Make me classification of diuretics and anti diuretics
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Classification of Diuretics and Antidiuretics
DIURETICS
A diuretic increases urine output. The most widely used classification mixes chemical identity, site of action in the nephron, and clinical effect. The diagram below shows exactly where each class acts:
1. Carbonic Anhydrase Inhibitors (Site 1 - Proximal Convoluted Tubule)
Mechanism: Inhibit carbonic anhydrase in the PCT, reducing NaHCO₃ reabsorption. This produces a bicarbonate-rich urine and mild natriuresis. They are among the weakest diuretics because downstream segments compensate by reabsorbing the extra Na⁺.
| Drug | Notes |
|---|---|
| Acetazolamide | Oral; also used for glaucoma, altitude sickness, epilepsy |
| Methazolamide | Primarily used for glaucoma |
| Dorzolamide | Topical ophthalmic use only |
Key effect: Cause hyperchloremic metabolic acidosis (lose HCO₃⁻). Self-limiting due to acidosis.
2. Osmotic Diuretics (Site 2 - PCT + Descending Limb + Collecting Duct)
Mechanism: Freely filtered at the glomerulus but not reabsorbed. They osmotically retain water in the tubular lumen throughout the nephron, preventing passive water reabsorption.
| Drug | Notes |
|---|---|
| Mannitol | IV only; used for cerebral edema, raised IOP, oliguric renal failure |
| Isosorbide | Used for glaucoma |
| Glycerin | Oral |
| Urea | IV; used for cerebral edema |
Key effect: Expand plasma volume before diuresis - contraindicated in pulmonary edema/anuria.
3. Loop Diuretics (Site 3 - Thick Ascending Limb of Loop of Henle)
Mechanism: Competitively inhibit the Na⁺-K⁺-2Cl⁻ (NKCC2) co-transporter on the apical membrane of the thick ascending limb. This is the most potent class - can excrete up to 20-25% of filtered Na⁺. They also inhibit the medullary concentration gradient, reducing water reabsorption even in the presence of ADH, and enhance free water clearance.
| Drug | Notes |
|---|---|
| Furosemide (Frusemide) | Prototype; oral bioavailability ~40-79%; short-acting (<3 hrs) |
| Bumetanide | Higher oral bioavailability than furosemide |
| Torsemide | Higher oral bioavailability; longer-acting |
| Ethacrynic acid | Greater ototoxic risk; reserved for patients allergic to sulfonamides |
Key effects: Hypokalemia, hypomagnesemia, hypocalcemia, ototoxicity, hyperuricemia, metabolic alkalosis. Furosemide also acts as a venodilator (reduces preload acutely via prostaglandin release).
Clinical use: First choice for pulmonary edema, acute heart failure, severe edema, hypertensive urgency, hypercalcemia.
4. Thiazide and Thiazide-like Diuretics (Site 4 - Distal Convoluted Tubule)
Mechanism: Inhibit the NaCl (NCC) co-transporter in the distal convoluted tubule, where ~5% of filtered Na⁺ is reabsorbed. Less potent than loop diuretics. They decrease free water clearance (can cause dilutional hyponatremia) and retain calcium (useful in hypercalciuria/nephrolithiasis).
Thiazides (benzothiadiazines):
| Drug | Half-life | Notes |
|---|---|---|
| Hydrochlorothiazide (HCTZ) | 6-15 hrs | Most widely used |
| Chlorothiazide | 6-12 hrs | Only IV thiazide available |
| Bendroflumethiazide | - | Used in UK |
Thiazide-like (not benzothiadiazines, but same mechanism):
| Drug | Notes |
|---|---|
| Chlorthalidone | Longer half-life (~40-60 hrs); preferred in hypertension |
| Metolazone | Retains efficacy at GFR <30 mL/min; useful in combination with loop diuretics |
| Indapamide | Additional vasodilatory properties |
Key effects: Hypokalemia, hyponatremia, hypercalcemia, hyperuricemia, hyperglycemia, hyperlipidemia, metabolic alkalosis. Lose efficacy at GFR < 30-40 mL/min (except metolazone/indapamide).
