2.2.1 Thiazides and related diuretics

ChoiceDrugDosage
1st choiceIndapamide tablets 2.5mg; m/r tablets 1.5mgDose:
Hypertension – 2.5mg once daily (or m/r 1.5mg once daily)
2nd choiceBendroflumethiazide tablets 2.5mgDose:
Hypertension - 2.5mg daily

Prescribing Notes

  • Allow 4 weeks for maximal antihypertensive effect of thiazide-like diuretics.
  • A dose of 2.5mg bendroflumethiazide daily gives the optimal hypotensive effect. Increasing the dose beyond this is of no benefit in lowering blood pressure but increases the likelihood of side-effects.
  • Both thiazide and loop diuretics can cause sodium and potassium depletion, glucose intolerance and gout. These effects are dose-related and may be more dramatic with thiazides because of their relatively long duration of action. Regular monitoring of potassium, sodium, glucose and uric acid is recommended. If potassium is persistently low, consider also measuring magnesium.
  • Patients receiving thiazide diuretics should be monitored carefully for hypokalaemia particularly if used as monotherapy.
  • Bendroflumethiazide is not generally recommended for the treatment of heart failure, as higher doses are associated with more profound electrolyte imbalances (see above) than loop diuretics.
  • Chlortalidone is recommended by NICE for the management of hypertension. It is not currently a formulary choice due to practical issues (requirement to cut tablets and supply problems).
  • Metolazone should only be initiated in secondary care; profound diuresis can occur and the patients should therefore be monitored carefully. It is only available from ‘special-order’ manufacturers or specialist importing companies.

Cautions

  • Thiazide and related diuretics can exacerbate diabetes, gout, and systemic lupus erythematosus. Electrolytes should be monitored particularly with high doses, long term use, or in renal impairment.
  • Thiazides are ineffective if eGFR is less than 30mL/minute/1.73m2 and should be avoided; metolazone remains effective but with a risk of excessive diuresis and should only be initiated in secondary care.
  • Thiazide and related diuretics should be used with caution in nephrotic syndrome, hyperaldosteronism and malnourishment.
  • Elderly patients are particularly susceptible to the side-effects of diuretics including increased risk of postural hypotension, collapse and falls. Confusion, dehydration, urinary incontinence and hyponatraemia may be particular problems.
  • Diuretics should not be used on a long term basis to treat simple gravitational oedema. This will usually respond to increased ambulation, raising the legs and support stockings.