Elizabeth Piñón-Segundo

The Tape-Stripping Technique as a Method for Drug Quantification in Skin

Quantification of drugs within the skin is essential for topical and transdermal delivery research. Over the last two decades, horizontal sectioning, consisting of tape stripping throughout the stratum corneum, has become one of the traditional investigative techniques. Tape stripping of human stratum corneum is widely used as a method for studying the kinetics and penetration depth of drugs. This paper shows the applications of the tape stripping technique to quantify drug penetration through the skin, underlining its versatile application in the area of topical and transdermal drugs.

Silica xerogels as pharmaceutical drug carriers

This review focuses on silica xerogels obtained by the sol-gel method and their application as drug delivery systems. SiO2 xerogels are potential biomaterials to be used as matrix materials for the extended and controlled release of different kinds of biologically active agents administered by various routes. The article includes some representative examples that describe the encapsulation of bioactive molecules and model compounds inside a silica matrix produced by the conventional sol-gel method or by ultrasound hydrolysis. The drug release rate from xerogels could be modified by adjusting several parameters, such as the type of precursor, the concentration of the catalyst and drying temperature. In vitro and in vivo studies have shown the efficacy and biodegradability of these composites. The potential application of silica xerogels as drug carrier systems is critically analyzed and discussed.

Single Emulsion-Solvent Evaporation Technique and Modifications for the Preparation of Pharmaceutical Polymeric Nanoparticles

In recent years, there has been an increased interest in using nanoparticles for drug delivery and pharmaceutical development. Nanoparticles can offer significant advantages over the conventional drug delivery systems in terms of high drug loading, stability and specificity, controlled release capability, and the ability to deliver both hydrophilic and hydrophobic drug molecules through various routes of administration. This review article focuses on the use of the single emulsion solvent evaporation method, the first method proposed for the preparation of polymeric nanoparticles, and modifications that have been developed over the years to improve the results obtained with this technique.

Pharmaceutical polymeric nanoparticles prepared by the double emulsion- solvent evaporation technique.

The most common technique to produce nanoparticles involves evaporation of a polymer emulsion to obtain polymeric particles less than 500 nm in size. And since its introduction in the late 1970s, this process has been widely used for pharmaceutical applications to obtain clinically applicable drug delivery systems. Many adjustments and adaptations of this technique have been made, attempting encapsulation of a wide variety of bioactive compounds. The advantages and drawbacks of the single-emulsion and especially double (multiple)-emulsion techniques are discussed in the present review article. It covers patent and patent applications literature, as well as peer reviewed research papers discussing pharmaceutical polymer-based nanoparticles obtained by the double emulsion-solvent evaporation technique using preformed polymers.

Determination of poloxamer 188 and poloxamer 407 using high-performance thin-layer chromatography in pharmaceutical formulations

Poloxamers (PXMs) are amphiphilic non-ionic block polymers commonly used in the cosmetic and pharmaceutical industries. In spite of the wide use of PXMs, few studies have dealt with the analysis of these polymers in pharmaceutical preparations. In this work, high-performance thin-layer chromatography (HPTLC) has been used to quantify both PXM-188 and PXM-407 in pharmaceutical preparations. The separation of these compounds was carried out using reverse phase HPTLC plates with a chloroform-methanol mixture as the mobile phase. Detection was performed densitometrically using the Dragendorffs reagent for the visualization of PXMs. Quality parameters were established, and the detection limits ranged from 24 to 47ng/spot. A good precision (day to day and run to run), with relative standard deviations <11.18%, was obtained. The proposed method was satisfactorily applied to the analysis of laboratory-made and commercial pharmaceutical products.

Evaluation of a combined drug-delivery system for proteins assembled with polymeric nanoparticles and porous microspheres; characterization and protein integrity studies

This work presents an evaluation of the adsorption/infiltration process in relation to the loading of a model protein, α-amylase, into an assembled biodegradable polymeric system, free of organic solvents and made up of poly(D,L-lactide-co-glycolide) acid (PLGA). Systems were assembled in a friendly aqueous medium by adsorbing and infiltrating polymeric nanoparticles into porous microspheres. These assembled systems are able to load therapeutic amounts of the drug through adsorption of the protein onto the large surface area characteristic of polymeric nanoparticles. The subsequent infiltration of nanoparticles adsorbed with the protein into porous microspheres enabled the controlled release of the protein as a function of the amount of infiltrated nanoparticles, since the surface area available on the porous structure is saturated at different levels, thus modifying the protein release rate. Findings were confirmed by both the BET technique (N2 isotherms) and in vitro release studies. During the adsorption process, the pH of the medium plays an important role by creating an environment that favors adsorption between the surfaces of the micro- and nano-structures and the protein. Finally, assays of α-amylase activity using 2-chloro-4-nitrophenyl-α-D-maltotrioside (CNP-G3) as the substrate and the circular dichroism technique confirmed that when this new approach was used no conformational changes were observed in the protein after release.

