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Diuretics forms one of the base pillars in treating hypertension and edema. These groups of drugs increases rate of urine flow. Based on their mechanism of action their efficacy varies. Before moving into diuretics I would recommend to revise renal physiology which will make it easier to get deeper and clear concept of mechanism of diuretics. In this section I will not go into details of each and every diuretics, I would rather try to provide concept and differentiating feature based on mechanism of action and adverse effects.
|
Efficacy |
Class of diuretics | Example |
| Carbonic Anhydrase Inhibitors (CAI) | WEAK | Acetazolamide |
| Osmotic diuretics | WEAK | Mannitol |
| Loop diuretics | HIGH | Furosemide |
| Thiazide | MEDIUM | Hydrochlorothiazide |
| Potassium sparring diuretics | WEAK |
Amiloride (Sodium channel inhibitors) Spironolactone (Aldosterone receptor antagonist) |
Lets revise different section of nephron, (see the figure)
- Bowman’s capsule
- Proximal Convoluted Tubule (PCT)
- Loop of Henle (LOH), Thin descending loop
- Loop of Henle (LOH), Thin ascending loop
- Loop of Henle (LOH), Thick ascending loop
- Distal Convoluted Tubule (DCT)
- Cortical collecting tubule
- Medullary collecting tubule
Different drugs mention above have different sites for action, they reason why their efficacy and side effects varies from each other. Action of drugs:
| Site of nephron | Action of drugs |
| 1. Bowman’s capsule | – |
| 2. Proximal Convoluted Tubule (PCT) | Carbonic Anhydrase Inhibitors |
| 3. Loop of Henle (LOH), Thin descending loop | Osmotic diuretics acts here (Osmotic Diuretics also acts in Proximal tubule) |
| 4. Loop of Henle (LOH), Thin ascending loop | – |
| 5. Loop of Henle (LOH), Thick ascending loop | Loop diuretics |
| 6. Distal Convoluted Tubule (DCT) | Thiazides diuretics |
| 7. Cortical collecting tubule | Potassium sparing diureticsPotassium sparing diuretics also acts in late distal tubule. |
| 8. Medullary collecting tubule | – |
As the normal mechanism of each section of the varies, so drugs acting on different section of nephron have different side effects, though their ultimate goal is to increase the rate of flow of urine.
Mechanism of action of these groups of drugs
- Carbonic Anhydrase Inhibitors
Carbonic Anhydrase Inhibitors
↓
Acts in Proximal Convoluted Tubules
↓
Inhibits carbonic Anhydrase
↓
Increases excretion of NaHCO3
↓
Increased rate of flow of urine
- Osmotic diuretics
Osmotic diuretics
↓
Acts in proximal tubules and thin descending loop of Henle, thin ascending loop of Henle
↓
Due to osmotic effect, increases excretion of water
↓
Increased rate of flow of urine
- Loop diuretics
Loop diuretics
↓
Acts in thick ascending loop of Henle
↓
Blocks sodium, potassium, chloride co transporter
↓
Increases sodium, potassium, chloride excretion
↓
Increased rate of flow of urine
- Thiazides
Thiazides
↓
Acts in Distal Convoluted Tubules (DCT)
↓
Blocks sodium chloride transporter
↓
Increased excretion of NaCI
↓
Increased rate of flow of urine
- Potassium sparing diuretics (Acts in late distal tubule and collecting tubules)
They can be of two types:
- Sodium channel blockers
- Aldosterone receptor antagonists
Sodium channel blockers
↓
Blocks sodium channel
↓
Increases sodium excretion and increases potassium retention
↓
Increased rate of flow of urine
Aldosterone receptor antagonists
↓
Acts as antagonist in aldosterone receptor
↓
Promotes sodium and chloride excretion without concomitant potassium loss
↓
Increased rate of flow of urine
ADVERSE EFFECTS of these groups of drugs
Side effects of Carbonic Anhydrase Inhibitors
| Hyper | Hypo |
| Apnea | Potassium |
| Metabolic acidosisAtaxia
Tinnitus |
|
Side effects of Osmotic Diuretics
| Hypo | |
| NatremiaVolemia | |
| Fluid and electrolytes imbalanceAcidosis
Dehydration Urinary retention |
|
Side effects of Loop Diuretics
| Hyper | Hypo |
| UreaGlucose | TensionVolemia
Magnesium Potassium Sodium Calcium |
| Metabolic AlkalosisArrhythmias
Ototoxicity |
|
Side effects of Thiazide diuretics
| Hyper | Hypo |
| UreaGlucose
Calcium |
TensionVolemia
Potassium Sodium Magnesium |
| Metabolic AlkalosisAzotemia | |
Side effects of Potassium sparing diuretics
| Hyper | Hypo |
| Potassium | Sodium |
| Metabolic AcidosisGynecomastia
Impotence |
|
Note:
Hyper Sodium: Hypernatremia
Hyper Potassium: Hyperkalemia
There are many more side effects, and more detailed mechanism of action, but it is important to have base concept before moving details of each drugs.
HAPPY READING.
If you find it fruitful, do not hesitate to share the information in your friends circle.
Dr Bivek Singh
Academic coordinator (MBBS)
Author “A journey into the human body”
Author “Pharmacology Simplified”
Board of Directors (Medical Outreach Nepal, USA)