PTCB Guide to Diuretics Pharmacology!

What are diuretics?

Diuretics are one of the most widely prescribed class of medicine – and one of the most widely tested drug classes on the pharmacy technician certification board exam. Here, we review the must-know diuretics pharmacology facts about these widely used medicines.

Also known as “water pills”, the function of diuretics is to promote water and electrolyte loss from the body. By eliminating water and salt, diuretics help to reduce blood pressure – acting as powerful antihypertensive drugs.

Diuretics are not only used in the treatment of hypertension, though.

Diuretics are also used to relieve fluid overload in patients with:

• Chronic heart failure – where the heart pumps less effectively and so fluid accumulation manifests.
• Edema – the medical term for swelling. Edema may occur as a consequence of many different disease states; such as acute pulmonary edema, edema due to liver disease, or edema due to renal failure.

There are many different classes of diuretic. As pharmacy technicians, you will regularly process and input prescriptions to dispense diuretics. It’s important for you to have a solid understanding of these medicines.

Here, we review the basic pharmacology of diuretics that pharmacy technicians should know.

Diuretics Pharmacology

There are four primary classes of diuretic: loop diuretics, thiazide diuretics, and potassium-sparing diuretics.

Loop diuretics include:

• furosemide (Lasix)
• bumetanide (Bumex)
• torsemide (Demadex)
• ethacrynic acid (Edecrin)

Loop diuretics act at the ascending limb of the loop of Henle to promote water and electrolyte loss.

Thiazide diuretics include:

• hydrochlorothiazide (Aquazide)
• metolazone (Zaroxolyn)
• chlorthalidone (Hygroton)

Thiazide diuretics are among the first-line agents in the treatment of hypertension, often where calcium channel blockers (amlodipine, nifedipine) would otherwise be prescribed.

One of the clinical challenges with diuretics is that they promote loss of potassium ions, leading to hypokalemia. Hypokalemia has its own set of challenges, such as increasing the risk of abnormal heart rhythms (arrythmias). To prevent this, diuretics are often given alongside another kind of diuretic, known as a potassium-sparing diuretic. In other words, this additional drug “spares” the loss of potassium to ensure that hypokalemia does not occur.

Examples of potassium-sparing diuretics include:

• amiloride / hydrochlorothiazide (Moduretic)
• triamterene (Dyrenium)
• spironolactone (Aldactone)
• eplerenone (Inspra)

Though loop, thiazide, and potassium-sparing diuretics are the most prescribed diuretics, there are others to consider. For example, osmotic diuretics – such as mannitol – increase blood flow to the kidney and promote water and electrolyte loss. Carbonic anhydrase inhibitors – such as acetazolamide and methazolamide – increase bicarbonate levels in the urine and reduce sodium absorption. Less sodium (salt) means less water. Sodium loss and water loss go hand in hand.

Side Effects of Diuretics

Each diuretic drug class has its own set of side effects, but there are many common side effects between all classes.

For example, common side effects of diuretics include:

• hypotension
• electrolyte abnormalities (low potassium, sodium etc.)
• gastrointestinal upset
• increased urination
• dizziness
• dehydration
• headache
• increased risk of gout

At high doses, loop diuretics cause ototoxicity – the property of being toxic to the ear. Impotence in men is also reported.

As we have learned, hypokalemia – should it occur – increases the risk of cardiac rhythm abnormalities.

Clinical Factors

There are several important clinical factors to bear in mind:

• Diuretics are typically recommended to be taken in the morning to prevent nocturia (urinating during the night).
• Taking potassium-sparing diuretics (amiloride, spironolactone etc.) with potassium-elevating drugs or supplements increases the risk of hyperkalemia.
• Diuretics are often combined with potassium-sparing diuretics to prevent excessive potassium loss. For example: the loop diuretic, furosemide, is available in a combination medicine with amiloride (Co-amilofruse).
• Loop diuretics increase the ototoxic (toxic to the ear) and nephrotoxic (toxic to the kidney) risks of antibacterial aminoglycosides, such as gentamicin and tobramycin and amikacin.

Conclusion

That concludes our review of diuretics pharmacology.

As a pharmacy technician, you will regularly handle diuretic medicines and on many occasions, these brand and generic drugs appear on the PTCB examination. Whilst pharmacy technicians are not required to have an in-depth knowledge of each drug class, they should have a rounded knowledge of:

• The definition of a diuretic
• The different classes of diuretic
• Brand and generic names of common diuretics
• Important side effects and common drug interactions

As always, the more PTCB practice test questions you practice, the better – it helps to identify strengths whilst plugging any gaps in your knowledge. Diuretic drugs are one of the most tested classes on the PTCB exam and – with 40% assigned to the Medications knowledge domain – it is important for you to commit this drug class to memory.

Check back to PTCB Test Prep soon for more content to help you master the 2020 PTCB exam and become a qualified and professional pharmacy technician in the United States.