Current Drug Delivery - Volume 5, Issue 4, 2008

The use of particulate polymeric carriers holds great promise for the development of effective and affordable DNA and protein subunit vaccines. Rational development of such vaccine formulations requires a detailed understanding of their physico-chemical properties, cell-free and in vitro behaviour, in addition to particle uptake and processing mechanisms to antigen presenting cells capable of stimulating safe and effective immune responses. We here provide an overview on functional polymeric nano- and micro-particles designed for surface adsorption of proteins and DNA antigens currently under investigation for the formulation of new vaccines, including comments on their preparation method, antigen delivery strategy, cell-free and in vitro behaviour. In addition, we focus on their influence in activating antigen-specific humoral and/or cellular immune responses and on their potential for the development of new vaccines.

Medicinal cannabis, cannabis extracts, and other cannabinoids are currently in use or under clinical trial investigation for the control of nausea, emesis and wasting in patients undergoing chemotherapy, the control of neuropathic pain and arthritic pain, and the control of the symptoms of multiple sclerosis. The further development of medicinal cannabinoids has been challenged with problems. These include the psychoactivity of cannabinoid CB1 receptor agonists and the lack of availability of highly selective cannabinoid receptor full agonists (for the CB1 or CB2 receptor), as well as problems of pharmacokinetics. Global activation of cannabinoid receptors is usually undesirable, and so enhancement of local endocannabinoid receptor activity with indirect cannabimimetics is an attractive strategy for therapeutic modulation of the endocannabinoid system. However, existing drugs of this type tend to be metabolized by the same enzymes as their target endocannabinoids and are not yet available in a form that is clinically useful. A potential solution to these problems may now have been suggested by the discovery that paracetamol (acetaminophen) exerts its analgesic (and probably anti-pyretic) effects by its degradation into an anandamide (an endocannabinoid) reuptake inhibitor (AM404) within the body, thus classifying it as prodrug for an indirect cannabimimetic. Given the proven efficacy and safety of paracetamol, the challenge now is to develop related drugs, or entirely different substrates, into pro-drug indirect cannabimimetics with a similar safety profile to paracetamol but at high effective dose titrations.

This work is focused on the development of controlled drug delivery systems using different wax/fat embedded indomethacin (IM). Discrete wax/fat embedded microspherules containing indomethacin were prepared by using cetostearyl alcohol, paraffin wax and stearic acid by employing emulsification-phase separation method. These matrices have been used as barrier coatings due to their hydrophobic nature. Chemically inert and tasteless nature of wax/fats promotes their use as taste masking agents for bitter drugs. Various waxes and fats are available having different physicochemical properties to suit the needs of formulation. Methyl cellulose (MC) 1% w/v, sodium alginate (SA) 0.5% w/v and Tween-80 (TW) 1% w/v were used as emulgents. The resulting microspherules were discrete, large, spherical and also free flowing. It is revealed from the literature that natures of wax/fat emulgents were found to influence the rate of drug release. In the present work the drug content in all the batches of microspherules were found to be uniform. The rate of drug release corresponded best to first order kinetics, followed by Higuchi and zero-order equations. The release of the model drug from these wax/fat microspherules was prolonged over an extended period of time and the drug release mechanism followed anomalous (non-Fickian) diffusion controlled as well as Super Case II transport. Among the three matrix materials used, paraffin wax retarded the drug release more than the other two. Surface characteristics of microspherules have been studied by Scanning Electron Microscope (SEM). A fair degree rank of correlation was found to exist between the size and release retardation in all the three-wax/fat emulgent combinations.

Novel pH-sensitive carboxymethylcellulose-(polyacrylamide-grafted-sodium alginate) interpenetrating network (IPN) hydrogel beads loaded with ketoprofen were prepared using ionotropic gelation and covalent crosslinking method. Polyacrylamide-graftedsodium alginate (PAAm-g-SA) copolymer was synthesized by free radical polymerization using ammonium persulfate (APS) as free radical initiator under the nitrogen atmosphere followed by hydrolysis using sodium hydroxide. The grafting, alkaline hydrolysis and crosslinking reactions were confirmed by Fourier transform infrared spectroscopy (FTIR). Beads were characterized by differential scanning calorimetric (DSC) analysis, thermogravimetric analysis (TGA), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The mechanical properties of the prepared IPNs were investigated. The erosion was observed with the beads containing only ionic crosslinks whereas it was negligible with the beads containing both ionic and covalent crosslinks. The swelling of the beads and drug release was significantly increased when pH of the medium was changed from acidic to alkaline (P<0.05). The swelling and release data were fitted to an empirical equation to determine the transport mechanism. Drug release followed case II transport mechanism in acidic medium whereas anomalous/non-Fickian transport mechanism was observed in alkaline medium.

