M.D. Blanco

Chitosan microspheres in PLG films as devices for cytarabine release.

Cytarabine was included in chitosan microspheres and several of these microspheres were embedded in a poly(lactide-co-glycolide) (PLG) film to constitute a comatrix system, to develop a prolonged release form. Chitosan microspheres, in the range of 92+/-65 microm, having good spherical geometry and a smooth surface incorporating cytarabine, were prepared. The cytarabine amount included in chitosan microspheres was 43.7 microg of ara-C per milligram microsphere. The incorporation efficiency of the cytarabine in microspheres was 70.6%. Total cytarabine release from microspheres in vitro was detected at 48 h. Inclusion of cytarabine-loaded microspheres in poly(lactide-co-glycolide) film initiated a slower release of the drug and, in this way, the maximum of cytarabine released (80%) took place in vitro at 94.5 h. Comatrices, with 8.7 mg of cytarabine, signifying a dose of 34.5 microg/kg, were subcutaneously implanted in the back of rats. Maximum plasma cytarabine concentration was 18.5+/-1.5 microg/ml, 48 h after the device implantation and the drug was detected in plasma for 13 days. The histological studies show a slow degradative process. After 6 months of implantation, most of the microspheres of the matrix seemed to be intact, the comatrix appeared surrounded by conjunctive tissue and small blood vessels and nerve packets were detected in the periphery of the implant.

Cytarabine trapping in poly(2-hydroxyethyl methacrylate) hydrogels: drug delivery studies

The release of cytarabine (ara-c) from poly(2-hydroxyethyl methacrylate) hydrogels cross-linked with different amounts of ethyleneglycol dimethacrylate (EGDMA) has been studied. The drug (range 5-25 mg) was trapped in polymer discs by including it in the feed mixture of polymerization. The drug delivery was followed by HPLC. The release was in accordance with Fickian behaviour. Total release of ara-C was reached after between 3 and 7 days depending on the percentage of EGDMA in the gels. A constant release rate of ara-C from the hydrogels was obtained, the time depending on the degree of cross-linking of the gels: 22 h for gels with 0.5% EGDMA, 32 h for gels with 5% EGDMA and 42 h for gels with 7% EGDMA; the amount of ara-C released being 50%, 80% and 85%, respectively, of the drug load of the gel discs. An increase of the release rate with the disc load was observed for each sort of hydrogel. Neither during the loading of the gels nor right through the drug release was degradation of ara-C observed.

5-Fluorouracil-loaded microspheres prepared by spray-drying poly(D,L-lactide) and poly(lactide-co-glycolide) polymers: Characterization and drug release

5-Fluorouracil (5-FU), a hydrosoluble anti-neoplastic drug, was encapsulated in microspheres of poly(D,L-lactide) (PLA) and poly(lactide-co-glycolide) (PLGA) polymers using the spray-drying technique, in order to obtain small size microspheres with a significant drug entrapment efficiency. Drug-loaded microspheres included between 47 ± 11 and 67 ± 12 µg 5-FU mg−1 microspheres and the percentage of entrapment efficiency was between 52 ± 12 and 74 ± 13. Microspheres were of small size (average diameter: 0.9 ± 0.4–1.4 ± 0.8 µm microspheres without drug; 1.1 ± 0.5–1.7 ± 0.9 µm 5-FU-loaded microspheres) and their surface was smooth and slightly porous, some hollows or deformations were observed in microspheres prepared from polymers with larger Tg. A fractionation process of the raw polymer during the formation of microspheres was observed as an increase of the average molecular weight and also of Tg of the polymer of the microspheres. The presence of 5-FU did not modify the Tg values of the microspheres. Significant interactions between the drug and each one of the polymers did not take place and total release of the included drug was observed in all cases. The time needed for the total drug release (28–129 h) was in the order PLA > PLGA 75/25 > PLGA 50/50. A burst effect (17–20%) was observed during the first hour and then a period of constant release rate (3.52 ± 0.82–1.46 ± 0.26 µg 5-FU h−1 per milligram of microspheres) up to 8 or 13 h, depending on the polymer, was obtained.

