# Renal Pharmacology: Diuretics in Clinical Practice **Level:** PA/Medical Student **Duration:** 45–60 minutes **Version:** 2026-02-12 ------------------------------------------------------------------------ ## Learning Objectives By the end of this module, students will be able to: 1. **Classify** diuretics by mechanism of action and nephron site 2. **Explain** the molecular mechanisms of loop, thiazide, and potassium-sparing agents 3. **Calculate** appropriate dosing and ceiling doses for clinical scenarios 4. **Recognize** diuretic resistance and implement management strategies 5. **Manage** electrolyte complications (hypokalemia, hyperkalemia, hyponatremia) 6. **Identify** the braking phenomenon and post-diuretic sodium retention 7. **Apply** sequential nephron blockade in decompensated heart failure and edematous states ------------------------------------------------------------------------ ## Overview: Nephron Segmental Pharmacology Diuretics act at specific sites along the renal tubule, following the principle of **sequential nephron blockade**: | **Nephron Segment** | **Diuretic Class** | **Primary Effect** | **K+ Loss** | |----|----|----|----| | Proximal convoluted tubule | Acetazolamide | ↓ HCO₃⁻ reabsorption | Mild | | Thick ascending limb (TAL) | Loop diuretics | ↓ Na-K-2Cl cotransport | Severe | | Distal convoluted tubule | Thiazides | ↓ NaCl cotransport | Moderate | | Collecting duct | K⁺-sparing | ↓ ENaC, ↑ K⁺ retention | Sparing | | Systemic | Osmotic (mannitol) | ↓ Tubular water reabsorption | Variable | ------------------------------------------------------------------------ ## LOOP DIURETICS ### Mechanism of Action Loop diuretics bind to the **Na-K-2Cl (NKCC2) cotransporter** on the apical membrane of thick ascending limb (TAL) cells, blocking reabsorption of ~25% of filtered sodium. **Key Insight:** The TAL is relatively impermeable to water and reabsorbs salt through NKCC 2. Potassium recycling helps create a lumen-positive voltage that supports paracellular calcium and magnesium reabsorption within this segment. Loop blockade reduces this process and increases downstream sodium delivery. ### Agents #### Furosemide - **Bioavailability:** 10–100% (highly variable; GI edema decreases absorption) - **IV bioavailability:** 100% - **Peak effect:** IV effect peaks within about 30 minutes; oral effect usually peaks within 1–2 hours. Assess response rather than relying on a clock alone. - **Duration:** IV diuretic effect is approximately 2 hours; oral effect is commonly 6–8 hours, with patient-dependent variation. - **Dose response:** There is no universal 40-mg IV ceiling. Threshold and effective ceiling depend on kidney function, prior exposure and the clinical response; use an individualized monitored regimen. - **Protein binding:** 91% (hepatic metabolism, renal excretion of metabolites) #### Bumetanide - **Potency:** 40× furosemide (1 mg bumetanide ≈ 40 mg furosemide) - **Bioavailability:** More consistent than furosemide (80–90%) - **Onset:** IV 1 minute; PO 30–60 minutes - **Duration:** 4–6 hours - **Label maximum:**10 mg/day; route, administration and repeat dosing require product-label and clinical review. - **Advantage:** Better absorption in GI edema; less ototoxicity at equivalent doses #### Torsemide - **Conversion:** Torsemide is not equivalent to furosemide at 1:40. Use a validated route-specific conversion and then assess clinical response; oral bioavailability and natriuretic response differ. - **Bioavailability:** 80–90% (superior to furosemide) - **Duration:** 6–8 hours - **Dose range:**20 mg is not a universal maximum. The label starts HF edema at 10–20 mg/day and CKD edema at 20 mg/day, then titrates to response; doses above 200 mg/day have not been adequately studied. Cirrhosis has separate lower studied