Pharmacology Flashcards
what force drives water out of capillaries
hydrostatic pressure in the capillary (Pc)
what drives water into the capillary
oncotic pressure of plasma (derived from plasma proteins)
examples of diseases that increase Pc and decrease oncotic pressure of plasma
nephrotic syndrome
CHF
hepatic cirrhosis with ascites
what causes nephrotic syndrome
there is a disruption to filtration barrier causing proteins to leave circulation and enter the filtrate
classic urine presentation of proteinuria
frothy urine
how does CHF cause oedema?
there is reduced CO and renal hypoperfusion activating RAAS causing retention of Na+ and H2O
how does cirrhosis with ascites cause oedema
increased pressure in hepatic portal veins and decreased production of albumin (liver disease) causes loss of fluid into peritoneal cavity which activates RAAS due to reduced circulating volume-thrombosis danger
where is the triple co-transporter Na+/K+/2Cl- found?
thick ascending loop of Henle
which diuretic blocks the triple co-transporter?
loop diuretics
which (now obsolete) diuretic blocks Na+/H+ exchange?
carbonic anhydrase inhibitors (found in PCT and early DCT)
where is the Na+/Cl- co-transporter found?
early DCT
which diuretic blocks Na+/Cl- co-transport?
thiazide diuretics
where is Na+/K+ exchanger found?
collecting duct
what blocks the Na+/K+ exchanger?
potassium-sparing diuretics
to act diuretics must enter the filtrate by?
- glomerular filtration (when not bound to large plasma proteins)
- secretion by PCT
two transport processes in PCT that secrete diuretics into the filtrate?
- organic anion transporters (OATs)
- organic cation transporters (OCTs)
what does OATs transport?
acidic/negatively charged molecules e.g. PAH, thiazides and loop
what do OCTs transport?
basic/ positively charged e.g. triamterene and amiloride
describe OA secretion
- OA- enters the tubular cell from the blood in exchange for alpha-KG via OAT1,2,3
- alpha-KG re-enters via NaDC3
- OA- crosses to the filtrate via MRP2/4 and BCRP
describe OC secretion
- OC+ enters the tubular cell via OCT2
- OC+ enters the lumen and filtrate via MATE or MDDR1
examples of loop diuretics
furosemide
bumetanide
what do loop diuretics bind to?
bind to Cl- on the triple co-transporter in PCT
action of loop diuretics
increased Na+ load is delivered to distal region of the nephron causing increased K+ loss with excretion of Ca2+ and Mg2+
also have a venodilator action
how do loop diuretics enter the filtrate?
strongly bind to plasma protein so enter via OAT
what are loop diuretics used in?
acute pulmonary oedema CHF CKF (increase UO in AKF) ascites nephrotic syndrome hypertension acute hypercalcaemia
contra-indications of loop diuretics
severe hypovolaemia
dehydration
cautions with loop diuretics
hypokalaemia
hyponatraemia
hepatic encephalopathy
gout
adverse effects of loop diuretics
- hypokalaemia (correct with potassium-sparing diuretics or supplements)
- metabolic alkalosis (Na+/H+)
- hypocalcaemia
- hypomagnesemia
- hypovolaemia
- hyperuricaemia (competition between uric acid and loop)
- dose related loss of hearing
which drugs does hypokalaemia increase toxicity of?
digoxin class III AADs
example of a thiazide diuretic
bendroflumethiazide
what do thiazides bind to?
Cl- binding site on Na+/Cl- in early DCT
action of thiazides
increase Na+ in collecting duct causing K+ loss and increased reabsorption of Ca2+ which causes diuresis
also vasodilation action
how do thiazides enter the filtrate?
OATs
clinical indications for thiazides
- hypertension (mild HF)
- severe resistant oedema
- renal stone disease (reduces Ca2+)
- nephrogenic DI
contra-indications and cautions of thiazides
hypokalaemia
hyponatremia
gout
adverse effects of thiazides
hypokalaemia metabolic alkalosis hypovolvaemia hypomagnesemia hyperuricaemia ED impaired glucose tolerance in diabetes
on what receptors does aldosterone act?
via cytoplasmic receptors
action of aldosterone
increase synthesis of protein that activates ENaC and increases Na+/K+ ATPase
why do spironolactone and eplerenone have limited diuretic action?
modulated by aldosterone
action of spironolactone and eplerenone
antagonists of aldosterone receptor so increase excretion of Na+ while decreasing excretion of K+
action of amiloride and triamterene
block luminal Na+ channels in collecting duct
how do potassium sparing diuretics enter the nephron
OCT in PCT
clinical indications of potassium-sparing diuretics
- in conjunction with diuretics that cause potassium loss (alone cause hyperkalaemia)
- heart failure
- primary aldosteronism (Conn’s) and secondary (cirrhosis and ascites)
- resistant hypertension
contra-indications of potassium-sparing diuretics
severe renal impairment
hyperkalaemia
Addisons
example of osmotic diuretic
mannitol
where does mannitol act
PCT
how does mannitol enter the filtrate?
glomerular filtration
clinical indications of mannitol
- prevent acute hypovolaemia renal failure to maintain UO
- acutely raised ICP and IOP
adverse of mannitol
transient expansion of blood volume and hyponatraemia
causes of osmotic diuresis
mannitol
hyperglycaemia
iodine radiocontrast dyes
examples of carbonic anhydrase inhibitors
azetazolamide
clinical uses of carbonic anhydrase inhibitors
no longer used as diuretics glaucoma following eye surgery (reduce IOP) prophylaxis of altitude sickness infantile epilepsy
when is alkalising the urine useful?
dysuria
prevention of uric stones
excretes weak acids
how to alkalinise the urine
- citrate salts (generate HCO3- in Krebs)
- carbonic anhydrase inhibitors
substances that inhibit ADH
lithium
demeclocycline
vaptans
example of vaptan
tolvaptan
action of tolvaptan
competitive antagonist of ADH receptors which causes excretion of water (but not Na+)
what is tolvaptan used in?
SIADH
when can glucose appear in the urine
diabetes when glucose concentration exceeds renal threshold (11mmol)
example of SGLT2i
empagliflozin
action of SGLT2i
excretes glucose
decreases HbA1c
weight loss
adverse of SGLT2i
genital bacterial and fungal infections
where is SGLT2 found?
PCT
responsible for reabsorption of glucose (against gradient with Na+ symport)
examples of prostaglandins synthesised by the kidney
PGE2 (medulla)
PGI2 (glomeruli)
action of prostaglandins
vasodilation
loss of Na+
when is synthesis of prostaglandins enhanced?
ischaemia trauma angiotensin II ADH bradykinin
when do prostaglandins have the largest effect
when there is vasoconstriction or hypovolaemia as vasodilates afferent arteriole and releases renin (angiotensin II vasoconstricts efferent) allowing kidneys to maintain UO
examples of NSAIDs
aspirin
naproxen
diclofenac
action of NSAIDs
inhibit COX and precipitate ARF in patients with low GFR e.g. bilateral RAS or hypovolaemia
describe the triple whammy effect
combination of ACEI/ARB, diuretic and NSAID
how is uric acid formed?
catabolism of purines
what does high urate in the serum predispose to?
gout
what blocks reabsorption of urate in PCT?
probenecid
sulfinpyrazole
action of allopurinol
stops urate synthesis