Current developments using emerging transdermal technologies in physical enhancement methods

Transdermal drug delivery using patches offers many advantages, but is limited primarily by the stratum corneum barrier. Amongst the various methods to overcome this barrier, physical methods are gaining in popularity and commercial devices development. Macroflux, MTS and Silex are based on microporation, involving use of microneedles that pierce thereby bypassing the stratum corneum. Intraject , Powderject and Helios are based on needleless jet injectors wherein very fine, solid particulate drug, is fired directly into the skin, using high-pressure gas. Med- Tats incorporate use of modified drug-containing tattoos, which bind to the skin, wherein the drug is absorbed. CHADD is based on use of heat, which increases skin - permeation of drugs. High-power, pulsed lasers transmit positive mechanical forces to the skin and create intercellular channels into the skin transiently. Sonophoresis involves use of ultrasound, which transiently disrupts the stratum corneum barrier. This technique offers a non-invasive transdermal extraction of interstitial fluids of sampling body fluids. Modified Liposomes include Ethosomes (containing alcohol) and Transferosomes (containing surfactants), which have enhanced skin permeability. Pulsed magnetic fields may create transient pores in cell membranes, including skin, resulting in increased permeation. Iontophoresis is based on application of electric potential for enhancing the movement of substances to and from the body. Dupel, Ionzyme, Liposite, ETrans, Phoresor and Drionic are based on iontophoresis. GlucoWatch offers non-invasive blood glucose monitoring, based on reverse iontophoresis. This review outlines recent commercial developments in physical transdermal drug delivery technology and the specific devices and applications being targeted by the pharmaceutical industry.

Exposure to alcohol-containing medications during pregnancy

QUESTION

A pregnant patient consulted her physician after discovering that a diphenhydramine preparation (Benadryl elixir) she used for allergy symptoms during the first trimester of her pregnancy contained 15% alcohol. Should she be concerned about fetal alcohol spectrum disorder in her baby?

ANSWER

Most ethanol-containing medical preparations are safe during pregnancy. Adult doses of some elixirs with high ethanol concentrations might produce blood levels similar to those achieved by drinking 1 alcoholic beverage. Caution is advisable when prescribing ethanol-containing elixirs to pregnant women, as is informing them about the alcohol content.

Preparation, Characterization and In vitro Dissolution Studies of Solid Dispersion of Meloxicam with PEG 60001)

The poor solubility and wettability of meloxicam leads to poor dissolution and hence showing variations in bioavailability. The present study is aimed to increase solubility and dissolution of the drug using solid dispersion techniques. The solid binary systems were prepared at various drug concentrations (5-40%) with polyethylene glycol 6000 by different techniques (physical mixing, solvent evaporation). The formulations were characterized by solubility studies, differential scanning calorimetry, fourier transform infrared spectroscopy and in vitro dissolution rate studies. The solubility of drug increased linearly with increase in polymer concentration showing A(L) type solubility diagrams. Infrared spectroscopy studies indicated the possibility of hydrogen bonding with polymer. The differential scanning calorimetry and powder X ray diffraction demonstrated the presence of polymer as eutectica or monotectica in solid dispersion along with the physical characteristics of the drug (crystalline, amorphous or a mixture of both). The solid dispersions of the drug demonstrated higher drug dissolution rates than physical mixtures and pure meloxicam, as a result of increased wettability and dispersibility of drug in a solid dispersion system.

Buccal bioadhesive drug delivery--a promising option for orally less efficient drugs

