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Definition:

Drug delivery refers to approaches, formulations, technologies, and systems

for transporting a pharmaceutical compound in the body as needed to safely

achieve its desired therapeuticpeutic effect.

Drugs have long been used to improve health & extend lives.

There are many success stories concerning the use of drugs and vaccines in

the in the treatment, prevention and in some cases even eradication of

diseases (e.g.smallpox)

It is necessary to develop suitable dosage forms or drug delivery systems to

allow the effective, safe and reliable application of these bioactive

compounds to the patient.

Indeed the drug delivery system employed plays a vital role in controlling

the pharmacological effect of the drug as it can influence the rate of drug

release, the site and duration of drug action and subsequently the side-effect

profile. An optimal drug delivery system ensure that the active drug is

available at the site of action for the correct time and duration.

In traditional drug delivery systems such as oral ingestion or intravascular

injection, the medication is distributed throughout the body through the

systems blood circulation for most therapeutic agents, only a small portion of

the medication reaches the organ to be affected.

Targeted drug delivery, sometimes called smart drug delivery or intelligent

drug delivery, is a method of delivering medication to a patient in a manner

that increases the concentration of the medication in some parts of the body

relative to others.

The conventional drug delivery system is the absorption of the drug across a

biological membranes, whereas the targeted release system release the drug

in a dosage form.

There are different types of drug delivery vehicle, such as liposomes, polymeric

micelles, lipoprotein-based drug carriers, nano-particle drug carriers, dendrimers, etc.

An ideal drug delivery vehicle must be non-toxic, biocompatible, non-immunogenic,

biodegradable, and must avoid recognition by the host’s defense mechanisms.

The most common vehicle currently used for targeted drug delivery is the liposomes. A

liposome is a spherical vesicle having at least one lipid bilayer. The liposomes. A

liposome can be used as a vehicle for administration of pharmaceutical drugs. A

liposome has an aqueous solution core surrounded by a hydrophobic membrane, in

the form of a lipid bilayer. Hydrophilic solutes dissolved in the core cannot readily pass

through the bilayer. Hence a liposome can be loaded with hydrophobic and/or and

hydrophilic molecules.

Liposomes are non-toxic, non-hemolytic, and non- immunogenic.

A liposome is a lipoidal bilayer which encapsulates a region of aqueous solution

inside a hydrophobic membrane, dissolved hydrophilic solutes cannot readily pass

through the lipids. Hydrophobic chemicals can be dissolved into the membrane, and

in this way liposome can carry both hydrophobic and hydrophilic molecules. To

deliver the molecules to sites of action, the lipid bilayer can fuse with other bilayer

such as the cell membrane, thus delivering the liposome contents.

Another type of drug delivery vehicle used is polymeric micelles. Micelles are

approximately spherical in shape. Micelles are usually formed by single-chain lipids. A

micelle is an aggregate of surfectant molecules dispersed in a liquid colloidal. In a

micelle, the hydrophobic tails of several surfactant molecules assemble into an oil-like

core.

Dendrimers are also polymer- based delivery vehicles. They have a core that branches

out in regular intervals to form a small, spherical, and very dense nanocarrier.

Dendrimers are highly branched, three-dimensional features that resemble the

architecture of a tree.

Two strategies are used for the application of dendrimers to drug delivery; drug

encapsulation by dendritic structure and drug conjugation to dendrimers. Firstly, the

drug molecules can be physically entrapped inside the dendrimers; secondly, the drug

molecules can be covalently attached onto the surface or other functional gp. Various

functional moieties based on dendrimers provide miscellaneous biomedical

applications of these promising materials, such as cancer targeting therapy.

Biodegradable particles have the ability to target diseased tissue as well as deliver their

drugs as controlled-release therapy. Biodegradable particles bearing ligands to P-

selectin, endothelial selectin (E-selectin) and ICAM-1 (All are receptors) have been

found to adhere to inflamed endothelium (heart muscle). Therefore, the use of

biodegradable particles loaded with drugs can also be used for cardiac tissue repair.

The success of DNA nanotechnology in constructing artificially designed

nanostructures out of nucleic acids such as DAN, can be used to target drug delivery

based upon directly sensing its environment. These methods make use of DNA solely

as a structural material and a chemical, and do not make use of its biological role as

the carrier of genetic information. Nucleic acid releases a drug only in response to a

stimulus such as a specific mRNA, have been demonstrated.

Targeted drug delivery can be used to treat many diseases, such as the cardiovascular

diseases and diabetes. However, the most important application of targeted drug delivery

is to treat cancer tumors.

Liposomes can be used as drug delivery for the treatment of tuberculosis. The

traditional treatment for TB is only chemotherapy which is not very effective, which may

be due to the failure of chemotherapy to make a high enough concentration at the

infection site. The liposome delivery system allows for better microphage penetration and

better builds a concentration at he infection site. The delivery of the drugs works

intravenously and by inhalation. Oral intake is not advised because the liposomes break

down in the Gastrointestinal System.

Medications can be taken in a variety of ways-by mouth, by inhalation, by absorption

through the skin, or by intravenous injection. Each method has advantages and

disadvantages, and not all methods can be used for every medication. Improving current

delivery methods or designing new ones can enhance the use of existing medications.

Microneedle arrays are one example of a new method to deliver medications

through the skin. In thses arrays, dozens of microscopic needles, each far thinner than a

strand of hair, can be coated or filled with a medicine. The needles are so small that,

although they penetrate the skin, they don’t reach nerves in the skin, thus delivering

medications painlessly.