Técnicas de remuestreo en la comparación de curvas de disolución de fármacos / Resampling techniques on the comparison of drug dissolution curves

De acuerdo con las directrices actuales (Guías EMEA y FDA/CDER) los ensayos de disolución son siempre necesarios y en consecuencia requeridos. Pueden servir para varios propósitos: (i) durante el desarrollo de un medicamento son utilizados como una herramienta para identificar los factores que influyen en la biodisponibilidad, (ii) en el control de calidad se utilizan para probar consistencia en la fabricación y para garantizar que los perfiles de disolución siguen siendo similares a los obtenidos con los lotes del ensayo clínico pivotal, además, (iii) en la inferencia de bioequivalencia subrogada el ensayo de disolución puede ser utilizado para demostrar similitud entre diferentes formulaciones de una sustancia activa y el producto de referencia. El interés de la normativa sobre la comparación de los perfiles está centrado en conocer cuál es el grado de similaridad de las curvas y disponer de una medida sensible a las diferencias grandes. Varios comités regulatorios han recomendado el factor de similaridad f2 como criterio para evaluar similaridad entre dos perfiles de disolución, por lo que su utilización está generalizada. El objetivo de este artículo fue desarrollar estudios teóricos y de simulación para evaluar por medio de intervalos de confianza bootstrap para f2, la similitud de los perfiles de disolución(AU)

According to the current Guidelines (EMEA and FDA/CDER) dissolution studies are always necessary and consequently required. Dissolution assays can serve several purposes: (i) during the development of a medicinal product a dissolution test is used as a tool to identify formulation factors that are influencing the bioavailability of the drug; (ii) in the quality control of scale-up and of production batches, a dissolution test is used to prove consistency in the manufacturing and to ensure that the dissolution profiles remain similar to those of pivotal clinical trial batches; furthermore, (iii) in bioequivalence surrogate inference a dissolution test can be used to demonstrate similarity between different formulations of an active substance and the reference medicinal product. Regulatory interest in dissolution profiles comparisons is in knowing how similar the curves are, and to have a measure sensitive to large differences at any particular time point. Similarity factor f2 is gaining popularity due to its recommendation by various regulatory committees as a criterion for the assessment of the similarity between two dissolution profiles. The aim of this study was to develop theoretical and simulation studies to assess by means of bootstrap confidence intervals for f2, the similarity of dissolution profiles(AU)

Influence of lactose addition to gentamicin-loaded acrylic bone cement on the kinetics of release of the antibiotic and the cement properties.

The purpose of this study was to characterize a poly(methyl methacrylate) bone cement that was loaded with the antibiotic gentamicin sulphate (GS) and lactose, which served to modulate the release of GS from cement specimens. The release of GS when the cement specimens were immersed in phosphate-buffered saline at 37 degrees Celsius was determined spectrophotometrically. The microstructure, porosity, density, tensile properties and flexural properties of the cements were determined before and after release of GS. A kinetics model of the release of GS from the cement that involved a coupled mechanism based on dissolution/diffusion processes and an initial burst effect was proposed. Dissolution assay results showed that drug elution was controlled by a diffusion mechanism which can be modulated by lactose addition. Density values and mechanical properties (tensile strength, flexural strength, elastic modulus and fracture toughness) were reduced by the increased porosity resulting from lactose addition, but maintained acceptable values for the structural functions of bone cement. The present results suggest that lactose-modified, gentamicin-loaded acrylic bone cements are potential candidates for use in various orthopaedic and dental applications.

Improvement of gentamicin poly(D,L-lactic-co-glycolic acid) microspheres for treatment of osteomyelitis induced by orthopedic procedures.

