S10: diuretics & UTIs Flashcards
What are diuretics?
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
Define diuresis and natriuresis
Diuresis = process of excretion of water in the urine Natriuresis = process of excretion of sodium in the urine
List the 5 main classes of diuretics
Carbonic anhydrase inhibitors Osmotic diuretics Loop diuretics Potassium sparing diuretics Thiazide and thiazide-like diuretics
Describe diuretics which act at the PCT
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
Describe osmotic diuretics
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
List side effects of osmotic diuretics
Hyponatraemia – headache, nausea & vomiting
ECF volume expansion
Contraindicated in chronic heart failure
Excessive use – dehydration and hypernatraemia
Describe loop diuretics
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
List side effects of loop diuretics
Hypovolemia Hyponatraemia Hypokalaemia – dietary K+ supplements/K-sparing diuretics should be used Hypomagnesemia Hypocalcaemia Metabolic alkalosis Postural hypotension
Describe thiazide and thiazide like diuretics
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
Describe potassium sparing and aldosterone antagonists
Act in the late DCT and collecting ducts Potassium sparing – amiloride Aldosterone antagonists - spironolactone Increases urinary Na+ excretion Decreases K+ and H+ excretion
List uses of potassium sparing and aldosterone antagonists
Uses: secondary hyperaldosteronism, CHF, hepatic cirrhosis, nephrotic syndrome, hypertension
Contraindicated in patients with: hyperkalaemia and liver disease
Describe pathophysiology of a UTI
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
Describe risk factors for developing a UTI
Female – short urethra
Obstructive causes – stones, enlarged prostate & retroperitoneal fibrosis
Neurological conditions affecting bladder emptying
Pregnancy
Abnormal renal tract
Impaired host defence
Describe the most common causative agent for UTIs & its features
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
Describe the clinical presentation for cystitis and pyelonephritis
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
Define uncomplicated UTI
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
List factors which make a UTI complicated
> 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
Describe investigations for a UTI
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
Describe urine dipstick
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
Describe imaging choices for UTI
Ultrasound
Considered in all children with UTI
Valuable in septic patients to identify renal involvement
Outline the treatment of a UTI
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
Outline the treatment for cystitis
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
Outline the treatment of pyelonephritis/septicaemia
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)
