Thiazide diuretics

Question 1

Indications

Answer 1

1. Alternative first-line treatment for hypertension where a calcium channel-blocker would be used but is unsuitable or there are features of heart failure
2. Also an add on treatment for hypertension not adequately controlled by other drugs

Question 2

Mechanism of action

Answer 2

Thiazides inhibit the Na+/Cl− co-transporter in the distal convoluted tubule of the nephron. This prevents reabsorption of sodium and its osmotically associated water.

Question 3

Adverse effects

Answer 3

Hyponatrenia

Question 4

Warnings

Answer 4

Thiazides should be avoided in patients with hypokalaemia and hyponatraemia. As they reduce uric acid excretion, they may precipitate acute attacks in patients with gout.

Question 5

Interactions

Answer 5

The effectiveness of thiazides may be reduced by non-steroidal anti-inflammatory drugs (although low-dose aspirin is not a concern). The combination of thiazides with other drugs that lower the serum potassium concentration (e.g. loop diuretics) is best avoided. If combination is essential, it should prompt intensive electrolyte monitoring.

Question 6

Prescribing

Answer 6

Indapamide (e.g. 2.5 mg daily) and chlortalidone (12.5–25 mg daily) are recommended for hypertension.

Question 7

Administration

Answer 7

It is generally best to take the tablet in the morning, so that the diuretic effect is maximal during the day rather than at night and does not therefore interfere with sleep.

Question 8

Communication

Answer 8

Explain to your patient that you are offering treatment with a ‘water tablet’ for their high blood pressure. If they have leg swelling, it may also help with this. Enquire whether they have any difficulty getting to the toilet in time (either because of mobility issues or sensations of urgency), since the water tablet is likely to make them pass water more often.

Question 9

Monitoring

Answer 9

BP monitoring