Thiazide diuretics

Question 1

Generic names: Thiazide diuretics and Thiazide-related diuretics

Answer 1

Thiazide
Hydrochlorothiazide
Thiazide-related
Chlortalidone
Indapamide

Question 2

Indication
Thiazide and related diuretics

Answer 2

• Hypertension
• Oedema associated with heart failure or hepatic cirrhosis
• Nephrogenic diabetes insipidus

Question 3

MOA
Thiazide and related diuretics

Answer 3

Inhibit reabsorption of sodium and chloride in the proximal (diluting) segment of the distal convoluted tubule, increased potassium excretion.

When used in recommended low doses for hypertension, thiazides lower BP mostly by a vasodilator effect.

Question 4

Precautions
Thiazide and related diuretics

Answer 4

Gout—may be aggravated by diuretic-induced hyperuricaemia

Heart failure with significant oedema—hyponatraemia may occur, particularly if higher doses are used with a salt-restricted diet and/or potassium-sparing diuretics and excess water intake.

Conditions or drugs that may cause hypokalaemia—further increases risk of hypokalaemia; monitor potassium concentration.

Conditions or drugs that cause volume depletion—further increases risk of renal impairment and hypotension (particularly in patients with heart failure); monitor renal function and BP (sitting and standing).

Question 5

Adverse effects
Thiazide and related diuretics

Answer 5

Effects on electrolytes, blood glucose and lipids are dose-dependent.

dizziness, weakness, muscle cramps, polyuria, orthostatic hypotension, electrolyte disturbances (eg hyponatraemia, hypokalaemia, hyperuricaemia, hypochloraemic alkalosis, hypomagnesaemia, hypercalcaemia)

Question 6

Nursing considerations
Thiazide and related diuretics

Answer 6

You may feel dizzy on standing when taking this medicine. Get up gradually from sitting or lying to minimise this effect; sit or lie down if you become dizzy.

most adverse effects are dose-related; start with a low dose and increase slowly

Heart failure
* may be given with loop diuretics to relieve symptoms of fluid retention; seek specialist advice
* start with a low dose and adjust according to clinical response; use small, intermittent doses with careful monitoring of renal function, electrolytes, BP and volume status
* advise patients to report any dizziness, thirst, or increased fluid loss due to diarrhoea, vomiting or excessive sweating
Diuretic-induced hypokalaemia
* reduce risk by using a low dose
* is less likely when also taking an ACE inhibitor, sartan or potassium-sparing diuretic
* potassium supplements may be used to treat mild hypokalaemia (each potassium chloride 600 mg tablet contains 8 mmol potassium; daily potassium replacement requirement is around 20–60 mmol (3–8 tablets))

Question 7

Drug interactions
Thiazide and related diuretics

Answer 7

ACE inhibitors + thiazide diuretics = hypotension
sartans + thiazide diuretics = Hypotension
loop diuretics + thiazide diuretics = hypokalemia + hypotension

NSAIDs + thiazide diuretics = reduced renal function

Hydrochlorothiazide is a thiazide diuretic; chlortalidone and indapamide are related to the thiazide diuretics and behave in the same way.

Thiazide diuretics cause hypotension; administration with other drugs* with this effect may result in additional hypotension.

They also cause hypokalaemia; additional potassium loss may occur if they are given with other drugs* that reduce potassium concentration; monitor potassium concentration and give potassium supplements if necessary. See also Prolonged QT interval.

High doses of thiazide diuretics can increase blood glucose concentration