Drugs on the Kidney
Key Points:
Importance of the kidney in effects of drugs
How the kidney eliminates drugs from the body
Importance of pH in drug elimination
Sites of drug action on the kidney
Drugs acting on the kidney
-Osmotic diuretics
-Carbonic anhydrase inhibitors
-Thiazides
-Loop diuretics
-K-sparing diuretics
Central Role of Kidney in Action of Drugs
We take a drug, maybe IV, intramuscularly etc. to get it into our system, it has to be
absorbed (A).
It is absorbed into a central compartment (e.g. intravascular - in our blood plasma).
This drug is then taken around the body and distributed (D) to sites of action and
hopefully produce effects on the body.
The drug will be metabolised (M) and excreted (E) at the same time, the excretion part
is very much linked to the kidney, as excretion through urine is the most important
way.
The effect of giving a dosage of a drug and how much drug gets to do what it needs to,
is called pharmacokinetics (kinetics means time). It takes time to be absorbed, time to
be distributed and time to be metabolised and excreted.
Pharmacokinetics is what the body is doing to the drug, is it metabolising it very fast
or excreting it very quickly? Pharmacokinetics = ADME
Pharmacodynamics is what the drug does to the body, is it blocking or stimulating a
receptor for example.
How much we excrete by the kidney, will determine how much drug we take (drug per
Kg, is linked to this, the ADME).
, The kidney is the most important organ for eliminating drugs from the body (note
though that some will be lost in stool).
Some drugs are excreted unchanged (e.g. aspirin).
To be eliminated by the kidney, drugs need to be hydrophilic (polar, charged), if they
are lipophilic (non-polar) then these drugs will be reabsorbed by the kidney. You need
the drug in a form that is polar and doesn’t like to cross the membrane of tubule cells,
so once filtered stays in the filtrate.
Most drugs are metabolised by the liver to a polar compound (often inactive) that can
be excreted by the kidney, sometimes this increases/decreases the drugs effect.
So the kidney is very important in excreting polar molecules and as said if not they
tend to be reabsorbed into the blood stream.
Excretion of Drugs by the Kidney—
When we excrete a drug we have three things going on:
1 – Glomerular filtration (filter drugs through GFR)
2 – Passive tubular reabsorption (due to movement of drug down their conc. gradient,
if non-polar)
3 – Tubular secretion
Key Points:
Importance of the kidney in effects of drugs
How the kidney eliminates drugs from the body
Importance of pH in drug elimination
Sites of drug action on the kidney
Drugs acting on the kidney
-Osmotic diuretics
-Carbonic anhydrase inhibitors
-Thiazides
-Loop diuretics
-K-sparing diuretics
Central Role of Kidney in Action of Drugs
We take a drug, maybe IV, intramuscularly etc. to get it into our system, it has to be
absorbed (A).
It is absorbed into a central compartment (e.g. intravascular - in our blood plasma).
This drug is then taken around the body and distributed (D) to sites of action and
hopefully produce effects on the body.
The drug will be metabolised (M) and excreted (E) at the same time, the excretion part
is very much linked to the kidney, as excretion through urine is the most important
way.
The effect of giving a dosage of a drug and how much drug gets to do what it needs to,
is called pharmacokinetics (kinetics means time). It takes time to be absorbed, time to
be distributed and time to be metabolised and excreted.
Pharmacokinetics is what the body is doing to the drug, is it metabolising it very fast
or excreting it very quickly? Pharmacokinetics = ADME
Pharmacodynamics is what the drug does to the body, is it blocking or stimulating a
receptor for example.
How much we excrete by the kidney, will determine how much drug we take (drug per
Kg, is linked to this, the ADME).
, The kidney is the most important organ for eliminating drugs from the body (note
though that some will be lost in stool).
Some drugs are excreted unchanged (e.g. aspirin).
To be eliminated by the kidney, drugs need to be hydrophilic (polar, charged), if they
are lipophilic (non-polar) then these drugs will be reabsorbed by the kidney. You need
the drug in a form that is polar and doesn’t like to cross the membrane of tubule cells,
so once filtered stays in the filtrate.
Most drugs are metabolised by the liver to a polar compound (often inactive) that can
be excreted by the kidney, sometimes this increases/decreases the drugs effect.
So the kidney is very important in excreting polar molecules and as said if not they
tend to be reabsorbed into the blood stream.
Excretion of Drugs by the Kidney—
When we excrete a drug we have three things going on:
1 – Glomerular filtration (filter drugs through GFR)
2 – Passive tubular reabsorption (due to movement of drug down their conc. gradient,
if non-polar)
3 – Tubular secretion