Transdermal application of bupivacaine-loaded poly(acrylamide(A)-co-monomethyl itaconate) hydrogels

Bupivacaine, an amide local anaesthetic agent of long-acting and intense anaesthesia, was incorporated into poly(acrylamide(A)-co-monomethyl itaconate (MMI)) hydrogels. The swelling behaviour of two gel compositions, without drug, 75A/25MMI and 60A/40MMI, through rabbit ear skin, mounted on a modified Franz diffusion cell, was studied. Both gel compositions reach the equilibrium swelling degree (88.9+/-0.7 wt.% for 75A/25MMI and 92.5+/-0.1 wt.% for 60A/40MMI). The swelling kinetics was in accordance with the second Ficks Law; diffusion coefficients indicate faster swelling for gels with lower amount of monomethyl itaconic acid. The skin flux of bupivacaine solution through rabbit ear skin was 105+/-24 microg/cm(2)/h, the effective permeability coefficient was 26 x 10(-3)+/-9 x 10(-3)cm/h, and 77+/-15% of bupivacaine was permeated. Bupivacaine-loaded gels allow the drug was permeated through the skin. 47+/-4% and 36+/-3% of the drug amount included in 75A/25MMI and 60A/40MMI hydrogels, respectively, was permeated. The skin flux of the drug was between 90+/-5 and 16+/-7 microg/cm(2)/h depending on the amount of bupivacaine included in the gel and the gel composition. Skin flux increases with the drug load of the gels. Furthermore, as more MMI in the gel slower skin flux of the drug due to bupivacaine-gel interactions.

Anticancer drug, ara-C, release from pHEMA hydrogels

This study investigates the controlled release of cytarabine (ara-C), an anticancer drug, from a polymeric matrix of lightly cross-linked poly(2-hydroxyethyl methacrylate) (pHEMA). The swelling of pHEMA discs in water was analysed as a function of temperature and thickness of xerogel discs. The fractional swelling was linear in (time)1/2 for short time periods. Drug release kinetics were examined as a function of temperature, initial drug load and thickness of pHEMA discs. The fraction of available drug release was also linear in (time)1/2 during the initial stages. These studies allow for the determination of diffusion coefficients for both the transport of water into the hydrogel and ara-C release from the polymer.

Tamoxifen‐loaded thiolated alginate‐albumin nanoparticles as antitumoral drug delivery systems

Nanoparticles based on disulfide bond reduced bovine serum albumin and thiolated alginate (alginate-cysteine conjugate) have been prepared by coacervation method and have been loaded with tamoxifen (TMX). The TMX load into the nanoparticles was optimized (4-6 μg/mg NP) by freeze-drying the systems before the loading procedure. Maximum TMX release (45-52%) took place between 2 and 25 h. Cytotoxicity of unloaded nanoparticles in MCF-7 and HeLa cells was not observed, although a small decrease in viability took place at very high concentration. Cell uptake of nanoparticles occurred in both cell types and the presence of polysaccharide in the nanoparticle composition allowed a better interaction with cells. The administration of 10 μM TMX by TMX-nanoparticles was effective in both cellular lines, and the effect of the drug-loaded systems on MCF-7 cell cycle showed the efficacy of the TMX-loaded nanoparticles.

