Diuretics Flashcards

1
Q

Resorption ion transporter regions in the nephron

A

Most resorption happens in the proximal convoluted tubule, too active to be affected by drugs
Ascending limb, early/late distal convoluted tubule, connecting tubule and collecting duct can be affected with drugs

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2
Q

Thick ascending limb

A

Primary point of resorption
Sodium/ potassium/ chloride transporters are significantly affected by drugs
Ions balance each other (passive)

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3
Q

What are diuretics? Give some (non-medical) examples

A

Drugs that increase urine flow and salts
Water and alcohol are diuretic as they dilute body fluids and inhibit ADH release
Water eliminated = amount ingested

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4
Q

Main clinical uses of diuretics

A

Cardiac failure
Oedema
Hypertension
Liver disease and some types of kidney disease
Overdose or poisoning to help excretion
Abuse- eating disorders patients to lose weight

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5
Q

Diuretic classification

A
  1. Chemical
  2. Pharmacological mechanism
  3. Site of action
  4. Potency
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6
Q

Inhibitors of carbonic anhydrase

A

H+ is actively secreted from the tubule and exchanges for sodium (i.e. resorbed)
If CA inhibited, less H+ for exchange with sodium (i.e. diuresis)
Less sodium and bicarbonate is resorbed (urine = alkaline)

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7
Q

Clinical use of inhibitors of carbonic anhydrase

A

They are of little value in long term value
Self limiting effect: As bicarbonate is lost from the body, plasma becomes acidified- the buffers start to release H+ (exchanges with sodium) without requiring CA
Effective in the eye

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8
Q

Thiazides (Benzothiadiazides)

A

Moderately potent diuretics

Structure contains a sulfonamide

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9
Q

Thiazides mechanisms of action

A

Main effect: inhibit sodium chloride co-transporter (i.e. resorption) in the early distal tubule&raquo_space;> water follows passively
Also inhibits potassium and bicarbonate resorption
Weak inhibitors of carbonic anhydrase

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10
Q

Thiazides advantages and disadvantages

A

Advantage: moderately potent and orally active
Disadvantage: potassium loss (hypokalaemia)

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11
Q

Mechanism of thiazide hypokaleamia in distal tubule

A

Potassium loss is dangerous in severe coronary artery disease and sensitizes the heart to cardiac glycosides
Use potassium supplements or combination with potassium sparing diuretic

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12
Q

Common side effects of thiazides

A
Hypokolaemia
Gout
Hypercalcaemia
Hypomagnesaemia
Hyponatraemia (sodium)
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13
Q

Thiazide related heterocyclics

A

Commonly used as less adverse effects e.g. indapamide
Use in hypertension and congestive heart failure 1.25-5mg daily
NB cost effective especially in combination with perindopril e.g. in type 2 diabetes

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14
Q

Loop diuretics

A
Very effective (high ceiling) e.g. furosemide
Rapid acting (peaks 30 mins), short duration (3-4 hours)
Use of sulphamoyl benzoates- mainly pulmonary oedema and oedema due to renal failure
Produce hypokolaemia, depending on duration of action rather than frequency >> thiazides are more likely to produce hypokalaemia as they are longer acting but cause potassium loss
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15
Q

Loop diuretics mechanisms

A

Main mechanism: inhibition of sodium potassium chloride cotransporter in thick ascending limb
Minor mechanism: transiently (5 mins) stimulates prostaglandin synthesis, increases renal blood flow

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16
Q

Torasemide

A

Used for oedema and hypertension
Dose: oedema- 5mg od
Hypertension 2.5-5mg od

17
Q

Potassium sparing diuretics

A

Two types: Alodsterone antagonists and sodium channel inhibitors
Aldosterone is a mineralocorticoid secreted from adrenal cortex response to the renin angiotensin cascade
Encourages sodium retention in the late distal tubule and collecting duct

18
Q

Effect of aldosterone in the distal convoluted tubule and collecting duct

A

Aldosterone binds to a mineralocorticoid receptor, causing nuclear protein synthesis
Inserts apical sodium channels
Stimulates basolateral sodium potassium ATPase
Stimulates apical potassium channel

19
Q

Aldosterone antagonists

A

Mechanism- reverses action of aldosterone at late distal tubule, cause loss of sodium, prevent loss of potassium and H+
Therefore potassium supplements are not necessary
Can be used to potentiate thiazide or loop diuretics

