Browsing by Author "Lakshmi, S"

Now showing 1 - 11 of 11
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    A floating-type oral dosage form for piroxicam based on hollow polycarbonate microspheres: In vitro and in vivo evaluation in rabbits
    (JOURNAL OF CONTROLLED RELEASE, 2002)
    A floating type dosage form (FDF) of piroxicam in hollow polycarbonate (PC) microspheres capable of floating on simulated gastric and intestinal fluids was prepared by a solvent evaporation technique. Incorporation efficiencies of over 95% were achieved for the encapsulation. In vitro release of piroxicam from PC microspheres into simulated gastric fluid at 37 C showed no significant burst effect. The amount released increased with time for about 8 h after which very little was found to be released up to 24 h. In intestinal fluid, the release was faster and continuous and at high drug payloads, the cumulative release reached above 90% in about 8 h. In vivo evaluation of different dosage forms of piroxicam such as free drug, drug-encapsulated microspheres and microspheres along with a loading dose of free drug in rabbits showed multiple peaking in the plasma concentration-time curve suggesting enterohepatic recirculation of the drug. Pharmacokinetic analysis showed that the bioavailability from PC microspheres alone was about 1.4 times that of the free drug and it was about 4.8 times for the dosage form consisting of the microspheres plus the loading dose. The elimination half life was increased by about three times for the microsphere preparation alone and nearly about six times for the dosage form comprising of microspheres and a loading dose in comparison to the free drug. Data obtained in this study demonstrated that FDF of piroxicam in PC microspheres was capable of sustained delivery of the drug for longer periods with increased bioavailability. (C) 2002 Elsevier Science B.V. All rights reserved.
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    Bacterial adhesion onto azidated poly(vinyl chloride) surfaces
    (JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, 2002)
    A plasticized poly(vinyl chloride) surface was modified by azidation using sodium azide in the presence of a phase transfer catalyst in aqueous media. Subsequent to azidation, the surface was crosslinked using ultraviolet radiation. Contact angle measurements showed that the surface became hydrophilic on azidation whereas photoirradiation did not have any further effect on the hydrophilicity of the azidated surface. Control, azidated, and photo-crosslinked surfaces were exposed to two strains of bacteria commonly implicated in device infection such as Staphylococcus aureus and Escherichia coli. Whereas the control and photocrosslinked surfaces showed no significant difference in bacterial adhesion, the azidated surface showed significantly reduced adhesion to both strains. Data obtained indicate that the presence of an intact azide function on the polymer Surface is responsible for the reduced bacterial adherence and the surface hydrophobicity/hydrophilicity did not exert any effect in the present case. Although azides are known to be effective only against Gram-negative species, surprising was the observation that the azidated polymer surface was equally effective against a Gram-positive species such as S. aureus. Because sodium azide is routinely used as a preservative to prevent bacterial and fungal growth in many microbiology reagents and diagnostic kits, covalent binding of the azide onto a polymer surface or synthesizing azide containing polymers may be an interesting method to investigate in tackling the problem of bacterial adhesion and colonization of medical devices. (C) 2002 Wiley Periodicals, Inc.
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    Immobile plasticizer in flexible PVC
    (NATURE, 1998) Jayakrishnan, K; Lakshmi, S
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    Iodination of plasticized poly(vinyl chloride) in aqueous media via phase transfer catalysis
    (JOURNAL OF APPLIED POLYMER SCIENCE, 2002) Lakshmi, S; Jayakrishnan, A
    Nucleophilic substitution of chlorine on plasticized poly(vinyl chloride) (PVC) was carried out using potassium iodide (KI) in the presence of a phase transfer catalyst (PTC) in aqueous media. Iodination was confirmed using energy dispersive X-ray analysis (EDAX). The extent of iodination was studied with respect to time, temperature, concentration of the reactants, as well as different PTCs. Among the different PTCs examined, tetrabutylammonium bromide (TBAB) and tetrabutylammonium hydrogen sulfate (TBAH) were found to be highly efficient for the reaction. About 25% increase in weight was observed for PVC sheets iodinated under optimal reaction conditions. The thermal stability of the modified PVC was found to be impaired upon iodination. The iodinated PVC released iodide ions when kept in distilled water, as evidenced by UV spectroscopy. Sustained release of iodide ion in distilled water was followed up for about 30 days. (C) 2002 John Wiley Sons, Inc.