Rapid developments in the field of molecular biology and gene technology resulted in generation of many macromolecular drugs including peptides, proteins, polysaccharides and nucleic acids in great number possessing superior pharmacological efficacy with site specificity and devoid of untoward and toxic effects. However, the main impediment for the oral delivery of these drugs as potential therapeutic agents is their extensive presystemic metabolism, instability in acidic environment resulting into inadequate and erratic oral absorption. Parenteral route of administration is the only established route that overcomes all these drawbacks associated with these orally less/inefficient drugs. But, these formulations are costly, have least patient compliance, require repeated administration, in addition to the other hazardous effects associated with this route. Over the last few decades' pharmaceutical scientists throughout the world are trying to explore transdermal and transmucosal routes as an alternative to injections. Among the various transmucosal sites available, mucosa of the buccal cavity was found to be the most convenient and easily accessible site for the delivery of therapeutic agents for both local and systemic delivery as retentive dosage forms, because it has expanse of smooth muscle which is relatively immobile, abundant vascularization, rapid recovery time after exposure to stress and the near absence of langerhans cells. Direct access to the systemic circulation through the internal jugular vein bypasses drugs from the hepatic first pass metabolism leading to high bioavailability. Further, these dosage forms are self-administrable, cheap and have superior patient compliance. Developing a dosage form with the optimum pharmacokinetics is a promising area for continued research as it is enormously important and intellectually challenging. With the right dosage form design, local environment of the mucosa can be controlled and manipulated in order to optimize the rate of drug dissolution and permeation. A rational approach to dosage form design requires a complete understanding of the physicochemical and biopharmaceutical properties of the drug and excipients. Advances in experimental and computational methodologies will be helpful in shortening the processing time from formulation design to clinical use. This paper aims to review the developments in the buccal adhesive drug delivery systems to provide basic principles to the young scientists, which will be useful to circumvent the difficulties associated with the formulation design.

Evaluation of Mucin as a Release Enhancer for Rectal Delivery of Glibenclamide

In this work mucin was evaluated as a release and absorption enhancer for glibenclamide from rectal glycerogelatin suppository. Glycerogelatin suppositories containing different ratios of glibenclamide to I-mucin (insoluble), S-mucin (soluble) and sodium salicylate respectively, were formulated using the fusion method. The suppositories were evaluated using standard parameters. Release studies were carried out in phosphate buffer (pH 7.6). The pharmacodynamic (PD) evaluation of the formulations was carried out on normoglycaemic albino rats. The results of the physical tests showed that the suppositories possessed high resistance to rupture and had uniformity of weight and drug contents. The erosion times of the suppositories with I-mucin, S-mucin and sodium salicylate were shorter than glycerogelatin suppositories BP without any release enhancer (control). Analysis of the release data showed that the release pattern was bi-phasic with initial fast release and subsequent slow release of the glibenclamide from the suppositories. The release mechanism followed first order kinetics. All the suppositories containing either S-mucin, I-mucin or sodium salicylate showed better glibenclamide release than the control without any release enhancer (p < 0.05). The pharmacodynamic studies showed that the overall glucose lowering effect in rats was greater in S-mucin suppositories than in sodium salicylate and I-mucin suppositories. The results of this study indicated that mucin extracted from Bovine spp. could be used to enhance the release and subsequent absorption of glibenclamide from rectal glycerolgelatin suppositories.

A Transdermal Delivery System for Glipizide

Glipizide is one of the most commonly prescribed drugs for treatment of type 2 diabetes. Oral therapy with glipizide comprises problems of bioavailability fluctuations and may be associated with severe hypoglycaemia 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 glipizide. For this purpose, inclusion complexes of the drug in beta-cyclodextrin (beta-CyD), dimethyl-beta-cyclodextrin (DM-beta-CyD), hydroxypropyl-beta-cyclodextrin (HP-beta-CyD), and hydroxypropyl-gamma-cyclodextrin (HP-gamma-CyD) were prepared. Several percutaneous formulations of the drug and the prepared complexes in different bases (o/w emulsion, polyethylene glycol, carboxymethyl cellulose and Carbopol) were developed. Release studies revealed an improved release of the drug from formulations containing glipizide-CyD complexes. Ex vivo permeation studies through full thickness rat abdominal skin were conducted, whereby the effect of several conventional penetration enhancers (propylene glycol [PG], oleic acid, urea, dimethyl sulfoxide, menthol, limonene and cineole) was monitored. Highest flux was obtained from ointments prepared with Carbopol gel base containing a combination of PG and oleic acid as well as ointments prepared in the same base utilizing glipizide-DM-beta-CyD complex and urea. In vivo studies on diabetic male Wistar rats revealed a marked therapeutic efficacy sustained for about 48 hours. In this respect, two formulations showed best biological performance. In the first formulation, the drug was incorporated in Carbopol gel base in the presence of 20% PG together with 15% oleic acid. The second was prepared by incorporating glipizide-DM-beta-CyD complex in Carbopol gel base in presence of 15% urea. The glucose tolerance test showed suppression of hyperglycaemia induced in glucose-loaded rats. The above-mentioned results might shed a strong beam of light on the feasibility of using glipizide in a transdermal delivery system for treatment of type 2 diabetes with the aim of improving both patient compliance and pathophysiology of the disease.

