Pharmacology Flashcards
Why does tubular reabsorption of drugs have an impact on half life of a drug?
Because if drugs are reabsorbed they stay longer in the
body(active or passive).
What are diuretics?
Drugs that increase the rate of urine flow and excretion of Na and water from the filtrate.
When is it appropriate to use diuretics?
. Oedema (of cardiac, hepatic or renal origin)
. Acute renal failure (shock) - iv
. Forced diuresis (stimulate the excretion of toxins,
intoxications)
. Correct specific ion imbalances
What are the 2 groups of diuretics and how do they work?
1st group: act specifically on cells in the tubule; most common used. They interfere with transport mechanisms of Na in tubule.
2nd group: are osmotic diuretics. Drugs of high osmolality which are filtering into the urine and by passing through the tubule will attract water.
What is carbonic anhydrase?
An enzyme catalyzing the reaction of carbon dioxide and water.
What do carbonic anhydrase inhibitors do?
Carbonic anhydrase inhibitois block the reaction of carbon dioxide and water and so prevent Na/H exchange and bicarbonate reabsorption.
The increased bicarbonate levels in the filtrate oppose water reabsorption.
Proximal tubule sodium reabsorption is also reduced because it is partly dependent on bicarbonate reabsorption.
What are carbonic anhydrase inhibitors used for?
Used for glaucoma, epilepsy (rarely), benign intracranial hypertension, and altitude sickness.
What are loop diuretics?
Loop diuretics are strong diuretics and include furoseinide, bumetanide and ethactynic acid.
They are highly plasma bound, but are secreted into the proximal tubule by the organic anion transporter.
How do loop diuretics work?
They bind the NKCC2 co-transporter in the thick
ascending limb of the loop of Henle. This binding inhibits sodium, potassium and chloride reabsorption causing diuresis with loss of these electrolytes.
The transcellular voltage difference falls, and paracellular calcium and magnesium reabsorption are also reduced.
Loop diuretics can reduce the ability of the kidney to concentrate urine.
Thiazide diuretics do what to calcium?
Reduce urinary calcium excretion.
Thiazides are generally weak diuretics and are secreted into the proximal tubule but where do they act?
They reversibly inhibit the NCC apical NaCl co-transporter in the early distal tubule by binding to
the chloride-binding site. More sodium is then delivered to the principal cells of the collecting duct.
How can thiazades sometimes cause hypokalaemia?
Some of this excess sodium delivered to the collecting duct is exchanged for potassium causing hypokalemia.
What are some adverse effects of thiazides?
Sodium, potassium. chloride, and
magnesium depletion.
Cholesterol and urate levels can rise.
What does aldosterone do?
Aldosterone promotes sodium reabsorption and potassium secretion by increasing transcription of the ENaC channel and the NaK ATPase.
What is the action of the aldosterone antagonists: SpronoIactone?
The cells are impermeable to Na+ in the absence of
aldosterone. Aldosterone acts on a nuclear receptor within the tubule cell and on membrane receptors.
Spironolactone competes with aldosterone at its
receptor site. Thereby reducing Na re absorption and K secretion.