Topical Gel: A Novel approach for drug delivery - Journal of ...

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Formulation...Sudhir Bharadwaj et al.1.2.4. Drug Factors in Percutaneous AbsorptionThe drug factors affecting percutaneous absorption are given as follows :1. Molecular size2. Chemical nature of drug3. Partition coefficient4. Binding to the skin5. Metabolism6. Thermodynamic activity of drug in donar1.3.5. Formulation Factors in Percutaneous AbsorptionThe nature of the dosage form is an extremely important factor in determination of skinpenetration characteristics and various formulation factors such as :1. Occlusivity2. Drug concentration3. pH4. Solubility5. Surfactant6. Penetration enhancer1.3 BASIC COMPONENTS OF TOPICAL DRUG DELIVERY SYSTEMS 17-18Topical gel may include the following components:(A).Polymer: Polymer is an integral and foremost important component of Topical Gel. Different classesof polymeric materials have been used to achieve rate controlled drug delivery. The mechanism of drugrelease depends upon the physicochemical properties of the drug and polymer used in the manufacture ofthe device.The following criteria should be satisfied for a polymer to be used in a topical system:1. Molecular weight, glass transition temperature, chemical functionality of polymer must allowdiffusion and release of the specific drug.2. The polymer should permit the incorporation of a large amount of drug.3. The polymer should not react, physically or chemically with the drug.4. The polymer should be easily manufactured and fabricated into the desired product andinexpensive.5. The polymer must be stable and must not decompose in the presence of drug and other excipientsused in the formulation, at high humidity conditions, or at body temperature.6. Polymers and its degradation products must be non-toxic 17 .No single material may have all these attributes, certain excipients may be incorporated to alter someproperties, e.g., Cosolvents such as ethanol, propylene glycol, PEG 400 could be added to increase drugsolubility.863 J. Chem. Bio. Phy. Sci. Sec.B, 2012, Vol.2, No.2,856-867
Formulation...Sudhir Bharadwaj et al.Table -1: Useful Polymers for Topical GelNatural polymers Semisynthetic polymers Synthetic polymersa. Proteinsi. Collagenii. Gelatinb. Polysaccharidesi. Agarii. Alginic acidiii. Sodium or Potassiumcarrageenaniv. Tragacanthv. Pectinvi. Guar Gumvii. Cassia toraviii. Xanthinix. Gellum Guma. Cellulose derivativesi. Carboxymethylcelluloseii. Methylcelluloseiii. Hydroxypropylcelluloseiv. Hydroxypropyl methylcellulosev. Hydroxyethylcellulosea. Carbomeri. Carbopol-940ii. Carbopol-934iii. Carbopol-941b. Poloxamerc. Polyacrylamided. Polyvinyl alcohole. Polyethylene and its copolymersVarious techniques have been employed to modify the polymer properties and thus drug release rates.a. Cross-linked polymers: The higher the degree of cross-linking, the more dense the polymer andslower the diffusion of drug molecules.b. Polymer blends: Polymers have been blended on varying ratios to combine the advantages of theindividual polymers. Advantages of polymer blends include easy fabrication of devices, manipulation ofdrug incorporating and other devices properties such as hydration, degradation rate and mechanicalstrength.(B).Drug Substance:Judicious choice of the drug plays an important role in the successful developmentof a topical product. The important drug properties that effect its diffusion through the device as well asthrough skin are as follows 18 :a. Physicochemical properties: Drug should have a molecular weight of less than 500 Daltons. Drug must have adequate lipophilicity. A saturated aqueous solution of the drug should have a pH value between 5 and 9. Drugs highly acidic or alkaline in solution are not suitable for topical delivery.864 J. Chem. Bio. Phy. Sci. Sec.B, 2012, Vol.2, No.2,856-867
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