Amphotericin B is a potent antifungal medication used to treat severe, often life-threatening fungal infections. This drug is a tool in combating serious mycoses, particularly when infections are widespread or unresponsive to other treatments. Despite its effectiveness, Amphotericin B is well-known for a significant side effect: nephrotoxicity. This potential for kidney damage necessitates careful monitoring during its administration.
How Amphotericin B Affects Kidneys
Amphotericin B primarily impacts the kidneys through two distinct mechanisms: direct damage to kidney cells and constriction of blood vessels. The drug directly interacts with the cell membranes of kidney tubules by forming pores or channels. This interaction increases cell permeability, leading to leakage of cytoplasmic contents and direct cellular injury. This tubular damage can result in renal tubular acidosis, an impaired ability to concentrate urine, and the loss of electrolytes like potassium, sodium, and magnesium.
In addition to direct cellular damage, Amphotericin B causes the constriction of blood vessels, specifically the afferent arterioles. This vasoconstriction reduces blood flow to the kidneys, leading to a decrease in the glomerular filtration rate (GFR), which is a measure of how well the kidneys are filtering waste from the blood. This reduced blood supply, combined with the direct cellular injury, contributes to overall kidney dysfunction and can lead to acute kidney injury.
Identifying Kidney Injury
Detecting kidney injury from Amphotericin B involves recognizing potential symptoms and closely monitoring kidney function through various tests. Patients may experience changes in urine output, such as producing less urine. Other general symptoms that could suggest kidney problems include fatigue and swelling.
Blood tests are routinely performed to monitor kidney health during Amphotericin B treatment. Measuring serum creatinine levels is a primary method, as an increase in creatinine indicates a decrease in kidney filtering capacity. Blood urea nitrogen (BUN) levels are also monitored, as elevated BUN can signify reduced kidney function. Additionally, electrolyte levels, particularly potassium and magnesium, are closely tracked because Amphotericin B can cause their loss. These regular laboratory assessments help healthcare providers identify kidney damage early, allowing for timely adjustments to treatment.
Mitigating Kidney Damage
Preventing or lessening kidney damage from Amphotericin B involves several established strategies, with adequate hydration being a primary measure. Administering intravenous hydration before and during Amphotericin B infusions helps maintain sufficient blood flow to the kidneys and can reduce the risk of nephrotoxicity.
Advancements in Amphotericin B formulations have also played a role in reducing kidney toxicity. Lipid-based formulations encapsulate the drug in a lipid carrier. This encapsulation reduces the drug’s direct exposure to kidney cells, lowering the incidence and severity of kidney damage compared to the conventional deoxycholate formulation. While these newer formulations are generally more expensive, they offer a safer alternative for patients at higher risk of kidney injury.
Beyond hydration and alternative formulations, other supportive measures help protect kidney health during treatment. Careful monitoring of other medications that might also affect the kidneys is important, as co-administration of multiple nephrotoxic drugs increases the risk of damage. Electrolyte supplementation, particularly for potassium and magnesium, is often necessary because Amphotericin B can cause their loss. Supplementation of these electrolytes can help prevent deficiencies and related complications.