Furosemide
Furosemide is a potent, rapidly acting **loop diuretic** widely used in veterinary medicine to manage fluid overload conditions. It is the cornerstone of therapy for **congestive heart failure (CHF)** and **pulmonary edema** across multiple species. By promoting profound diuresis, it rapidly reduces cardiac preload and relieves venous congestion. Beyond its primary cardiac applications, furosemide is utilized for: * **Oliguric renal failure:** To convert oliguria to polyuria and promote urine flow. * **Hypercalcemia:** To promote renal calcium excretion (requires prior volume expansion). * **Exercise-Induced Pulmonary Hemorrhage (EIPH):** Used prophylactically in racehorses to reduce epistaxis. * **Udder edema:** FDA-approved for post-parturient use in cattle. Because of its potency, furosemide can lead to significant fluid and electrolyte shifts, necessitating careful monitoring of hydration status and serum electrolytes (especially potassium).
Mecanismo: Furosemide acts primarily on the **thick ascending limb of the loop of Henle** in the nephron. * **Inhibition of NKCC2:** It reversibly binds to and inhibits the **Na⁺/K⁺/2Cl⁻ cotransporter** on the luminal membrane → prevents the reabsorption of sodium, potassium, and chloride. * **Loss of Medullary Hypertonicity:** This disruption abolishes the hypertonic medullary interstitium → impairs the kidney's ability to concentrate urine → results in profound, dose-dependent diuresis. * **Electrolyte Excretion:** It significantly increases the renal excretion of water, Na⁺, K⁺, Cl⁻, Ca²⁺, Mg²⁺, H⁺, NH₄⁺, and bicarbonate. * **Hemodynamic Effects:** Furosemide induces mild **renal venodilation** and transiently increases glomerular filtration rate (GFR) via prostaglandin release. This venodilation provides rapid relief in acute cardiogenic pulmonary edema, often before the onset of significant diuresis.
Dosificación por especie
- As a general diuretic · 2.5-5 mg/kg (lower dose suggested for cats) · PO, IV or IM · once or twice daily at 6-8 hour intervals
- For severe acute pulmonary edema (parenteral dosing) · Initially 2- 4 mg/kg IV or IM. The dose may be repeated within 1-2 hours. · IV, IM · Repeat within 1-2h · Cats that can tolerate an IV injection may benefit from a faster onset of action. Reduce dosing sharply once respiratory rate starts to decrease.
- For heart failure (oral dosing) · Maintenance dose usually ranges from 6.25 mg once a day to 12.5 mg PO q8h (higher doses, up to 37.5 mg PO q12h have been used) · PO · SID to q8h · Doses must be titrated carefully. Instruct owner to count sleeping respiration rates.
- For chronic therapy (CHF) · initially, try 6.25 mg/cat/day. Some can be maintained on 6.25 mg every other day. · PO · SID or EOD · Goal is to give the 'lowest possible dose'.
- In combination with rest, vasodilators and rate-control · 1-4 mg/kg · IV, IM or PO · q1-12 hours
- For adjunctive treatment of moderate to severe hypercalcemia · 2-4 mg/kg · IV, SC or PO · two to three times daily · Volume expansion is necessary prior to use.
- For acute oliguric renal failure · Initially 2 mg/kg IV; if no substantial diuresis develops in one hour, double to 4 mg/kg. If successful, repeat at 8 hour intervals · IV · q8h
- For acute oliguric renal failure (fluid replete patients) · bolus at 1-6 mg/kg IV. If diuresis ensues, can repeat dose every 6-8 hours or a CRI at 0.1-1 mg/kg/hr · IV · q6-8h or CRI
Vías de administración
Contraindicaciones
- Anuria
- Hypersensitivity to furosemide
- Progressive renal disease if increasing azotemia and oliguria occur during therapy
- Seriously depleted electrolytes
- Severe dehydration
- Severe electrolyte depletion
- Hepatic coma
- Dehydration
- Pericardial effusion where cardiac tamponade is confirmed
Efectos adversos
- Fluid and electrolyte abnormalities (hyponatremia, hypokalemia, hypocalcemia, hypomagnesemia)
- Prerenal azotemia (secondary to dehydration)
- Ototoxicity (especially in cats with high-dose IV therapy)
- Gastrointestinal distress
- Hematologic effects (anemia, leukopenia)
- Weakness and restlessness
- Hypokalaemia
- Hypochloraemia
- Hypocalcaemia
- Hypomagnesaemia
- Hyponatraemia
- Dehydration
- Polyuria/polydipsia (PU/PD)
- Prerenal azotaemia
- Ototoxicity (especially in cats)
- Gastrointestinal disturbances
Interacciones farmacológicas
- ACE INHIBITORS (e.g., enalapril, benazepril) · Increased risks for hypotension, particularly in patients who are volume or sodium depleted secondary to diuretics
- AMINOGLYCOSIDES (gentamicin, amikacin, etc.) · Increased risk for ototoxicity
- AMPHOTERICIN B · Loop diuretics may increase the risk for nephrotoxicity development; hypokalemia
- CORTICOSTEROIDS · Increased risk for GI ulceration; hypokalemia · moderate
- DIGOXIN · Furosemide-induced hypokalemia may increase the potential for digoxin toxicity · major
- INSULIN · Furosemide may alter insulin requirements
- MUSCLE RELAXANTS, NON-DEPOLARIZING (e.g., atracurium, tubocurarine) · Furosemide may prolong neuromuscular blockade
- PROBENECID · Furosemide can reduce uricosuric effects
- SALICYLATES · Loop diuretics can reduce the excretion of salicylates
- SUCCINYLCHOLINE · Furosemide may potentiate effects
- THEOPHYLLINE · Pharmacologic effects of theophylline may be enhanced when used with furosemide · moderate
- Aminoglycosides · Potentiates nephrotoxicity and ototoxicity · major
Monitoreo
- Serum electrolytes (especially potassium, sodium, calcium, magnesium)
- BUN, creatinine
- Blood glucose
- Hydration status
- Blood pressure, if indicated
- Clinical signs of edema, patient weight, if indicated
- Evaluation of ototoxicity, particularly with prolonged therapy or in cats
- Resting respiratory rate (at home by owner)
- Serum electrolytes (Potassium, Sodium, Chloride, Calcium, Magnesium)
- Renal parameters (BUN, Creatinine)
- Blood pressure
- Clinical signs of ototoxicity (especially in cats)
- Serum electrolytes (especially Potassium, Sodium, Chloride)
- Renal function (BUN, Creatinine)
- Clinical signs of edema/heart failure resolution
Sobredosis
The LD50 in dogs after oral administration is >1000 mg/kg; after IV injection >300 mg/kg. Chronic overdosing at 10 mg/kg for six months in dogs led to development of calcification and scarring of the renal parenchyma. **Acute overdosage** may cause severe electrolyte and water balance problems, CNS effects (ranging from lethargy to coma and seizures), and cardiovascular collapse. **Treatment:** * Empty the gut after recent oral ingestion using standard protocols. * **Avoid concomitant cathartics** as they may exacerbate fluid and electrolyte imbalances. * Aggressively monitor and treat electrolyte and water balance abnormalities supportively. * Monitor respiratory, CNS, and cardiovascular status.
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