Diuretics Pharmacology
Introduction
Diuretics are drugs that promote diuresis, or increased urine production. Here, we review the fundamental details about diuretics pharmacology – drug classes, indications, mechanisms of action, side effects and drug interactions.
As part of your NAPLEX exam, or other clinical pharmacy exam, you will be asked many questions on diuretics. It’s imperative, therefore, that you understand how diuretics work and are used – both in terms of their pharmacology and clinical pharmacy applications and implications.
Diuretics are used in the treatment of a wide range of conditions. These include:
- Chronic heart failure
- Hypertension
- Glaucoma
- Liver disease
- Kidney disease
- Hyperaldosteronism
- Edema
- Hypokalemia
Some diuretic drugs – such as acetazolamide – are used to alkalinize urine. This makes acetazolamide effective at promoting the elimination of drugs, such as aspirin, in cases of acute overdose.
Not all diuretics are taken on their own. Many are available as combination products.
Take amiloride, for example:
- Co-amilofruse – amiloride and furosemide
- Co-amilozide – amiloride and hydrochlorothiazide
These combined formulations are important. Given that loop and thiazide diuretics promote potassium loss, amiloride is given to counter that effect and ensure that potassium levels do not fall too low.
Pharmacology of Diuretics
Below, we’ve tabulated diuretics pharmacology into three columns – detailing the facts about drug classes, side effects and clinical factors you need to know.
| Drug Class | Side Effects | Comments |
|---|---|---|
| Loop diuretics Furosemide Bumetanide Ethacrynic acid Torsemide | Dehydration Hypotension Low electrolyte state Hearing loss / tinnitus | Increased risk of renal failure when taken with an NSAID and ACE inhibitor. Ethacrynic acid is the only member that is not a sulfonamide drug. Act at ascending limb of loop of Henle. Increase risk of digoxin and lithium toxicity. Increase ototoxicity / nephrotoxicity risk of aminoglycosides. |
| Thiazide diuretics Hydrochlorothiazide Indapamide Chlorthalidone | Hyponatremia Hypokalemia Hypotension Hyperglycemia Hyperlipidemia Hypercalcemia | Increase risk of acute gout. Effectiveness reduced by NSAIDs. Act at distal convoluted tubule. |
| Osmotic diuretics Mannitol | Dehydration Electrolyte imbalance Thirst Dry mouth | Promotes osmotic diuresis by acting at proximal tubule / descending limb. Lowers intracranial pressure. Lowers ocular pressure. |
| Potassium-sparing Amiloride | GI upset Hypotension Dizziness Hyperkalemia | Side effects uncommon at low doses. Avoid with K-elevating drugs. Increase digoxin/lithium toxicity. Avoid in severe renal impairment. Blocks epithelial sodium channels, inhibiting sodium reabsorption in the late distal convoluted tubules and collecting ducts. |
| Aldosterone antagonists Spironolactone Eplerenone | Hyperkalemia Gynecomastia Liver impairment Muscle weakness Electrolyte imbalance Nausea / vomiting Dry skin / rash Decreased libido Dehydration Menstrual disturbance | Competitively bind to aldosterone receptors to increase sodium and water excretion and promote potassium retention. Can cause Stevens-Johnson syndrome. Avoid with K-elevating drugs. Avoid in Addison’s disease, severe renal impairment and hyperkalemia. |
| Carbonic anhydrase inhibitors Acetazolamide Dorzolamide | Paresthesia Fatigue Decreased libido Metallic taste Electrolyte imbalance GI effects Drowsiness Decreased libido | Act at the proximal tubule. Decreases hydrogen and bicarbonate ions in the body. Used to treat glaucoma, intracranial hypertension and heart failure. |
| V2 antagonists Tolvaptan | Liver damage Dry mouth Blurred vision Fruity breath odor Constipation Weakness Increased thirst | Vasopressin V2 receptor antagonist – decreasing the number of aquaporin channels in renal collecting ducts, decreasing water reabsorption. Should not be used for more than 30 days. Aquaretic drug – promotes water, but not electrolyte loss. Used to treat hyponatremia linked to SIADH, heart failure and cirrhosis. |
Final Thoughts
Learning about diuretics pharmacology shouldn’t be a hassle.
Diuretics remain an important drug class in the treatment of heart failure, hypertension, glaucoma and certain liver diseases. Some diuretics are helpful at making the urine more alkaline, enhancing elimination of drugs such as aspirin in cases of overdose.
You must have a thorough knowledge of each drug class and how to apply those drugs at the clinical level. We’ve put together a comprehensive range of NAPLEX sample questions to help you on your way – examining the fundamental details that you need to know. Take a few seconds to become a registered member.
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