Clinical use: Hypertension (first-line), mild-moderate heart failure edema, hypercalciuria, nephrogenic diabetes insipidus, osteoporosis.
5. Potassium-Sparing Diuretics (Site 5 - Collecting Duct / Aldosterone-Sensitive Distal Nephron)
Weakest diuretics when used alone (~2% Na⁺ excretion). Main value is preventing K⁺ and Mg²⁺ loss when combined with loop or thiazide diuretics.
5a. Aldosterone (Mineralocorticoid) Receptor Antagonists
Mechanism: Competitively block aldosterone at the mineralocorticoid receptor in the principal cells of the collecting duct, reducing ENaC expression and Na⁺ reabsorption, thereby decreasing K⁺ secretion.
| Drug | Notes |
|---|---|
| Spironolactone | Steroidal; anti-androgenic side effects (gynecomastia, menstrual irregularity); proven mortality benefit in heart failure (RALES trial) |
| Eplerenone | Steroidal but more selective; fewer anti-androgenic effects |
| Finerenone | New non-steroidal MRA; used in CKD with T2 diabetes |
5b. ENaC (Epithelial Sodium Channel) Blockers
Mechanism: Directly block apical ENaC in the connecting tubule and cortical collecting duct, independent of aldosterone. Reduce Na⁺ reabsorption and dissipate the electrochemical gradient for K⁺ secretion.
| Drug | Notes |
|---|---|
| Amiloride | Used alone for hypertension; also used in Liddle syndrome |
| Triamterene | Often combined with HCTZ (Dyazide, Maxzide) |
Key effect of all K⁺-sparing: Hyperkalemia - avoid in renal impairment or with ACE inhibitors/ARBs.
6. SGLT2 Inhibitors (Site 1 - Proximal Convoluted Tubule)
Mechanism: Inhibit the sodium-glucose co-transporter 2 (SGLT2) in the PCT, preventing reabsorption of glucose and Na⁺. This causes glucosuria and mild natriuresis (osmotic diuresis). They also have hemodynamic and cardiorenal protective effects beyond simple diuresis.
| Drug | Notes |
|---|---|
| Empagliflozin | HFrEF, HFpEF, T2DM, CKD |
| Dapagliflozin | HFrEF, HFpEF, T2DM, CKD |
| Canagliflozin | T2DM, CKD |
| Ertugliflozin | T2DM |
7. Aquaretics (Water Diuretics - Vasopressin V2 Receptor Antagonists)
Mechanism: Selectively block V2 receptors on collecting duct cells, preventing aquaporin-2 insertion into the apical membrane. This causes excretion of free water without significant Na⁺ loss (electrolyte-sparing diuresis = "aquaresis"). These are classified separately because they cause water diuresis (solute-free water excretion), unlike all the above which cause solute diuresis.
| Drug | Receptor | Notes |
|---|---|---|
| Tolvaptan | V2 selective | Oral; FDA-approved for hypervolemic/euvolemic hyponatremia; limit 30 days (hepatotoxicity risk) |
| Conivaptan | V1a/V2 | IV only; FDA-approved for hyponatremia |
| Lixivaptan | V2 selective | Under investigation |
| Satavaptan | V2 selective | Under investigation |
Use: SIADH, dilutional hyponatremia in HF, cirrhosis with ascites, autosomal dominant polycystic kidney disease (tolvaptan).
8. Miscellaneous / Aquaretic-like (via ADH Antagonism)
These induce nephrogenic DI by interfering with ADH action on the collecting duct:
| Drug | Mechanism |
|---|---|
| Lithium | Inhibits adenylyl cyclase downstream of V2 receptor |
| Demeclocycline | Inhibits ADH action on the collecting duct (used in SIADH) |
| Amphotericin B | Reduces tubular water permeability (side effect) |
ANTIDIURETICS
Antidiuretics reduce urine output by promoting water reabsorption in the collecting duct.
