====== Hydrochlorothiazide (Microzide®) ======

<WRAP right 340px>
<WRAP infobox>
^ Hydrochlorothiazide | {{ :cardio:diuretics:hydrochlorothiazide.svg?150 |}} |
| Brand Names | Microzide®, HydroDIURIL® |
| Drug Class | [[cardio:diuretics:start|Thiazide Diuretic]] |
| Primary Indication | Hypertension |
| Site of Action | Distal Convoluted Tubule |
| Mechanism | Na⁺/Cl⁻ Cotransporter Inhibition |
| Potassium Effect | ↓ (Hypokalemia risk) |
| Calcium Effect | ↑ Reabsorption |
| Half-Life | ~6–15 hours |
| FDA Approval | 1959 |
</WRAP>
</WRAP>

===== Overview =====

Hydrochlorothiazide (HCTZ) is a thiazide diuretic used primarily for the treatment of hypertension and mild edema.

It lowers blood pressure by promoting natriuresis and reducing plasma volume, followed by long-term reduction in systemic vascular resistance.

Thiazides remain first-line therapy for uncomplicated hypertension in many patients.

<WRAP clear></WRAP>

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===== Mechanism of Action =====

**Site of Action**
  * Distal convoluted tubule  

**Transporter Blocked**
  * Na⁺/Cl⁻ cotransporter (NCC)  

**Physiologic Effects**
  * ↑ Sodium and water excretion  
  * ↑ Potassium excretion  
  * ↑ Calcium reabsorption  
  * ↓ Plasma volume  
  * ↓ Peripheral vascular resistance (long term)  

Net effect:
  * Reduction in blood pressure  

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===== Indications =====

  * Primary hypertension  
  * Mild edema  
  * Nephrolithiasis (calcium stone prevention)  
  * Adjunct in heart failure (mild cases)  

Often combined with:
  * [[cardio:raas:acei|ACE inhibitors]]  
  * [[cardio:raas:arb|ARBs]]  
  * [[cardio:beta_blockers:start|Beta-blockers]]  

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<WRAP contra>
===== Contraindications =====

Absolute:
  * Anuria  
  * Sulfonamide allergy (relative; cross-reactivity low)  

Relative / Caution:
  * Severe renal impairment (ineffective at low GFR)  
  * Gout  
  * Diabetes mellitus  
  * Hyponatremia  
  * Hypokalemia  

</WRAP>

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<WRAP details>
===== Dosing =====

Hypertension:
  * 12.5–25 mg once daily  

Edema:
  * 25–100 mg daily  

Higher doses increase metabolic side effects without significant additional BP benefit.

</WRAP>

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<WRAP details>
===== Pharmacokinetics =====

Absorption:
  * Oral  

Bioavailability:
  * ~65–75%  

Half-life:
  * ~6–15 hours  

Elimination:
  * Renal  

Effectiveness decreases when eGFR < 30 mL/min/1.73 m².

</WRAP>

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<WRAP details>
===== Adverse Effects =====

Electrolyte:
  * Hypokalemia  
  * Hyponatremia  
  * Hypomagnesemia  
  * Hypercalcemia  

Metabolic:
  * Hyperglycemia  
  * Hyperuricemia (gout)  
  * Hyperlipidemia (mild)  

Other:
  * Photosensitivity  

</WRAP>

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<WRAP details>
===== Drug Interactions =====

Increased lithium levels  
Additive hypokalemia with:
  * Loop diuretics  
  * Corticosteroids  

RAAS inhibitors:
  * May mitigate potassium loss  

</WRAP>

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<WRAP monitoring>
===== Monitoring =====

  * Blood pressure  
  * Electrolytes (Na⁺, K⁺)  
  * Renal function  
  * Uric acid (if history of gout)  
  * Glucose (diabetics)  

</WRAP>

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<WRAP pearls>
===== Clinical Pearls =====

  * First-line therapy for uncomplicated hypertension.  
  * Lower doses (12.5–25 mg) preferred.  
  * Causes hypokalemia and metabolic alkalosis.  
  * Increases calcium reabsorption — useful in kidney stones.  
  * Less effective when eGFR < 30.  

</WRAP>

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===== Comparison Within Class =====

Compared to [[cardio:diuretics:chlorthalidone|Chlorthalidone]]:
  * Shorter half-life  
  * Less potent  
  * Less outcome data  

Compared to [[cardio:diuretics:indapamide|Indapamide]]:
  * More metabolic effects  
  * Shorter duration  

Compared to [[cardio:diuretics:furosemide|Furosemide]]:
  * Less potent diuretic  
  * Ineffective in severe renal failure  

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===== Related =====

  * [[cardio:diuretics:start|Diuretics]]
  * [[cardio:diuretics:chlorthalidone|Chlorthalidone]]
  * [[cardio:raas:acei|ACE Inhibitors]]
  * [[cardio:hypertension:start|Hypertension]]