Pharmacokinetics diffusion

The CAT model estimates not only the extent of drug absorption, but also the rate of drug absorption that makes it possible to couple the CAT model to pharmacokinetic models to estimate plasma concentration profiles. The CAT model has been used to estimate the rate of absorption for saturable and region-depen-dent drugs, such as cefatrizine [67], In this case, the model simultaneously considers passive diffusion, saturable absorption, GI degradation, and transit. The mass balance equation, Eq. (51), needs to be rewritten to include all these processes ... 

Many drugs have been recognized to cross the intestinal epithelial cells via passive diffusion, thus their lipophilicity has been considered important. However, as described above, recent studies have demonstrated that a number of drug transporters including uptake and efflux systems determine the membrane transport process. In this chapter, we provide an overview of the basic characteristics of major drug transporters responsible not only for absorption but also for disposition and excretion in order to delineate the impact of drug transport proteins on pharmacokinetics. 

Fig. 1. Schematic compartmental pharmacokinetic representation of different classes of contrast agents a. nonspecific agent (NSA e.g. iobitridol) b. low-diffusion agent (LDA) c. rapid-clearance blood-pool agent (RCBPA e.g. P743) d. slow-clearance blood-pool agent (SCBPA, e.g. P840). From Id e et al. (2001) Invest Radiol 26 41,with permission ( Lippincott Williams Wilkins)...

DIFFUSION OF LIGAND TO RECEPTOR Drug clearance, dosage, PHARMACOKINETICS Drug distribution kinetics, PHARMACOKINETICS Drug excretion rates,... 

Because of its pharmacokinetic features (pronounced bioaccessability upon oral use, diffusion to tissues and permeation into them, broad spectrum of antibacterial activity, and so on), fluoroquinolones have considerable potential for treating infections of practically any anatomic localization. Fluoroquinolones are very effective in treating infections of the respiratory tract, urinary tract, bones, skin, soft tissues, and so on. 

Mechanism of Action Clioquinol is a broad-spectrum antibacterial agent but the mechanism of action is unknown. Hydrocortisone is a corticosteroid that diffuses across cell membranes, forms complexes with specific receptors and further binds to DNA and stimulates transcription of mRNA (messenger RNA) and subsequent protein synthesis of various enzymes thought to be ultimately responsible for the anti-inflammatory effects of corticosteroids applied topically to the skin Therapeutic Effect Alters membrane function and produces antibacterial activity Pharmacokinetics Clioquinol may be absorbed through the skin in sufficient amounts. 

Pharmacokinetics Well absorbed after parenteral administration poorly absorbed from fhe gasfroinfesfinal (GI) tract. Penetrates to extracellular fluid and slowly diffuses into cerebrospinal fluid (CSF). No metabolism occurs. Excreted in the urine either unchanged or as the metal chelates. Half-life 20-60 min (IV), 1.5 hr (IM). 

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