Hypertension

Diuretics A-Z

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What is it and how does it work?
Diuretics are commonly and incorrectly known as “water pills”. Their most important effect is to reduce total body sodium or salt. Long-acting diuretics are very helpful in the treatment of hypertension. They are inexpensive and effective for up to 24 hours.

These drugs work on the kidneys and mainly cause salt to be eliminated. They also relax the arteries. The end result is a reduction in blood pressure.

A few diuretics

Thiazide or thiazide like diuretics: (most commonly used for hypertension)
Hydrochlorothiazide or Indapamide

Short-acting loop diuretics: Furosemide in Lasix, Puresis.These drugs should not be be used for hypertension because of their short duration of action unless there is co-existent advanced renal disease or heart failure.

Potassium-sparing diuretics: Spironolactone (Aldactone, Spiractin) and amiloride. Amiloride is only avaialble in combination with hydrochlorothiazide, e.g. Amiloretic.

Combining thiazide and potassium diuretics: Amiloretic, Moduretic, Hexa-retic

Who benefits from diuretics?
All patients with hypertension benefit from treatment with thiazide or thiazide, which combine especially well with Ace inhibitors or angiotensin receptor blockers (ARBs). Patients who are sensitive to salt (e.g. Africans, the elderly and obese patients) respond best to diuretics with Stage I hypertension. Potassium-sparing diuretics are particualrly useful in patients with resistant hypertension, but should be used with caution in patients with kidney disease. Combination diuretics like Amiloretic should be used with extreme caution, as fatal changes in sodium and potassium in the blood may occur if used in full doses. Dosage should not exceed half a tablet per day.

Compelling indications for use of diuretics as anti-hypertensive drug:

  • African patients
  • The elderly
  • Patients with Isolated Systolic Hypertension
  • Heart failure

How to take diuretics:
Your doctor will choose the appropriate diuretic and dosage for you. It should be taken in the morning, since it causes increased urination, especially initially.

An example could be: Hydrochlorothiazide 12,5 to 25 mg, taken in the morning

By limiting dietary salt, the pressure lowering effect of diuretics will be enhanced, and the dosage required may be reduced.

Increase your intake of potassium rich foods, as diuretics may reduce potassium in the body. Eat plenty of fruit and vegetables. High doses should be avoided and combination with an Ace inbibitor or ARB reduces the problems related to potassium depletion.

Who should not take diuretics?

Compelling contraindications:

  • Gout - attacks may be precipitated.

Possible contraindications/take with caution:

  • Dyslipidaemia (abnormal blood cholesterol)
  • Erectile dysfunction  
  • Safety in pregnancy and lactation not established
  • Diabetes – use low dosages.
  • Patients with impaired kidney or liver function. Thiazide diuretics are ineffective with impaired renal function and loop duiuretics given twice daily are preferred.

Inform your doctor if:

  • You have ever had gout.
  • You have any sexual dysfunction.
  • You have diabetes.
  • You have any kidney or liver problems.
  • You are taking any other drugs, including self-medication.

Possible side effects
The level of potassium in the blood may decrease. This may alter the rhythm of the heart, increase toxicity of digoxin or lithium, cause weakness and predispose to diabetes. In modern treatment of hypertension, potassium depletion is uncommon because low doses are used and the combination with ACE inhibitors reduces the potassium loss. Potassium-sparing diuretics can be used if necessary. But the current fixed combinations like amiloretic should not be used in full doses because of potentially fatal side effects.

Leg cramps can be a common side effect. Some patients may feel thirsty, dizzy or lethargic.

Males may experience erection problems on diuretics, and gout may be precipitated.

Can it be taken with other drugs? Possible drug interactions:

  • Non-steroidal anti-inflammatory drugs: these drugs block the action of diuretics.
  • The adverse effects of digitalis and lithium may be increased.
  • If taken with corticosteroids, it may increase the loss of potassium from the body.
  • Alcohol and narcotics may aggravate postural hypotension. Diuretics may increase dehydration and hangovers after taking alcohol.

 Written by Dr Kathleen Coetzee, MBChB

Reviewed  by Prof Brian  Rayner, head of the division of nephrology and hypertension, University of Cape Town and Groote Schuur Academic Hospital, December  2010

Read more:
Hypertension and fasting

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