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CONTENTS Introduction Classification of Organogel Factors affecting gel formation Types of Organogel Applications Conclusions References


INTRODUCTION Gel – Contains both solid & liquid. Components of gel -Solid -Liquid -Drug. Thermoreversible.


INTRODUCTION In the last decade, interest in organogels has grown rapidly with the discovery and synthesis of a very large number of diverse molecules, which can gel organic solvents at low concentrations. A simple working definition of the term ‘gel’ is a soft, solid or solid-like material, which contains both solid and liquid components, where the solid component (the gelator) is present as a mesh/network of aggregates, which immobilises the liquid component. This solid network prevents the liquid from flowing, primarily via surface tension.

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The gel is said to be a hydrogel or an organogel depending on the nature of the liquid component: water in hydrogels and an organic solvent in organogels. However, only a few organogels are currently being studied as drug delivery vehicles as most of the existing organogels are composed of pharmaceutically unacceptable organic liquids and/or unacceptable/untested gelators. In this seminar a brief overview of organogels is presented, followed by a more in-depth review of the gels that have been investigated for drug delivery.


Organogel Gel is a soft solid which contains both solid & liquid components where the solid component ( gelator ) is present as a mesh/network of aggregates, which immobilizes the liquid component The solid network prevents the liquid from flowing The gel is called as hydrogel or organogel depending on the nature of the liquid component( water in hydrogels & an organic solvent in organogels In hydrogels the gelator is a polymer while in case of organogel , gelators are small molecules

Advantages :

Advantages 7 Ease of administration. Avoids first pass effect. Absorption enhancement. Overcome the problems of conventional dosage forms. Site specific drug delivery. Avoid systemic adverse effects associated with oral administration of drug.


Organogelators n-alkanes such as hexadecane & organic liquids Non ionic surfactant- sorbitan monostearate Steroids & their derivatives Anthranyl derivatives Macrocyclic gelators (calixarenes)

Organogel structure & mechanism of organogelling:

Organogel structure & mechanism of organogelling The organogelling or gelation of lecithin solutions in organic solvents is induced as a result of incorporation of a polar solvent Lecithin when dissolved in nonpolar media alone , self assembles into reverse micelles. The growth of spherical reverse micelles & further transformation into tubular & cylindrical micellar aggregates (sphere to cylinder transformation) is triggered by addition of small & critical amounts of polar additive


CLASSIFICATION Nature of solvent Nature of Gelators Nature of IMI The specific process leading to the formation of the gelling matrix depends on the physicochemical properties of gel components and their resulting interactions.

Organogel preparation:

Organogel preparation Gelators + Liquid phase Heat Organic Solution/dispersion Cool Gel Why heating and cooling ? Is this gel form or not ?

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Most of the organogels are prepared by heating a mixture of the gelator & the liquid component to form organic solution/dispersion Heating allows dissolution of gelator in the liquid Following cooling, the solubility of gelator in the liquid phase decreases & gelator-solvent interactions are reduced, which results in gelator molecules coming out of solution Entanglement of the aggregates & connections among them result in the formation of three dimensional network, which immobilizes the fluid phase The physical organogels, held together by noncovalent forces are thermoreversible

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Following heating the gel melts to the sol phase as the gelator aggregates dissolve in the organic liquid, whereas cooling the hot sol phase results in gelation The temperature at which the sol-to-gel or gel-to-sol transition occurs is called the gelation temp. The Tg of 10% w/v sorbitan monostearate is 41-44 0 C Solutions of lecithin in an organic solvent such as iso-octane can be gelled by the addition of trace amounts of a polar substance e.g. water ,glycerol, ethylene glycol or formamide

Factors affecting gel formation:

Factors affecting gel formation Molecular shape of Solvent Ex. SNO in t-Decalin ,Cyclohexane. Functional Group of solvent Ex. CAB in 1-Octanol & n-alkens Presences/Addition of other component


TYPES OF ORGANOGEL Sorbitan Monostearate Organogels In Situ Formation Of An Organogel Of L-alanine Derivative Eudragit Organogels Microemulsion-based Gels Lecithin Organogels Pluronic Lecithin Organogels

Sorbitan Monostearate Organogels:

Sorbitan Monostearate Organogels Sorbitan monostearate (Span 60) and sorbitan monopalmitate (Span 40) have been found to gel a number of organic solvents at low concentrations. They are prepared by heating the gelator /liquid mixture in a water bath at 60°C (which results in dispersion of the gelator in the liquid medium) and cooling of the resulting suspension, following which the latter sets to an opaque, white, semisolid gel. Sorbitan monostearate molecules are arranged in inverted bilayers within the tubules, as shown in Figure. Sorbitan Monostearate Organogel

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The tubules form a three-dimensional network, which immobilizes the liquid, and hence a gel is formed. Sorbitan monostearate gels has been investigated as delivery vehicles for hydrophilic vaccines

L-alanine derivative Organogel:

L- alanine derivative Organogel LAM + O.S. + Soyabin oil Gel Addition of ethanol – Form solution. (Used as Sustained released implant)

Eudragit Organogel:

Eudragit Organogel Drug + Polyhydric Alcohol ( PG ) Pour into Eudragit L or S Solution (30 to 40%) Gelling property – Vary.