1. Vasopressin (Antidiuretic Hormone, ADH) and Analogues
Physiology: Vasopressin is a nonapeptide secreted by the posterior pituitary in response to rising plasma osmolality (>280-285 mOsm/kg) or falling blood pressure. It acts via:
- V2 receptors (renal collecting duct) → activate adenylyl cyclase → insert aquaporin-2 → water reabsorption (antidiuretic effect)
- V1a receptors (vascular smooth muscle) → vasoconstriction
- V1b receptors (pituitary) → ACTH release
| Drug | Key Features |
|---|---|
| Vasopressin (ADH) | IV or IM; t½ ~15 min; also used in esophageal variceal bleeding, septic shock (vasopressor) |
| Desmopressin (DDAVP) | Synthetic analogue (1-desamino-8-D-arginine vasopressin); t½ 1.5-2.5 hrs; antidiuretic:pressor ratio 4000× greater than vasopressin; minimal V1 activity; available IV, SC, intranasal, oral, sublingual |
Pharmacokinetics of Desmopressin:
- Intranasal spray: 10 mcg/spray; bioavailability ~3-4%
- Oral: bioavailability <1%; taken fasting for better absorption
- SC dose: 1-4 mcg every 12-24 hrs
Clinical Uses of Desmopressin:
- Central (pituitary) diabetes insipidus - treatment of choice
- Nocturnal enuresis
- Hemophilia A (mild-moderate) - increases factor VIII
- von Willebrand disease (type 1)
- Uremic coagulopathy
- Bleeding due to platelet dysfunction
Toxicity: Water intoxication (hyponatremia) - can cause seizures/coma with overdose. Vasopressin (not desmopressin) can cause coronary ischemia.
2. Other Antidiuretic Mechanisms
| Drug/Agent | Mechanism | Use |
|---|---|---|
| Carbamazepine | Potentiates ADH action on the collecting duct; also stimulates ADH release | Neurogenic DI; SIADH treatment |
| Chlorpropamide | Sulfonylurea; potentiates ADH action | Partial central DI (largely obsolete) |
| Clofibrate | Stimulates ADH secretion | Partial central DI (largely obsolete) |
| Indomethacin | Prostaglandin inhibition increases tubular sensitivity to ADH | Nephrogenic DI (adjunct) |
| Thiazides | Paradoxically reduce urine volume in DI by causing mild volume depletion → increased proximal tubular reabsorption | Nephrogenic and central DI |
| Amiloride | Blocks lithium entry into collecting duct cells via ENaC | Lithium-induced nephrogenic DI |
Quick Summary Table
| Class | Site of Action | Na⁺ Excretion | Key Drugs | Special Feature |
|---|---|---|---|---|
| Carbonic anhydrase inhibitors | PCT | Low | Acetazolamide | Metabolic acidosis |
| Osmotic diuretics | PCT, descending limb | Moderate | Mannitol | Expand plasma vol first |
| Loop diuretics | Thick ascending LoH | High (20-25%) | Furosemide, Torsemide | Most potent; hypoCa |
| Thiazides | DCT | Moderate (5-10%) | HCTZ, Chlorthalidone | HyperCa; lose effect at low GFR |
| K⁺-sparing | Collecting duct | Low (~2%) | Spironolactone, Amiloride | Hyperkalemia risk |
| SGLT2 inhibitors | PCT | Low-moderate | Empagliflozin | Cardio/renal protective |
| Aquaretics (vaptans) | Collecting duct | None (water only) | Tolvaptan, Conivaptan | Hyponatremia treatment |
| Antidiuretics | ||||
| ADH/Desmopressin | Collecting duct | - | DDAVP | Central DI, enuresis |
| Potentiators (carbamazepine, chlorpropamide) | Collecting duct | - | Carbamazepine | Partial central DI |
| Thiazides (paradoxical) | PCT (vol depletion) | - | HCTZ | Nephrogenic/central DI |
Sources: Comprehensive Clinical Nephrology, 7th Edition, p. 136; Braunwald's Heart Disease, 2-Vol Set, Chapter 50; Katzung's Basic and Clinical Pharmacology, 16th Edition, Chapter 37
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