Mechanism

Aminoglycosides (gentamicin, tobramycin, amikacin) are polar cations that bind to brush border proteins in proximal tubule → accumulate intracellularly → generate reactive oxygen species (ROS) → mitochondrial dysfunction → cell necrosis.

Pharmacokinetics and Toxicity Risk

Factors predicting aminoglycoside nephrotoxicity: - Dose and duration: Single daily dosing (<3% ATN risk) vs. q8h dosing (5–10% risk) - Duration >7 days: Cumulative toxicity - eGFR <60: Increased drug accumulation - Age >60: Risk ↑ (reduced renal reserve) - Volume depletion: ↓ Renal perfusion → ↑ drug concentration - Concurrent nephrotoxins: NSAIDs, radiocontrast, vancomycin (synergistic)

Clinical Presentation

Timeline: Days 3–7 of therapy

Presentation: - AKI: Cr ↑ 2–3× from baseline (non-oliguric in 50%) - Urine output: Usually maintained (non-oliguric ATN favorable prognosis) - Urinalysis: Muddy brown granular casts, epithelial cells (classic but non-specific) - Monitoring: Cr rise gradual; may continue for 1–3 days post-cessation (drug still in cells)

Management

1. Discontinue aminoglycoside immediately if possible
2. Hydration: Normal saline to optimize renal perfusion (if not volume-overloaded)
3. Avoid nephrotoxins: NSAIDs, contrast agents, other aminoglycosides
4. Nephrology referral if Cr rise >0.5 mg/dL/day or eGFR <15
5. Renal replacement therapy if oliguria, hyperkalemia, or fluid overload
6. Monitoring: Daily Cr, K⁺, phosphate; manage complications (hyperkalemia, metabolic acidosis)

Recovery

• Most recover Cr within 7–14 days post-cessation
• Permanent renal loss if late recognition; 5–10% may have ↓ eGFR baseline

Prevention

• Single daily dosing preferred (once daily gentamicin 5–7 mg/kg ideal; ↓ ATN risk vs. q8h)
• Therapeutic drug monitoring: Trough levels <1 µg/mL (gentamicin) for efficacy/safety
• Hydration: Pre-infusion hydration; maintain urine output
• Limit duration: <7 days if possible; reserve for severe infections
• Monitor Cr baseline, day 3, day 7 of therapy

Overview

AIN: Acute inflammation of renal tubules and interstitium with minimal/no glomerular involvement. Drug-induced AIN represents 10–15% of AKI in hospitalized patients.

Pathophysiology

Mechanism varies by drug: 1. Immune-mediated (most common): - Drug acts as hapten (binds tubular protein) - Generates T-cell and B-cell response - Infiltration of CD8+ T cells, macrophages into interstitium - Example: β-lactam antibiotics, NSAIDs, PPIs

2. Toxic metabolite:
   • Direct tubular toxicity from drug metabolite
   • Example: Acyclovir (crystalline AIN), TMP-SMX (crystal-induced)

Clinical Presentation

Classic Triad (50% have all three): 1. Fever (20–30%; non-specific) 2. Rash (5–20%; maculopapular; often urticarial) 3. Arthralgias/arthritis (less common than fever/rash)

Renal manifestations: - AKI: Often abrupt Cr rise (50–100% ↑ in days); non-oliguric in 70% - Urinalysis: Sterile pyuria (pyuria without bacteria), hematuria, WBC casts, eosinophils - Absence of eosinophiluria does NOT exclude AIN (only present in 50%)

Common Causative Drugs

Diagnosis

Clinical suspicion key: Recent medication change + fever, rash, AKI + sterile pyuria

Confirmation: - Kidney biopsy: Gold standard (rarely needed if clinical presentation classic) - Histology: Interstitial infiltration of lymphocytes, plasma cells, eosinophils; tubulitis (lymphocyte invasion of tubular epithelium); glomeruli typically spared - Immunofluorescence: Negative (distinguishes from anti-GBM, lupus, ANCA)

Biomarkers (research only): - Urine eosinophils: >5 eosinophils per high-power field suggests AIN but low sensitivity/specificity - Urinary β₂-microglobulin: Marker of tubular injury; not diagnostic

Management

1. Discontinue offending drug immediately (foundation of therapy)
2. Supportive care: Hydration if prerenal component; avoid nephrotoxins
3. Corticosteroids: Controversial; consider if:
   • Delayed recovery (Cr not trending down after 3–5 days off drug)
   • Severe renal dysfunction (eGFR <30)
   • Systemic symptoms (fever, rash)
   • Dosing: Prednisolone 1 mg/kg/day (max 60 mg) × 1–2 weeks, then taper over 2–4 weeks
   • Evidence: Limited; some observational studies suggest faster recovery if corticosteroids given early
   • Randomized data sparse: iPIKACY trial (ongoing) evaluating corticosteroids in AIN
4. Renal replacement therapy if oliguric, hyperkalemic, volume-overloaded

Recovery

• Most recover within 7–14 days of drug cessation
• Complete renal recovery: 80–90% achieve baseline Cr
• Residual renal dysfunction: 10–20% have ↓ baseline eGFR (suggests chronic TIN component)

Prevention

• Drug allergy documentation: If AIN suspected, document allergy to drug class
• Caution with re-exposure: Even after years, re-exposure may trigger AIN quickly
• Alternative agents: Use unrelated drug if future infection requires antibiotics

Acyclovir-Induced Crystalline Nephropathy

Mechanism: Acyclovir (especially IV, high-dose) crystallizes in tubular lumen → obstructive AKI + AIN.

