Medication Overview

Furosemide is a potent diuretic used to treat fluid retention (edema) and high blood pressure (hypertension). It belongs to the class of medications known as loop diuretics, which work by blocking the absorption of sodium and chloride in the kidneys, promoting the excretion of salt and water.

Indications and Usage

Furosemide is indicated for the treatment of edema associated with congestive heart failure, cirrhosis of the liver, and renal disease, including the nephrotic syndrome. It is also used in the management of hypertension, either alone or in combination with other antihypertensive agents.

Dosage Forms and Strengths

Furosemide is available in several dosage forms, including oral tablets, oral solution, and injectable solution. Common tablet strengths include 20 mg, 40 mg, and 80 mg. The oral solution is typically available in a concentration of 10 mg/mL, and the injectable form is available as 10 mg/mL in various vial sizes.

Mechanism of Action

Furosemide inhibits the sodium-potassium-chloride cotransporter in the thick ascending limb of the loop of Henle in the kidneys. This inhibition leads to increased excretion of sodium, chloride, and water, resulting in diuresis and decreased blood volume. Consequently, it reduces edema and lowers blood pressure.

Pharmacokinetics

Furosemide is rapidly absorbed after oral administration, with peak plasma concentrations occurring within one to two hours. The bioavailability of oral furosemide varies significantly, ranging from 10% to 90%. The drug is extensively bound to plasma proteins (over 95%) and is primarily eliminated by renal excretion. The half-life of furosemide is approximately 30 to 60 minutes in patients with normal renal function but can be prolonged in those with impaired renal function.

Dosing and Administration

The dosing of furosemide should be individualized based on the patient’s response and clinical condition. For edema, the initial dose is typically 20 to 80 mg orally once daily, with adjustments made based on the patient’s needs. In cases of hypertension, the usual starting dose is 40 mg twice daily. Intravenous administration of furosemide is used in emergency situations, with doses ranging from 20 mg to 40 mg initially, given over 1-2 minutes.

Drug Interactions

Furosemide can interact with numerous medications. Concurrent use with aminoglycosides or other ototoxic drugs can increase the risk of ototoxicity. Combining furosemide with nonsteroidal anti-inflammatory drugs (NSAIDs) may reduce its diuretic effect. Co-administration with antihypertensive agents can lead to additive blood pressure-lowering effects. It may also interact with digoxin, increasing the risk of cardiac arrhythmias due to hypokalemia.

Contraindications

Furosemide is contraindicated in patients with anuria (lack of urine production), hypersensitivity to furosemide or sulfonamides, and in those experiencing hepatic coma or pre-coma states. Caution should be exercised when administering furosemide to patients with severe renal impairment or hepatic disease.

Side Effects

Common side effects of furosemide include electrolyte disturbances (e.g., hypokalemia, hyponatremia), dehydration, hypovolemia, dizziness, headache, and an increase in blood urea nitrogen (BUN). Less common but serious side effects include ototoxicity, particularly with high doses or rapid intravenous administration, and blood dyscrasias such as thrombocytopenia and leukopenia.

Special Populations

In elderly patients, furosemide should be used with caution due to a higher likelihood of renal impairment and electrolyte disturbances. In pregnant patients, furosemide should be administered only if the potential benefit justifies the potential risk to the fetus. For breastfeeding mothers, caution is advised since furosemide may inhibit lactation.

Monitoring Requirements

Regular monitoring of electrolytes, renal function, and fluid status is essential for patients on furosemide. Serum potassium levels should be frequently checked, especially in patients at risk for hypokalemia. Blood pressure should be regularly monitored to ensure the effectiveness of the therapy and to avoid hypotension.

Storage and Handling

Furosemide tablets should be stored at room temperature, away from light and moisture. The oral solution should also be protected from light and stored at controlled room temperature. Injectable furosemide should be stored at room temperature and protected from light. Any unused portion of the injectable solution should be discarded if it appears discolored or contains particulate matter.

Patient Counseling Information

Patients should be advised to take furosemide exactly as prescribed and not to change the dose or frequency without consulting their healthcare provider. They should be informed about the potential for increased urination and the importance of maintaining adequate hydration. Patients should also be educated on recognizing the signs of electrolyte imbalance, such as muscle cramps, weakness, and arrhythmias, and instructed to report any such symptoms immediately. Additionally, they should be aware of the potential for dizziness, particularly when rising from a sitting or lying position. Lastly, patients should be informed to avoid over-the-counter medications that may interact with furosemide, such as NSAIDs, unless approved by their healthcare provider.