dosing limits. - **Advantage:** Longer half-life; once-daily dosing feasible - **Note:** TRANSFORM-HF trial [PubMed](https://pubmed.ncbi.nlm.nih.gov/36648467/) did not show mortality benefit of torsemide vs furosemide despite superior bioavailability ### Clinical Use **Indications:** - Acute decompensated heart failure (preferred agent) - Pulmonary edema - Peripheral edema in CKD - Ascites in cirrhosis (combined with spironolactone) - Nephrotic syndrome with edema - Hypertension (less commonly, reserve for specific scenarios) **Dosing Strategy:** 1. Start IV in acute decompensation: 40–80 mg bolus 2. Double dose every 30–60 min if inadequate response (40 → 80 → 160 mg) 3. Transition to continuous infusion if repeated boluses needed: 5–10 mg/hr 4. Chronic oral dosing: once or twice daily; titrate based on fluid status **Special populations:** In AKI, loop diuretics can help manage fluid overload but have not been shown to improve survival or kidney recovery; do not use them to postpone indicated kidney replacement therapy. [Systematic review](https://pubmed.ncbi.nlm.nih.gov/17352669/). In cirrhosis, spironolactone and furosemide are often combined with laboratory monitoring. Reduced kidney function may require higher loop doses, guided by response, blood pressure, and electrolytes. ------------------------------------------------------------------------ ## THIAZIDE AND THIAZIDE-LIKE DIURETICS ### Mechanism of Action Thiazides block the **Na-Cl cotransporter (NCC)** on the distal convoluted tubule (DCT), inhibiting reabsorption of ~5–10% of filtered sodium. Lower natriuretic potency than loop diuretics but sustained antihypertensive effect. **Metabolic Effects:** - ↑ Urinary K⁺ loss (hypokalemia risk) - ↑ Urinary Mg²⁺ loss (hypomagnesemia risk) - ↑ Urinary Ca²⁺ retention → hypercalcemia risk - ↑ Uric acid retention → hyperuricemia - ↑ Glucose intolerance (dose-dependent) - ↑ LDL, triglycerides (generally mild) ### Agents #### Hydrochlorothiazide (HCTZ) - **Dose:** 12.5–25 mg daily (doses \>25 mg not more effective, increased side effects) - **Bioavailability:** ~70% - **Duration:** 12–24 hours - **Onset:** 2 hours - **Protein binding:** Low (renal secretion) - **Metabolism:** Unchanged, renal excretion #### Chlorthalidone - **Potency:** ~1.5–2× HCTZ - **Dose:** 12.5–25 mg daily (half HCTZ equivalent dose) - **Duration:** 24–72 hours (much longer) - **Onset:** 4–6 hours - **Advantage:** Once-daily dosing; often more sustained BP effect than HCTZ; ACCOMPLISH did not compare chlorthalidone with HCTZ - **Disadvantage:** Hypokalemia and hyponatremia risk higher; slower offset if adverse effects #### Indapamide - **Mechanism:** Similar to thiazides but some vasodilatory properties - **Dose:** 1.25–2.5 mg daily - **Advantage:** Less metabolic derangement (modest glucose, K⁺, lipid effects) - **Duration:** 12–18 hours ### Metolazone (Quinazoline; Thiazide-Like) **Metolazone:** A thiazide-like NCC inhibitor that can augment a loop diuretic in refractory congestion even with low GFR. It is not the only thiazide-like drug that can work in advanced CKD: CLICK demonstrated chlorthalidone blood-pressure benefit in G4. Select by indication, and monitor sodium, potassium, magnesium, creatinine and orthostatic symptoms. **Clinical Use in Diuretic Resistance:** - **Sequential blockade:** IV furosemide + metolazone 2.5–10 mg PO daily produces profound natriuresis - **Mechanism:** DCT sodium–chloride transport blockade complements loop inhibition in the TAL - **Caution:** Close monitoring—risk of severe hypokalemia, hyperglycemia, hyperuricemia - **Monitoring:** During inpatient intensified combination diuresis, check electrolytes and kidney function at least daily and more often with major shifts or arrhythmia risk; outpatient timing depends on risk and dose