A method for developing sustained release multiple unit dosage form consisting of pellets of a proteolytic enzyme blend using extrusion spheronization as a process is demonstrated in this paper. Effect of Cellulose and Methacrylate based polymers and plasticizers on stability of the enzyme blend are determined. The effect of type & concentration of the sustained release polymer, spheronization rpm and plasticizer on the yield & sphericity of pellets is studied. The results indicated that the SR pellets could be formulated for this enzyme blend using both HPMC K15 and EUDRAGIT® RSPO. The best rpm for spheronization turned out to be 1200 rpm. Use of plasticizer improved yield and sphericity. Triethyl citrate was better over polyethylene glycol 400 and EUDRAGIT® RSPO was better over HPMC K15 with respect to yield and sphericity of pellets. The pellets could be suitably enteric coated for protection of enzyme blend in lower pH of GIT. The in vitro release profile indicated release extension could be extended up to 12 hours in intestinal condition postulating to an acceptable bioavaliablity in vivo.

The present study was aimed at in vitro and in vivo evaluation of PEGylated elastic liposomal formulation for lymphatic targeting of zidovudine (AZT). PEGylated elastic liposomal formulation was prepared and characterized for characteristic in vitro, ex-vivo and in vivo parameters. The plain and PEGylated elastic liposomal formulation showed transdermal flux of 99.8±5.8 and 119.5±5.2 μg/cm2/hr, respectively across the rat skin. Results of biodistribution study indicated 27-fold higher accumulation of AZT in lymphoid tissues after application of PEGylated elastic liposomes as compared to free drug. The efficient localization of elastic liposomal formulation in lymphatic system is of particular interest for HIV therapy, taking in account that replication of HIV mainly takes place in the lymphoid system. The Cellular uptake studies showed significantly higher cellular uptake in lymphoid cells (MT-2 cell line) from PEGylated elastic liposomal formulation (88.9±8.7%) in comparison to phosphate buffer saline (PBS, pH 7.4) solution of drug (27.1±2.8%). The entrapment of AZT into PEGylated elastic liposomes represents a potential approach for overcoming the toxicity by its selective uptake in lymphoid organs. This represents attractive approach for sustained and targeted delivery of AZT.

Inspite of the various impediments in the bioavailability of orally delivered drugs, oral dosage forms, both solid and liquid, occupy a center stage in the therapeutic regimen of diseases. However, liquid dosage forms are more prone to low bioavailability because of their quick transit from the stomach/ duodenum. This could be a serious problem for drugs, which are absorbed from these sites of the GIT. The gastric retention of an oral liquid formulation could be successfully augmented substantially through a strategy of liquid in-situ gelling system. Natural polymers like alginate, gellan and chitosan can undergo sol to gel transformation in the presence of either divalent cations or due to a change in pH. The gel so formed, being lighter than gastric fluids, floats over the stomach contents and is retained there in for periods upto 24 hours. The in-situ gel formation enhances the local or systemic bioavailability of the administered drug. This concept is a redesign of liquid oral dosage form, which fulfills the requirement for a sustained release liquid preparation. This review discusses the various aspects associated with the in-situ gelling systems and their therapeutic applications.

Glimepiride is a third generation oral antidiabetic sulphonylurea drug frequently prescribed to patients of type 2 diabetes. However, its oral therapy is encountered with bioavailability problems due to its poor solubility leading to irreproducible clinical response, in addition to adverse effects like dizziness and gastric disturbances. As a potential for convenient, safe and effective antidiabetic therapy, the rationale of this study was to develop a transdermal delivery system for glimepiride. Chitosan polymer was utilized in developing transdermal films for glimepiride. Chitosan has film forming ability, bioadhesive and absorption enhancing properties. Aiming at optimizing the drug delivery and circumventing the skin barrier function, inclusion complexation of glimepiride with beta-cyclodextrin (β-CyD) as well as the use of several conventional penetration enhancers were monitored for augmenting the drug flux. The physical and mechanical properties of the prepared films were investigated using tensile testing, IR spectroscopy and X-ray diffractometry. Release studies revealed adequate release rates from chitosan films. Permeation studies through full thickness rat abdominal skin were conducted. High flux values were obtained from films comprising a combination of the drug with limonene and ethanol as well as from films containing glimepiride-β-CyD complex. In vivo studies on diabetic rats for selected formulae revealed a marked therapeutic efficacy sustained for about 48 hours. The above-mentioned results shed light on feasibility of utilizing chitosan as an effective, safe transdermal delivery system for glimepiride characterized by increased patient compliance and better control of the disease.

