Pharmacology Flashcards
Give examples of drugs which act on the kidney
Diuretics
Vasopressin (ADH) agonists/antagonists
SGLT2 inhibitors
Uricosuric drugs (promote uric acid excretion)
When does oedema occur?
When there is an imbalance between the rate of formation and absorption of interstitial fluid
What 4 forces are responsible for the constant water exchange between blood and the interstitium?
STARLING FORCES
Pc - hydrostatic pressure in capillary
Pi - hydrostatic pressure in interstitial fluid
Op - oncotic pressure of plasma
Oi - oncotic pressure of interstitial fluid
Changes in which of the 4 starling forces promotes Oedema?
Increased Hydrostatic Capillary pressure
Decreased Plasma Oncotic pressure
What diseases change the Hydrostatic capillary pressure and plasma oncotic pressure therefore leading to oedema?
- nephrotic syndrome
- congestive heart failure
- hepatic cirrhosis with ascites
How does nephrotic syndrome contribute to oedema?
- Increased production of interstitial fluid
- Decreased blood vol and cardiac output
- Activates RAAS
- Salt and water retention
- Increased Pc, Decreased Op
=> oedema
How does congestive heart failure cause oedema?
Decreased cardiac output => renal hypoperfusion => activates RAAS => Water and Na retention => blood volume and pressure increases BUT Op decreases => pulmonary and peripheral oedema
How does Hepatic cirrhosis with Ascites contribute to oedema?
- Increased pressure in the hepatic portal vein
- decreased production of albumin
=> loss of fluid into the peritoneal cavity and oedema (ascites)
Activation of RAAS occurs in response
What subtype of diuretics work in the proximal convoluted tubule?
carbonic anhydrase inhibitors
Where do LOOP diuretics complete their action?
Thick ascending limb of the LOOP of Henle
What diuretics work in the early distal convoluted tubule?
Carbonic Anhydrase inhibitors
thiazides
Where in the nephron do potassium sparing diuretics act?
Collecting duct
Why must diuretics get into the filtrate in order to act?
site of action of most diuretics is the apical membrane of tubular cells
How do diuretics get into the filtrate?
glomerular filtration (for drug not bound to large plasma protein) secretion in prox. tubule via OATs/OCTs
What are OATs and OCTs?
organic anion transporters (OATs) – transport acidic drugs
organic cation transporters (OCTs) – transport basic drugs
How does secretion of a diuretic into the filtrat contribute to pharmacological selectivity?
secretion means concentration of diuretic in the filtrate is higher than that in blood
=> more likely to act on receptors in nephrons than elsewhere in the body
How do Organic anion transporters move from the interstitium into the lumen of the nephron?
Na/K ATPase regulates low intracellular Na
=> Na outside cell moves IN via conc. gradient
=> Na moves in on transporter which also brings in α-KG
=> α-KG exchanges back out of cell for an OAT
=> Then moved into lumen via PRIMARY ACTIVE transport
Give examples of drugs that use OATs?
Diuretics (bumetanide, furosemide) Simvastatin Many penicillins NSAIDs Endogenous urate
Describe how OCTs travel from the interstitium to the tubule lumen?
- Na/K ATPase regulates membrane potential
- OC+ moves into cell due to negative membrane potential attraction
- Move into lumen via antiport with H+
OR primary active transport MDR1
What drugs are known to use OCTs?
diuretics (amiloride, triamterene => potassium sparing) atropine metformin morphine procainamide endogenous catecholamines
Describe the normal function of the Na/K/2Cl triple cotransporter
Na moves in via triple transporter and out via Na/K pump
Cl moves in via triple transporter and out via CIC-Kb/Barttin
K moves in via triple transporter and out via apical or basolateral K channels
Why is it important to have K channels on the apical membrane
So K moves back into lumen
=> can rebind to transporter
What creates the charge difference between the lumen (+ve) and interstitium (-ve)?
K moving back into lumen
=> allows Ca and Mg to move paracellulary
What genetic diseases can affect the function of the triple co-transporter?
