



Q:Ans:Aspirirn should be taken during or immediate after meal although food decreases its absorption. If aspirin is given in the empty stomach then it produces gastrointestinal irritation which causes gastic ulcer. To avoid this, aspirin is taken during or immediate after meal.Define bioavailability with example.Bioavailability: Bioavailability can be defined as the amount or percentage of active drug that is being absorbed from a given dosage form and is made available to the site of action is called bioavailability of that particular drug.Example: Bioavailability of digoxin is 62%. It means if a patient orally takes 250 mg of digoxin, only 155 mg (62%) of drug will reach to the systemic circulation.Examplified by,Intravenous-* 100% bioavaiabilityTransdermal80-100% bioavailabilityOral —> 5 - < 100% bioavailabilityDefine the distribution of drugs.Distribution of drugs: All the consequences of delivery of drugs to the tissue are called distribution of drugs. Distribution of drug means dividing and spreading of drug to the tissue.Define selective distribution of drug with examples.Selective distribution of drug: Selective distribution of drug means special distributionof drug in the certain tissue of the body due to special affinity between particular drugand particular body constituents.Example: 12 --> Thyroid glandHeavy metals (Arsenic) —> Hair & nail.Digoxin—> HeartTetracycline —> Ca"containing tissue (e.g. bones & teeth)Q:Volume of distribution (Vd):The volume of fluid into which drug appears to be distributed in the body in a concentration equal to that in the plasma is called volume of distribution of that drug. Amount of drug in the bodyVd=Conc.of drug in plasma/blood at that timeVd= 13000 L means 13000 L fluid is required to keep all the drug, administered in the plasma in a concentration equal to normally remaining in plasma.