pharmacology Flashcards
what is natriuresis?
the process of excretion of sodium in the urine via action of the kidneys. ↓ the concentration of NA+ in the blood.
what promotes natriuresis?
promoted (more sodium is excreted) by ventricular and atrial natriuretic peptides as well as calcitonin
what inhibits natriuresis?
inhibited (sodium is conserved) by chemicals such as aldosterone
what is required to compensate for the body’s tendency to decrease pH due to metabolic production of CO2 (glycolysis)?
formation of acidic urine
how do diuretics work?
↑ the volume of urine produced by promoting the excretion of Na+, Cl-, HCO3 and water from the kidneys
NET result is ↑ urine flow, altered pH and altered ionic composition of blood and urine
what are the different classes of diuretics?
Osmotic diuretics
Carbonic anhydrase inhibitors
Loop diuretics
Thiazide diuretics
Potassium sparing diuretics
where do carbonic anhydrase inhibitors act and what do they do?
proximal tubules
inhibit bicarbonate reabsorption
where do osmotic diuretics act and what do they do?
proximal tubules, loop of henle and collecting duct
inhibit water and Na+ reabsorption
where do loop diuretics act and what do they do?
thick ascending limb of loop of henle
inhibition of Na+, K+ and Cl-
where do thiazides act and what do they do?
early distal tubule
inhibit Na+, Cl- co-transport
loss of Na+, increase of Ca2+
where do potassium sparing diuretics act and what do they do?
late distal tubule and collecting duct
inhibit Na+ reabsorption and K+ secretion
what are examples of osmotic diuretics?
mannitol, isosorbide, glycerine and urea
what is the result of osmotic diuresis?
blood volume decreased
large volume of dilute urine produced
why is mannitol the osmotic diuretic of choice?
1) it is inherently non-toxic
2) it is freely filtered
3) it is non-reabsorbable
4) it is not metabolised
5) the other agents may pass into cells to a limited extent
what are the adverse effects of osmotic diuretics?
cardiovascular toxicity immediately after injection - increases workload of the heart
don’t use on patients with congestive heart failure
what are some examples of carbonic anhydrase inhibitors?
Acetazolamide, Methazolamide
what are indications to give carbonic anhydrase inhibitors?
Raised intra-ocular pressure in open-angle glaucoma
Ocular hypertension when monotherapy is inadequate
what are the side effects of carbonic anhydrase inhibitors?
Metabolic acidosis
Renal stones (Calcium and phosphate)
Renal potassium wasting (enhanced K+ secretion due to NaHCO3)
what are examples of loop diuretics and what do they do?
furosamide, torasamide - act on the chloride-binding site and directly inhibit the carrier
when would you prescribe a loop diuretic?
to treat water imbalances associated with congestive heart failure and kidney failure and pulmonary oedema
what are the contraindications of loop diuretic?
Loop diuretics can interact negatively with other medications - NSAIDs reduce their effect & aminoglycoside antibiotics used with them can increase risk of hearing loss and kidney damage
Low potassium levels associated (hypokalemia) with loop diuretics increase the risk of digoxin toxicity, a medicine prescribed for congestive heart failure
what are some examples of thiazide diuretics?
Hydrochlorothiazide, clorothiazide, bendroflumethiazide
when would you prescribe a thiazide diuretic?
to treat high blood pressure and congestive heart failure, oedema arising due to heart failure, cirrhosis, chronic kidney failure and nephrotic syndrome
when should you not give a thiazide?
if the patient has:
Hypotension
Gout
Renal failure
Lithium therapy
Hypokalemia
May worsen diabetes so a consideration but often still prescribed due to the benefits
chronic administration can also cause hyperglycaemia
