2. Conventional vs. targeted drug delivery systems

#### 2.1 Conventional drug delivery systems

Conventional drug delivery system is also known as classical drug delivery system or traditional drug delivery system, which sometimes unable to maintain the steady-state plasma concentration as desired for a specific time period and may not be able to deliver the drugs to the specific site of organ or tissues may be because of barriers in transportation for which it may be needed to administer with multiple doses at a regular time interval or need to go for targeted drug delivery systems.

and retain the active drug en route, while they deliver the drug within or in the vicinity of a target is popularly known as colloidal drug carrier. These colloidal drug carriers comprise nanoparticles, liposome, niosome, nanospheres, multiple emulsion, and nanosuspensions, etc. [6]. Colloidal carriers aid in solubilization of lipophilic drug, protect the sensitive drug from degradation in biological fluid, reduce toxic side effect, improve patient compliances, prolong the duration of action and

Solid Lipid Based Nano-particulate Formulations in Drug Targeting

Though the polymeric nanoparticulate DDS have shown hugely impressive performance for providing therapeutic benefits in the case of long term delivery of a therapeutic agent, but still, the number of polymeric nanoparticulate formulations in the market is still limited. This is because of polymeric toxicity, high cost of polymers, and lack of feasibility for scaling up. Lipid based nanoparticulate DDSs are proposed as an alternative to polymeric nanoparticulate DDS and gained tremendous attention in the field of nanomedicine. These comprise liposomes,

niosomes, nanoemulsions, solid lipid nanoparticles (SLNs) and nanostructured lipid

SLNs are the second generation lipid nanocarriers that overcome most of the limitations associated with conventional drug delivery system and other colloidal lipid/polymeric nano carriers. It promises to offer numerous benefits including biocompatibility and biodegradability, physiochemical stability, lower toxicity, ability to incorporate both hydrophilic and lipophilic drugs, improved bioavailability, enhanced in vitro and in vivo stability of drugs, controlled-release characteristics, site specificity in drug delivery as well as feasibility in pilot scale up along with its suitability in drug delivery through different routes of administration [4].

In the emerging field of nanomedicine, SLNs is at the forefront. It is made up from biocompatible/physiological lipids (e.g. partial glycerides, triglycerides, fatty acids, wax, and steroids) that remain in solid form at room temperature. Numerous techniques are being developed for the fabrication of SLNs using the biocompatible/ physiological lipid which has records of innocuous use in medicine [8]. Apart from drugs, the essential materials for fabricating SLNs are solid lipids as matrix materials, emulsifiers, stabilizers, and water. The nanometric size and larger surface area of SLNs is suitable to be embedded with some potential functionalized ligands, antibodies, moieties, and other functional groups that help in drug targeting [5]. The real success of lipid nanoparticles relies on the development of dosage forms

that are able to improve the therapeutic index of the drugs by mounting their concentration specifically at the targeted site or organs. Drugs can be incorporated in SLNs which lead to offer a new model in drug delivery that could be applied for drug targeting. The therapeutic payload of various categories of drugs (such as antiinfective, anticancer drugs, anti-inflammatory, etc.), antigens, proteins, and nucleotides can be enhanced in specific site and organs by associating with SLNs. On another side, SLNs face numerous challenges which include rapid clearance, serum instability (dependent on the specific formulation) and nonspecific uptake by the mononuclear phagocytic system (play a major role for opsonizing the foreign particles and remove SLNs from the circulation) [9]. The above mentioned limitations can be nullified by conjugating different ligands to the surface of SLNs which could help to increase the circulation time and targeted delivery of the drug to the specific site. The targeting properties to a specific site can be further enhanced by selecting surface markers [10]. Thus, in this article, we focused on SLNs and various ligand conjugated SLNs which act as suitable carriers for targeting to different sites such as

drug targeting potentiality [7].

DOI: http://dx.doi.org/10.5772/intechopen.88268

carrier (NLCs), etc. [5].

2.5 Solid lipid nanoparticles and drug targeting

lungs, brain, liver, breast, eyes, colon, kidney, etc.

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