EXCRETION OF DRUGS
Drugs are excreted either unchanged or as metabolites Generally more polar lipid insoluble and water soluble drugs are excreted unchanged Non -polar and lipid soluble drugs one metabolized to polar and lipid insoluble drugs and hence are excreted as metabolites
Drugs are mostly excreted through urine (kidney) They may also be excreted through stool (colon) and expiration (lungs) minor excretion of drugs also occurs through sweat bile milk tears and even through foetal circulation hair and nails
Kidneys ::
They play an important role in excretion They do so by 1.Glomerular filtration 2. Active tubular secretion 3.Tubular reabsorption and excretion
The excretion by kidney (renal excretion ) is an irreversible process of first order reaction i.e.a constant fraction of drug is excreted at a given time
Glomerular filtration ::
It depends on permeability of capillaries area of filtration and difference between hydrostatic and osmotic pressure of plasma Thus any condition affecting any of these factors may alter the excretion of drugs In glomerular filtration proteins are not filtered hence protein bound drugs cannot be excreted They are excreted only if they are released from proteins
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