Synthesis and transdermal permeation-enhancing activity of ketone, amide, and alkane analogs of Transkarbam 12

Transkarbam 12 (5-(dodecyloxycarbonyl)pentylammonium-5-(dodecyloxycarbonyl)pentylcarbamate, T12) is a highly active transdermal permeation enhancer. In this study, ketone, amide, and alkane analogs of T12 have been synthesized and evaluated for their permeation-enhancing activity using porcine skin and theophylline as a model drug. Replacement of ester by methylene and ketone, respectively, led to a significant decrease of activity. Amide analogs displayed lower activity in 60% propylene glycol and were comparable to T12 in isopropyl myristate. An intramolecular H-bond between ester and ammonium-carbamate group was suggested to be important for the permeation-enhancing activity of T12.

Influence of an adjuvant on the distribution of herbicides in a sediment/water system

This study concerned the influence of a mineral oil adjuvant used as tank-mix, on the sorption of commercially formulated compounds in soil using a laboratory-scale sediment/water system. The laboratory experiment was conducted with the adjuvant Atpolan 80 EC and the triazine herbicide atrazine and isoxaflutole which belong to the isoxazole class of herbicides. Ditch bed sediment was the medium. Pesticide distribution was measured in the aqueous phase, both in systems with and without the sediment. The proportion of pesticide moving into the sediment layer was depended on physicochemical properties of the compounds, but it was also influenced by the adjuvant in case of atrazine and only slightly in that of isoxaflutole. Atpolan 80 EC also caused an increase of Kd and Koc values of atrazine.

Effect of lipophilic counter-ions on membrane diffusion of benzydamine

Many topically applied drugs are ionized molecules that exhibit poor penetration across the lipid domains of the stratum corneum. Reduction of the charge on the molecule would be expected to enhance skin penetration. The objective of this study was to investigate the interaction of the non-steroidal anti-inflammatory drug benzydamine hydrochloride with suitable counter-ions including ibuprofen sodium. The influence of pH of the donor solution and hence degree of ionization on partitioning between n-octanol:buffer and the flux of benzydamine hydrochloride across polydimethyl siloxane (PDMS) membrane and human epidermis was determined. The maximum flux was determined at pH 7.6 when the fraction unionized was 2.51%, rather than at pH 9 when the fraction unionized was 38.7%. This suggests that at higher pH, although the permeability coefficient is increased, the decrease in solubility and therefore concentration of dissolved benzydamine in the medium results in a decrease in flux across the PDMS membrane. Ion-pair formation or interaction with each of the counter-ions was confirmed by NMR spectroscopy. Significant increases in logP and flux across PDMS membrane were determined for the ion-pairs (0.087, 12.54, 11.31, 0.121 microg cm(-2)h(-1) for benzydamine hydrochloride and ion-pairs with ibuprofen sodium, sodium benzoate and sodium octane sulfonate respectively). This study shows that it is possible to significantly enhance the flux of salts across a lipophilic membrane in the presence of counter-ions, resulting from intermolecular interaction and/or ion-pair formation.

