And localization of drug action

Advantages of the intramuscular and subcutaneous routes include an increased reliability and precision in the drug blood level Anally achieved and reasonably rapid absorption and onset of drug action. There are, however, serious disadvantages as well. Pain, tenderness, local tissue necrosis (primarily with highly alkaline injections), microbial contamination, and nerve damage may be associated with these forms of parenteral administration. 

CELLULAR SITES OF DRUG ACTION Drugs act by altering the activities of their receptors. The sites at which drugs act and the extent of this action are determined by the location and fimctional capacity of receptors. Selective localization of drug action within an organism therefore... 

Heparin is prescribed on a unit (lU) rather than milligram basis. Tlie dose must be determined on an individual basis. Heparin is not absorbed after oral administration and therefore must be given parenterally. Intravenous administration results in an almost immediate anticoagulant effect. There is an approximate 2-hour delay in onset of drug action after subcutaneous administration. Intramuscular injection of heparin is to be avoided because of unpredictable absorption rates, local bleeding, and irritation. Heparin is not bound to plasma proteins or secreted into breast mUk, and it does not cross the placenta. 

The site of drug action means where a drug acts and mechanism means how the drug acts. Drug which act only at the site of application (i.e. localized region) are termed as local or topical action for example, ointments, paste, creams and certain other local preparations used externally produce only local effect. The local anaesthetics like lignocaine, procaine produce anaesthesia (local) in a localized region only. 

Caterall, W. A. Common modes of drug action on Na+ channels local anesthetics, antiarrhythmics and anticonvulsants, Trends Pharmacol. Sci. 1987, 8, 57-65. 

The total surface area of the nasal cavity is about 150 cm2, with the area available for absorption enhanced by the convolutions of the turbinates and the presence of microvilli on the surface of the ciliated and unciliated cells of the respiratory epithelium. The arterial supply of the nose is particularly rich in the respiratory epithelium where the Kiesselbach s plexus lies, an area that is rich in numerous capillary loops. The nasal blood flow has been shown to be sensitive to the action of a variety of inhaled compounds, both locally or systemically acting. Clonidine has been shown to decrease the blood flow whereas histamine and phenylephrine have been shown to induce the converse effect. Such direct changes to blood flow are important in determining the rate and extent of drug absorption from the nasal cavity. 

As pointed out by Anderson et al. (15), starvation, malnutrition, and protein deficiency may all cause differences in drug disposition and thereby differences of drug action. Even relatively minor food deficiencies as observed in Berlin after the second World War (16) caused some unusual reactions, e.g., death from injection of the old and generally safe local anesthetic drug procaine (17). 

Both the rate and extent of drug distribution across tissue barriers can have a profound impact on pharmacokinetic and pharmacodynamic properties. The extent of drug distribution manifests itself locally as the tissue to plasma (or blood) concentration ratio. Collectively, the extent of distribution into all the tissues results in the apparent volume of distribution. Simply put, the pharmacokinetic parameter volume of distribution reflects the ratio of individual tissue to plasma drug concentration weighed for tissue volume. The rate of distribution (together with the extent of distribution) can influence the shape of the plasma versus time profile for a drug, which can give rise to differences in elimination half-life as well as onset and duration of action. 

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