Thiazide Diuretics for Hypertension

Thiazide diuretics are an important mainstay of the hypertensive treatment formulary. Here is a bit on how they work, and what problems they can cause

Diuretics – Thiazides

Thiazides are the classic potassium-depleting anti-hypertension medication. In many guidelines, thiazides are the first drug of choice for treating hypertension. Although the initial reduction in blood pressure is due to volume depletion this effect should be a transient one as patients on thiazide diuretics are apparently no more dehydrated than anyone else and the mechanism is therefore as yet unclear although it has been suggested that they cause vasodilation and subsequent reduction in vascular resistance. Their apparent function is on the distal convoluted tubule in the kidney. Thiazide diuretics are often combined with an angiotensin-converting enzyme inhibitor (ACEI) for increased effect.

Side effects and contraindications

A limitation of thiazide diuretics is that they are based on the patency of renal function. When kidney function is reduced thiazides are less effective and are usually considered to have no benefit in patients with a creatinine above 1.6. As diuretics, thiazides deplete magnesium as well as potassium. This can lead to refractory hypokalemia. Uric acid is elevated which can lead to gout and depositions. Thiazide diuretics can also cause problems in blood cholesterol. Chronic administration of thiazides has been associated with the development of hyperglycemia although the mechanism is unknown. Retention of calcium can theoretically lead to hypercalcemia. Treatment with lithium is a contraindication for thiazide use.

Other uses for thiazides

As a diuretic – thiazides are used to reduce the volume overload in congestive heart failure. Also, thiazides are calcium sparing by their mechanism. This means that in situations of hypercalciuria leading to kidney stones, thiazide diuretics can be of use. Thiazides have been shown to have a beneficial effect on osteoporosis possibly by stimulating osteoblasts to promote bone growth.