Poly(D,L-lactide-co-glycolide) (PLGA) biodegradable microspheres with gentamicin for local treatment of microbial bone infection were prepared and characterized. Gentamicin was assayed spectrophotometrically at 332 nm after derivation with the o-phthalaldehyde; biodegradable polymers studied did not interfere with this method of gentamicin analysis. PLGA microspheres were made by the double emulsion solvent evaporation method with modifications. The first W(1)/O emulsion was obtained by ultrasonication or high-speed homogenization, and a large aqueous phase W(2) (200 ml) was used. The ultrasonication method increases the microsphere percentage observed in the 20-40 microm size range and, in all cases SEM-microphotographs revealed homogeneous and spherically shaped particles with smooth surfaces. The method including ultrasonication proposed in the present work improved the encapsulation efficiency of gentamicin by nearly 100% (97.94%). Several mathematical models based on heterogeneous hydrolytic degradation were applied to evaluate their suitability in describing gentamicin released from PLGA microspheres. Two models, one of them including an autocatalytic process, were finally proposed to contribute to understand the mass transport mechanism involved in drug release from these microspheres.

Comparative therapeutic efficacy of a novel lyophilized amphotericin B lecithin-based oil-water microemulsion and deoxycholate-amphotericin B in immunocompetent and neutropenic mice infected with Candida albicans.

The in vivo efficacy of a new amphotericin B (AmB) oil-in-water lecithin-based microemulsion delivery system (M-AmB) compared to deoxycholate-AmB (D-AmB) was studied in an immunocompetent and neutropenic murine model of systemic candidiasis. D-AmB was administered at the maximum tolerated dose of 1 mg/kg whereas M-AmB was given at the doses of 1, 2 and 3 mg/kg; doses were well tolerated due to their reduced toxicity. Both formulations were administered 24, 48 and 72 h after infection in immunocompetent mice, and 2, 6 and 24 h after infection in neutropenic mice. Kaplan-Meier survival curves showed that the M-AmB treated group had a better survival time than infected mice without treatment used as a control group (P = 4.66 x 10(-6)), and the Mann-Whitney W statistical test indicated that it reduced the percentage of mortality and fungal load in the most representative organs. This new formulation is a designed competitor which has proved to present better results than D-AmB in an established infection not only in immunocompetent but in neutropenic mice as well.

The influence of the copolymer composition on the diltiazem hydrochloride release from a series of pH-sensitive poly[(N-isopropylacrylamide)-co-(methacrylic acid)] hydrogels.

A series of poly[(N-isopropylacrylamide)-co-(methacrylic acid)] (P[(N-iPAAm)-co-(MAA)]) hydrogels was investigated to determine the composition that exhibits a better pH-modulated release of diltiazem hydrochloride (DIL.HCl). For this purpose hydrogel slabs were loaded with DIL.HCl by the immersion method, and its release under acidic medium (0.1N HCl, pH 1.2) and in phosphate buffer pH 7.2, using United States Pharmacopeia (USP) 24 Apparatus 1, was investigated. According to the results from the slabs, copolymers with 85% mol N-iPAAm content were selected to prepare tablets with different particle size. The effect of pH and particle size changes on DIL.HCl release from these last hydrogel tablets was investigated by a stepwise pH variation of the dissolution medium. The amount of DIL.HCl released from high N-iPAAm content copolymer slabs under acidic pH medium was not only very low but it was also released at a slow rate. In the 85% N-iPAAm tablets, significant differences between and within release profiles were found as a function of particle size and pH, respectively. A relationship between particle size and release rate has been found. The lower DIL.HCl release at acidic pH from enriched N-iPAAm copolymers is interpreted by a cooperative thermal- and pH-collapse. Although for the whole range of copolymer composition a dependence of the equilibrium of swelling on the pH was found, DIL.HCl release experiments indicated that hydrogels with 85% mol N-iPAAm are the more adequate to be used for modulated drug delivery systems. Additionally, the particle size of the tablet can be used to tailor the release rate.

Comparative pharmacokinetics and safety of a novel lyophilized amphotericin B lecithin-based oil-water microemulsion and amphotericin B deoxycholate in animal models.

