What is the difference between Lasix (furosemide) and Diuril (chlorothiazide)?

Differences Between Lasix (Furosemide) and Diuril (Chlorothiazide)

Lasix (furosemide) and Diuril (chlorothiazide) differ primarily in their mechanism of action, potency, and site of action in the kidney, with furosemide being a loop diuretic that acts at the loop of Henle while chlorothiazide is a thiazide diuretic acting in the distal tubule. 1

Mechanism of Action and Site of Action

• Furosemide (Lasix) is a loop diuretic that acts at the loop of Henle, inhibiting the Na-K-2Cl cotransporter in the thick ascending limb 1
• Chlorothiazide (Diuril) is a thiazide diuretic that acts in the distal portion of the renal tubule 1
• Loop diuretics like furosemide increase sodium excretion up to 20-25% of the filtered sodium load 1
• Thiazide diuretics like chlorothiazide increase fractional sodium excretion to only 5-10% of the filtered load 1

Potency and Efficacy

• Loop diuretics (furosemide) generally produce a more potent diuretic effect than thiazides in patients with normal renal function 1
• Furosemide has a rapid onset of action, providing relief of pulmonary and peripheral edema within hours or days 1
• Common formulations of thiazides (like chlorothiazide) may actually produce greater 24-hour diuresis and natriuresis than common formulations of loop diuretics in healthy subjects 2
• Loop diuretics maintain their efficacy unless renal function is severely impaired 1
• Thiazides lose effectiveness in patients with impaired renal function (creatinine clearance less than 40 ml/min) 1

Effects on Water and Electrolytes

• Furosemide enhances free water clearance 1
• Thiazides like chlorothiazide tend to decrease free water clearance 1
• Loop diuretics can cause hypokalemia but have less sustained effect on potassium levels 1
• Thiazide diuretics more commonly cause significant hypokalemia and may also cause hypomagnesemia 1, 2

Clinical Applications

• Loop diuretics (furosemide) are preferred in patients with:

  • Heart failure with significant fluid retention 1
  • Advanced renal failure (creatinine clearance < 40 ml/min) 1
  • Acute pulmonary edema requiring rapid diuresis 1

• Thiazide diuretics (chlorothiazide) are preferred in:

  • Hypertensive patients with mild fluid retention 1
  • Patients with normal renal function 1
  • Hypertension management due to more persistent antihypertensive effects 1

Pharmacokinetics

• Furosemide has a shorter half-life and duration of action, often requiring multiple daily doses 1
• Furosemide has variable bioavailability (12-112%), which can complicate dosing 2
• Thiazides generally have longer half-lives and more consistent effects throughout the day 2
• Loop diuretics often show a rebound effect 6-24 hours after dosing, which can reduce their 24-hour efficacy 2, 3

Common Pitfalls and Considerations

• Loop diuretics like furosemide can cause more severe renal decline in heart failure patients, with higher doses causing more rapid decline in eGFR 1
• Thiazides are ineffective as monotherapy in advanced renal failure, while loop diuretics maintain efficacy 1
• In some patients with resistant hypertension or severe renal failure, combination therapy with both a loop and thiazide diuretic may be more effective than either agent alone 4, 5
• Monitoring of electrolytes is essential with both medications, but particularly with thiazides due to risk of hypokalemia 1