Study Set Content:
Drug clearance principles are similar to the
clearance concepts of
renal physiology.
Clearance of a drug is the factor that predicts the
rate of
elimination in relation to the drug concentration:
“Other” tissues of elimination could include the (blank) and additional sites of metabolism, eg, (blank)
lungs, blood or
muscle.
The two major sites of drug elimination:
Kidneys
Liver
Clearance of unchanged drug in the urine represents
renal clearance.
Within the liver, drug elimination
occurs via (blank) of parent drug to one or
more metabolites,
biotransformation
Clearance of unchanged drug in the urine represents
renal clearance. Within the liver, drug elimination
occurs via biotransformation of parent drug to one or
more metabolites, or(blank)
into the bile, or both.
excretion of unchanged drug
In the kidneys, drugs are excreted through
glomerular filtration, tubular reabsorption, and
active tubular secretion.
uses a passive process
where small molecules and drugs are filtered
through the glomerulus of the nephron.
Glomerular filtration
There are
drugs bound to plasma proteins that are too large
to be filtered at the glomerulus. Drugs like
creatinine and inulin
There are
drugs bound to plasma proteins that are too large
to be filtered at the glomerulus. Drugs like
creatinine and inulin are not actively secreted or
reabsorbed, which is why they are used to
measure
glomerular filtration rate or (GFR).
In other cases of drugs, there is a (blank) that is reabsorbed easily from
the lumen of the nephron.
non-ionized
(lipid-soluble form)
But there are also
drugs that exist in an (blank) which is excreted more readily in the urine.
ionized (water-soluble
form)
But there are also
drugs that exist in an ionized (water-soluble
form) which is excreted more readily in the urine.
This is helpful in cases of
poisoning or
overdosage.
Another process is
active tubular secretion.
There are 2 active tubular secretion pathways in
the kidneys:
kidneys: 1 system for weak acids and 1
system for weak bases.
For most drugs, clearance is constant over the
concentration range encountered in clinical settings, ie,
elimination is not
saturable
rate of drug
elimination is directly proportional to
concentration
Rate of Elimination =
CL x C
For most drugs, clearance is constant over the
concentration range encountered in clinical settings, ie,
elimination is not saturable, and the rate of drug
elimination is directly proportional to concentration
(rearranging equation [2]):
first-order elimination.