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    Metabolic Modulation by Medium-Chain Triglycerides Reduces Oxidative Stress and Ameliorates CD36-Mediated Cardiac Remodeling in Spontaneously Hypertensive Rat in the Initial and Established Stages of Hypertrophy
    (J Cardiac failure, 2017-03) Ismael, S; Lakshmi, S; Remani, K; Nair, RR
    Background: Left ventricular hypertrophy (LVH) is characterized by a decrease in oxidation of longchain fatty acids, possibly mediated by reduced expression of the cell-surface protein cluster of differentiation 36 (CD36). Spontaneously hypertensive rats (SHRs) were therefore supplemented with medium-chain triglycerides (MCT), a substrate that bypasses CD36, based on the assumption that the metabolic modulation will ameliorate ventricular remodeling. Methods: The diet of 2-month-old and 6-month-old SHRs was supplemented with 5% MCT (Tricaprylin), for 4 months. Metabolic modulation was assessed by mRNA expression of peroxisome proliferator– activated receptor α and medium-chain acyl-CoA dehydrogenase. Blood pressure was measured noninvasively. LVH was assessed with the use of hypertrophy index, cardiomyocyte cross-sectional area, mRNA expression of B-type natriuretic peptide, cardiac fibrosis, and calcineurin-A levels. Oxidative stress indicators (cardiac malondialdehyde, protein carbonyl, and 3-nitrotyrosine levels), myocardial energy level (ATP, phosphocreatine), and lipid profile were determined. Results: Supplementation of MCT stimulated fatty acid oxidation in animals of both age groups, reduced hypertrophy and oxidative stress along with the maintenance of energy level. Blood pressure, body weight, and lipid profile were unaffected by the treatment. Conclusions: The results indicate that modulation of myocardial fatty acid metabolism by MCT prevents progressive cardiac remodeling in SHRs, possibly by maintenance of energy level and decrease in oxidative stress. (J Cardiac Fail 2017;23:240–251)
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    Migration resistant, blood-compatible plasticized polyvinyl chloride for medical and related applications
    (ARTIFICIAL ORGANS, 1998)
    Plasticized polyvinyl chloride (PVC), although not a blood-compatible polymer, is the material of choice for the manufacture of blood bags and hemodialysis tubing throughout the world. PVC is usually plasticized with di-(2-ethylhexyl phthalate) (DEHP) to impart flexibility and low temperature properties to the final product. DEHP belongs to a class of agents called hypolipidemic hepatocarcinogens, and it migrates in small quantities into the storage medium such as blood, plasma, or serum, resulting in a number of toxic effects. It has been shown that the migration resistance and blood compatibility of flexible PVC could be significantly improved by grafting polyethylene glycol (PEG), the most blood-compatible polymer known today, onto the surface of flexible PVC by the classical Williamson ether synthesis reaction. The technique is simple and versatile enough to produce blood-compatible, migration resistant PVC surfaces for many medical applications. The method may also find use for preventing plasticizer migration from PVC cling films and polyvinylidene chloride films used extensively in food packaging.
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    Photocross-linking of dithiocarbamate-substituted PVC reduces plasticizer migration
    (POLYMER, 1998) Lakshmi, S; Jayakrishnan, A
    Medical grade poly(vinyl chloride) (PVC) sheets and tubes were surface modified by nucleophilic substitution of chlorine atoms of PVC by photoactive N,N-diethyl dithiocarbamate (DTC) in aqueous media in the presence of a suitable phase transfer catalyst (PTC) at 55 degrees C. The modified surface was cross-linked by irradiation with u.v. light in an attempt to create a barrier for the diffusion of the plasticizer di-(2-ethylhexyl phthalate) (DEHP). Of the various PTCs examined for the reaction, tetrabutyl ammonium salts were found to be very effective, whereas crown ethers such as 18-crown-6 was least effective. The effect of concentration of PTC and DTC, time of reaction and irradiation dose on the extent of plasticizer migration was examined in petroleum ether for various periods of time at 30 degrees C. The migration of DEHP from PVC modified under optimum conditions was less than 5% in 120 h, whereas the unmodified PVC lost virtually all its plasticizer (> 30%) during the same period. Determination of the stress-strain properties of modified PVC sheets showed a reduction of approximately 30%. However, the values were still within the range prescribed for vinyl chloride plastics used for medical applications. (C) 1997 Elsevier Science Ltd.
