Absorption routes

I Ahmed, TF Patton. (1985). Importance of the noncorneal absorption route in topical ophthalmic drug delivery. Invest Ophthalmol Vis Sci 26 584-587. 

Hazardous substances are chemical substances with properties that may have certain harmful effects on humans and on the envirorrment upon contact or exposure. The risk arises from the degree of hazard presented by the substance (including any of its metabolites) as well as the nature and interrsity of contact (duration, dosage, absorption route, frequency). Hazardous substances in a legal sense are chemicals which must be classified as hazardous due to certain predefined criteria and available information or which have been classified as hazardous by official bodies. 

FIGURE 1.11 A scheme of the various absorption routes across the intestinal epithelium and cellular barriers to xenobiotics absorption. A, Transcellular absorption (plain diffusion) B, paracellular absorption C, carrier-mediated transcellular absorption D, facilitated diffusion E, the MDR and P-gp absorption barrier and F, endocytosis. (From Hunter, J. and Hirst, B.H., Adv. Drug Deliv. Rev., 25, 129, 1997. With permission.)... 

In addition to the corneal route, topically applied ocular drugs may be absorbed via a noncorneal absorption route that involves drug transport across the bulbar conjunctiva and underlying sclera into the uveal tract and vitreous humor.65 The intercellular spaces of the conjunctival epithelium are wider than those of the corneal epithelium. As a result, the conjunctiva has higher permeability than the cornea to agents such as mannitol, inulin, and FITC-dextran.86 The penetration of peptides, however, is limited by enzymatic degradation.87 The limit of molecular size for conjunctival penetration is between 20,000 and 40,000 Da. Vitreous can act as an aqueous and unstirred diffusion barrier to drug permeation.64... 

In contrast, Absolute Bioavailability involves comparison of the chug s bioavailability with respect to the corresponding bioavailability after iv administration. Absolute bioavailability may be calculated by comparing the total area under the Cp vs T curve obtained from the absorption route in question (often the oral route, although the approach can be used for other routes, such as the nasal, buccal, transdermal routes etc ), with that of the Cp vs T curve following iv administration ... 

Absorption Route Epithelial Type Surface Specialization Presence of Mucus Primary Role ... 

In this section, the pharmacokinetics for systemic dosage forms should be described, including absorption, routes of excretion, protein binding, metabolic changes to compounds of lesser or greater activity, and distribution into various pharmacokinetic compartments. References to the locations in the NDA of the full reports of the pharmacokinetics studies should be provided. 

Figure 2-4 Cross-section of the eye and various drug absorption routes. (From Hosoya K, Lee VHL, Kim KJ. Roles of the conjunctiva in ocular drug delivery a review of conjunctival transport mechanisms and their regulation. Eur J Pharm Biopharm 2005 60 227-240.)...

Notwithstanding these factors, the physical characteristics of compounds for optimal intranasal absorption are the same as for other absorption routes. The drug must dissolve in the fluids of the nasal mucosa and must be sufficiently lipophilic to cross the membranes of the nasal epithelium. Nasal absorption is facilitated by the high permeability of small venules and capillaries associated with the nasal mucusa. 

Fig. 1 Lateral view of the female pelvis showing the absorption route to the systemic circulation.

The lymphatic system, which is highly permeable even to large protein molecules, slowly collects some of the phenol in the interstitial fluid. The total daily volume carried by the lymphatic system is approximately equal to the volume of blood of the same individual. This absorption route is very slow and therefore negligible from a toxicological point of view. 

The dose absorbed through a primary absorption route depends on ... 

There are three main absorption routes to enter the body inhalation into the lungs, ingestion into the gastrointestinal tract, or penetration across the skin, or through placenta in the case of a fetus (Vander et al., 1998). A chemical can also enter the body by direct injection into the bloodstream or under the skin, but these are not ordinary means of entry. 

Xenobiotics enter in the bloodstream, following one of the described absorption routes, are distributed into the body and undertaken by different organs. It is possible that a part of the xenobiotics distributed into the body may be stored in tissues or even in the blood. A word commonly used to refer to storage of a pollutant at higher levels than those found in the environment is bioaccumulation, for example, PAHs, PCBs, dioxins and some organometallic forms of metals bioaccumulate in fat, fluoride and lead in bones etc. Sometimes biomagnification takes place, as a bioaccumulation process within the trophic chain, in indirect relationship with biota. 

Highly toxic by oral, ocular, inhalation, and skin absorption routes exposure to 27 ppm/4 hr was lethal to mice following lacrimation and somnolence ocular and oral intake prodnced tremor, convulsion, coma, and death subcutaneous dose of 15 mg/kg was lethal to mice LD50 oral (mice) 10 mg/kg LD50 skin (rabbits) ... 

Absorption route Can enter the body by inhalation or ingestion. Insufficient data on the rate at whioh harmful concentrations can build up. ... 

Absorption route Can enter the body by inhtfation or ingestion. Harmful atmospheric concentrations can build up fairly rapidly on evaporation at approx. 20 C even more rapidly in aerosol form. Immediate effects Corrosive to the eyes, skin and respiratory tract. Inhalation of vapor/fumes can cause severe breathing difficulties (king edema). In serious cases risk of death. ... 

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