Mutation in transporter itself
CIC-Kb/Barttin mutation
K+ channel mutation
What does Bartter syndrome cause?
Na and H2O wasting
hypokalemia, alkalosis, and normal to low blood pressure
What are the main jobs of loop diuretics?
- decrease hypertonicity of the medulla
- prevent dilution of the filtrate in the thick ascending limb
- increase the load of Na+ delivered to distal regions (=> lose K+)
- increase excretion of Ca2+ and Mg2+
How soon after IV and oral administrations does furosemide tend to take effect?
IV - within 30 mins
Oral - within an hour
What are the contra-indications to a loop diuretic?
Severe hypovolaemia, or dehydration
What are the cautions with loop diuretics?
Severe hypokalaemia and/or hyponatraemia
hepatic encephalopathy
gout
What are the main adverse effects in loop diuretics?
- hypokalaemia
- metabolic alkalosis
- hypocalcaemia, hypomagnesaemia
- Hypovolaemia and hypotension
- Hyperuricaemia
- Dose-related loss of hearing
What mechanism do the thiazide diuretics block?
The Na/Cl co-transporter
What site of the Na/Cl co-transporter do thiazide diuretics bind to?
Cl site
What site of the triple transporter do loop diuretics bind to?
Na site
What are the main jobs of thiazide diuretics?
- prevent the dilution of filtrate in the early distal tubule
- increase the load of Na+ delivered to the collecting tubule
- increase reabsorption of Ca2+
Thiazides are becoming less commonly used for heart failure and hypertension. What drugs are beginning to be used more?
mild heart failure - loop agents
hypertension - indapamide or chlortalidione
Why are thiazides thought to be useful in renal stone disease?
Reduced urinary excretion of Ca2+ discourages Ca2+ stone formation
What are the contra-indications to thiazide diuretics?
Hypokalaemia
What are the cautions with thiazide diuretics?
Hyponatraemia
gout
What are the main differences in adverse effects between loop and thiazide diuretics?
Thiazide do NOT cause hypocalcaemia
They CAN, however, cause Erectile Dysfunction and impaired glucose tolerance in diabetes
Describe how loop and thiazide diuretics cause loss of K+
Increased Na+ load caused by loop/thiazide
=> enhanced reabsorption of Na+
=> charge separation makes lumen more -ve
=> K+ moves across the lumenal membrane (enhanced secretion)
=> Secreted K+ ‘washed away’ by increased urinary flow in these areas of nephron
=> hypokalaemia
What do potassium sparing diuretics Amiloride and Triamterene block?
Block the apical Na channel
=> decrease Na+ reabsorption
What do Spironolactone and Eplerenone block?
Compete with aldosterone for binding to intracellular receptors
What are spironolactone and eplerenon dependent on?
Aldosterone levels of Pt already
What active form is spironolactone metabolised to?
canrenone
Triamterene is well absorbed from the G.I tract, absorption of amiloride is poor. TRUE/FALSE?
TRUE
Given alone, potassium sparing diuretics cause hyperkalaemia. TRUE/FALSE?
TRUE
They are usually used in combination with agents that cause potassium loss
In what conditions are aldosterone antagonists used?
- heart failure
- primary hyperaldosteronism (Conn’s syndrome)
- resistant essential hypertension
- secondary hyperaldosteronism (due to hepatic cirrhosis with ascites)
In what conditions are aldosterone antagonists contra-indicated?
Severe renal impairment
hyperkalaemia
Addison’s disease
Give an example of an osmotic diuretic?
Mannitol
Must be given IV as extremely hydrophilic
How do osmotic diuretics enter the filtrate?
via glomerular filtration, but are not reabsorbed
Briefly explain how osmotic diuretics work?
osmotic diuretic in the filtrate increases osmolality
=> water is not reabsorbed
=> larger vol. of water dilutes the concentration of sodium in the filtrate
=> sodium is ALSO not reabsorbed
=> both Na and H2O are lost
When are osmotic diuretics used?
