Nephrotoxicity

Nephrotoxins damage the kidneys through several distinct pathways. The proximal tubule is a primary target because it actively reabsorbs and secretes many substances, concentrating them to toxic levels. Aminoglycoside antibiotics are taken up by proximal tubular cells via megalin-mediated endocytosis, causing phospholipidosis and mitochondrial dysfunction¹. Contrast media induce renal vasoconstriction and direct tubular toxicity, leading to contrast-induced nephropathy². Cisplatin forms reactive metabolites that cause DNA damage and oxidative stress in tubular cells³. Glomerular injury, interstitial nephritis, and crystal nephropathy (e.g., from methotrexate or acyclovir) are other mechanisms.

Nonsteroidal anti-inflammatory drugs (NSAIDs) reduce renal blood flow by inhibiting prostaglandin synthesis, particularly in volume-depleted patients. ACE inhibitors and ARBs can cause hemodynamic acute kidney injury in bilateral renal artery stenosis. Calcineurin inhibitors (cyclosporine, tacrolimus) cause afferent arteriolar vasoconstriction and chronic tubulointerstitial fibrosis. Amphotericin B, used for fungal infections, is directly toxic to tubular membranes. Tenofovir disoproxil fumarate, an antiretroviral, can cause proximal tubular dysfunction (Fanconi syndrome). Herbal remedies containing aristolochic acid are a notable cause of chronic interstitial nephritis and urothelial cancer⁴.

Risk factors for nephrotoxicity include pre-existing chronic kidney disease, diabetes, hypertension, advanced age, hypovolemia, and concurrent use of multiple nephrotoxins. Prevention strategies include dose adjustment based on renal function, adequate hydration, and avoidance of nephrotoxic combinations. For aminoglycosides, once-daily dosing reduces toxicity while maintaining efficacy. N-acetylcysteine has been studied for contrast-induced nephropathy, though evidence is mixed⁵. Biomarkers such as neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) are being evaluated for early detection of tubular injury.

Beyond common drugs, several less-known agents cause nephrotoxicity. Lithium, used for bipolar disorder, can cause chronic interstitial nephritis and nephrogenic diabetes insipidus after long-term use. Proton pump inhibitors (PPIs) are associated with acute interstitial nephritis, often presenting silently. Methotrexate can precipitate in tubules, especially in acidic urine. The environmental toxin ochratoxin A, a mycotoxin found in contaminated grains, is a suspected nephrotoxin linked to Balkan endemic nephropathy⁶. Additionally, some traditional Chinese medicines containing aristolochic acid have caused widespread kidney failure in Belgium in the 1990s. Genetic polymorphisms in transporters like OAT1 and OAT3 influence individual susceptibility to drug-induced nephrotoxicity⁷.

Acute kidney injury (AKI)

A sudden episode of kidney failure or damage that happens within a few hours or days.

Proximal tubule

The segment of the nephron that reabsorbs most filtered water and solutes; a common site of toxic injury.

Fanconi syndrome

A disorder of proximal tubular function leading to excessive excretion of glucose, amino acids, and phosphate.

Nephrogenic diabetes insipidus

A condition where the kidneys fail to respond to antidiuretic hormone, causing excessive urination and thirst.