Jagadeeswaran Appusamy

Prolonging drug action Action of a drug may be prolonged to 1.   Reduce the frequency of administration 2.   Avoid large fluctuations in plasma concentration 3.   Maintain drug effect overnight without disturbing sleep. This can be achieved by 1.   Delaying absorption - It is desirable to delay absorption, either to reduce the systemic actions of drugs that are being used to produce a local effect or to prolong systemic action. Addition of epinephrine or norepinephrine to local anaesthetic delays absorption due to vasoconstriction. This prolongs the anaesthetic effect and in addition reduces systemic toxicity. From the subcutaneous or intramuscular administration sites, absorption can be delayed by using a relatively insoluble 'slow-release' form. A poorly soluble salt, ester or complex -   injected either as an aqueous solution or an oily solution will have delayed absorption. Procaine penicillin is a poorly soluble salt of penicillin which w...

Pharmacokinetics - Drug elimination The concentration of a drug in the plasma or at its receptor sites may be reduced in three basic ways: 1.      distribution or redistribution into various compartments, 2.      metabolic inactivation and 3.      excretion from the body via one of the several possible routes. Routes of elimination - Drugs are excreted mainly by the kidneys into the urine and the liver into the bile and subsequently into the feces. Alveolar elimination is of major significance when inhalant anaesthetics are used. The main factors governing elimination by this route are concentration in plasma and alveolar air and the blood/gas partition coefficient. Other less common routes of elimination include saliva, milk, and sweat. The salivary route of excretion is important in ruminants because they secrete such voluminous amounts of alkaline saliva. Some drugs excreted unchanged but the vast majority...

Pharmacokinetics - Drug metabolism / biotransformation             Drugs and other foreign chemicals (collectively called as Xenobiotics) may be present in two forms in animal’s body: 1. Polar , water soluble compounds that usually are not metabolized to any appreciable extent & are excreted unchanged, 2. Non-polar , lipid soluble compounds that first must be metabolically transformed to more polar & water soluble forms that only then can be efficiently excreted in urine / bile.             Elimination of drugs refers to all processes that operate to reduce the concentration of the drug in the body fluids. Hepatic metabolism and renal excretion are the principal mechanisms of drug elimination. Metabolism is the term used to denote normal anabolic and catabolic reactions of the body. Biotransformation is probably the best term useful for describing the biologi...