Antipyretic, analgesic and anti-inflammatory activities of ketoprofen beta-cyclodextrin inclusion complexes in animals

Ketoprofen is a nonsteroidal anti-inflammatory drug (NSAID) orally effective in treating fever, pain, and inflammation but gastrointestinal side effects were observed. Preparation of ketoprofen beta-cyclodextrin inclusion complexes was to increase the solubility and reduce the irritation. The complexes were prepared and preliminarily confirmed using X-ray diffraction and dissolution test. Antipyretic, analgesic and anti-inflammatory models were induced by 10% yeast using rabbits, 0.8% acetic acid using mice and 1% carrageenin using rats, respectively. Results showed that the dissolution rate of ketoprofen was significantly improved by complexation. X-Ray diffraction pattern of the complexes exhibited a diffuse pattern that differed from that of physical mixture of ketoprofen and beta-cyclodextrin. Ketoprofen markedly inhibited the fever reactions at a single dose of 2 mg/kg as follows: 64.53% (inhibition rate %) at 1 h for ketoprofen, 73.04% at 1 h for ketoprofen beta-cyclodextrin inclusion complexes, respectively. Alleviating pain reaction rates following a single dose of 8 mg/kg at 20 min were 39.25% for the inclusion complexes and 26.72% for ketoprofen, respectively. Inhibition rates to rat edema following a single dose of 5 mg/kg at 1 h were 39.47% for the inclusion complexes and 23.86% for ketoprofen. Results for antipyretic, analgesic and anti-inflammatory activities showed that the rapid and stronger effects were found in the treatment group of ketoprofen beta-cyclodextrin inclusion complexes in comparison with those of free ketoprofen.

Trimethylated chitosan as polymeric absorption enhancer for improved peroral delivery of peptide drugs

The absorption enhancing effects of chitosan and its derivatives have been intensively studied in recent years. It has been shown that these compounds are potent absorption enhancers. Chitosan is only soluble in acidic environments and is therefore incapable of enhancing absorption in the small intestine, the main absorption area in the gastrointestinal tract. Special emphasis has been placed on the absorption enhancing properties of N-trimethyl chitosan chloride (TMC), a partially quaternised derivative of chitosan, due to its solubility in neutral and basic environments. TMC is prepared by the reductive methylation of chitosan. The degree of quaternisation can be altered by increasing the number of reaction steps or by increasing the reaction time. Although the molecular weight of the polymer increases with addition of the methyl groups, a net decrease in the molecular weight is observed due to a decrease in the chain length of the polymer. TMC, like chitosan, possesses mucoadhesive properties. In vitro studies performed on Caco-2 cell monolayers showed a pronounced reduction in the transepithelial electrical resistance (TEER). TMC is also able to increase the permeation of hydrophilic compounds such as [14C]-mannitol and [14C] polyethylene glycol 4000 ([14C] PEG 4000, MW4000) across the cell monolayers. It was also shown that the degree of quaternisation of the polymer plays an important role on its absorption enhancing properties, especially in neutral environments where chitosan is ineffective as an absorption enhancer. The reduction in TEER is an indication of the opening of the tight junctions located between epithelial cells. Opening of the tight junctions will result in enhancement of absorption via the paracellular route. Confocal laser scanning microscopy confirmed transport of large hydrophilic compounds via the paracellular route as well as the mechanism of action of the polymer in which redistribution of the cytoskeletal F-actin is provoked, which leads to the opening of the tight junctions. Various in vivo studies in different animal models confirmed the ability of TMC to increase the absorption of the peptide drugs buserelin and octreotide after intraduodenal or -jejunal administration. However, TMC has always been administered as a solution in these studies. The impracticality of administering a solution, as well as the fact that most peptides are unstable in the presence of water, have led to the need for a solid oral dosage form with which TMC can be administered together with peptide drugs. Recent studies have focused on the development and in vivo evaluation of solid oral dosage forms.

Applicability of (SBE)7m-beta-CD in controlled-porosity osmotic pump tablets (OPTs)

The purpose of this study was to investigate the general application of a controlled-porosity osmotic pump tablet (OPT) utilizing (SBE)7m-beta-CD as both a solubilizer and an osmotic agent for drugs with varying physical properties. OPTs utilizing (SBE)7m-beta-CD were prepared for five poorly soluble and two highly water-soluble drugs. The Japanese Pharmacopoeia dissolution method was used to study the drug and (SBE)7m-beta-CD release from the OPTs. The drug concentration in the OPT core after the OPT was placed in the release medium for two hours was assayed gravimetrically and by HPLC. An appropriate composition ratio (ACR) of (SBE)7m-beta-CD to drug at which drug release from the OPT was complete and pH-independent within the physiological pH range of the GI tract was determined for each drug. The ACR values correlate to the drug concentration in the OPT core when the OPTs were placed in the release medium for two hours. The release profiles of prednisolone (a poorly water-soluble drug) and sodium chloride (a water-soluble compound) from the OPTs were almost the same as that of (SBE)7m-beta-CD. Also, the release rate of each drug per unit membrane surface area from the OPTs was similar, regardless of the differences in drug solubility. The present results confirmed that (SBE)7m-beta-CD serves as both a solubility modulator and as an osmotic pumping agent for OPTs, from which the release rate of both water-soluble and poorly water-soluble drugs can be controlled.