- acute hypovolaemic renal failure (maintain urine flow)
- acutely raised ICP/IOP (plasma osmolality extracts water from these compartments)
What are the adverse effects of osmotic diuretics?
- transient expansion of blood volume
- hyponatraemia
When can an osmotic diuresis occur pathologically?
hyperglycaemia (Glucose remaining in the filtrate retains fluid)
Iodine contrast dyes
filtered at the glomerulus, but it not reabsorbed
=> creates osmotic load that takes water with it
What can carbonic anhydrase inhibitors cause as a result of promoting electrolyte excretion?
alkaline* diuresis and metabolic acidosis
Due to excretion of HCO3- with Na+, K+ and H2O
Carbonic anhydrase inhibitors are no longer used for their diuretic effect. TRUE/FALSE?
TRUE
What are carbonic anhydrase inhibitors used for?
- glaucoma/ following eye surgery (Reduce IOP by suppressing formation of aqueous humour)
- prophylaxis of altitude sickness
- some forms of infantile epilepsy
By alkalanising the urine with substances such as citrate salts, what can this help?
- relief of dysuria
- prevention of the crystallization of weak acids
=> decrease formation of uric acid stones - enhance the excretion of weak acids (e.g. salicylates such as Aspirin)
What is the difference between Neurogenic and Nephrogenic Diabetes Insipidus?
Neurogenic DI – lack of vasopressin secreted from posterior pituitary.
Nephrogenic DI – inability of the nephron to respond to vasopressin.
What drug is used to treat neurogenic DI and why?
Desmopressin* (synthetic analogue)
Has V2 receptor selectivity – avoids increase in blood pressure associated with V1 receptor activation
There is no current pharmacological treatment for Nephrogenic DI. TRUE/FALSE?
TRUE
Give examples of substances which affect vasopressin RELEASE from pituitary.
ethanol inhibits secretion
nicotine enhances
Give examples of substances that affect the ACTION of vasopressin on the kidney
Lithium
demeclocycline (antibiotic)
“vaptans”
Why are the “vaptan” class of drugs known as aquaretics?
They cause H2O excretion without any loss of Na
Where are the “vaptans” looking to be used?
Tx of heart failure
- most likely of value in hypervolaemic hyponatraemia (to reduce preload)
What is tolvaptan currently used to treat?
Syndrome of Inappropriate Anti-Diuretic Hormone (SIADH)
-to correct the hyponatraemia
Why do drugs only aim to inhibit SGLT2 and not also SGLT1?
SGLT1 also expressed in intestine
=> SGLT2 specific to kidney (responsible for 90% glucose reabsorption)
Explain why the SGLT2 co-transporter has low affinity and high capacity, whilst the SGLT1 co-transporter has
high affinity and low capacity?
At level of SGLT2 glucose is plentiful => dont need high affinity.
However lots of it need removed from blood so you need the transporter to have a high capacity.
Further down at SGLT1 theres not a lot of glucose floating about
=> you need a high affinity, but a low capacity doesnt matter
Inhibition of SGLT2 mimics what condition?
Familial Renal Glucosuria
SGLT2 inhibitors treat independent of insulin in T2DM. TRUE/FALSE?
TRUE
What is relevant in the formation of prostaglandins?
formed from fatty acid arachidonic acid by the cyclo-oxygenase enzymes (COX1 and 2)
Name the 2 major prostaglandins made by the kidney
PGE2 – medulla
PGI2 (prostacyclin) – glomeruli
When are prostaglandins synthesised?
In response to:
- ischaemia
- mechanical trauma
- angiotensin II
- ADH
- Bradykinin
How do prostaglandins affect the GFR?
vasodilate the afferent arteriole
How do NSAIDs precipitate renal failure
- inhibit COX enzymes
=> Not forming prostaglandins
=> no vasodilation of afferent arteriole
=> decreased GFR
What is the difference between uricosuric drugs and Allopurinol which is now widely used for gout prophylaxis?
Uricosuric drugs = block reabsorption of urate in proximal tubule => pee it out
Allopurinol = inhibits urate synthesis