Thiazide diuretic

Question 1

Example of a Thiazide diuretic

Answer 1

Bendroflumethiazide

Question 2

How does bendroflumethiazide work?

Answer 2

Inhibits the Na/Cl co transporter in the distal convoluted tubule of the nephron. This prevents re absorption of sodium, aits osmotically associated water.

Question 3

Indications of thiazide diuretics

Answer 3

Hypertension: alternative first line to CCB if unsuitable or as an add on treatment is it is not adequately controlled by a CCB + ACE inhibitor or ARB.

Clinical tip—One of the main adverse effects of thiazides is hypokalaemia, while one of the main adverse effects of ACE inhibitors and ARBs is hyperkalaemia. Moreover, these drug classes have a synergistic blood pressure lowering effect: thiazides tend to activate the renin–angiotensin system, while ACE inhibitors/ARBs block it. Consequently, the combination of a thiazide and an ACE inhibitor/ARB is very useful in practice, both to improve blood pressure control and to maintain neutral potassium balance.

Question 4

Contraindications of thiazide diuretics

Answer 4

Acoided in patients with hypokalaemia and hyponattraemia.

As they reduce uric acid excretion, they may precipitate acute attacks in patients with gout.

Question 5

Side effects of thiazide diuretics

Answer 5

Preventing Na reabsorbtion can cause hyponaturaemia. This increased uptake of sodium to the distal tubule, where it can be exchanged for potassium, increases urinary potassium losses and may therefore cause hypokalaemia. This in turn may cause cardiac arrhythmias.

Thiazides may increase plasma concentrations of gluocse (which may unmask Diabetes II), LDL-cholesterol and triglycerides. However, their net effect on CV risk is protective.

They may cause impotence in men.

Question 6

Possible interactions of thiazide diuretics

Answer 6

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 7

Elimination of thiazide diuretics

Answer 7

Renal

Question 8

Patient information on thiazide diuretics

Answer 8

Thiazides are taken orally as part of the patient’s regular medication

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.

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. Advise patients that anti-inflammatory drugs like ibuprofen, which can be bought without prescription, may interact with water tablets and interfere with the way they work. At review, ask men directly about the possible side effect of impotence, as this may not be volunteered without prompting.