S10: diuretics & UTIs

Question 1

What are diuretics?

Answer 1

Drugs that increase renal excretion of sodium and water resulting in an increase in urine volume
Reduce plasma volume & cardiac output
Reduce blood pressure
Reduce oedema/ascites

Question 2

Define diuresis and natriuresis

Answer 2

Diuresis = process of excretion of water in the urine 
Natriuresis = process of excretion of sodium in the urine

Question 3

List the 5 main classes of diuretics

Answer 3

Carbonic anhydrase inhibitors 
Osmotic diuretics 
Loop diuretics 
Potassium sparing diuretics 
Thiazide and thiazide-like diuretics

Question 4

Describe diuretics which act at the PCT

Answer 4

Carbonic anhydrase inhibitors – inhibit carbonic anhydrase
Amiloride – main site of action in late DCT/CD
SGLT-2 inhibitors (flozins) – not diuretics but they do reduce Na+ absorption

Question 5

Describe osmotic diuretics

Answer 5

Mannitol – administered via IV
Increases water excretion, less effect on Na+
Expands ECF initially, decreases blood viscosity, inhibits renin release -> increases renal blood flow
Uses:
1) Acute renal failure due to shock/trauma
2) Acute drug poisoning
3) Decrease intracranial and intraocular pressure before ophthalmic/brain procedures

Question 6

List side effects of osmotic diuretics

Answer 6

Hyponatraemia – headache, nausea & vomiting
ECF volume expansion
Contraindicated in chronic heart failure
Excessive use – dehydration and hypernatraemia

Question 7

Describe loop diuretics

Answer 7

Blocks the Na/K/2Cl transporter in loop of Henle
Most potent diuretic – bumetanide & furosemide
Given orally/via IV, has a fast onset of action = suitable for emergency situations
Uses:
1) Severe oedema associated with congestive heart failure, nephrotic syndrome
2) Treatment for oliguric ARF
3) Treatment of hypercalcaemia
4) Acute pulmonary oedema
5) Acute hyperkalaemia, acute hypercalcemia

Question 8

List side effects of loop diuretics

Answer 8

Hypovolemia 
Hyponatraemia 
Hypokalaemia – dietary K+ supplements/K-sparing diuretics should be used 
Hypomagnesemia 
Hypocalcaemia 
Metabolic alkalosis 
Postural hypotension

Question 9

Describe thiazide and thiazide like diuretics

Answer 9

Blocks the Na/Cl symporter in the DCT
1st line antihypertensive – Bendroflumethiazide, indapamide
Increases NaCl, K+ and magnesium excretion
Increases calcium reabsorption
Uses:
1) Essential hypertension
2) Mild heart failure
3) Calcium nephrolithiasis due to hypercalciuria
4) Osteoporosis
5) Nephrogenic diabetes insipidus polyuria

Question 10

Describe potassium sparing and aldosterone antagonists

Answer 10

Act in the late DCT and collecting ducts 
Potassium sparing – amiloride 
Aldosterone antagonists - spironolactone
Increases urinary Na+ excretion 
Decreases K+ and H+ excretion

Question 11

List uses of potassium sparing and aldosterone antagonists

Answer 11

Uses: secondary hyperaldosteronism, CHF, hepatic cirrhosis, nephrotic syndrome, hypertension
Contraindicated in patients with: hyperkalaemia and liver disease

Question 12

Describe pathophysiology of a UTI

Answer 12

Urinary tract normally sterile and resistant to bacterial colonisation – emptying of bladder during micturition, vesico-ureteral valves, immunological factors, mucosal barriers & urine acidity
Ascending colonisation of bacteria from urethra:
-bladder = cystitis
-kidney = pyelonephritis

Question 13

Describe risk factors for developing a UTI

Answer 13

Female – short urethra
Obstructive causes – stones, enlarged prostate & retroperitoneal fibrosis
Neurological conditions affecting bladder emptying
Pregnancy
Abnormal renal tract
Impaired host defence

Question 14

Describe the most common causative agent for UTIs & its features

Answer 14

Majority of UTIs caused by coliforms (gram negative organisms)
E Coli most common
-flagellar = movement
-pili = attachment
-capsular polysaccharide = colonisation
-haemolysin, toxins = damages host membranes and causes renal damage

Question 15

Describe the clinical presentation for cystitis and pyelonephritis

Answer 15

Cystitis = dysuria, cloudy urine, nocturia or frequency, urgency, suprapubic tenderness, haematuria & pyrexia (usually mild)
Pyelonephritis = high fever +/- rigors, loin pain and tenderness, nausea/vomiting +/- symptoms of cystitis

Question 16

Define uncomplicated UTI

Answer 16

Defined as infection by a usual organism in a patient with a normal urinary tract and normal urinary function
May occur in males and females of any age

Question 17

List factors which make a UTI complicated

Answer 17

> 1 factors that predispose to persistent infection, recurrent infection or treatment failure:

1) Abnormal urinary tract
2) Virulent organism
3) Impaired host defence
4) Impaired renal function
5) Suspected pyelonephritis

Question 18

Describe investigations for a UTI

Answer 18

Healthy, non-pregnant women of children bearing age, no need for urine culture
Visual inspection of urine
Culture in complicated UTI:
-mid-stream urine: cleansing not required, ideally holding labia apart in women
-clean catch in children
-culture urine within 4 hours of collection, refrigerate or using boric acid preservation
Urine dipstick – aid to diagnosis

Question 19

Describe urine dipstick

Answer 19

Not useful in patients > 65 years old (asymptomatic infection common) & catheterised patients
Useful in patient presenting with just 1 of the following – dysuria, new nocturia & cloudy urine present
If negative for nitrites, positive for LE suggests staphylococcus saprophyticus is causative pathogen

Question 20

Describe imaging choices for UTI

Answer 20

Ultrasound
Considered in all children with UTI
Valuable in septic patients to identify renal involvement

Question 21

Outline the treatment of a UTI

Answer 21

Increase fluid intake 
Regular analgesia 
Address underlying disorders 
Antibiotics:
-3 day course for uncomplicated UTI
-5-7 day course for complicated lower UTI eg. pregnant, male, underlying disorders

Question 22

Outline the treatment for cystitis

Answer 22

Can be treated with nitrofurantoin, trimethoprim, pivmecillinam or Fosfomycin
Uncomplicated cystitis – 3 day course (reduces the selection pressure for resistance)
Complicated UTI eg. male, pregnant women, catheter associated UTI – 5-7 day course

Question 23

Outline the treatment of pyelonephritis/septicaemia

Answer 23

Pyelonephritis = 7-10 day course
Use agent with systemic activity (NOT nitrofurantoin, Fosfomycin)
Possibly IV initially unless good oral absorption and patient well enough/tolerating orally
Co-amoxiclav
Ciprofloxacin (effective as a 7 day course)
Gentamicin (IV only, nephrotoxic)