Amphotericin B (AmB) has been a most effective systemic antifungal agent, but its use is circumscribed by the dose-limiting toxicity of the conventional micellar dispersion formulation Fungizone (D-AmB). To lower AmB-associated toxicity, AmB may be integrated into oil-in-water lecithin-based microemulsions. The present study compares the pharmacokinetic characteristics of D-AmB with the alternative formulation of AmB in microemulsion (M-AmB), which has proved effective in a murine candidiasis model. Both formulations were given by intravenous bolus: D-AmB 1 mg/kg, and M-AmB 0.5, 1 or 2 mg/kg. The pharmacokinetics of D-AmB and M-AmB have several differences, specifically with regard to the respective Cmax and AUC0- infinity values. Elimination of AmB from serum was biphasic for both M-AmB and D-AmB. Single-dose D-AmB (1 mg/kg) achieved a Cmax of 3.89 +/- 0.48 mg/L and an AUC0- infinity of 32.28 +/- 7.31 mg.h/L, whereas single-dose M-AmB (1 mg/kg) by comparison achieved a lower Cmax (2.92 +/- 0.54 mg/L) and a lower AUC0- infinity (21.89 +/- 5.17 mg.h/L). To evaluate the safety of M-AmB, a multiple-dose toxicity study was performed in groups of 10 mice, each receiving D-AmB 1 mg/kg, or M-AmB 1, 1.5, 2 or 3 mg/kg. The findings suggest that, in comparison with D-AmB, M-AmB produces no histologically demonstrable renal lesions, or changes in clinical chemistry.

Gentamicin sulphate release from a modified commercial acrylic surgical radiopaque bone cement. I. Influence of the gentamicin concentration on the release process mechanism.

The purpose of the present work was the study of the gentamicin sulphate (GS) release from a commercial acrylic bone cement CMW-1 with the aims of establishing the influence of the slabs preparation as well as the release mechanism and kinetics. The effect of the amount of GS on the release kinetic parameters has been also investigated. In vitro release studies were performed in a buffered saline solution at pH 7.4 and 37 degrees C. The GS concentration was determined using an indirect spectrophotometric method with an o-phthaldialdehyde as a derivatizing reagent. A commercial and three modified samples were tested. The free and fractured surfaces of the GS cement slabs before and after the release studies were observed by means of scanning electron microscopy (SEM). For low GS concentration loading the release was very incomplete because most of the GS beads were encapsulated by the hydrophobic PMMA matrix. A higher amount of antibiotic was released from cement that has a higher amount incorporated. A model and therefore a mechanism of release based on this model have been proposed. It has allowed us to explain the changes in dissolution kinetics of an acrylic matrix type controlled release system up to 12% GS loading. The cumulative amount of GS released M(t)/M(i), was fitted as a function of time. For lower amounts of GS, the regression analysis (R(2)>0.99) revealed that the release is most adequately represented by M(t)/M(i)=b+kt(n), where b represents a burst effect. The goodness of fit decreases as the amount of GS increases. The influence of some other type of release mechanism for higher amounts of GS must be taken into account and a second model for the release, M(t)/M(i)=b+k x [1-exp(-kt)], is proposed.

Amphotericin B in oil-water lecithin-based microemulsions: formulation and toxicity evaluation.

A novel lecithin-based microemulsion containing AmB was developed to reduce the toxic effects of the drug, comparing it with the commercial formulation Fungizone. Phase diagrams containing the microemulsion region were constructed for pseudoternary systems composed of isopropil myristate (IPM)/Brij((R)) 96V/lecithin/water. The incorporation of AmB to the microemulsions was done following the Phase Inversion Temperature (PIT) method or by diluting the drug in the aqueous phase of the disperse system before forming the microemulsion. The percentage of drug entrapped in the microemulsion was analyzed by an HPLC method obtaining recoveries > 98%. Mean droplet size of the microemulsions chosen for the acute toxicity evaluation was of 45 nm, and the rheological studies showed that those microemulsions mentioned followed a Newtonian behavior. Different studies are described in this work to prove the stability of these new dosage forms. Acute toxicity results, determined by a graphic method, the probit binary model and the Reed and Muench method showed that lethal dose 50 (LD(50)) for AmB microemulsions was of 2.9 mgkg(-1) compared to 1.4 mgkg(-1) for the commercial deoxycholate suspension, Fungizone. The overall results indicate that treatment with AmB microemulsions was less toxic than Fungizone, suggesting a potential therapeutic application.