Disintegration-dissolution analysis of percent dissolved-time data

Applying Biopharmaceutical Classification System criteria to predict the potential effect of Cremophor® RH 40 on fexofenadine bioavailability at higher doses

Aim: To study the impact of various permeability enhancers on fexofenadine bioavailability. Furthermore, to predict the potential effect of Cremophor^® RH 40 on fexofenadine pharmacokinetics at higher doses using Biopharmaceutical Classification System criteria. Experimental methods: The effect of the dose increase (60-360 mg) on the dissolution and permeability behavior of fexofenadine-Cremophor RH 40 formulations was studied in humans. The Biopharmaceutical Classification System criteria of the drug was determined. Results & conclusion: Cremophor RH 40 improved the dissolution and bioavailability of fexofenadine. The pharmacokinetics increased linearly with the dose increase. Absorption number (A_n) was significantly increased after addition of Cremophor RH 40 in comparison to an unprocessed drug. Similar A_n values were observed throughout the same dose range. The dose number (D₀) values were <1 whereas, all the dissolution number (D_n) values were >1 at the same dose level.

Miniaturized ionophore-based potentiometric sensors for the flow-injection determination of metformin in pharmaceutical formulations and biological fluids

Miniaturized potentiometric sensors based on β-cyclodextrins (β-CDs) are described for determination of metformin (Mf) in pharmaceutical preparations and biological fluids. Electrode matrix compositions are optimized on the basis of the nature and content of sensing ionophore, ionic sites and plasticizers. Coated wire electrodes (CWEs) modified with heptakis(2,3,6-tri-O-methyl)-β-CD, sodium tetrakis(4-fluorophenyl)borate (NaTFPB) and 2-fluorophenyl 2-nitrophenyl ether (f-NPE), work satisfactorily in the concentration range from 10(-6) to 10(-1) mol L(-1) with Nernstian compliance (55.7 ± 0.4 mV per decade activity) and a detection limit of 8 × 10(-7) mol L(-1). Incorporation of β-CD as a molecular recognition element improved the electrode sensitivity and selectivity due to encapsulation of Mf into the β-CD cavity (host-guest interaction). The developed electrodes have been successfully applied for the potentiometric determination of Mf under batch and flow injection analysis (FIA). FIA allows analysis of 90 samples per h offering the advantages of simplicity, accuracy and automation feasibility. The dissolution profile for metformin pharmaceutical samples (Cidophage®) was monitored using the proposed electrode in comparison with the official spectrophotometric methods. Characterization of the formed Mf-β-CD inclusion complexes is discussed in detail.

Dissolution test optimization for meloxicam in the tablet pharmaceutical form

Meloxicam is a broadly used drug in the therapeutics for the osteoarthritis and rheumatoid arthritis treatments in adults, and it is available in the Brazilian market, as tablet and capsule pharmaceutical forms. The present work aimed to establish conditions for accomplishment of the dissolution test of 15 mg meloxicam tablets (A and B test products), compared with the reference product, since there is no monograph about dissolution assays for meloxicam in official summaries. To optimize the conditions several parameters were tested and, according to obtained results, the use of pH 7.5 phosphate buffer (900mL, at 37 ± 0.5ºC) as dissolution medium, paddle method (apparatus 2), stirring speed of the dissolution medium at 100 rpm and collect time of 60 minutes were considered satisfactory. The samples were quantified by UV spectrophotometric method at 362 nm. The products presented kinetics of first-order. Dissolution efficiency values were of 83.25, 83.73 and 88.10% for the A, B and reference products, respectively. Factors f1 and f2 were calculated and similarity of the tested medicines was demonstrated. The dissolution test was validated presenting selectivity, linearity, precision and accuracy within of the acceptance criteria.

Modeling the deagglomeration of micronized benzodiazepines from powder mixtures added to dissolution media

The objective of this research was to model benzodiazepine deagglomeration profiles of percent agglomerated versus time when interactive mixtures containing micronized benzodiazepines were added to water. Micronized diazepam, nitrazepam, oxazepam, and, for ternary mixtures, micronized sodium lauryl sulfate were mixed with lactose-povidone granules (250-355 microm). After rapid dissolution of the lactose granules, bimodal particle size distributions of benzodiazepines, determined by laser diffraction particle sizing, represented dispersed and agglomerated distributions. The concentrations of agglomerated particle decreased with time and approached constant values. Deagglomeration profiles were determined and best modeled by a three-parameter single-exponential decay equation. A nonlinear least-squares approach was used to estimate the concentration of dispersible (C(0)) and nondispersible agglomerates (C(0a)) and the deagglomeration rate constant (K(a)). Increasing benzodiazepine and sodium lauryl sulphate concentrations in the lactose-povidone mixtures increased both dispersible and nondispersible agglomerate concentrations. Deagglomeration rate was relatively fast with half-lives around 15 min. The estimated parameters of C(0a) and K(a) may provide useful information in optimizing the design of formulations of poorly water soluble, micronized drugs to maximize their dispersion.

Direct determination of triamterene by potentiometry using a coated wire selective electrode

A coated wire triamterene-selective electrode based on the incorporation of a triamterene-tetraphenylborate ion-pair in a poly(vinylchloride) coating membrane was constructed. The influence of membrane composition, temperature, pH of the test solution, and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian response over a triamterene concentration range from 1.0 x 10(-6) to 3.5 x 10(-2) M, at 25 degrees C, and was found to be very selective, precise, and usable within the pH range 4.5-7.5. The standard electrode potentials, E degrees, were determined at 15, 20, 25, 30, 35, 40 and 45 degrees C and used to calculate the isothermal temperature coefficient (dE degrees /dt) of the electrode. Temperatures higher than 45 degrees C seriously affected the electrode performance. The electrode was successfully applied to the potentiometric determination of triamterene hydrochloride both in pure solutions and in pharmaceutical preparations.

Preparation of a cimetidine ion-selective electrode and its application to pharmaceutical analysis

A novel cimetidine ion-selective electrode is prepared, characterized and used in pharmaceutical analysis. The electrode incorporates PVC-membrane with cimetidine-phospohotungstate ion pair complex. The electrode exhibits a Nernstian response for cimetidine in the concentration range 1.0 x 10(-5)-1.0 x 10(-2) M with a slope of 58+/-1 mV per decade. The limit of detection is 5.0 x 10(-6) M. The electrode displays a good selectivity for cimetidine with respect to a number of common foreign inorganic and organic species. It can be used in the pH range 3.0-5.5. The membrane sensor was successfully applied to the determination of cimetidine in its tablets as well as its recovery from a urine sample.

Simple methods for estimating percent disintegrated--time data

Two techniques are described for the treatment of dissolution rates to estimate the percent disintegrated--time data for tablets and capsules. The first is an extension of an equation derived previously with the assumption of first-order disintegration and dissolution processes; whereas, the second involves the determination of the rate constant from the terminal segment of the curve and the use of numerical derivatives according to a disintegration kinetics-independent approach. The dissolution data of six commercial tablet and capsule formulations were treated according to the described techniques. Good agreement was found between the percent disintegrated--time data estimated by the second approach for an acetaminophen tablet and those obtained by a well-established model where a Weibull function was employed.