In vitro and in vivo evaluation of a sulfobutyl ether beta-cyclodextrin enabled etomidate formulation

In this study, we report the formulation and in vivo evaluation of etomidate in an aqueous solution using sulfobutyl ether-7 beta-cyclodextrin (SBE-CD, Captisol) as a solubilizing agent. The phase-solubility behavior of etomidate as a function of SBE-CD concentration was evaluated, and accelerated solution stability studies of 2 mg/mL etomidate in a 5% w/v SBE-CD solution were conducted. The intravenous administration of the SBE-CD etomidate formulation in dogs was compared with Amidate, the commercial etomidate drug product formulated with propylene glycol as a cosolvent. The etomidate plasma concentration-time data were fit to a three-compartment mamillary model and the derived standard pharmacokinetic parameters were not statistically different between the two formulations (n = 4, p > 0.050). Concurrent pharmacodynamic analysis provided statistically equivalent maximum effects and median inhibitory concentrations for the two formulations. In vivo hemolysis after intravenous administration of Amidate was 10-fold higher than the SBE-CD formulation. Whereas Amidate cannot be given subcutaneously because of the cosolvent in the formulation, a 12 mg/mL aqueous solution of etomidate in 20% (w/v) SBE-CD was well tolerated by this route. The results suggest that the SBE-CD formulation is a viable clinical drug product with a reduced side-effect profile.

State of insulin self-association does not affect its absorption from the pulmonary route

This study is designed to compare and contrast the pulmonary absorption profiles of monomeric and hexameric insulin in the presence or absence of ethylene diamine tetraacetic acid (EDTA) or n-tetradecyl-beta-d-maltoside (TDM). The pulmonary absorption of two forms of insulin was studied by monitoring the changes in plasma insulin and glucose levels after intratracheal administration of monomeric or hexameric insulin into anesthetized rodents. EDTA or TDM was added to the formulation in order to evaluate if either of these agents has effects on the rate and extent of pulmonary absorption of monomeric and hexameric insulin. The biochemical changes that may occur after acute administration of TDM-based formulation have also been investigated by estimating lung injury markers in bronchoalveolar lavage fluid. A dose-dependent increase in the plasma insulin and decrease in plasma glucose levels was observed when increasing concentrations of hexameric or monomeric insulin were administered via the pulmonary route. Pulmonary administration of monomeric and hexameric insulin produced comparable absorption profiles in the presence or absence of EDTA or TDM. The bronchoalveolar lavage fluid analysis did not show differences in the levels of injury markers produced in TDM-treated rats and that produced in saline-treated rats, indicating no evidence for adverse effects of TDM in these short-term studies. Overall, in terms of rapidity of action and efficacy to reduce blood sugar, monomeric insulin did not provide advantages over hexameric insulin when administered via the pulmonary route.

Quil A–lipid powder formulations releasing ISCOMs and related colloidal stuctures upon hydration

