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NIOSOMES- AS NOVEL DRUG DELIVERY SYSTEM


ABOUT AUTHOR:
Deepika Kadodiya
Mahakal Institute Of Pharmaceutical Studies,
Ujjain M.P.
deepikakadodiya05@gmail.com

ABSTRACT
Niosomes are a novel drug delivery system that are finding application in drug targeting antineoplastic treatment, leishmaniasis treatment, delivery of peptide drugs, transdermal drug delivery systems, cosmetics, immunological application of peptide drugs, carriers for haemoglobin, sustained release etc. A niosome is a non-ionic surfactant based liposomes. It is formed by cholesterol with the use of other excipients. The various methods used in the formation of niosomes such as ether injection method, sonication, microfluidization, hand shaking method for the different types of niosomes. The goal of this article focuses on the recent advances in niosomal drug delivery, potential advantages over other delivery systems, formulation methods, methods of characterization, limitation of niosomes, comparision of niosomes v/s liposomes, application of niosomes, marketed products of niosomes and the current research in the field of niosomes.

REFERENCE ID: PHARMATUTOR-ART-1901

INTRODUCTION
The skin that covers throughout the body severs as a platform for drug delivery, but the stratum corneum the outer layer act as an obstacle for the delivery of drug through the skin1. Several technologies was  developed to bypass or modulate this barrier, thereby delivers definite amount of drug at a defined rate to the dermal microcirculation; which includes physical, chemical and carrier approaches2. Thereby, making it a more prominent carrier than the oral delivery as it circumvents the variables that influence gastrointestinal absorption, overcome the hepatic metabolism and delivers the drug at controlled and constant rate thereby reducing the side effects3. Colloidal carrier have distinct advantages over conventional drug delivery as it act as drug containing reservoirs, modification of the particle composition or surface can adjusts the release rate to the target site. Even though, these carriers produce some problem with the industrial production and clinical application, are likely to play an increasingly important role in drug delivery4,5. Among the various colloid carriers, liposome and niosomes can encapsulate both hydrophilic and lipophilic drugs. The hydrophilic drug is encapsulated inside the vesicles whereas the lipophilic drug is partitioned between the hydrophilic domains. Liposomes are produced by the self-assembly of phospholipids in aqueous phase to form bilayer which may be spherical unilamellar or multilamellar vesicles. They were considered to as an efficient carrier to transdermal drug delivery as it can loosen the stratum corneum and hence help in the penetration of drug. Though they produce potent action in pharmaceutics as drug delivery, still produces significant problems. That is, liposome may undergo some problems like degradation by hydrolysis in aqueous solution, sedimentation and aggregation on storage and cannot sterilize for clinical use. Still, chemical instability like oxidation of phospholipids was not avoided. These pave the way to the discovery of non-ionic surfactant vesicles known as niosomes. Niosomes first reported in the seventies in the field of cosmetics and now used in drug targeting. In both these colloidal carrier, phospholipids and non-ionic surfactant used act as penetration enhancer and hence can overcome the barrier of transdermal drug delivery. Although the niosomes, overcame the problem associated with chemical stability on storage, has some physical problems like aggregation, fusion, leakage of drug from the vesicles and hydrolysis of drug on storage were produced6.

Non-ionic surfactant vesicles or niosomes whose structure and properties are similar to liposomes have been developed. Niosomes are microscopic lamellar structures formed on admixture of non-ionic surfactant of the alkyl or dialkyl polyglycerol ether and cholesterol with subsequent hydration in aqueous media and are capable of entrapping hydrophilic and hydrophobic solutes.7-10 Technically, niosomes are promising drug carriers because they posses greater stability, less purity variability, and lower cost. Niosomes also have the advantages of simple method of production for the routine laboratory use and the possibility of large scale production, when needed.11,12

Historical aspect
Niosomes were first reported in the seventies as a feature of the cosmetic industry by Vanlerberghe et al, Handjani-vila et al., Van Abbeexplained that the non-inonic surfactants are preferred because the irritation power of surfactants decreases in the following order:13-19 cationic > anionic > ampholytic > non-ionic.