Cytarabine release from comatrices of albumin microspheres in a poly(lactide-co-glycolide) film: in vitro and in vivo studies

Cytarabine (ara-C) was included in albumin microspheres and these microspheres were immersed in a poly(lactide-co-glycolide) (PLGA) film to constitute a comatrix system to develop a prolonged form of release. Cytarabine-loaded albumin microspheres were synthesized by emulsion, and 25 or 50 mg of drug were included in the disperse phase. Thus, microspheres with 46+/-4 microg drug/mg microspheres and 50+/-5 microg drug/mg microspheres were obtained, which means a percentage of incorporation efficiency of 42+/-4% and 25+/-2%, respectively. These cytarabine-loaded microspheres were used to prepare PLGA-comatrices. Kinetic release studies indicated that total cytarabine release only takes place in the presence of protease, probably due to the fact that glutaraldehyde establishes covalent links with the amine side group of the drug and cross-links it with the protein matrix. A slower kinetic release of the drug was obtained from PLGA-comatrices, although only 80% of the included cytarabine was released on day 7. The comatrices were subcutaneously implanted in the back of rats and in both cases the ara-C administered dose was 36 mg of ara-C per kg of body weight. The drug was detected in plasma 10 days. The mean residence time (MRT) of the drug administered by these comatrices was 87-91 times larger when compared to the value obtained when the drug was administered in solution by intraperitoneal injection. The histological studies show that a degradative process of the comatrices takes place. The comatrices do not damage surrounding tissue; a normal regeneration of the implanted zone was observed.

In-vivo Drug Delivery of 5-Fluorouracil using Poly(2-hydroxyethyl methacrylate-co-acrylamide) Hydrogels

Poly(2‐hydroxyethyl methacrylate‐co‐acrylamide) hydrogels crosslinked with ethylen glycol dimethacrylate were used as devices for the in‐vivo drug release of 5‐fluorouracil (5‐FU).

Effects of lead administration at low doses by different routes on rat spleens. Study of response of splenic lymphocytes and tissue lysozyme

The aim of this study was to evaluate the effects of low doses of lead (200 ppm of PbAc(2) for 4 weeks) on rat spleens using different routes of administration. The study has been carried out at different levels: a histological evaluation has been made, and alterations of cell proliferation, B and T lymphocyte subpopulations, and CD4(+) and CD8(+) T cell subpopulations have been evaluated. Apoptosis and necrosis of lymphoid cells were also analysed. Furthermore, lysozyme activity was measured. Results indicate a large increase in spleen size when lead is administered by intraperitoneal injection, being this route in which lead causes larger modifications in all of the parameters measured. Lead administered orally causes histological modifications, such as an increase in the number of lymphocytes as well as edema. However, significant alterations in other parameters studied have not been detected. Lead administration by intraperitoneal route causes more evident histological modifications as well as an increase in the number of lymphocytes, and also induces a decrease in the percentage of B(+), T(+) and CD4(+) cells, and an increase in CD8(+) cells. Cell death of splenic lymphocytes is not altered by lead. With regard to the immune innate response, lead behaves as an immunomodulator as can be deduced from data on lysozyme activity in tissue. Therefore, it is possible to affirm that the effect of low doses of lead depends on the route of administration. Thus, the intraperitoneal route, through which lead goes directly to the bloodstream, causes drastic effects, generating important immunological alterations.

Sustained release of bupivacaine from devices based on chitosan.

Chitosan beads loaded with bupivacaine (16+/-3 microg of drug per milligram of beads) were prepared by cross-linking with glutaraldehyde. In vitro drug release at pH and temperature conditions similar to those of the biological systems were studied. Maximum release of bupivacaine was obtained between 100 and 120 h, depending on the presence of lysozyme in the release medium, since the enzyme facilitates the release process. A constant release rate of the drug, between 11 and 15 microg/h, was observed for 30 h. In order to prolong bupivacaine release, the drug-loaded chitosan beads were coated with a poly(DL-lactide-co-glycolide) film. The resulting device allows the drug to be released in a sustained form; a constant release rate between 28.5 and 29.5 microg/h was obtained for 3 days, and the maximum release of bupivacaine took place at day 9. The in vitro results indicate a possible application of these bupivacaine loaded chitosan systems as drug release devices with an analgesic action. Thus, they could be used in the treatment of dental pain in the buccal cavity, where drug release would be made easier by lysozyme of the saliva.