The aim of the present study was to prepare solid Quil A-cholesterol-phospholipid formulations (as powder mixtures or compressed to pellets) by physical mixing or by freeze-drying of aqueous dispersions of these components in ratios that allow spontaneous formation of ISCOMs and other colloidal structures upon hydration. The effect of addition of excess cholesterol to the lipid mixtures on the release of a model antigen (PE-FITC-OVA) from the pellets was also investigated. Physical properties were evaluated by X-ray powder diffractometry (XPRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and polarized light microscopy (PLM). Characterization of aqueous colloidal dispersions was performed by negative staining transmission electron microscopy (TEM). Physically mixed powders (with or without PE-FITC-OVA) and pellets prepared from the same powders did not spontaneously form ISCOM matrices and related colloidal structures such as worm-like micelles, ring-like micelles, lipidic/layered structures and lamellae (hexagonal array of ring-like micelles) upon hydration as expected from the pseudo-ternary diagram for aqueous mixtures of Quil A, cholesterol and phospholipid. In contrast, spontaneous formation of the expected colloids was demonstrated for the freeze-dried lipid mixtures. Pellets prepared by compression of freeze-dried powders released PE-FITC-OVA slower than those prepared from physically mixed powders. TEM investigations revealed that the antigen was released in the form of colloidal particles (ISCOMs) from pellets prepared by compression of freeze-dried powders. The addition of excess cholesterol slowed down the release of antigen. The findings obtained in this study are important for the formulation of solid Quil A-containing lipid articles as controlled particulate adjuvant containing antigen delivery systems.

Characterization and biological evaluation of a microparticle adjuvant formulation for plasmid DNA vaccines

We describe the physiochemical characterization and immunological evaluation of plasmid DNA vaccine formulations containing a nonionic triblock copolymer adjuvant (CRL1005) in the presence and absence of a cationic surfactant, benzalkonium chloride (BAK). CRL1005 forms particles of 1-10 microns upon warming above its phase-transition temperature (approximately 6-8 degrees C) and the physical properties of the particles are altered by BAK. DNA/CRL1005 vaccines formulated with and without BAK were evaluated in rhesus macaques to determine the effect of CRL1005 and BAK on the ability of plasmid DNA to induce a cellular immune response. Immunogenicity results indicate that the addition of CRL1005 to human immunodeficiency virus-1 gag plasmid DNA formulated in phosphate-buffered saline leads to an enhancement in the gag-specific cellular immune response. Moreover, the addition of BAK to human immunodeficiency virus-1 gag plasmid DNA/CRL1005 formulations produces an additional enhancement in gag-specific cellular immunity. In vitro characterization studies of DNA/CRL1005 formulations indicate no detectable binding of DNA to CRL1005 particles in the absence of BAK, suggesting that the enhancement of cellular immunity induced by DNA/CRL1005 formulations is not due to enhanced DNA delivery. In the presence of BAK, however, results indicate that BAK binds to CRL1005 particles, producing cationic microparticles that bind DNA through electrostatic interactions. If BAK is present at the phase-transition temperature, it reduces the particle size from approximately 2 microns to approximately 300 nm, presumably by binding to hydrophobic surfaces during particle formation. Zeta potential measurements indicate that the surface charge of CRL1005-BAK particles changes from positive to negative upon DNA binding, and DNA bound to the surface of CRL1005-BAK particles was visualized by fluorescence microscopy. These results indicate that the addition of BAK to DNA/CRL1005 formulations leads to the formation of approximately 300 nm CRL1005-BAK-DNA particles that enhance the cellular immune response in rhesus monkeys.

Transdermal delivery of zidovudine: effect of terpenes and their mechanism of action

The effect of various oxygen-containing monoterpenes such as cineole, menthol, alpha-terpineol, menthone, pulegone and carvone was investigated on ex vivo permeation of zidovudine (AZT) across rat skin. Furthermore, saturation solubility of AZT, its stratum corneum (SC)/vehicle partition coefficient and activation energy for diffusion across skin with or without terpene(s) in vehicle (66.6% ethanol in water) were determined to understand their mechanism of action. All the terpenes studied significantly increased transdermal flux of AZT in comparison to vehicle (p<0.05) and their enhancement activities are in the following decreasing order: cineole>menthol>menthone approximately pulegone approximately alpha-terpineol>carvone>vehiclewater. On the other hand, saturation solubility and SC/vehicle partition coefficient of AZT were not significantly altered (p>0.05) by terpenes. Activation energies of AZT permeation across rat skin from water, vehicle and cineole in vehicle were measured to be 20.4, 18.6 and 10.6 kcal/mol, respectively. Interactions between terpenes and SC lipids were studied with molecular modeling and found that terpenes form hydrogen bonds (bond lengths<2 A) with lipid head groups. The mechanism of permeation enhancement of AZT by terpenes was explained with thermodynamic activity, SC/vehicle partition coefficient, activation energy and molecular modeling studies.