changes. ------------------------------------------------------------------------ ## POTASSIUM-SPARING DIURETICS ### Mechanism: ENaC Blockers **Amiloride and Triamterene** block the epithelial sodium channel (ENaC) on the apical membrane of collecting duct principal cells, preventing Na⁺-driven K⁺ secretion. ### Agents and Properties | **Agent** | **Dose** | **Onset** | **Mechanism** | **Note** | |----|----|----|----|----| | **Amiloride** | 5–10 mg daily | 2–4 hours | ENaC blocker | Renal excretion; avoid NSAIDs, ACEi/ARB | | **Triamterene** | 50–100 mg 1–2×/day | 2–4 hours | ENaC blocker | Hepatic metabolism; risk of crystalluria (rare) | | **Spironolactone** | 12.5–50 mg daily | 2–3 days | MRA | See below | | **Eplerenone** | 25–50 mg daily | 1–2 hours | MRA | CYP3A4 substrate; fewer hormonal side effects | ### Aldosterone Receptor Antagonists (MRAs) #### Spironolactone - **Mechanism:** Competitive aldosterone receptor antagonist in collecting duct - **Potency:** Weak diuretic alone; potent when combined with loop/thiazide - **Onset:** 2–3 days (slow); peak effect 7–14 days - **Duration:** 18–24 hours (prolonged half-life ~13 hours) - **Indications:** Heart failure (RALES trial—↓ mortality 30%), resistant hypertension, primary aldosteronism, cirrhotic ascites - **Metabolites:** Active (canrenone) and inactive; undergo enterohepatic circulation - **Adverse effects:** - Hyperkalemia (especially if combined with ACEi/ARB or renal impairment) - Gynecomastia (10–15%; due to androgen receptor antagonism), menstrual irregularities - Mastodynia, sexual dysfunction - **Monitoring:** K⁺ and Cr at baseline, 3–7 days, then monthly × 3, then every 3 months; LFTs #### Eplerenone (Selective MRA) - **Mechanism:** Selective aldosterone antagonist; 50–70% aldosterone selectivity vs. spironolactone - **Potency:** Similar to spironolactone but weaker anti-androgen - **Onset:** 1–2 hours (rapid) - **Indication:** Heart failure with reduced ejection fraction (EMPHASIS-HF trial) - **Dose:** 25–50 mg daily - **Advantage:** - No gynecomastia/sexual dysfunction - Shorter onset; more favorable drug interaction profile - **Disadvantage:** - Expensive (branded drug Inspra) - CYP3A4 substrate (drug interactions with clarithromycin, diltiazem, etc.) ### Clinical Application **Combination therapy:** A loop plus thiazide-like drug blocks different nephron segments. A potassium-sparing drug may be useful for a specific indication, but is not automatic protection against hypokalemia; kidney function, potassium and interacting medicines determine safety. **Safety selection:** Follow the individual drug and indication label. Hyperkalemia and impaired clearance increase risk; symptoms do not justify a higher potassium threshold. For HFrEF, steroidal MRA initiation generally requires eGFR\>30 and K\<5.0 with close monitoring. ACEi/ARB plus MRA may be indicated, while adding NSAIDs or other potassium-retaining drugs increases harm. ------------------------------------------------------------------------ ## ACETAZOLAMIDE (Carbonic Anhydrase Inhibitor) ### Mechanism Inhibits **carbonic anhydrase II** in proximal tubule epithelium, blocking reabsorption of HCO₃⁻ and ~5–10% of Na⁺. Weak diuretic alone. ### Properties - **Dose:** 250–500 mg once or twice daily - **Onset:** 1–4 hours (PO); 2–5 minutes (IV) - **Duration:** 8–12 hours (PO) - **Metabolism:** Renal excretion (unchanged) ### Clinical Uses 1. **Selected metabolic alkalosis** (after volume, chloride, potassium and kidney assessment): - Inhibits proximal HCO₃⁻ reabsorption - Allows urinary HCO₃⁻ wasting - Dose: 250–500 mg PO daily until alkalemia resolves - In chloride-depleted hypovolemia, indicated saline plus potassium chloride addresses the cause. Acetazolamide is a selected option when bicarbonate excretion is needed and volume expansion is unsuitable; it can worsen hypokalemia. 