الفهرس 
General introductionOnly 14 pages are availabe for public view
Abstract
Oral route for drug delivery is the most convenient and commonly employed route of drug delivery due to its ease of administration, high patient compliance, cost-effectiveness, least sterility constraints and flexibility in the design of dosage form.
Despite the many advantages of the oral route, any xenobiotic faces different obstacles in order to pass through the intestinal epithelium and reach the blood stream.
The absorption of the drug through GIT is a complex process, and is affected by many factors; some of which are related to the physiological conditions inside the GIT, while others depend on the physicochemical properties of the drug itself such as drug solubility, stability and particle size.
Even after the passage of drug molecules through the intestinal wall, they are usually carried to the liver where most of the drug is degraded and/or deactivated via hepatic first pass metabolism.
<The amount of drug that reaches the systemic circulation and is readily available to carry out its action represents the oral bioavailability.
< Oral bioavailability of any drug depends on the amount absorbed through the gut wall, together with the percentage that survived the hepatic first pass metabolism.
<Drugs in which the poor solubility is the main cause of their poor absorption are classified by the Biopharmaceutics Classification System (BCS) as class II drugs.
<In such case, the pharmaceutical formulation plays a critical role in the absorption of such drugs from gastrointestinal tract. Sadly, in today’s market more than 40% of oral drug products contain poorly soluble drugs.
< Attempts to overcome the solubility problem and improve oral absorption have been investigated in many recent studies, and many technologies have been employed to improve the oral absorption of poorly soluble drugs, including salt formation, prodrugs, complexation, crystal engineering and solid dispersions.
<Solid lipid nanoparticles (SLNs) represent an alternative carrier system to traditional colloidal carriers (emulsions, liposomes and polymeric micro- and nanoparticles) in enhancing the oral bioavailability of poorly soluble drugs.
<SLNs are composed of physiological and compatible lipids with a high melting point as the solid core, which is coated by nontoxic amphiphilic surfactants as the outer shell.
The nanoparticles are in the submicron size range (50–1000 nm) and in the solid state at both body and room temperatures.
SLNs can improve the oral bioavailability of the poorly soluble drugs by several mechanisms, including adhesion to the gut wall and release the drug exactly where it should be absorbed, promoting the oral absorption of lipophilic drugs, and protecting the drug from pre-systemic metabolism due to their small size and filtration into the lymphatic system that bypasses the hepatic first pass metabolism.