Orally delivered drugs absorption

Opioids maybe administered in a variety of routes including oral (tablet and liquid), sublingual, rectal, transdermal, transmucosal, intravenous, subcutaneous, and intraspinal. While the oral and transdermal routes are most common, the method of administration is based on patient needs (severity of pain) and characteristics (swallowing difficulty and preference). Oral opioids have an onset of effect of 45 minutes, so intravenous or subcutaneous administration maybe preferred if more rapid relief is desired. Intramuscular injections are not recommended because of pain at the injection site and wide fluctuations in drug absorption and peak plasma concentrations achieved. More invasive routes of administration such as PCA and intraspinal (epidural and intrathecal) are primarily used postoperatively, but may also be used in refractory chronic pain situations. PCA delivers a self-administered dose via an infusion pump with a preprogrammed dose, minimum dosing interval, and maximum hourly dose. Morphine, fentanyl, and hydromorphone are commonly administered via PCA pumps by the intravenous route, but less frequently by the subcutaneous or epidural route. 

Grass GM (1997) Simulation models to predict oral drug absorption from in vitro data. Adv. Drug Deliv. Rev. 23 199-219. 

Hunter, J., and B.H. Hirst. 1997. Intestinal secretion of drugs. The role of P-glycoprotein and related drug efflux systems in limiting oral drug absorption. Adv Drug Deliv Rev 25 129. 

The nasal route of drug delivery is used for the direct administration of medicines to the nose for treatment of local conditions or the systemic delivery of compounds that are not easily delivered by the oral route. It is also suggested that there may be a direct route for drug absorption to the central nervous system (CNS) from the olfactory region of the nose. 

Thanou, M., Verhoef, J.C. and Junginger, H.E. (2001c) Oral drug absorption enhancement by chitosan and its derivatives. Adv. Drug Deliv. Rev. 52 117-126. 

Poly(alkyl-cyanoacrylate) Nanoparticles The applications of poly(alkyl-cyanoacrylate) nanoparticles have been reviewed elsewhere and therefore only representative examples are described [102], Because of their adhesive properties, nanoparticles have the potential to prophylactically treat candidiasis of the oral cavity [121], Not surprisingly, poly(alkyl-cyanoacrylate) nanoparticles have been used to deliver drugs to tumors [122], Enhanced absorption and prolonged hypoglycemic effect were observed when insulin was delivered in poly(alkyl-cyanoacrylate) nanoparticles [121], Nuclear accumulation of antisense oligonucleotides into vascular smooth muscle cells was increased when delivered using poly(alkyl-cyanoacrylate) nanoparticles [123]. Dextran-coated poly(alkyl-... 

Ability to maintain a constant drug input in the colon for up to 24 h or to deliver drug over an interval as short as 4 h Oral delivery of peptides and proteins. The system can be used to study colonic absorption in humans prior to development of colon-specific delivery systems. 

Upon intranasal administration, a drug is not as susceptible to dilution and first-pass effects as in oral delivery.46 47 The nasal route may also be an effective means of delivering drugs to the brain 46 Barriers to nasal delivery include the enzymes of the nasal mucosa, the epithelial barrier, the mucus layer, and limited absorption time resulting from mucociliary clearance.48... 

In this chapter, we summarize the general approaches that have been used to successfully achieve the formulation goals for oral delivery minimize enzymatic degradation enhance intestinal absorption maximize blood level reproducibility deliver drug through the gut wall and produce a palatable and acceptable dosage form. Then insulin will be used as an example to show how oral bioavailability has been achieved through chemical modification. 

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