20
Q

Spironolactone

A

Antagonises renal effects of other corticosteroids e.g. hydrocortisone (i.e. aldosterone-like effects)
Use is limited because action depends on presence of aldosterone (not useful for oedema of pregnancy- low aldosteron levels)
Side effect = gynecomastia
Dose: 100-400mg od

21
Q

Clinical uses of aldosterone antagonists

A

Main use- hepatic oedema- metabolic capacity of the liver for aldosterone is impaired
Also used for primary hyperaldosteronism (Conn’s syndrome)- output capacity of adrenal cortex is increased, hypertension due to tumour/ hyperplasia
Eplerone (spironolactone analogue) 50-100mg od, no gynecomastia, with optimal medical therapy reduces morbidity/ mortality in patients with left ventricular dysfunction after MI

22
Q

Sodium channel inhibitors

A

Occupy sodium channels in late distal tubule/ collecting duct epithelial cell membranes
Don’t inhibit sodium pumps

23
Q

Triamterene

A

Weak diuretic
Dose 150-200mg daily
May conserve potassium- used with thiazides/ loop diuretics

24
Q

Amiloride

A

Weak diuretic
Dose 5-20mg daily
May conserve potassium- used with thiazides/ loop diuretics

25
Hyperkalaemia through potassium sparing diuretics
Potassium supplements must not be given with potassium sparing diuretics as this may cause hyperkaleamia- malaise, palpitations, muscle weakness, arrythmia, sudden death
26
Osmotic diuretics
Any substance filtered but not resorbed at the glomerlus may act as an osmotic diuretic e.g. glucose is normaly totally resorbed but in diabetes mellitus found in urine (polyuria) Once osmotic diuretic is filtered it increases lumen OP thus water passes in by osmosis
27
Osmotic diuretic characteristics
Ideal osmotic diuretic has low molecular weight, easily filtered but not resorbed, high osmotic activity
28
Examples of osmotic diuretics
Mannitol must be given in large volumes e.g. 50-200g (10-20% soln) slow IV over 24 hours Used for osmotic relief of cerebral oedema (raised intercranial pressure) Urea does not cross BBB, also draws water out of cranial tissue
29
Drugs acting on renal circulation
Glomerular filtration rate is raised by agents which increase renal blood flow, cardiac output or blood volume
30
Cardiac glycosides
Increase cardiac output during heart failure, cause secondary rise in RBF and filtration, digoxin often combined with conventional diuretics
31
Colloidal substances (plasma expanders)
If blood volume falls e.g. blood or protein loss (RBF/GFR falls= renin-angiotensin cascade= oedema) colloidal substances may be given IV to restore RBF/GFR
32
Dextran
Repeating glucose units joined by glucoside linkages Plasma expander (10% soln) Not normally given as primary diuretic Molecular mass = 70-80kD
33
Xanthines
e.g. caffeine, theophylline, theobromine Inhibit sodium and chloride resorption Raise filtration pressure (dilate afferent > efferent arterioles to glomeruli) Stimulate cardiac output
34
Potency/ efficacy of diuretics
High efficacy diuretics: >15% filtered sodium loss: loop diuretics- sulphamoyl benzoates e.g. furosemide Medium efficacy diuretics: 5-10% filtered sodium loss: thiazides e.g. bendroflumethiazide; thiazide reelated heterocyclics e.g. indapamide Weak/ adjunctive diuretics: <5% filtered sodium loss: potassium sparing agents e.g. spironolactone, amiloride, mannitol, urea, dextran, caffeine
35
Give examples of carbonic anhydrase inhibitors. What structure binds the active site?
Acetazolamide, dorzolamide | Sulphonamide binds the active site
36
Give examples of thiazides and their doses
``` Bendroflumethiazide 2.5-10mg Cyclopenthiazide 250-500 mg Hydrochlorothiazide 25-50 mg Polythiazide 0.5-4.0 mg All should be taken in the morning ```
37
How do thiazides cause hypokalaemia?
Mechanism: diuretic inhibits sodium resorption> high sodium concentration arrives at distal tubule> sodium potassium exchange occurs
38
What are the four groups of thiazide related heterocyclics? Give examples of each
Pthalimidines e.g. Chlorthalidone 50-200mg Quinazolines e.g. Metolazone 5-20mg Benzene sulphonamides e.g. mefruside 12.5-50mg Chlorbenzamides e.g. indapamide 25mg