The asialoglycoprotein receptor (ASGPR), an endocytotic cell surface receptor expressed by hepatocytes, is triggered by triantennary binding to galactose residues of macromolecules such as asialoorosomucoid (ASOR). The capacity of this receptor to import large molecules across the cellular plasma membrane makes it an enticing target for receptor-mediated drug delivery to hepatocytes and hepatoma cells via ASGPR-mediated endocytosis. This study describes the preparation and characterization of 125I-ASOR, and its utility in the assessment of ASGPR expression by HepG2, HepAD38 and Huh5-2 human hepatoma cell lines. ASOR was prepared from human orosomucoid, using acid hydrolysis to remove sialic acid residues, then radioiodinated using iodogen. 125I-ASOR was purified by gel column chromatography and characterized by SDS-PAGE electrophoresis. The ASOR yield by acid hydrolysis was 75%, with ∼87 % of the sialic acid residues removed. Electrophoresis and gel chromatography demonstrated substantial differences in 125I-ASOR quality depending on the method of radioiodination. ASGPR densities per cell were estimated at 76,000 (HepG2), 17,000 (HepAD38) and 3,000 (Huh- 5-2). 125I-ASOR binding to ASGPR on HepG2 cells was confirmed through galactose- and EDTA- challenge studies. It is concluded that 125I-ASOR is a facilely-prepared, stable assay reagent for ASGPR expression if appropriately prepared, and that HepG2 cells, but not HepAD38 or Huh-5-2 cells, are suitable for studies exploiting the endocytotic ASGPR.

Serrapeptase is an anti-inflammatory, proteolytic enzyme isolated from the microorganism, Serratia sp. HY-6. Very few methods are available for the quantification of serrapeptase. The activity of the enzyme is determined by an ELISA assay, colorimetric method using casein as substrate or by HPLC method. These methods are lengthy, time consuming and require a number of reagents and solvents. Therefore an attempt was made to develop a simple alternative method for regular estimation of drug in formulations. Serrapeptase enzyme was estimated in formulations by using microplate readers which uses the principle of vertical photometry. Further this method was validated and the robustness of this method was checked by estimating the drug in various formulations including liposomes and marketed tablet formulations. A linear relationship between drug concentration and absorbance was observed between 1-4 μg/ml at 230 nm (R2=0.9911). The percentage recovery values of the drug in serrapeptase liposomes were found to lie within the standard limit (97- 98%) which confirms the method is accurate and free from any positive or negative interference of the excipient. The low value of standard deviation obtained confirms the precision of the method. (±0.020 - ±0.044). The drug content values in marketed tablets values obtained matched the label claim. The proposed microplate UV-method for determination of serrapeptase in formulations is novel, simple, inexpensive, fast, specific and robust. Thus this method could be a better alternative for regular estimation of drug in the various marketed formulations of serrapeptase.

Elementary osmotic pumps (EOP) are well known for delivering moderately soluble drugs at a zero order rate. A push-pull osmotic system was developed and commercialized for poorly water-soluble drugs [Procardia XL (Nifedipine), Glucotrl XL (Glipizide)]. However, the technology is complex comprising of bilayer compression and the suspension of drug formed in the core has more viscosity and has to withstand the osmotic pressure within the tablet, for which the membrane must be thicker than that of EOP. The aim of the present study was to develop a solid dispersion based EOP system for a poorly water-soluble drug, nifedipine and deliver it in a zero order fashion over an extended period of time. Solid dispersions were prepared by hot melt technique using Poloxamer-188 at various ratios of drug and polymer (1:1, 1:5 and 1:10, on weight basis) and investigated for solubility study. Formation of complex and decrease in crystallinity was confirmed from differential scanning calorimetry (DSC) and X-ray crystallography (XRD) study. Core tablets using solid dispersions were prepared and coated with cellulose acetate and PEG-400. An orifice was drilled manually to create passage for drug release. The system was optimized for amount of osmogent, membrane weight gain, amount of plasticiser and diameter of the orifice, to achieve desired release profile. The osmotic system was found to deliver nifedipine at a zero order rate for 20 h. The drug release from the developed formulation was independent of pH and agitational intensity.

