The role of hyaluronan as a drug carrier to enhance the bioavailability of extended release ophthalmic formulations. Hyaluronan-timolol ionic complexes as a model case.

The aim of this work was to obtain information concerning the properties of ophthalmic formulations based on hyaluronic-drug ionic complexes, to identify the factors that determine the onset, intensity and duration of the pharmacotherapeutic effect. Dispersions of a complex of 0.5% w/v of sodium hyaluronate (HyNa) loaded with 0.5% w/v of timolol maleate (TM) were obtained and presented a counterionic condensation higher than 75%. For comparison a similar complex obtained with hyaluronic acid (HyH) was also prepared. Although the viscosity of HyNa-TM was significantly higher than that of HyH-TM, in vitro release of TM from both complexes showed a similar extended drug release profile (20-31% over 5h) controlled by diffusion and ionic exchange. Ocular pharmacokinetic study performed in normotensive rabbits showed that HyNa-TM complex exhibited attractive bioavailability properties in the aqueous humor (AUC and Cmax significantly higher and later Tmax) compared to commercial TM eye-drops. Moreover, a more prolonged period of lowered intra-ocular pressure (10h) and a more intense hypotensive activity was observed after instillation of a drop of HyNa-TM as compared to the eye-drops. Such behavior was related to the longer pre-corneal residence times (400%) observed with HyNa-TM complex. No significant changes in rabbit transcorneal permeation were detected upon complexation. These results demonstrate that the ability of HyNa to modulate TM release, together with its mucoadhesiveness related to the viscosity, affected both the pharmacokinetic and pharmacodynamic parameters. The HyNa-TM complex is a potentially useful carrier for ocular drug delivery, which could improve the TM efficacy and reduce the frequency of administration to improve patient compliance.

Ivermectin-loaded lipid nanocapsules: toward the development of a new antiparasitic delivery system for veterinary applications.

Ivermectin (IVM) is probably one of the most widely used antiparasitic drugs worldwide, and its efficacy is well established. However, slight differences in formulation may change the plasma kinetics, the biodistribution, and in consequence, the efficacy of this compound. The present study focuses on the development of a novel nanocarrier for the delivery of lipophilic drugs such as IVM and its potential application in antiparasitic control. Lipid nanocapsules (LNC) were prepared by a new phase inversion procedure and characterized in terms of size, surface potential, encapsulation efficiency, and physical stability. A complement activation assay (CH50) and uptake experiments by THP-1 macrophage cells were used to assess the stealth properties of this nanocarrier in vitro. Finally, a pharmacokinetics and biodistribution study was carried out as a proof of concept after subcutaneous (SC) injection in a rat model. The final IVM-LNC suspension displayed a narrow size distribution and an encapsulation rate higher than 90 % constant over the evaluated time (60 days). Through flow cytometry and blood permanence measurements, it was possible to confirm the ability of these particles to avoid the macrophage uptake. Moreover, the systemic disposition of IVM in the LNC administered by the SC route was higher (p < 0.05) (1367 ng h/ml) compared to treatment with a commercial formulation (CF) (1193 ng.h/ml), but no significant differences in the biodistribution pattern were found. In conclusion, this new carrier seems to be a promising therapeutic approach in antiparasitic control and to delay the appearance of resistance.

Effects of ascorbate fatty ester derivatives on erythrocyte membrane lipoperoxidation.

6-O-alkyl ascorbic acid esters (ASC(n)) are amphiphilic molecules that behave as surfactants in aqueous solution. ASC(n) have shown some physical and rheological properties that suggest a potential utility as drug carriers. The present paper aims to evaluate the effect of ASC(n) on erythrocyte properties in order to get information regarding the relationship between osmotic fragility, erythrocyte deformability and membrane lipoperoxidation process. The assays were performed at the following concentrations: the critical micelar concentration (CMC), producing 10% hemolysis (CH(10)) and producing 50% hemolysis (CH(50)). We observed that ASC(n) (ASC(8), ASC(10) and ASC(12)), at concentration nearby CMC, neither affected cell deformability nor produced lipoperoxidation. Nevertheless, at higher concentrations (CH(10) and CH(50)), the RBCs incubated with ASC(n) were affected by a significant and progressive loss of deformability, simultaneously with an increase of osmotic fragility and membrane lipoperoxidation.

