Drug Kinetics

Today I am discussing the concept of ‘how body gives response to the drug?’ Well, it refers to movement of the drug in and alteration of the drug by the body. Now, one can think there are various routes of administration, then, how would body become effective in all routes? Of course, the effects by the body will not be same, and the choice of appropriate route depends both on drug as well as patient related factors. Anyway, routes can be broadly classified into those for (a) local action and (b) systemic action. Local routes can only be used for localized lesions at sites where it’ll be easier access of drugs and, of course, systemic absorption of drugs from that site is minimal or absent. Thus high concentrations are attained at the desired site without exposing rest of the body. Besides, in case of oropharyngeal/nasal mucosa, eyes, ear canal, anal canal or vagina in the form of lotion, ointment, cream, powder etc. in case one has back injury or ankle injury or burnt issues and some sort of chemical contamination, then, primarily treatment is done topically. In case of deeper tissues, drugs are approachedby using syringe and needle, but the drug should have low systemic absorption. Systemic action introduces several terms and concepts and that’s where I am going to mention different routes which are oral, buccal, rectal, cutaneous, inhalation, nasal, and parenteral routes. However, systemic action defines by four principles which are, when the drug is administered into the body,

it undergoes Absorption, Distribution, Metabolism and Excretion. And the whole process is carried out by the body; 
1. Absorption; is mostly due to formation of insoluble and poorly absorbed complexes in the gut lumen as occurs between tetracyclines and calcium/iron salts, antacids or sucralfate.
2. Distribution; of drug describes the reversible transfer of a drug from one location to another within the body,once, a drug enters into systemic circulation by absorption or direct administration, and it must be distributed into interstitial and intracellular fluids.
3. Metabolism; is the metabolic breakdown of drugs by living organisms, usually through specialized enzymatic systems, especially microsomal enzymes. 
4. Excretion; of a drug is understood to be any one of a number of processes by which a drug is eliminated from an organism either in an unaltered form or modified as a metabolite. 

I hope this can extremely be useful, if, you have any question, let me know by dropping comment and be safe and make others too..