Mucoadhesive polymers have recently gained interest among pharmaceutical scientists as a means of improving drug delivery by promoting the residence time and contact time of the dosage form with the mucous membranes. Mucoadhesion is the process whereby synthetic and natural polymers adhere to mucosal surfaces in the body. If these materials are then incorporated into pharmaceutical formulations, drug absorption by mucosal cells may be enhanced or the drug will be released at the site for an extended period of time. Microspheres, in general, have the potential to be used for targeted and controlled release drug delivery; however, coupling of mucoadhesive properties to microspheres has additional advantages like, a much more intimate contact with the mucus layer, efficient absorption and enhanced bioavailability of the drugs due to a high surface to volume ratio. The present review describes the potential applications of mucoadhesive microspheres as a novel carrier system to improve drug delivery by various routes of administration like buccal, oral, nasal, ocular, vaginal and rectal, either for systemic or for local effects. The mucoadhesive polymers, methods of preparation of microspheres and their in vitro and in vivo evaluation are also described.

Cetrorelix is a GnRH antagonist of the third generation. Its manifold therapeutic potential requires the adjustment of its resorption rates and effect profiles. The method of non-covalent complexation with suitable partner molecules enables the development of customized depot formulations. Investigating new partners and synthesis methods for Cetrorelix complexes we focused on maximal biocompatibility of the complexes. Compared to traditional depot forms the application of complexes aims at decreased aggregation of the peptide and increased biophily of the depots. The pharmacological properties of the new Cetrorelix complexes were analyzed by standardized dynamical in vitro liberation experiments. A new pharmacokinetic model has been developed and successfully applied for the quantitative analysis of the liberation profiles. With aromatic carboxylic acids and dipeptides we could synthesize stable complexes that have nearly linear release characteristics in aggregating environments close to in vivo conditions. The release rates were specific and very different for the complex partners. Thus several complexes have a great potential for a linear, characteristic release of the peptide in vivo and can be the basis for new depot forms for Cetrorelix.

The first generation of solid lipid carrier systems in nanometer range, Solid Lipid Nanoparticles (SLN), was introduced as an alternative to liposomes. SLN are aqueous colloidal dispersions, the matrix of which comprises of solid biodegradable lipids. SLN are manufactured by techniques like high pressure homogenization, solvent diffusion method etc. They exhibit major advantages such as modulated release, improved bioavailability, protection of chemically labile molecules like retinol, peptides from degradation, cost effective excipients, improved drug incorporation and wide application spectrum. However there are certain limitations associated with SLN, like limited drug loading capacity and drug expulsion during storage, which can be minimized by the next generation of solid lipids, Nanostructured lipid carriers (NLC). NLC are lipid particles with a controlled nanostructure that improves drug loading and firmly incorporates the drug during storage. Owing to their properties and advantages, SLN and NLC may find extensive application in topical drug delivery, oral and parenteral administration of cosmetic and pharmaceutical actives. Cosmeceuticals is emerging as the biggest application target of these carriers. Carrier systems like SLN and NLC were developed with a perspective to meet industrial needs like scale up, qualification and validation, simple technology, low cost etc. This paper reviews present status of SLN and NLC as carrier systems with special emphasis on their application in Cosmeceuticals; it also gives an overview about various manufacturing techniques of SLN and NLC.

Gastroretentive drug delivery systems (GRDDS) of Ranitidine hydrochloride (RHC) has been designed based on the osmotic technology, with the floating and swelling features in order to prolong the gastric retention time. The developed system consisted of osmotic core (containing drug, osmotic agent and hydrophilic polymers), coated with semipermeable membrane (SPM) which is then further coated with compression coating of gelling agent (HPMC K4M) containing gas generating agent (citric acid). All the developed formulations were evaluated for floating lag time, duration of floating, drug content and in-vitro drug release profile. Formulation variables like levels of hydrophilic polymer (0-18.26%w/w), type of plasticizer (PEG-400, Dibutyl phthalate), coat thickness of SPM (60-100μm), were found to affect the drug release from the developed formulations. Drug release was directly proportional to hydrophilic nature of plasticizer but inversely proportional to the levels of hydrophilic polymer and coat thickness of SPM. Drug release from developed formulations was independent of level of gas generating agent in compression coat, pH and agitation intensities of release media but dependent on osmotic pressure of the release media. All the developed formulation showed floating lag time of less than 2 min (desired) and were floated for more than 12 hr. Floating lag time was inversely related to level of citric acid in compression coat and directly related to the density of the developed formulations. The manufacturing procedure was found to be reproducible and formulations were stable after 3 months accelerated stability study. Prediction of steady state levels showed the plasma concentrations of RHC to be within desired range.