Albendazole sulphoxide kinetic disposition after treatment with different formulations in dogs.

New therapeutic strategies based on the search of alternative formulations of albendazole (ABZ) and albendazole sulphoxide (ABZSO) are under current development to optimize posology and antiparasite efficacy in dogs. In an incomplete block design, nine dogs were randomly divided into three groups (n = 6). Treatments were carried out in two phases as follows. Phase I: Group I (treatment A), animals received ABZ at 25 mg/kg of conventional formulation. Group II (treatment B), dogs received 25 mg/kg of a modified poloxamer-ABZ formulation. Group III (treatment C), animals were treated with ABZSO in equimolar amount to ABZ doses. After 21 days of wash-out period the experiment was repeated (Phase II). Blood samples were collected over 24 h and subsequently analysed by high performance liquid chromatography. ABZSO and ABZSO(2) were the analytes recovered in plasma. Significant higher (P < 0.001) ABZSO area under the concentration-time curve (+500%) and C(max) (+487%) values were obtained for the treatment C in comparison with treatments A and B. However, no statistical differences on pharmacokinetic parameters were found between formulations A and B. In conclusion, the enhanced plasma concentration profile obtained for the ABZSO formulation used in treatment C may contribute to optimize the anthelmintic control in dogs.

Optimization of skin permeation and distribution of ibuprofen by using nanostructures (coagels) based on alkyl vitamin C derivatives.

In this investigation two vitamin C-based -6-O-ascorbic acid esters (ASC12 and ASC16), able to form liquid-crystal structures (coagels) was evaluated for their potential usefulness to promote the permeation and distribution of ibuprofen (IBU). Two coagel formulations and the same coagels added of polyethylene glycol (PEG-400) were assayed in comparison with a commercial product (Arfen®) by using hairless rat skin as model. The ASC16 and ASC12 derivatives gave rise to stable supramolecular assemblies in water and in water/PEG mixtures (coagels), allowing the solubilization of IBU (0.85%) and producing a IBU controlled release systems, as evidenced by the dynamic dialyse test: the n values were near 1.0, indicative of a linear kinetic, for all coagel formulations, except for the ASC12PEG/C formulation (n=1.51). Our results evidenced the enhancement activity of coagels and the synergic effect of the combination with PEG: all coagels showed a higher amount of IBU permeated through the skin compared to commercial Arfen® with an enhancement factor of 52.94 and 21.53 for ASC12PEG/C and ASC16/C respectively. Otherwise, coagels formulations appeared to produce a low IBU depot in the skin and in the same order of magnitude in epidermis and derma, in spite of significant increase of IBU cutaneous permeation. The positive synergic effect of the coagel-PEG mixtures was demonstrated by the high amount of IBU accumulated in the upper skin layers. The effect of the coagels on the IBU skin permeation and distribution depending on their hydro-lipophilic character could allow a rational design and an optimization of topical formulations.

Novel mucoadhesive extended release tablets for treatment of oral candidosis: "in vivo" evaluation of the biopharmaceutical performance.

Mucoadhesive tablets containing nystatin (10 mg) were evaluated in vivo. The assays were carried out with 12 healthy volunteers and the concentration of nystatin in saliva was determined at different times. Tablets remained attached to the buccal mucosa during 270 min +/- 30 min. No evidence of ulceration or bleeding was observed. Typical appearance of intact human buccal mucosa was seen before and after contact with the tablet. The tablets were well accepted by the volunteers, although most of the volunteers reported a light bitter taste, probably due to nystatin. Concentration of nystatin in saliva was several times higher than MIC over a period of approximately 4.5 h, which was in agreement with the behavior observed in vitro. These results allow us to infer that the administration of these mucoadhesive tablets could be advantageous compared to conventional formulations and mucoadhesive extended-release tablets might produce better therapeutic performance than conventional formulations in the treatment of oral candidosis.

