Drug Excretion Flashcards
What are the primary routes in which drugs are excreted from the body?
renal and hepatic
other routes are pulmonary, salivary, and mammary
Active tubular excretion
the active transport of drug from blood into the renal tubule, occurring primarily in the proximal tubule
competitive, saturable
Tubular reabsorption
the movement of solute from inside the renal tubule back into the blood. This is primarily a passive process of drugs and is driven by the high concentration effect that occurs as a result of the large fraction of filtrate that is reabsorbed.
Increasing urine flow will decrease reabsorption of drugs. The reabsorption of ionizable drugs is also sensitive to changes in urine pH.
Enterohepatic recirculation
the reabsorption of drug from the small intestine after drug has been excreted through the bile into the intestine
Dose dumping
the process by which food stimulates release of bile, and drug contained therein, into the small intestine, followed by reabsorption of the drug. This occurs because release of bile into small intestine in man is periodic, allowing drug to accumulate in gall bladder
What are the most important mechanisms of renal excretion?
filtration, active tubular secretion, and tubular reabsorption
What is Glomerular filtration largely influenced by?
molecular size and plasma protein binding
number of nephrons
renal blood flow
Drugs which undergo active tubular secretion
exhibit saturation at high concentration and are subject to competitive interactions with other drugs that undergo transport by the same renal transporters
What happens when carrier-mediated tubular reabsorption occurs?
as a consequence, increasing the dose will increase the fraction of drug excreted in the urine.
saturable
ascorbic acid and glucose are examples
Hepatic elimination involves two processes
metabolism (biotransformation) and biliary excretion
What primary factors determine biliary excretion
molecular weight and polarity
large polar molecules are mostly eliminated in the bile
What is the effect of enterohepatic recirculation on the half-life of a drug?
Increases half-life, thus prolonging their actions
Plot the relationship between molecular weight and renal clearance
linear decrease
slide 6
Plot the relationship between dose and urinary excretion rate
Filtration is linear increase
Saturation at high concentration begins to increase then starts to flat line
Plot the relationship between molecular weight and percent of drug excreted in
bile
excretion increases as MW increases
linear relationship