Micro emulsion based :

Micro emulsion based Gelatin is used as Gelator. 2-(ethylhexyl) Na Sulfosuccinates + Isooctane hot water Gelatin

Lecithin Organogel :

Lecithin Organogel Lecithin + O.S. Polar Solvent Gel Water: Lecithin (2:10) Incorporate both types of drugs small amt. of water requied long chain, short chain

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Figure 1. Schematic diagram of the preparation of lecithin organogels . Note: Lipophilic drugs are solubilized in the organic phase (stage 1), whereas hydrophilic compounds can be solubilized in the polar phase (stage 2). For the preparation of pluronic lecithin organogel (PLO gel), the co-surfactant pluronic is taken along with polar phase (stage 2).

Table 1. Various Salient Features of Lecithin Organogels:

Table 1. Various Salient Features of Lecithin Organogels Salient Features Template vehicle LOs provide opportunities for incorporation of a wide range of substances with diverse physicochemical characters (e.g. chemical nature, solubility, molecular weight, size) Process benefits Spontaneity of organogel formation, by virtue of self-assembled supramolecular arrangement of surfactant molecules, makes the process very simple and easy to handle. Structural/physical stability Being thermodynamically stable, the structural integrity of LOs is maintained for longer time periods. Chemical stability LOs are moisture insensitive, and being organic in character, they also resist microbial contamination. Topical delivery potential Being well balanced in hydrophilic and lipophilic character, they can efficiently partition with the skin and therefore enhance the skin penetration and transport of the molecules. LOs also provide the desired hydration of skin in a lipid-enriched environment so as to maintain the bioactive state of skin. Safety Use of biocompatible, biodegradable, and non immunogenic materials makes them safe for long term applications.

Pluronic lecithin organogel:

Pluronic lecithin organogel PLO is an opaque, yellow gel, composed of isopropyl palmitate , soy lecithin, water and the hydrophilic polymer, Pluronic F127. The difference between PLO and its precursor, lecithin gels, is the presence of Pluronic F127 (a hydrophilic polymer that gels water) and the greater amount of water compared with the oi PLO gel looks and feels like a cream but is actually a gel. When the aqueous phase ( pluronic gel) is combined with the lecithin oil base creates an emulsion that forms together due to the pluronic gel and the viscosity of that gel at room temperature.

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PLO has been shown in vivo and in vitro to modulate the release and permeation of drugs applied transdermally. It improves the topical administration of drug mainly due to the desired drug partitioning, biphasic drug solubility and the modification of skin barrier system by organogel components. It shows low skin irritation, increases patient compliance, reduces side effects, avoids first pass metabolism and increases efficiency of drug.

Organogels In Drug Delivery:

Organogels In Drug Delivery Despite the large abundance and variety of organogel systems, relatively few have current applications in drug delivery, owing mostly to the lack of information on the biocompatibility and toxicity of organogelator molecules and their degradation products. This review focuses on organogel systems that have been geared towards pharmaceutical applications and are at various stages of development, from preliminary in vitro experiments to clinical studies. Table I provides a summary of the key drug delivery studies conducted using organogels . Organogels In Drug Delivery

Table I: Organogel Formulations Used In Drug Delivery:

Table I: Organogel Formulations Used In Drug Delivery Sr.No. Types Route of administration Study conducted Model drugs 1 Lecithin Transdermal Clinical trials In vivo skin permeation & efficacy In vitro skin Permeation In vitro release Diclofenac Piroxicam, tetrabenzamidine Scopolamine and boxaterol Propranolol, nicardipine Aceclofenac, indomethacin & Diclofenac 2 Sorbitan monostearate (SMS) Nasal Oral Subcutaneous & intramuscular In vitro release In vitro release In vivo efficacy Propranolol Cyclosporin A BSA 1 and HA 2 3 PLOs Transdermal Clinical trials In vivo skin permeation & efficacy In vitro release Promethazine, Ondansetron & Diclofenac Methimazole , Fluoxetine, Dexamethazone , Amitriptyline, Methadone, Morphine, Buprenorphine & Buspirone Scopolamine, Metoclopramide, Haloperidol & Prochlorperazine

