PHARMACOLOGY

 BIOAVAILABILITY ::

Bioavailability is the term used to describe the proportion of the administered drug that reaches the systemic circulation in the unchanged form and is available at the site of drug action Thus Bioavilability of Drugs decribes a number of aspects associated with the effects of drugs after it is being administered for instance the extent of absorption its first by -pass metabolism in the liver its distribution and excretion there are number of factors that affect these processes Moreover different formulations of the same drug will not necessarily produce identical drug levels and hence pharmacological response would vary it is possible that a formulation producing lower blood levels may be ineffective or a formulation producing higher blood levels may produce toxic manifestations 

        The bioavailability of any drug after IV administration is 100 percent and is usually assumed to be close to this value when given IM or SC However some highly insoluble drugs like phenytoin digoxin and diazepam partly precipitate at the site of injection and then are slowly absorbed The bioavailability of drugs after oral administration is frequently less than 100 percent In view of this problems regarding drug bioavailability usually refer to the oral administration of drugs