetin in human plasma.

Naringenin and hesperetin, the aglycones of the flavanone glucosides naringin and hesperidin occur naturally in citrus fruits. They exert a variety of pharmacological effects such as antioxidant, blood lipid-lowering, anticarcinogenic and inhibit selected cytochrome P-450 enzymes resulting in drug interactions. A specific, sensitive, precise, and accurate solid-phase extraction high-performance liquid chromatographic (HPLC) assay for the simultaneous determination of naringenin and hesperetin in human plasma was developed and validated. After addition of 7-ethoxycoumarin as internal standard, plasma samples were incubated with beta-glucuronidase/sulphatase, and the analytes were isolated from plasma by solid-phase extraction using C(18) cartridges and separated on a C(8) reversed phase column with methanol/water/acetic acid (40:58:2, v/v/v) as the eluent at 45 degrees C. The method was linear in the 10-300 ng/ml concentration range for both naringenin and hesperetin (r>0.999). Recovery for naringenin, hesperetin and internal standard was greater than 76.7%. Intra- and inter-day precision for naringenin ranged from 1.4 to 4.2% and from 1.9 to 5.2%, respectively, and for hesperetin ranged from 1.3 to 4.1% and from 1.7 to 5.1%, respectively. Accuracy was better than 91.5 and 91.3% for naringenin and hesperetin, respectively.

Simultaneous reversed-phase high-performance liquid chromatographic method for the determination of diosmin, hesperidin and naringin in different citrus fruit juices and pharmaceutical formulations.

Diosmin, hesperidin and naringin are flavonoid glycosides that occur naturally in citrus fruits. They exert a variety of pharmacological properties such as anti-inflammatory, antioxidant and free radical scavenging and antiulcer effects and also inhibit selected cytochrome P-450 enzymes resulting in drug interactions. A reversed-phase high-performance liquid chromatographic method has been developed for the simultaneous determination of diosmin, hesperidin and naringin in different citrus fruit juices and pharmaceutical preparations. Diosmin, hesperidin, naringin and the internal standard rhoifolin were separated using tetrahydrofuran/water/acetic acid (21:77:2, v/v/v) as the mobile phase at 34 degrees C, using a C8 reversed-phase column. The method was linear in the 0.25-20.0 microg/ml concentration range for all three flavonoid glycosides (r>0.999). The method has been successfully applied to the determination of all three flavonoid glycosides in several samples of different citrus fruit juices sold in Greece and for the determination of diosmin and hesperidin in pharmaceutical preparations.