Vesicular System
In recent years, vesicles have become the vehicle of choice in drug delivery. Lipid vesicles were found to be of value in immunology, membrane biology, diagnostic techniques, and most recently, genetic engineering. Vesicles can play a major role in modelling biological membranes, and in the transport and targeting of active agents.20-23 Conventional chemotherapy for the treatment of intracellular infections is not effective, due to limited permeation of drugs into cells. This can be overcome by use of vesicular drug delivery systems. Encapsulation of a drug in vesicular structures can be predicted to prolong the existence of the drug in systemic circulation, and perhaps, reduces the toxicity if selective uptake can be achieved. The phagocytic uptake of the systemic delivery of the drug-loaded vesicular delivery system provides an efficient method for delivery of drug directly to the site of infection, leading to reduction of drug toxicity with no adverse effects. Vesicular drug delivery reduces the cost of therapy by improved bioavailability of medication, especially in case of poorly soluble drugs. They can incorporate both hydrophilic and lipophilic drugs. Vesicular drug delivery systems delay drug elimination of rapidly metabolizable drugs, and function as sustained release systems. This system solves the problems of drug insolubility, instability, and rapid degradation. Consequently, a number of vesicular delivery systems such as liposomes, niosomes, pharmacosomes etc, were developed.24-26

Definition of Niosomes
Niosomes are a novel drug delivery system, in which the medication is encapsulated in a vesicle. The vesicle is composed of a bilayer of non-ionic surface active agents and hence the name niosomes. The niosomes are very small, and microscopic in size. Their size lies in the nanometric scale. Although structurally similar to liposomes, they offer several advantages over them. Niosomes have recently been shown to greatly increase transdermal drug delivery and also can be used in targeted drug delivery, and thus increased study in these structures can provide new methods for drug delivery.

Niosomes are non-ionic surfactant vesicles obtained on hydration of synthetic nonionic surfactants, with or without incorporation of cholesterol or other lipids.They are vesicular systems similar to liposomes that can be used as carriers of amphiphilic and lipophilic drugs. Niosomes are promising vehicle for drug delivery and being non-ionic, it is less toxic and improves the therapeutic index of drug by restricting its action to target cells.27-29

COMPONENTS OF NIOSOMES
Surfactant:
Non-ionic surfactants are used; they considered the important structural component. They act as Vesicle Forming Agents. The nature of vesicles formed depends upon HLB value in addition, phase transition temperature. HLB  value is a good indicator to predict the vesicle formation and entrapment efficiency. HLB number in between 4 and 8 is compatible with vesicle formation. Another important parameter is the phase transition temperature, higher TºC are more likely in the ordered gel form forming less leaky bilayer, thus having higher entrapment efficiency, while surfactants of lower T° C are more likely in the less ordered liquid form.

Cholesterol: Cholesterol acts as “vesicular cement” in the molecular space that formed by the aggregation of monomer to form the bilayer. Thereby increasing the rigidity decreases the permeability drug through the membrane and hence improves the entrapment efficiency. However, beyond certain concentration cholesterol will compete with the drug for the space within the bilayer, thereby excluding drug and can disrupt the regular linear structure of vesicular membrane. In addition to this, it can also act stabilizing agent.

Solvents: The solvent can act as penetration enhancer and in turn affect the vesicular size formation. Solvents commonly used are alcohols, mainly, ethanol, propanol, butanol, isopropanol. Researchers have reported that ethanol showed larger vesicular size due to the slow phase separation as it has greater solubility in water, whereas due to the branching of isopropanol it showed smaller vesicular size.In addition, reports suggest that the drug penetration is maximal for isopropanol due to the reason that the branched structure will act as co-surfactant and might loosen the bilayer packing resulting into the increased release of drug.30-32

STRUCTURE OF NIOSOMES
Niosomes are microscopic lamellar structures, which are formed on the admixture of non-ionic surfactant of the alkyl or dialkyl polyglycerol ether class and cholesterol with subsequent hydration in aqueous media. Structurally, niosomes are similar to liposomes, in that they are also made up of a bilayer. However, the bilayer in the case of niosomes is made up of non-ionic surface active agents rather than phospholipids as seen in the case of liposomes. Most surface active agents when immersed in water yield micellar structures, however some surfactants can yield bilayer vesicles which are niosomes. Niosomes may be unilamellar or multilamellar depending on the method used to prepare them. The niosome is made of a surfactant bilayer with its hydrophilic ends exposed on the outside and inside of the vesicle, while the hydrophobic chains face each other within the bilayer. Hence, the vesicle holds hydrophilic drugs within the space enclosed in the vesicle, while hydrophobic drugs are embedded within the bilayer itself.


Fig.1  Structure of Niosomes

A typical niosome vesicle would consist of a vesicle forming ampiphile i.e. a non-ionic surfactant such as Span-60, which is usually stabilized by the addition of cholesterol and a small amount of anionic surfactant such as diacetyl phosphate, which also helps in stabilizing the vesicle.33

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