Drug delivery systems oral route

Liu, L. S., Fishman, M. L., Kost, J., and Hicks, K. B. (2003), Pectin-based systems for colon-specific drug delivery via oral route, Biomaterials, 24, 3333-3343. 

According to the online resource, Pharmacircle, 53% of all commercialized pharmaceutical dosage forms are oral drug-delivery systems. Oral drug delivery is the most common route of administration due to the fact that it is more convenient, less invasive, and less painful compared to other routes of administration. Of the various oral drug-delivery systems shown in Figures 27.1 and 27.2, 68% are tablets and 20% are capsules. In particular, tablets are relatively easy to manufacture and are generally well-accepted by patients. 

Historically, the oral route of administration has been used the most for both conventional and novel drug-delivery systems. There are many obvious reasons for this, not the least of which would include acceptance by the patient and ease of administration. The types of sustained- and controlled-release systems employed for oral administration include virtually every currently known theoretical mechanism for such application. This is because there is more flexibility in dosage design, since constraints, such as sterility and potential damage at the site of administration, axe minimized. Because of this, it is convenient to discuss the different types of dosage forms by using those developed for oral administration as initial examples. 

There are few occasions where a drug is delivered alone in a pure form into the body, but it is usually combined with other materials (called excipients) to form drug delivery systems ( medicines , formulations or dosage forms ). These promote accurate dosing, therapeutic effectiveness, stability and patient acceptability. By far the most common route for delivering drugs into the body is by the oral route, swallowing a tablet or capsule. 

In case of systemic delivery of nucleic acid drugs via the oral route only comparatively small therapeutic agents such as oligonucleotides seem to reach the systemic circulation in significant quantities via the paracellular route of uptake. 

Absorption is the transfer of a drug from its site of administration to the blood stream. The rate and efficiency of absorption depend on the route of administration. For intravenous delivery, absorption is complete, that is, the total dose of drug reaches the systemic circulation. Drug delivery by other routes may result in only partial absorption and thus lower bioavailability. For example, the oral route requires that a drug dissolve in the gastrointestinal fluid and then penetrate the epithelial cells of the intestinal mucosa disease states or the presence of food may affect this process. 

Drugs chosen for delivery via a transdermal drug-delivery system must adequately penetrate the skin in such a way that the system determines the delivery rate that should be fairly constant. In addition, the drug must not irritate or sensitize the skin. It is hoped that in the future more drugs will be developed for transdermal delivery. This could become an alternative route for drug delivery to children who have difficulty with oral administration. 

Table 9.5 Commercially available drug-delivery systems for systemic delivery by the oral mucosal route ...

For many pharmaceutical compounds administered as transdermal drug delivery systems, absorption can be assessed by determining the area under the curve (AUC) of the plasma concentration-time profile, the peak plasma flux, and time of peak flux, much as it is for determining bioavailability from oral and other routes of administration. These are classical metrics of biophar-maceutical bioequivalence studies and are extensively covered in other texts... 

Parenteral administration is the primary route of testing delivery for nucleic acid therapeutics irrespective of whether systemic or local effects are desired. However, to some extent, pulmonary and oral routes are also investigated as potential routes for local targeting to treat cystic fibrosis or colonic tissue (171-173). For nonparenteral delivery, the use of pharmaceutical excipients in the formulation is critical. In addition, the production costs of nucleic acid therapeutic-containing drug delivery systems should be minimized. Even for intravenously or subcutaneously injected nucleic acid-based therapeutics, the use of protective carriers is most likely necessary, and advantageous as compared to injection of the naked RNA or DNA. Carriers can be divided into viral or... 

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