2. **Altitude sickness:** ↓ CSF HCO₃⁻ → respiratory compensation → ↓ periodic breathing 3. **Glaucoma:** ↓ aqueous humor production (chronic use only; alternative agents preferred) ### Metabolic Consequences - **Hypokalemia** (high risk) - **Hyperchloremic metabolic acidosis** (from proximal HCO₃⁻ wasting) - **Hyperammonemia/encephalopathy risk:** Acetazolamide can impair urinary ammonium trapping; it is contraindicated in cirrhosis. - **Hyperuricemia** - **Paresthesias** (secondary to HCO₃⁻ wasting) ### Contraindications - Hypokalemia (exacerbates) - Cirrhosis/marked liver disease, marked kidney dysfunction, and hyperchloremic acidosis; check the label as well as sodium and potassium before use - Sulfonamide allergy (acetazolamide is sulfonamide derivative) ------------------------------------------------------------------------ ## OSMOTIC DIURETICS ### Mannitol **Mechanism:** Freely filtered at glomerulus; poorly reabsorbed in tubule. Creates osmotic gradient that draws water into tubular lumen, reducing water reabsorption throughout the nephron and increasing urine output. **Properties:** - **Dose/concentration:** Use the specialist indication and specific product label; there is no routine mannitol dose for preventing pigment AKI. - **Onset:** 15–30 minutes - **Peak effect:** 30–60 minutes - **Duration:** 1.5–6 hours - **Elimination:** Mainly renal; impaired clearance can cause accumulation and worsening volume/osmotic complications **Clinical uses:** Mannitol has selected specialist indications for raised intracranial or intraocular pressure. It is not routinely recommended to prevent rhabdomyolysis-associated AKI or to convert oliguric AKI to nonoliguric AKI. Anuria and pre-existing severe pulmonary congestion/edema are important contraindications. **Adverse Effects:** - **Hypernatremia:** From free water loss - **Osmotic/volume complications:** Monitor for initial extracellular expansion, pulmonary edema, and later depletion if diuresis occurs - **Hyperkalemia:** Initially—from cell water loss concentrating K⁺; later hypokalemia if diuresis sustained - **Volume depletion:** If used injudiciously - **Rebound cerebral edema:** If osmotic gradient dissipates **Monitoring:** Follow the specialist indication/protocol, renal function, electrolytes, urine output and osmolar status. A universal osmolality ceiling alone does not establish safety; stop and reassess worsening renal, cardiac or pulmonary status. ------------------------------------------------------------------------ ## DIURETIC RESISTANCE: Mechanisms and Management ### Definition Failure to achieve adequate diuresis despite escalating doses of diuretic (typically loop diuretics). ### Mechanisms **1. Pharmacokinetic Resistance** - **Poor GI absorption:** Furosemide absorption ↓ in acute decompensation (splanchnic vasoconstriction, bowel edema) - **Solution:** Switch to IV or more reliable agent (bumetanide, torsemide) **2. Pharmacodynamic Resistance** - **Tubular refractoriness:** Chronic diuretic use → compensatory upregulation of Na⁺ transport in salt-sparing segments, blunting response - **Response:** Reassess sodium intake, dose delivery and ongoing congestion; use an appropriate dosing interval or sequential blockade with monitoring. Routine diuretic holidays are not a treatment for congested patients. **Renal drug delivery:** Loop diuretics reach the tubular lumen largely through proximal tubular secretion, not glomerular filtration. CKD, poor perfusion and competing organic anions reduce delivery; assess response and adjust the regimen. The DOSE trial did not establish routine superiority of continuous infusion over bolus dosing. **4. Hypoalbuminemia** - **Mechanism:** Diuretics bound to albumin; hypoalbuminemia (nephrotic syndrome, liver disease) ↓ tubular secretion of diuretic - **Solution:** Larger doses; consider albumin infusion if severe (controversial) **5. Elevated Renal Vascular Resistance** - **NSAIDs, sepsis, hepatorenal syndrome:** Vasoconstriction ↓ renal perfusion - **Solution:** Remove offending agent; improve cardiac output; consider vasodilators ### Management Algorithm **Step 1: Verify Diagnosis** - Confirm volume overload (not dry weight, medications, poor adherence) - Check compliance (24-hr urine Na⁺, K⁺ if question of diuretic use) - Verify adequate dosing (may be subtherapeutic) **Step 2: Assess perfusion and contributors** - Treat shock, infection and true depletion when present. Inotropes/vasodilators require specific hemodynamic indications, not edema alone. Stop NSAIDs; review RAAS therapy for symptomatic hypotension, important AKI or hyperkalemia, with a restart plan when appropriate. **Step 3: Maximize Diuretic Delivery** - Switch from PO to IV (especially furosemide) - Increase frequency (TID dosing vs. daily) - Escalate dose (doubling protocol until ceiling reached) - Switch to continuous infusion (5–10 mg/hr furosemide equivalent) **Step 4: Sequential Nephron Blockade** - **Combination therapy:** IV loop + metolazone 2.5–10 mg PO - **Mechanism:** Blocking compensatory distal sodium uptake complements loop blockade and can markedly increase sodium loss - **Monitoring:** Potassium, sodium, magnesium and creatinine at least daily during active inpatient escalation; check sooner for high-risk or symptomatic changes - **Caution:** May precipitate electrolyte derangement; avoid if not monitored closely **Step 5: Reassess the volume goal and adverse effects** - Reduce or hold diuresis for depletion, symptomatic hypotension or other clinically important harm. Persistent congestion calls for a revised treatment plan, not an automatic 24–48-hour holiday intended to reset transporters. **Step 6: Advanced Options** - **Vasopressin antagonists (vaptans):** Aquaretic; useful in cardiorenal syndrome + hyponatremia (but mortality neutral in HF—EVEREST trial) - **Inotropy:** Dobutamine infusion ± continuous diuretic (in decompensated HF with hypotension) - **Ultrafiltration (UF):** Mechanical removal of fluid; reserved for refractory cases unresponsive to pharmacotherapy ------------------------------------------------------------------------ ## THE BRAKING PHENOMENON ### Definition Despite ongoing diuretic therapy, sodium excretion and urine output gradually return toward baseline over **3–5 days** of continuous diuretic use. ### Mechanism **Adaptation occurs via:** 1. **Increased proximal reabsorption:** Reduction in GFR and peritubular capillary hydrostatic pressure → enhanced proximal Na⁺ reabsorption 2. **Increased renin-angiotensin system (RAS) activation:** Volume depletion → aldosterone ↑ → distal K⁺/Na⁺ exchange ↑ 3. **Increased sympathetic nervous system (SNS) activation:** Baroreceptor response to hypotension/volume depletion 4. **Tubular adaptation:** Upregulation of salt transporters in distal nephron segments ### Post-Diuretic Sodium Retention **Phenomenon:** After stopping diuretics, there is often a rebound period of **sodium retention (anti-natriuresis)** lasting 1–3 days, causing rapid weight gain if dietary sodium not restricted. **Clinical Significance:** - Explains why chronic diuretic therapy plateaus in effect despite stable dosing - Supports adequate dosing frequency to limit post-diuretic sodium retention - Emphasizes importance of dietary sodium restriction as cornerstone of volume management ### Clinical Implications 1. **Chronic diuretic therapy:** Requires either - Escalating doses (leading to tachyphylaxis and side effects), OR - Intermittent dosing with sodium restriction + dietary counseling 2. **Loop