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    Preparation and evaluation of photocrosslinkable chitosan as a drug delivery matrix
    (JOURNAL OF APPLIED POLYMER SCIENCE, 2002) Jameela, SR; Lakshmi, S; James, NR; Jayakrishnan, A
    Epichlorohydrin (1-chloro-2,3-epoxypropane) was reacted with sodium azide in the presence of a phase transfer catalyst to obtain 1-cliloro-2-hydroxy-3-azidopropane, which was further coupled onto chitosan to prepare. a photocrosslinkable derivative of the biopolymer. Elemental analysis and infrared (IR) spectroscopy confirmed the incorporation of azide groups onto chitosan. Films were cast from an aqueous acetic acid solution of azidated chitosan containing a model drug, such as theophylline. Irradiation of the film with ultraviolet (UV) light led to crosslinking of the drug incorporated film. IR spectra indicated complete surface crosslinking within 2 h of irradiation. Release of theophylline from uncrosslinked and crosslinked films was examined in simulated gastric and intestinal fluids without enzymes at 37 degreesC. The release of the drug from the crosslinked films was slower than the release from uncrosslinked films. Although the system is far from being optimized to obtain sustained release of a pharmacologically active agent for long periods, the data obtained indicate the possibility of developing photocrosslinkable matrices of biopolymers, such as chitosan, for sustained drug delivery with many advantages over chemical crosslinking. (C) 2002 Wiley Periodicals, Inc.
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    Properties and performance of sulfide-substituted plasticized poly(vinyl chloride) as a biomaterial
    (JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART B-APPLIED BIOMATERIALS, 2003)
    Plasticized poly(vinyl chloride) (PVC) was surface modified by nucleophilic substitution of the chlorine atoms of PVC by sulfide ions in aqueous media in the presence of a phase-transfer catalyst (PTC) to make it migration resistant. The modified PVC was sterilized by steam autoclaving and gamma radiation and subjected to plasticizer extraction in an extraction medium such as hexane. Virtually no plasticizer migrated out of modified PVC into the medium even after prolonged incubation for 30 d. The properties of the modified surface were evaluated by contact angle measurements, scanning electron microscopy (SEM), cell-culture studies, hemolysis assay, and whole-blood clotting time measurements. The mechanical properties of modified sheets were evaluated by measurements of tensile strength and strain at break after subjecting the specimens to different modes of sterilization. The modified PVC surface showed enhanced wettabillity and was found to be non-hemolytic and non-cytotoxic. Whole-blood clotting profiles of unmodified and modified PVC were virtually the same. Modification imparted slight yellow color to the material. Surface modification resulted in an 8% decrease in the ultimate stress and 28% decrease in the strain at break values. The sulfide-substituted PVC was found to be blood compatible and would be useful in applications such as tubing for transfusion, dialysis etc., where migration resistance is important. (C) 2003 Wiley Periodicals, Inc.
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    Synthesis and polymerization of a new iodine-containing monomer
    (JOURNAL OF APPLIED POLYMER SCIENCE, 2003) Lakshmi, S; James, NR; Nisha, VS; Jayakrishnan, A
    A new iodine-containing methacrylate monomer, 3,4,5-triiodobenzoyloxyethyl methacrylate (TIBEM), was synthesized by coupling 2-hydroxyethyl methacrylate (HEMA) with 3,4,5-triiodobenzoic acid. The monomer was characterized by H-1 nuclear magnetic resonance, infrared (IR), and ultraviolet spectra. Homopolymerization and copolymerization of the monomer with methyl methacrylate (MMA) were carried out using 2,2'-azobis isobutyronitrile as the initiator. A terpolymer of TIBEM, MMA, and HEMA was also synthesized. The copolymers were characterized by IR, gel permeation chromatography, differential thermal analysis, and thermogravimetric analysis (TGA). High molecular weight polymers were produced with MMA at different feed compositions of TIBEM. The polymers were found to be freely soluble in common solvents for acrylic polymers. TGA showed little decomposition of the copolymer below 280degreesC. Copolymers showed good radiopacity at 25 wt % of TIBEM in the feed. These copolymers could find applications in medical and dental areas where radiopacity is a desirable feature of the implants. (C) 2003 Wiley Periodicals, Inc.
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    Synthesis, surface properties and performance of thiosulphate-substituted plasticized poly(vinyl chloride)
    (BIOMATERIALS, 2002)
    Plasticized poly(vinyl chloride) (PVC) was surface modified by nucleophilic substitution of the chlorine atoms of PVC by thiosulphate in aqueous media in the presence of a phase-transfer catalyst. The properties of the modified surface were evaluated by contact angle measurements, attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. Migration of the plasticizer di-(2-ethylhexyl) phthalate from control as well as modified PVC was examined in hexane, in cottonseed oil and in poly(ethylene glycol)-400 (PEG-400). While the modified PVC was found to be highly migration resistant in hexane, cottonseed oil and PEG-400 extracted the plasticizer. The modified PVC was found to cause haemolysis and was cytotoxic. A possible explanation for the difference in performance of the modified material in different extraction media and its toxicity is presented from a mechanistic view of the substitution process. (C) 2002 Elsevier Science Ltd. All rights reserved.