Preparation of Nanoparticles by Solvent Displacement Using a Novel Recirculation System

Submicron colloidal suspensions of poly(ε-caprolactone) (PCL) were prepared by the solvent displacement method, using either the conventional form or a new recirculation device. In the latter case, a process that allows the recirculation of the aqueous phase into a device, providing a continuous flow, is proposed. The influence of the organic solution injection rate and polymer concentration on mean particle size and process yield were studied for both methods. The recirculation rate was also analyzed for the recirculation system. Nanoparticles (NPs) showed mean sizes that ranged from 156 to 381. The smallest particles were obtained when recirculation rate, injection rate and polymer concentration were maximized but at the expense of the yield. The only acceptable yields (83–96%) were obtained at the lowest PCL concentration (2.5% w/v). ANOVA tests (α = 0.05) showed that the variables implicated in the recirculation system significantly affected the mean particle size and the process yield. The entrapment efficiencies of NPs prepared by the conventional method were not significantly different (α = 0.05) from those obtained by the recirculation system.

The release kinetics of β-carotene nanocapsules/xanthan gum coating and quality changes in fresh-cut melon (cantaloupe)

The main aim of this work was to evaluate the effect of the β-carotene release rate from nanocapsules incorporated into a xanthan gumcoating on the physical and physicochemical properties of fresh-cut melon (var. cantaloupe). Several coatings were studied: xanthan gum alone (XG), xanthan gum combined with nanocapsules (Ncs/XG), xanthan gum combined with nanospheres (Nsp/XG), nanocapsules (Ncs), and nanospheres (Nsp), all of which were compared to untreated fresh-cut melon in order to determine their preservation efficiency. The β-carotene release profiles from the Ncs and Ncs/XG treatments corresponded better to a Higuchi-type behavior (t1/2) for matrix systems (R2>0.95). Also observed was a good correlation between the release of β-carotene by the Ncs/XG treatment and the minor changes observed in the whiteness index (≤10%) and firmness (≤2%). These results lead to the conclusion that incorporating β-carotene nanocapsules into a polysaccharide matrix improves the properties of the coatings, thereby increasing storage time to 21days at 4°C.

Evaluation of SiO2 Sonogels, Prepared by a New Catalyst-Free Method, as Drug Delivery System

Recently, we reported on the synthesis of catalyst-free SiO2 sonogels prepared by the sonication of a neutral distilled water/ tetraethyl ortosilicate mixture. The purpose of the present study was to evaluate the feasibility of using these sonogels as pharmaceutical delivery systems. A certified color additive (sunset yellow, SY) was used as a model compound for the release experiments. Different amounts of dye were incorporated into the gels before drying. Sonogels were characterized by scanning electron microscopy and differential scanning calorimetry. The effect of three drying temperatures (25°C, 40°C and 80°C) and two mean grain sizes (1125 and 630 μm) on release behavior was analyzed. The analysis of variance showed no significant differences between the Higuchis constants (KH) obtained for SY-loaded sonogels dried at 80°C with different SY loads, irrespective of the mean grain size. In contrast, for SY-loaded sonogels dried at 40°C, differences were found between sonogels loaded with 2.7, 7.7, 12.2, and 18.2% of SY, and no significant differences were detected between the mean grain sizes analyzed. Considering that the preparation of sonogels by the catalyst-free method allows an easy encapsulation, sonogels may offer an interesting alternative for drug release in the pharmaceutical field.

Sucrose Esters as Transdermal Permeation Enhancers

Surfactants are widely used excipients in topical formulations, not only for their solubilizing and emulsifying properties but also for their well-known capacity to enhance drug permeation. Although nonionic surfactants are frequently chosen because of their mild effect on the skin, they share a low efficacy as permeation enhancers. Among nonionic surfactants, sucrose fatty acid esters (SEs) have awoken the interest of different research groups due to their interesting properties, such as biodegradability, nontoxicity, low irritation to the skin, and their ability to form liquid crystals and microemulsions (among other systems). Furthermore, as described in this chapter, SEs have shown a good capacity to enhance the transcutaneous transport of drugs. Their enhancing ability depends on different factors such as the physicochemical properties of the drug, the type of SEs, and the characteristics of the vehicle or the delivery system. This chapter gathers information about the studies related to SEs as transdermal penetration enhancers.