diuretic monotherapy:** Often insufficient long-term; combine with ACEi/ARB/MRA to suppress RAS and SNS 3. **Patient education:** Sodium restriction \<3 g/day essential; often underemphasized ------------------------------------------------------------------------ ## Clinical Scenarios ### Scenario 1: Acute Decompensated Heart Failure, Pulmonary Edema **Clinical:** 58-year-old male with LVEF 30% presenting with orthopnea, 3+ edema, bibasilar rales. **Approach:** 1. **Assess volume status:** Orthopnea, rales, elevated JVP → euvolemic/hypervolemic 2. **Initial diuresis:** IV furosemide 80 mg bolus; reassess after 1 hour 3. **If inadequate urine output (\<200 mL/hr):** Double to 160 mg bolus or start continuous infusion 5 mg/hr 4. **Goal:** ↓ weight 1–2 lbs/day; resolution of orthopnea/rales 5. **Add ACEi + aldosterone antagonist** to suppress compensatory RAS/SNS activation 6. **Transition to PO:** Choose the oral regimen from the effective inpatient dose, kidney function and observed response; confirm adequate control before discharge rather than automatically switching everyone to torsemide 10 mg 7. **Sodium restriction:** \<3 g/day; monitor daily weights ------------------------------------------------------------------------ ### Scenario 2: Diuretic-Resistant Edema in CKD Stage 4 with FSGS **Clinical:** 52-year-old female with eGFR 22, nephrotic syndrome (proteinuria 8 g/day, albumin 2.8), peripheral edema unresponsive to furosemide 240 mg daily PO. **Assess apparent resistance:** Review adherence, dietary sodium, bowel edema, drug absorption, tubular delivery, interacting drugs and the current loop dose. Low GFR can increase dose requirements; it does not make every thiazide or thiazide-like agent ineffective. **Approach:** 1. **Switch to IV:** Furosemide 80 mg IV daily or 40 mg IV BID (better delivery) 2. **Add metolazone:** 5 mg PO daily (retains efficacy in low GFR) 3. **Monitor:** Check electrolytes, creatinine, orthostasis and weight early after combined therapy; inpatient escalation generally needs at least daily labs, with individualized early outpatient reassessment. 4. **Goal:** ↓ weight 1–2 lbs/week; reduce proteinuria with ACEi/ARB 5. **Add albumin:** Consider albumin infusion (25 g IV) with diuretic to enhance natriuresis (controversial; evidence limited) ------------------------------------------------------------------------ ### Scenario 3: Metabolic Alkalosis in Vomiting **Clinical:** 72-year-old with vomiting × 5 days: pH 7.52, HCO₃⁻ 48, K⁺ 2.8, Cl⁻ 82. **Mechanism:** Contraction alkalosis (loss of HCl in gastric secretions) **Approach:** Treat the vomiting and assess perfusion, congestion and ECG risk. With demonstrated chloride-depleted hypovolemia, give indicated isotonic saline and replace potassium chloride with frequent reassessment. K 2.8 requires correction; acetazolamide is not a substitute while saline is delayed and can worsen this hypokalemia. Follow potassium, pH/bicarbonate, urine output and volume response. ------------------------------------------------------------------------ ## Practice Questions ### Question 1 A 64-year-old man with systolic heart failure (LVEF 25%), hypertension, and CKD Stage 3a (eGFR 48) is admitted with acute decompensation. He is dyspneic at rest and has 4+ peripheral edema. He has been taking lisinopril 10 mg daily, carvedilol 25 mg BID, and furosemide 40 mg daily. In the hospital, he receives IV furosemide 80 mg bolus but produces only 150 mL urine in the first hour despite clinical evidence of volume overload. Which of the following is the MOST appropriate next step? 1. Increase furosemide to 160 mg IV bolus 2. Add metolazone 5 mg PO daily 3. Initiate continuous IV furosemide infusion 5 mg/hr 4. Hold all diuretics for 24 hours (diuretic-free interval) 5. Add IV albumin 25 g **Answer:** A (escalate to ceiling dose per DOSE trial; consider C if repeated boluses fail) **Rationale:** - Initial inadequate response likely reflects suboptimal dosing or decreased diuretic delivery due to splanchnic vasoconstriction in acute decompensation - Double the dose (80 → 160 mg) before advancing to infusion - Metolazone useful if loop alone fails after dose escalation - Diuretic-free interval dangerous in acute decompensation - Albumin controversial; not first-line ------------------------------------------------------------------------ ### Question 2 A 58-year-old woman with lupus nephritis (Class IV) is being treated with IV methylprednisolone and mycophenolate mofetil. After 2 weeks, she develops peripheral edema and proteinuria persists at 6 g/day. Labs: Na⁺ 128 mmol/L (hyponatremia), K⁺ 5.8 mmol/L (hyperkalemia), Cr 1.4 mg/dL (baseline 0.8). She is on losartan 100 mg daily and lisinopril 10 mg daily (dual RAAS blockade for proteinuria reduction). Which medication adjustment is MOST appropriate? 1. Start spironolactone 25 mg daily for additional proteinuria reduction 2. Discontinue lisinopril; continue losartan monotherapy 3. Start chlorthalidone 25 mg daily 4. Start furosemide 40 mg daily 5. B and D **Answer:** E (discontinue ACEi, start diuretic) **Rationale:** - **Hyperkalemia (K⁺ 5.8) + dual RAAS blockade = contraindication** to K⁺-sparing agents - Lisinopril + losartan = dual RAAS blockade associated with hyperkalemia and worsening renal function without mortality benefit (failed VA NEPHRON-D, ONTARGET trials) - Stop one RAAS inhibitor (typically the ACEi if ARB continued, though either acceptable) - Hyponatremia plus hyperkalemia does not prove depletion or aldosterone excess. Here, dual RAAS blockade and worsening kidney function increase potassium risk; assess true volume status and treat hyperkalemia, adding a loop only when congestion and urine response support it - Edema requires assessment of its mechanism and effective circulating volume; creatinine 1.4 alone does not determine the drug or dose ------------------------------------------------------------------------ ### Question 3 A 71-year-old woman with CKD Stage 4 (eGFR 28), hypertension, and diabetes presents with persistent peripheral edema despite furosemide 120 mg PO daily and lisinopril 10 mg daily. 24-hour urine Na⁺ is 45 mmol/day. This reflects intake, collection completeness, timing and response; it cannot by itself establish nonadherence or poor absorption. She denies missing medications. Urine dipstick shows 2+ protein. She has never taken a thiazide or thiazide-like diuretic. Which diuretic addition is MOST appropriate? 1. Hydrochlorothiazide 25 mg daily 2. Metolazone 5 mg daily 3. Acetazolamide 500 mg daily 4. Spironolactone 25 mg daily 5. Amiloride 5 mg daily **Answer:** B (metolazone) **Rationale:** For persistent congestion despite an adequate loop regimen, add a thiazide-like drug such as metolazone when appropriate and monitor closely for hypovolemia, AKI, and electrolyte loss. For G4 hypertension, chlorthalidone can still lower blood pressure (CLICK); avoid a categorical eGFR \<30 exclusion. The indication and monitoring capacity determine selection. ------------------------------------------------------------------------ ## Clinical Pearl Summary 1. **Loop diuretics** inhibit NKCC 2 in the water-impermeable TAL. Dose response depends on delivery to the lumen, kidney function and prior exposure; titrate to clinical response and adverse effects. 2. Thiazide and thiazide-like drugs can cause hypokalemia, hyponatremia, hyperuricemia and reversible creatinine increases. Chlorthalidone has randomized evidence for G4 hypertension; use an individualized dose and close monitoring rather than assuming loss of all efficacy below eGFR 30. 