What is the recommended IV dose of Lasix (furosemide) for an 86-year-old lady with congestive heart failure (CHF) and significant weight gain due to fluid overload, with impaired renal function (GFR of 28)?

IV Furosemide Dosing for Elderly CHF Patient with Renal Impairment

For an 86-year-old lady with CHF showing 1kg/day weight gain and GFR of 28, the initial IV furosemide dose should be 40-80mg, with careful monitoring of renal function and electrolytes. 1

Initial Dosing Considerations

When determining the appropriate IV furosemide dose for this patient, several factors must be considered:

• Advanced age (86 years)
• Significant fluid retention (1kg/day weight gain)
• Impaired renal function (GFR 28 ml/min)
• Active CHF requiring diuresis

Recommended Dosing Algorithm:

1. Initial IV dose: 40-80mg furosemide 1

   • If patient was previously on oral furosemide, use 1:1 or 1:2 ratio for IV conversion
   • For diuretic-naive patients, start at the lower end (40mg)

2. Monitoring after initial dose:

   • Urine output (target 0.5-1.0 kg weight loss daily)
   • Electrolytes (especially potassium, sodium, magnesium)
   • Renal function (creatinine, BUN)
   • Blood pressure

3. Dose adjustment:

   • If inadequate response within 6 hours, double the dose
   • Maximum daily IV furosemide dose can reach 160-240mg in divided doses with careful monitoring 2

Special Considerations for Renal Impairment

With a GFR of 28, this patient has significant renal impairment which affects both drug clearance and response:

• Loop diuretics require delivery to the renal tubules to be effective
• Reduced GFR may require higher doses to achieve therapeutic concentrations at the site of action
• However, higher doses increase risk of ototoxicity and electrolyte disturbances

Management of Diuretic Resistance

If the patient shows signs of diuretic resistance (inadequate response to escalating doses):

1. Consider continuous infusion: 5-10mg/hour after initial bolus 3

   • Continuous infusions may be more effective than bolus dosing in patients with renal impairment

2. Add sequential nephron blockade:

   • Consider adding IV chlorothiazide 500mg or oral metolazone 2.5-5mg 1, 4
   • This combination significantly enhances natriuresis even in patients with reduced renal function

Monitoring and Safety

• Daily monitoring: Weight, fluid balance, electrolytes, renal function 5
• Electrolyte management: Aggressive correction of hypokalemia and hypomagnesemia to prevent arrhythmias 1
• Renal function: Accept mild increases in creatinine as long as the patient remains asymptomatic and diuresis is achieved 1
• Avoid NSAIDs: These can blunt diuretic response and worsen renal function 1

Treatment Goals

• Eliminate clinical evidence of fluid retention
• Achieve target weight (pre-fluid retention baseline)
• Maintain stable electrolytes and renal function
• Prevent recurrence of volume overload

Pitfalls to Avoid

• Underdosing: Excessive concern about renal function can lead to inadequate diuresis and persistent edema 1
• Overly rapid diuresis: May cause hypotension and worsen renal function
• Neglecting electrolyte replacement: Particularly potassium and magnesium
• Failure to adjust maintenance therapy: Once euvolemia is achieved, establish an effective oral regimen

Remember that diuretics are the cornerstone of managing fluid overload in heart failure, and appropriate dosing is essential for successful treatment of this elderly patient with renal impairment and active CHF.