Furosemide Dosing for a 17-Year-Old with PSGN
Use pediatric dosing for this 17-year-old patient with PSGN, starting with furosemide 0.5-2 mg/kg per dose (up to 6 times daily), with a maximum of 10 mg/kg/day, rather than the standard adult dose of 40 mg. 1, 2, 3
Rationale for Pediatric Dosing
At age 17, this patient falls within the pediatric dosing range, as the guidelines for furosemide in children with edema and nephrotic conditions do not specify an upper age cutoff, and weight-based dosing is more appropriate for adolescents who may have variable body mass. 1, 2, 3
The clinical presentation of PSGN with significant edema (bipedal and periorbital) and decreased urine output requires aggressive diuresis, which is better achieved with weight-based dosing that can be titrated to response rather than a fixed adult dose. 1, 3
Specific Dosing Algorithm
Initial dose:
- Start with furosemide 0.5-1 mg/kg IV or oral per dose, administered up to 6 times daily based on the degree of edema and achieved diuresis. 1, 2, 3
- For a typical 17-year-old weighing 50-70 kg, this translates to 25-70 mg per dose initially. 2, 3
Dose escalation:
- Increase by 1 mg/kg increments if adequate diuresis is not achieved. 2
- The absolute maximum is 10 mg/kg/day for severe edema. 1, 2, 3
- Doses exceeding 6 mg/kg/day should not be continued for more than 1 week due to significant ototoxicity risk. 1, 2, 3
Administration considerations:
- Administer IV infusions over 5-30 minutes to minimize ototoxicity. 1, 2, 3
- Ensure the patient does not have marked hypovolemia before initiating therapy, as furosemide can worsen intravascular volume depletion. 1, 3
Why Not Standard Adult Dosing
The standard adult dose of 40 mg furosemide (often used in heart failure or cirrhosis) is not weight-adjusted and may be insufficient for a larger adolescent or excessive for a smaller one. 1
In PSGN with significant fluid overload, response to furosemide is related to urinary drug concentration and excretion rate, not plasma levels, making weight-based dosing more predictable. 4, 5
Research in children with acute renal failure shows a broad dose-response relationship (1.2 to 30.8 mg/kg), suggesting that fixed adult dosing may not achieve adequate diuresis in all patients. 6
Critical Monitoring Requirements
Before each dose, assess for:
- Intravascular volume status: Good peripheral perfusion and adequate blood pressure indicate it is safe to proceed. 1, 3
- Avoid furosemide if there is marked hypovolemia, hypotension, or anuria. 1, 7, 3
During therapy, monitor:
- Fluid status and urine output (target adequate diuresis without excessive volume depletion). 1, 2, 3
- Electrolytes (particularly potassium and sodium) to detect hypokalemia or hyponatremia. 1, 2, 3
- Blood pressure (watch for hypotension indicating volume depletion). 1, 2, 3
- Renal function (serum creatinine and estimated GFR) to detect worsening azotemia. 1, 2, 3
Common Pitfalls to Avoid
Do not exceed 6 mg/kg/day for more than 1 week to prevent permanent hearing loss from ototoxicity. 1, 2, 3
Do not administer furosemide if the patient has marked hypovolemia, as this can worsen renal perfusion and promote thrombosis, which is already a risk in nephrotic states. 1, 7, 3
Avoid rapid IV bolus administration; always infuse over 5-30 minutes to reduce ototoxicity risk. 1, 2, 3
Do not continue furosemide in the setting of anuria, as it will be ineffective and potentially harmful. 7, 3
Special Considerations for PSGN
PSGN typically presents with fluid overload and hypertension (which this patient has, given the amlodipine prescription), making diuretic therapy appropriate. 1, 3
The patient's refusal of indwelling Foley catheter (IFC) makes accurate urine output monitoring more challenging, but this should not preclude diuretic therapy; use clinical assessment of edema resolution and weight loss as surrogate markers. 1, 2
If potassium-sparing diuretics are needed (e.g., for persistent hypokalemia), amiloride is preferable to spironolactone in this setting. 1, 3