3. **Potassium-sparing agents** have specific indications and hyperkalemia risks. They are not mandatory companions to every diuretic; use the drug/indication label, kidney function, baseline potassium and monitoring plan. Avoid dual ACEi/ARB blockade. 4. **Braking and post-diuretic sodium retention** call for sodium-intake review and an effective, monitored regimen. Do not prescribe a drug holiday or add RAAS drugs solely to reset the response. 5. **Diuretic resistance:** Escalate doses to ceiling, switch to IV, add sequential nephron blockade (metolazone + loop), optimize renal perfusion, consider continuous infusion. 6. **Hypoalbuminemia** (nephrotic syndrome) impairs diuretic secretion; may require albumin infusion or larger doses. 7. **Advanced CKD:** Use a loop diuretic for congestion and consider sequential nephron blockade for inadequate response. Chlorthalidone may be useful for hypertension; metolazone is one add-on option for congestion. Check blood pressure, orthostasis, weight, electrolytes and creatinine after starting or increasing therapy. ------------------------------------------------------------------------ ## References 1. Felker GM, Lee KL, Bull DA, et al. Diuretic strategies in patients with acute decompensated heart failure. N Engl J Med. 2011;364(9):797-805. [PubMed](https://pubmed.ncbi.nlm.nih.gov/21366472/) 2. **Kidney Disease: Improving Global Outcomes (KDIGO)** — CKD management; diuretic selection in renal insufficiency. 3. Brater DC. Diuretic therapy. N Engl J Med. 1998;339(6):387-395. [PubMed](https://pubmed.ncbi.nlm.nih.gov/9691107/) 4. Ellison DH, Felker GM. Diuretic Treatment in Heart Failure. N Engl J Med. 2017;377(20):1964-1975. [PubMed](https://pubmed.ncbi.nlm.nih.gov/29141174/) 5. Pitt B, Zannad F, Remme WJ, et al. The effect of spironolactone on morbidity and mortality in patients with severe heart failure. Randomized Aldactone Evaluation Study Investigators. N Engl J Med. 1999;341(10):709-717. [PubMed](https://pubmed.ncbi.nlm.nih.gov/10471456/) 6. Heidenreich PA, Bozkurt B, Aguilar D, et al. 2022 AHA/ACC/HFSA Guideline for the Management of Heart Failure: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2022;145(18):e895. [PubMed](https://pubmed.ncbi.nlm.nih.gov/35363499/) 7. Ellison DH, Berl T. Clinical practice. The syndrome of inappropriate antidiuresis. N Engl J Med. 2007;356(20):2064-2072. [PubMed](https://pubmed.ncbi.nlm.nih.gov/17507705/) 8. Mentz RJ, Anstrom KJ, Eisenstein EL, et al. Effect of Torsemide vs Furosemide After Discharge on All-Cause Mortality in Patients Hospitalized With Heart Failure: The TRANSFORM-HF Randomized Clinical Trial. JAMA. 2023;329(3):214-223. [PubMed](https://pubmed.ncbi.nlm.nih.gov/36648467/) 9. **Pharmaceutical References:** Lexicomp, UpToDate, micromedex for dosing, interactions, pharmacokinetics (access via institution or subscription). ------------------------------------------------------------------------ ## See Also ### Related Student Handouts - RAAS Inhibitors and Renoprotective Therapy - Hyperkalemia Management - Hypokalemia Management - Hypertension Management - CKD Complications - GDMT: Four Pillars of Therapy ### Clinical Content (01-Clinical-Medicine/Nephrology & Cardiology) - Hypertension Management Hub - Essential Renal Laboratory Tests - Heart Failure Clinical Reference ### Butler-COM Resources - Butler COM - Nephrology Deep Dive - Butler COM - Heart Failure GDMT Deep Dive ------------------------------------------------------------------------ **Created:** 2026-02-12 **Last Updated:** 2026-02-12 **Suggested Citation:** “Renal Pharmacology: Diuretics in Clinical Practice.” Medical Education Handout, 2026. --- [Website version](https://urinenephrology.org/student-resources/pharmacology/diuretics-student-handout.html) · Markdown synchronized October 3, 2026.