Bendroflumethiazide is routinely used to relieve oedema – fluid collecting in the cavities or tissues of the body – in conditions such as congestive heart failure, cirrhosis of the liver and in the management of hypertension. However, it is no longer considered a first-line treatment for these conditions.
How it works
It is important you understand the mechanism of action of thiazide diuretics, as this not only improves your understanding of these medicines, but is something your patients may ask you to explain.
The primary function of thiazide diuretics is to remove excess water from the body. They do this by reducing the reabsorption of electrolytes from the distal convoluted renal tubules in the kidney. This results in an increased excretion of sodium and chloride, subsequently leading to loss of water through the kidneys. This process can also result in a loss of potassium.
In addition, different processes caused by thiazide diuretics lead to an increase in serum uric acid, as this is not cleared.
It is important to establish if the patient is taking the correct dose and if they are adhering to their prescribed treatment regimen. For example:
- For oedema, the initial dose is 5-10mg daily or on alternate days; and then at a maintenance dose of 5-10mg 1-3 times a week
- For hypertension, the dose is 2.5mg daily.
Thiazide diuretics usually act within 1-2 hours, with a long duration of action between 12-24 hours. They should be taken in the morning to avoid frequent urination that can potentially interfere with sleep.
You should be aware of some of the common side effects that can occur when taking bendroflumethiazide, such as:
- mild gastrointestinal disturbances
- electrolyte disturbances (sodium, potassium and magnesium loss; increased calcium – due to reduced renal clearance of calcium)
- hypotension – including on standing (postural)
- hyperglycaemia (high blood sugar)
- hyperuricaemia (excess uric acid in the blood) – due to reduced renal clearance of uric acid
- acute gout.
Blood dyscrasias and impotence are less common, but can also occur.
Although it is not necessary to explain the range of side effects of thiazide diuretics, it is important you are able to recognise them and ask appropriate questions that may help you understand whether a patient is suffering from these symptoms.
In MURs, diuretics are listed as a high-risk medicine due to the severity of their side-effects and their potential to cause electrolyte disturbances. These can cause alterations in myocardial and neurological function, fluid balance and renal function.
With this in mind, particular care should be exercised in elderly patients taking bendroflumethiazide. This age group often struggle to maintain adequate daily fluid intake, and may have a degree of existing renal impairment, which will potentiate the adverse effects of thiazide diuretics. It is therefore advisable for elderly patients to take lower initial doses when beginning therapy with this class of medication.
In addition, if an elderly patient is taking bendroflumethiazide for gravitational oedema, the treatment should not be used on a long-term basis – as gravitional oedema usually responds to non-medicinal measures such as increased movement, stocking support or leg raising.
What should you discuss with patients?
During your MUR, it is important to clarify that the patient knows why they are taking their medicine, and how long they will be taking it for.
Patients will have several monitoring requirements when taking this medication. For example, blood pressure checks should be carried out routinely, and are especially important at the initiation of treatment and during dose changes. As thiazide diuretics can cause hyperglycaemia – as well as aggravate or unmask diabetes mellitus – blood glucose levels should be monitored periodically during treatment, especially in those taking antidiabetic medication, as requirements may change.
In addition, you should advise patients to attend appointments for their blood and kidney function tests, as this will help detect any electrolyte abnormalities or renal impairment.
You may want to make patients aware that postural hypotension is a side effect of thiazide diuretics. Patients may experience light-headedness or dizziness, and as a result some patients may experience falls. The consequences of this can be severe; for example, an elderly patient – who may already be at risk of hypotension – may experience hip fractures, due to concurrent osteoporosis.
If a patient does describe symptoms of dizziness or light-headedness, you could check their blood pressure during the MUR, and refer them to their GP to check for electrolyte disturbances.
You should also check if a patient's symptoms have worsened, as this may be an indicator that they are not adhering to their therapy.
Patients being treated for heart failure should be encouraged to weigh themselves regularly, as putting on a large amount of weight (over 2kg) in a few days may be indicative of fluid retention rather than weight gain.
Dehydration can be managed by counselling the patient about their fluid intake. Adequate fluid intake is defined as between 1.5-2 litres per day – this may be less in patients with heart failure.
Some elderly patients may actively reduce their fluid intake due to fear of incontinence or difficulty in getting to the bathroom. You could encourage these patients to speak to their GP or nurse about aids for the bathroom, such as a commode or incontinence pads.
In addition, prescribers may permit patients to delay a dose if they have a special occasion (for example, a wedding), but patients should take it that same day at their earliest convenience. Patients should not double their dose the next day if they missed their scheduled dose.
During the MUR, you can also identify other potential risk factors in the patient’s lifestyle that may contribute to their cardiovascular risk – such as diet, exercise, smoking habit or alcohol intake – and appropriate counselling can be given on these.
What else should you be aware of?
Caution is recommended in patients with diabetes, gout and systemic lupus erythematosus (an autoimmune disease), as these conditions can be exacerbated by the use of thiazide diuretics. You should be aware of the symptoms of these conditions, to ensure you can provide the best advice.
Hypokalaemia – low potassium levels in the blood – can occur with thiazide diuretic use, so it is appropriate to watch out for signs of this, including peripheral muscle weakness, polyuria, polydipsia (extreme thirst), tiredness and cramps.
Bendroflumethiazide should be used with caution in mild-to-moderate hepatic impairment and avoided in patients with severe hepatic impairment, as hypokalaemia may precipitate coma among these patients.
Concomitant illness may cause dehydration or reduced kidney function, and you should advise patients to make an appointment with their GP if they become unwell, as they may need to adjust their regimen.
- BNF 74: bendroflumethiazide
- Mayo Clinic – bendroflumethiazide
- Electronic Medicines Compendium – bendroflumethiazide
- PubChem Compound Summary – bendroflumethiazide