Skin Metabolism in Transdermal Therapeutic Systems

Skin has at least two barriers with protective functions: the stratum corneum physical barrier and a biochemical barrier in the epidermis and dermis. Numerous chemical and physical enhancers exist for transdermal therapeutic systems; some cause irritation, and possibly influence enzyme deactivation. Knowledge of enzymatic skin reactions is important for developing safe and efficacious transdermal systems for treatment not only of skin diseases but also for systemic application. This paper overviews the effects of (a) chemical enhancers and additives, (b) drug structure, and (c) physical enhancement on skin metabolism.

Transdermal Drug Delivery: Penetration Enhancement Techniques

There is considerable interest in the skin as a site of drug application both for local and systemic effect. However, the skin, in particular the stratum corneum, poses a formidable barrier to drug penetration thereby limiting topical and transdermal bioavailability. Skin penetration enhancement techniques have been developed to improve bioavailability and increase the range of drugs for which topical and transdermal delivery is a viable option. This review describes enhancement techniques based on drug/vehicle optimisation such as drug selection, prodrugs and ion-pairs, supersaturated drug solutions, eutectic systems, complexation, liposomes, vesicles and particles. Enhancement via modification of the stratum corneum by hydration, chemical enhancers acting on the structure of the stratum corneum lipids and keratin, partitioning and solubility effects are also discussed. The mechanism of action of penetration enhancers and retarders and their potential for clinical application is described.

New Prospects for Glycopeptide Based Analgesia: Glycoside-Induced Penetration of the Blood-Brain Barrier

Antinociceptive effects and BBB transport properties of glycosylated enkephalin derivatives are reviewed. Previously, the application of enkephalins as analgesics has been retarded by their poor stability in vivo and by their inability to effectively penetrate the blood brain barrier. This shortcoming has been overcome by glycosylation, paradoxically leading to enhanced BBB transport via transcytosis. Principal design considerations required for enhanced binding, stability and transport of opioid peptides are reviewed. Modifications of the peptide backbone and side chains to achieve optimal receptor binding (micro/delta-selectivity) are presented. The importance of reversible binding between the glycopeptide and membranes is emphasized, and several pertinent examples of peptide-membrane interactions are discussed in the light of glycopeptide transport and opioid binding. An "amphipathic hypothesis" is introduced as a rationale for the observed BBB penetration of the opioid glycopeptides.

Permeation enhancing polymers in oral delivery of hydrophilic macromolecules: thiomer/GSH systems

Thiolated polymers (= thiomers) in combination with reduced glutathione (GSH) were shown to improve the uptake of hydrophilic macromolecules from the GI tract. The mechanism responsible for this permeation enhancing effect seems to be based on the thiol groups of the polymer. These groups inhibit protein tyrosine phosphatase, being involved in the closing process of tight junctions, via a GSH-mediated mechanism. The strong permeation enhancing effect of various thiomer/GSH systems such as poly(acrylic acid)-cysteine/GSH or chitosan-4-thio-butylamidine (chitosan-TBA)/GSH could be shown via permeation studies on freshly excised intestinal mucosa in Ussing-type chambers. Furthermore, the efficacy of the system was also shown in vivo. By utilizing poly(acrylic acid)-cysteine/GSH as carrier matrix, an absolute oral bioavailability for low molecular weight heparin of 19.9 +/- 9.3% and a pharmacological efficacy--calculated on the basis of the areas under the reduction in serum glucose levels of the oral formulation versus subcutaneous (s.c.) injection-for orally given insulin of 7% could be achieved. The incorporation of salmon calcitonin in chitosan-TBA/GSH led on the other hand to a pharmacological efficacy based on the areas under the reduction in plasma calcium levels of the oral thiomer formulation versus intravenous (i.v.) injection of 1.3%. Because of this high efficacy (i), the possibility to combine thiomer/GSH systems with additional low molecular weight permeation enhancers acting in other ways (ii) and minimal toxicological risks as these polymers are not absorbed from the GI tract (iii), thiolated polymers represent a promising novel tool for the oral administration of hydrophilic macromolecules.

