Onset of Action of Furosemide (Lasix)

Furosemide has an intravenous onset of action within minutes and an oral onset of action of approximately 1 hour. 1, 2

Route-Specific Onset of Action

Intravenous administration: Onset of diuresis occurs within 5 minutes 2
Oral administration: Onset of diuresis occurs within approximately 1 hour 1, 2
Peak effect: Occurs within the first 30 minutes after administration regardless of route 2

Furosemide is extensively bound to plasma proteins (91-99% at therapeutic concentrations) 2
The duration of diuretic effect is approximately 2 hours 2
Terminal half-life is approximately 2 hours in adults 2
Bioavailability from oral formulations is variable (60-64% compared to intravenous administration) 2
Absorption is more rapid from oral solution (50 minutes) than from tablets (87 minutes) 2

The diuretic response correlates better with urinary excretion rates of furosemide than with plasma concentrations 3
In patients with heart failure, the peak diuretic and natriuretic effect is typically observed within 60-120 minutes after administration 4
The lowest mean furosemide urinary excretion rate associated with significant diuresis in pediatric patients was found to be 0.58 ± 0.33 μg/kg/min 5

Geriatric patients: May have reduced binding to albumin and decreased renal clearance, potentially affecting onset and duration of action 2
Pediatric patients: Pharmacokinetic differences exist between adults and children, including reduced clearance and prolonged half-life 1
Patients with renal impairment: May require higher doses to achieve therapeutic effect due to reduced drug delivery to site of action 1

Electrolyte monitoring is essential during furosemide therapy due to potential for hypokalemia and metabolic alkalosis 1
The greatest diuretic effect is seen with the first few doses, causing significant electrolyte shifts within the first 3 days of administration 1
Repeated dosing may result in diminishing effects (up to 25% less than the first dose for the same concentration) 1

Furosemide should be administered in combination with nitrate therapy in patients with moderate-to-severe pulmonary edema resulting from acute heart failure 1
Aggressive diuretic monotherapy is unlikely to prevent the need for endotracheal intubation compared with aggressive nitrate monotherapy in acute heart failure 1
During the first 1-2 hours after intravenous administration, furosemide may transiently worsen hemodynamics, including increased systemic vascular resistance and left ventricular filling pressures 1
Diuretics should be administered judiciously due to potential association with worsening renal function 1