Effect of ascorbic acid based amphiphiles on human erythrocytes membrane.

6-O-alkyl ascorbic acid esters (ASCn) are amphiphilic molecules that behave as surfactants in aqueous solution. These compounds show physico-chemical and aggregation properties that depend on the alkyl chain length, pH and temperature. It must consider that ASCn have shown some physical and rheological properties that suggest a potential utility as drug carriers. The present paper aims to evaluate the effects of these surfactants on human erythrocyte membranes. The membrane properties studied were: osmotic resistance in hypotonic media, shape transformation, and vesicle release at lytic concentration. According to our results, all properties depended on the length of the hydrophobic chain and they did not evolve monotonically. Finally, the study of ASCn interaction with erythrocyte membrane allowed us to postulate the crucial influence that the molecular structure exerts upon the manner in which amphiphiles interact with biological membranes and the effects involved in them.

Design of novel antifungal mucoadhesive films. Part II. Formulation and in vitro biopharmaceutical evaluation.

This paper deals with the formulation of the mucoadhesive films containing nystatin. The design and formulation of the films were based on the mucoadhesive properties of carbomer 934P (CB) and carboxymethycellulose (NaCMC), and also on the plasticizer properties of polyethyleneglycol 400 (PEG400). A surfactant (ascorbyl palmitate, ASC16) was added to the system to aid in nystatin dispersion. Addition of these last two components produced a significant improvement in physical-mechanical properties (flexibility and strength) as well as an increase in the nystatin release rate. X-ray powder diffraction (XRPD) and scanning electronic microscopy (SEM) were used to evaluate the morphological changes in the films while PEG400 and ASC16 were added to the formulations. Furthermore, the in vitro nystatin profile release was determined.

Design of novel antifungal mucoadhesive films Part I. Pre-formulation studies.

In this work, pre-formulation studies concerning the design of novel mucoadhesive films have been carried out. The rationality of the design is based on the utilization of mucoadhesive polymers (carbomer and carboxymethylcellulose), a plasticizer (polyethyleneglycol 400, PEG400) and a surfactant (ascorbyl palmitate, ASC16). In the gel preparation, the casting method using water as a solvent was employed. To provide a better understanding of the structural arrangements produced during the casting process, the changes in morphology (Cryo-TEM) and rheology (viscosity) of the film forming gel were evaluated. When PEG400 was included as a plasticizer, a disorder was produced in the network, reflected in the globular structure adopted by the gel and the consequent decrease in viscosity. The addition of ASC16 improved the solubilization of nystatin and provoked a decrease in gel viscosity. However, as water was removed during casting, ASC16 produced a significant increase in the viscosity at the point in which the polymer concentrations were sufficient to strengthen the inter-polymeric interactions, giving rise to a more rigid tri-dimensional network.

Potential use of ascorbic acid-based surfactants as skin penetration enhancers.