Preparation and ex vivo evaluation of TEC as an absorption enhancer for poorly absorbable compounds in colon specific drug delivery

In previous studies, it was established that chitosan and its quaternized derivatives are potent enhancers of hydrophilic compounds absorption across intestinal epithelia. The aim of this study was to evaluate the application of a new quaternized chitosan, triethyl chitosan (TEC), in pharmaceutical approaches. TEC was synthesized by a one step process via a 2(2) factorial design to optimize the preparation conditions. In ex vivo experiments, everted rat colon sac was used to determine the effect of TEC on the penetration of hydrophilic compounds of different molecular masses (e.g., sodium fluorescein and brilliant blue) through colonic epithelia in comparison with chitosan at pH 7.4. These studies indicated a significant increase in absorption of sodium fluorescein and brilliant blue in the presence of TEC compared to chitosan. TEC bearing positive charge is able to interact with the tight junctions of colon epithelia and hence increase the permeation of sodium fluorescein and brilliant blue through the tight junctions. This investigation has shown that triethyl chitosan could be used as a penetration enhancer for poorly absorbable compounds in the colon drug delivery system.

Influences of Osmotic Agents in Diffusion Layer on Drug Release from Multilayer Coated Pellets

Nonpareil beads were coated with three different functional layers, namely inner chlorpheniramine maleate-loaded hydroxypropylmethylcellulose (HPMC, 4 mPa x s) deposition layer, middle HPMC (400 mPa x s) diffusion layer, and outer polyacrylic polymer (Eudragit RS30D) retention layer. The osmotic agents, including sodium chloride, glycine, citric acid, and disodium hydrogen phosphate, were incorporated in different amounts into the diffusion layer and the influences on drug release were studied. The osmotic agent competed with HPMC for imbibed water and subsequently caused more water influx owing to the osmotic pressure gradient. An appropriate amount of osmotic agent in the diffusion layer was necessary to exert its effect on retarding drug release. The osmotic effect on drug release was compromised with pellets at a higher coating level of the diffusion layer due to the extensive swelling and rupture of coat. The release parameters, including dissolution T50% and mean dissolution time, showed linear relationship with osmolalities of osmotic agents studied. The effect of the osmotic agent in the diffusion layer played an important role in determining the unique multiphase drug release profiles, particularly in the initial phase of dissolution, and reduced with depletion of the osmotic agent in the later phase of dissolution.

Transdermal Delivery of Ondansetron Hydrochloride: Effects of Vehicles and Penetration Enhancers

The effects of vehicles and penetration enhancers on the in vitro permeation of ondansetron hydrochloride (OS) across dorsal hairless mouse skins were investigated. Various types of vehicles, including ester, alcohol, and ether and their mixtures were used, and then a series of fatty acids and fatty alcohols were employed as enhancers. Among pure vehicles used, water and ethanol showed high permeation fluxes, which were 48.2+/-23.7 and 41.9+/-17.9 microg/cm2 per h, respectively. Even though propylene glycol monocaprylate (PGMC) alone did not show a high permeation rate, the skin permeability of OS was increased by the addition of diethylene glycol monoethyl ether (DGME); the highest flux was achieved at 40% of DGME. Also, the combination of PGMC and ethanol (80:20) or PGMC and propylene glycol (PG) (60:40) increased the permeation flux by six- and two-fold, respectively, compared to PGMC alone. The synergistic enhancement was also obtained by using PG-oleyl alcohol (OAl) cosolvent. The greatest flux was attained by the addition of unsaturated fatty acids at 3% concentration to PG. The enhancement factors with the addition of oleic acid or linoleic acid to PG were about 1250 and 450, respectively. But saturated fatty acids failed to show a significant enhancing effect. When the PGMC-DGME (60:40) cosolvent system was used as a vehicle, all fatty acids, including unsaturated fatty acids, failed to show significant enhancing effects. The results indicate that the combinations of oleic acid, linoleic acid, or oleyl alcohol with PG, or PGMC-DGME (60:40) cosolvent could be used for the design of the OS transdermal system.