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Sr.No Types Route of administration Study conducted Model drugs 4 L-alanine derivative Subcutaneous In vitro/in vivo release In vitro/in vivo release and efficacy Rivastigmine Leuprolide 5 Eudragit organoges Rectal Buccal In vivo efficacy In vivo efficacy Salicylic acid BSA

Characterization Of Organogels:

Characterization Of Organogels In contrast to the ease of preparation, characterization of organogels is relatively complicated on account of their interior structural design build-up on the self-associated supramolecules. These microstructures, the result of varied polar-nonpolar interactions, are highly sensitive and pose difficulties in the investigative studies. However, different characterization studies are extremely useful while investigating the potential applications of organogel systems as a topical vehicle. It has been reported that many of the physicochemical properties of organogels viz Rheological behavior, physical and mechanical stability and drug release behavior are dependent upon how molecules arrange themselves to provide the specific structural network within the organogel system. Characterization of Organogels

Evaluation Of Organogels :

Gelation Studies Rheological Behavior Structural Features Phase Transition Temperatures Gel Strength Water Content Percentage Drug Content In-vitro / Permeation Study In-vivo Study Stability Study Evaluation Of Organogels

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Gelation Studies :-A simple visual test to determine whether gelation has taken place involves inverting the reaction vessel,gelation has occurred if the sample does not flow Rheological Behavior :- are viscoelastic in nature, prior to gelling exhibit Newtonian behavior & follows viscoelastic behavior on addition of polar phase. It has been observed that increasing the gelator conc. leads to increase in the viscosity & hence gel strength Structural features :-Molecular architecture of organogels has been evaluated using NMR spectroscopy, hydrogen bonding has been established by FTIR spectroscopy. The knowledge of molecular packing within organogel network has been obtained using scanning & transmission electron microscopy

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Phase transition Temperature:- gives insight into the nature of microstructures that form the gelling cross linked network. A narrow PTT range(3-5 0 C) is indicative of homogeneous microstructures within the gel. It is determined by hot stage microscopy (HST)& high sensitivity DCS Gelation study:- A simple visual test to determine whether gelation has taken place involves inverting the reaction vessel; gelation is said to occurred if the sample does not flow. Water Content :-water loss by evaporation can lead to decrease in viscisity thus affecting the gel stability. Near infrared spectroscopy(NIR,1800-2200) is used for determining water content

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Stability study:- The organogels were tested under following condition of temperature and relative humidity. 25°C ± 2°C at 75 ± 5% RH 40°C ± 2°C at 75 ± 5% RH In vitro study:- The formulation is subjected to in vitro diffusion through dialysis membrane. In vivo study:- Carrageenan induce rat paw edema method was used as a model.

Area Of Application:

Area Of Application The site of application can drastically affect the distribution and absorption of a drug. If a systemic effect is desired, the gel should be applied to neck, inner thigh, or inner wrist area. For a local effect, the gel should be applied directly to the joint or painful region, then rub in well Area of Application


Application Ease of preparation & scale up, easier quality monitoring, thermodynamic stability, enhanced topical performance, biocompatibility, safety upon applications for prolonged period make the organogels a vehicle of choice for topical drug delivery Ease of administration. Site specific drug delivery. Avoids first pass effect. Absorption enhancement. Overcome the problems of conventional dosage forms. Application


Limitation The major limitation in the formation of Los is the requirement of high purity lecithins High purity lecithin is expensive Difficult to obtain in large quantities Inclusion of pluronics as cosurfectant makes organogelling feasible with lecithin of relatively less purity


Conclusions Very Few Organogels are used in drug delivery - Component of Organogel are not pharmaceutically acceptable. LO – good for TDDs Eudragit gel – Under investigation. LAM – used as Implant.


References Murdan S. Organogels in drug delivery, Expert Opin Drug Deliv , 2(3), 2005,p.489-505. Anda V., Leroux J. , Organogels and Their Use in Drug Delivery - A Review, Journal of Controlled Release, Accepted 27 September 2007,p. 18-59. Kumar R and Katare OP. Lecithin organogels as a potential phospholipid-structured system for topical drug delivery: a review, AAPS PharmaSciTech, 6(2), 2005,p. 298-310. Murdan S. A review of pluronic lecithin organogel as a topical and transdermal drug delivery system, Hospital Pharmacist, 12, 2005, p. 267-270. Shchipunov YA. Lecithin organogel: a micellar system with unique properties, Colloids and Surfaces: A Physicochemical and Engineering Aspects, 183-185, 2001, p. 541-554.

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