6-O-Ascorbic acid alkanoates (ASCn) are amphiphilic molecules having physical-chemical properties that depend on the alkyl chain length. The derivatives of low molecular weight (n < 11) have enough aqueous solubility to produce self-assemblies at room temperature ( approximately 25 degrees C), while those with longer alkyl chains possess a critical micellar temperature (CMT) higher than 30 degrees C. At higher temperatures (T degrees > CMT), ASCn aqueous suspensions turn into either micellar solutions or gel phases, depending on the length of the hydrophobic chain. On cooling, coagels are produced, which possess a lamellar structure that exhibit sharp X-ray diffraction patterns and optical birefringence. The semisolid consistency of such coagels is an interesting property to formulate dermatological pharmaceutical dosage forms able to solubilize and stabilize different drugs. The objective of the present study was the evaluation of the enhancing permeation effect of ASCn with different chain lengths and to correlate permeability changes with histological effects. With this purpose, ASCn coagels containing anthralin (antipsoriasic drug) or fluorescein isothiocyanate (FITC, hydrophobic fluorescent marker) were assayed on rat skin (ex vivo) and mice skin (in vivo), respectively. Also, histological studies were performed aimed at detecting some possible side effects of ASCn. No inflammatory cellular response was observed in the skin when ASCn coagels were applied, suggesting non-irritating properties. Light microscopy indicated slight disruption and fragmentation of stratum corneum. The penetration of ASCn through rat skin epidermis was very fast and quantitatively significant. The permeation of anthralin was significantly increased when the drug was vehiculized in ASCn coagels, compared to other pharmaceutical systems. The results indicated that ASC12 seems to have the highest enhancing effect on FITC permeation. ASC12 appears to be the compound that possesses the highest capacity to enhance the penetration of the drugs. Furthermore, it has the highest permeation of the serie.

The improvement of aqueous chemical stability of a model basic drug by ion pairing with acid groups of polyelectrolytes.

Carbomer (C) and procaine (P) were selected respectively as models of polyelectrolyte (PE) and basic drug (B) of low stability in aqueous solution. The purpose of this investigation was to test if a (C-P) aqueous system provides a microenvironment in which P is less exposed to hydroxyl ion catalyzed degradation, its main degradation pathway over a wide pH range. It was determined that in (C-P) a high fraction of P was present in the form of ion pairs [RCOO-PH+] with the carboxylate groups of C. The [RCOO-PH+] fraction was above 97% for compositions containing higher than 50 mol% of P. The chemical stability of C-P was assayed at two selected pHs (7.5 and 8.5) in comparison with conventional reference solutions (RS) without C. Procaine in (C-P) was 4.2 and 6.2 times more stable than in its respective RS at the two conditions assayed. The stabilizing factor was calculated as the ratio of the rate constants k(obs)(RS)/k(obs)(C-P).Since C-B systems exhibit negative electrokinetic potential that attracts positive ions such as (H+) and repels negative ones such as (OH(-)), the stabilizing effect would be associated with the higher acidity of (C-P) environment, in which PH+ molecules attached to the PE should also have lower kinetic energy than those in the bulk medium.

Equilibrium properties and mechanism of kinetic release of metoclopramide from carbomer hydrogels.

Equilibrium properties and kinetics of metoclopramide release of carbomer-metoclopramide (C-M) hydrogels are reported. A set of (C-M)(X) (x=moles percent of M=50, 75, 100) that covers a pH range between 6.49 and 8.40 was used. Hydrogels exhibited a high negative electrokinetic potential (zeta). Concentrations of ion pair [R-COO(-)MH(+)] and free species [M] and [MH(+)] were determined by the selective extraction of M with 1,2-dichloroethane (DCE) together with pH measurements. The system (C-M) is characterized by a high proportion of drug present in the form of ion pairs and a negative zeta potential that attracts MH(+) and H(+) and repeals OH(-), providing a microenvironment of higher acidity than the bulk medium. Delivery rates of M were measured in a Franz type bi-compartmental device using water and NaCl 0.9% solution as receptor media. (C-M) hydrogels behave as a reservoir that releases the drug at a slow rate to water; the rate increases 14 times as water is replaced by NaCl solution. The pH effect on delivery rate suggests that, under the main conditions assayed, the rate of dissociation of R-COO(-)MH(+) together with the low change of pH in the polyelectrolyte environment are the factors that control releasing rates.

Release kinetics and up-take studies of model fluoroquinolones from carbomer hydrogels.

