💊 Thiazide Diuretics
Drug Class & Overview
Thiazide diuretics are a class of diuretics that act on the distal convoluted tubule of the nephron. They are widely used in the management of hypertension and mild-to-moderate oedema.
Mechanism of Action
These drugs inhibit the Na+/Cl- co-transporter (NCC) in the luminal membrane of the distal convoluted tubule. This reduces the reabsorption of sodium and chloride, leading to increased excretion of water. They also promote calcium reabsorption, which is a unique feature.
Key Indications
Thiazide diuretics are a first-line treatment for essential hypertension, particularly in older adults and those of Afro-Caribbean descent. They are also used for mild-to-moderate oedema, nephrogenic diabetes insipidus, and to prevent recurrent calcium kidney stones.
Contraindications
Absolute contraindications include anuria and severe renal impairment (creatinine clearance below 30 mL/min). They should be used with caution in patients with severe hepatic impairment, gout, or uncontrolled diabetes due to potential exacerbation of these conditions.
Adverse Effects
Common adverse effects include electrolyte disturbances such as hypokalaemia, hyponatraemia, and hypercalcaemia. Hyperglycaemia, hyperuricaemia (leading to gout), and dyslipidaemia are also known side effects. Photosensitivity reactions can occur.
Monitoring
Regular monitoring of electrolytes (potassium, sodium, calcium) and renal function (urea, creatinine) is important. Blood glucose levels should be monitored in diabetic patients, and uric acid levels in those prone to gout. Blood pressure should also be checked regularly.
Prescribing Safety (OSCE)
When prescribing, check for a history of gout or diabetes, as thiazides can worsen these conditions. Counsel patients on the importance of regular blood tests and to report symptoms of dehydration or muscle weakness. Be aware of interactions with lithium (increased toxicity) and NSAIDs (reduced efficacy).
MLA High-Yield Notes
High-yield facts include their first-line use in hypertension, especially in older and Afro-Caribbean patients, and their unique effect on calcium (increasing reabsorption). Remember the metabolic side effects: hyperglycaemia, hyperuricaemia, and dyslipidaemia. Bendroflumethiazide and indapamide are commonly encountered examples.
Common SBA Themes
SBAs often test knowledge of thiazide use in hypertension, especially in specific patient populations. Questions might present a patient with hypertension and ask about the most appropriate initial diuretic. Another common theme is the specific electrolyte disturbances (e.g., hypokalaemia, hypercalcaemia) and metabolic side effects like hyperglycaemia or gout.
References
- BNF (British National Formulary)
- NICE (National Institute for Health and Care Excellence)
- Joint Formulary Committee. British National Formulary (online)