Hydrogels of carbomer (C) loaded with model slightly soluble fluoroquinolone antimicrobials (AMFQ), norfloxacin (I) and ciprofloxacin (II) were prepared to evaluate their physical and delivery properties. Thus, dispersions of 0.25% of C loaded with 0.2-0.5 mol equivalents of AMFQ and 0.2-0.5 mol equivalents of NaOH yielded pseudoplastic hydrogels with a high negative electrokinetic potential and good physical stability. Concentration of AMFQ in the hydrogels was, respectively, 7.2 and 34 times higher than I and II aqueous solubility, indicating a high increase in aqueous compatibility. Release of AMFQ in bicompartimetal Franz type cell occurred by zero order kinetics. Delivery rate constant (k(0)) was five to six times higher as water was replaced by NaCl solution as receptor medium. Release in agar dishes revealed that, even under high dilution, delivery remains modulated. Intestinal absorption flux coefficient in everted rat intestine (k(U)) were measured with reference solutions (RS) of free AMFQ (k(U)(RS) II>k(U)(RS) I) and with hydrogels (H), in which the pattern was reversed since k(U)(H) I>k(U)(H) II. As expected k(U)(H) II was 0.55 times lower than k(U)(RS) II. However, k(U)(H) I was 1.37 times higher than its reference, which cannot be explained from the analysis of k(0) and k(U)(RS) alone. Hydrogels C-AMFQ behave as a reservoir of AMFQ able to deliver it at a constant rate and would be useful to design topical and or systemic dosage forms.

Dry plant extracts loaded on fumed silica for direct compression: preparation and preformulation.

This paper describes the development of a method to load fumed silica with vegetal material (solid residue) from a liquid extract to obtain a solid loaded silica product (LSP) with satisfactory flow properties and compressibility to be processed by direct-compression technology. Extracts of Melissa officinalis L. (M.o.), Cardus marianus L. (C.m.), and Peumus boldus L. (P.b.) were used to load silica support. The release of boldine from LSP (P.b.) reached 100% in HCl 0.1 N solution and only approximately 70% in water. Some physical-mechanical properties of LSP (M.o. and C.m.) alone and LSP-excipient mixtures were determined. The densities (bulk and tap) of LSP were higher than those of fumed silica alone. Consequently, good flow properties of LSP products were observed. On the other hand, flowability, densities, and compactibility of directly compressible excipients (lactose, dicalcium phosphate dihydrate, and microcrystalline cellulose) were not adversely affected when mixed with LSP.

Formulation of a neutral solution of ciprofloxacin upon complexation with aluminum.

Clear solutions of 0.5 and 1.0% ciprofloxacin (CF) of pH 7.2 were prepared by the addition of aluminum chloride hexahydrate (AlCl3.6H2O) in the molar proportion CF:AlCl3.6H2O (3:1). Minimum inhibitory concentrations (MIC) of these solutions were the same as an equimolar solution of CF.HCl. Solutions exhibited good physical, chemical and microbiological stability and satisfactorily overcame an ocular irritation test on rabbits.

In-vitro activity of new sulphanilil fluoroquinolones against Staphylococcus aureus.

Two new quinolones, NSFQ-104 and NSFQ-105, derivatives of ciprofloxacin and norfloxacin with a 4-(4-aminophenylsulphonyl)-1-piperazinyl at position 7 showed better in-vitro activity against strains of methicillin-susceptible and methicillin-resistant Staphylococcus aureus than ciprofloxacin or norfloxacin. Their in-vitro activity was enhanced at pH 5.5.

Use of differential scanning potentiometry in pharmaceutical analysis.

The use of differential scanning potentiometry (DSP) to assay pure drugs and mixtures is illustrated through a set of model cases. The profiles obtained by scanning glycine (0.3 mmol), sulfanilamide (0.3 mmol), epinephrine (0.06 mmol), and norfloxacin (0.05 mmol) are reported, as well as the areas (A+, A-, and At) obtained in each scan. Such information is useful to assess identity and/or chemical purity and to get the pKa of the ionizing groups of the drugs. The degree of hydrolysis of a parenteral solution of procaine hydrochloride is also determined through DSP as an example of mixture assay. Comparison with conventional aqueous acid-based potentiometry shows that the new technique exhibits much better performance to assay small samples or samples carrying weak acidic and/or basic groups.