Incidence: 1–5% IV acyclovir; rare with oral

Risk factors: - High-dose IV: >500 mg/m² q8h (HSV encephalitis, VZV) - Rapid infusion: <1 hour (↑ renal concentration) - Volume depletion: ↓ Urine flow → crystal precipitation - eGFR <60: ↓ clearance - Age >60: Reduced renal reserve

Clinical presentation: - AKI: Rapid onset (hours–days); oliguric possible - Urine: Needle-shaped crystals (acyclovir monohydrate) on microscopy

Management: 1. Discontinue acyclovir or reduce dose 2. Aggressive hydration: Normal saline IV to ↑ urine flow (↓ crystal concentration) 3. Maintain urine pH >6: Alkaline urine ↑ acyclovir solubility 4. Monitor Cr, K⁺: Daily during acute phase 5. Renal replacement therapy if severe AKI with complications 6. Recovery: 7–10 days post-cessation in most; permanent loss if delayed recognition

Methotrexate-Induced Crystalline Nephropathy

Mechanism: Methotrexate and metabolites (7-OH-methotrexate) precipitate in tubules → crystal-induced AKI.

Incidence: 2–5% high-dose MTX (cancer treatment); rare with low-dose (rheumatologic)

Risk factors: - High-dose MTX: >1 g/m² (cancer therapy) - Volume depletion - Acidic urine: pH <5.5 (↓ MTX solubility) - eGFR <60

Prevention (crucial for high-dose MTX): 1. Aggressive hydration: 3–4 L/day with alkaline saline pre- and post-MTX 2. Alkaline urine: Sodium bicarbonate to maintain urine pH >6.5 (↑ solubility) 3. Leucovorin (folinic acid) rescue: Reduces MTX toxicity 4. Monitoring: Baseline Cr; recheck at day 1–2 post-MTX

NSAIDs: Renal Hemodynamic Effects

Mechanism: NSAIDs inhibit prostaglandin synthesis (COX-1, COX-2) → loss of afferent arteriolar vasodilation → ↓ GFR

Particularly risky in: - Chronic kidney disease (eGFR <45) - Congestive heart failure (dehydration risk) - Hepatic cirrhosis (altered renal autoregulation) - Acute volume depletion (dehydration, diarrhea, diuretic use)

Clinical presentation: - Acute Cr rise: Often 1–3 days post-NSAID - Oliguria possible but often non-oliguric - FeNa typically <1% (prerenal pattern) but ↑ tubular dysfunction possible - Urinalysis: Usually bland (no casts, cells, or protein)

Management: 1. Discontinue NSAID immediately 2. Hydration: IV saline if dehydrated 3. Monitor Cr: Usually recovers in 3–7 days post-discontinuation 4. Renal replacement therapy if severe AKI with complications

Contrast-Associated Acute Kidney Injury (CA-AKI)

Modern understanding: Risk lower than previously believed; contrast osmolality, hydration status more important than contrast agent choice.

Mechanism: 1. Direct tubular toxicity: Contrast renal accumulation; ROS generation 2. Renal hemodynamic: Transient vasoconstriction → ↓ renal perfusion 3. Viscosity: High osmolality ↑ blood viscosity → ↓ renal perfusion

Incidence: - Baseline eGFR >60: <1% risk - Baseline eGFR 30–60: 5–10% risk - Baseline eGFR <30: 15–25% risk (especially if diabetes) - ESRD (not on dialysis): 25–50% risk

Risk factors for CA-AKI: - eGFR <30 (strongest predictor) - Diabetes mellitus (↑ risk 3–5×) - Dehydration (major preventable factor) - Proteinuria (marker of worse outcomes) - Acute illness (sepsis, heart failure) - Age >70 years - Heart failure (ejection fraction <40%) - High contrast volume (>5 mL/kg iodine load)

Epidemiology and Historical Context

Incidence: Rare in modern era (↓ chronic NSAID use) but still significant cause of ESRD globally (2–3% of dialysis patients in some regions).

Classic patient: Women age 50–70 with history of decades-long daily analgesic use (paracetamol, aspirin, ibuprofen combinations); more common historically before NSAID restrictions.

Mechanism

Proposed pathway: 1. NSAID/aspirin accumulation in renal papilla (high local concentration) 2. Conversion to reactive metabolites (e.g., N-acetylbenzoquinone imine from acetaminophen) 3. Direct papillary toxicity: Mitochondrial oxidative stress → papillary necrosis 4. Chronic inflammation → TIN, fibrosis, atrophy

Critical distinction: Acute NSAID-induced AKI is usually reversible; chronic analgesic nephropathy = cumulative, progressive, often irreversible.

Clinical Presentation

Features: - Slowly progressive renal insufficiency: ↑ Cr over years (often subtle initial decline) - Non-obstructive renal failure: Normal renal ultrasound; creatinine progressive despite normal urinalysis initially - Recurrent UTIs: Often lower UTI symptoms (dysuria, frequency) with negative cultures - Hematuria: Microscopic or gross (from papillary sloughing) - Anemia: ↓ Hgb proportional to renal dysfunction - Hypertension: Common, often mild - Urinary findings: Minimal proteinuria, mild pyuria/hematuria

Diagnosis

Imaging (CT with contrast—caution if eGFR <30): - Classic finding: “Bumpy contour” of renal outline (papillary degeneration) - “Ring sign”: Contrast-enhanced ring sign (calcification in areas of papillary necrosis) - Papillary blunting/flattening - Generalized cortical thinning (chronic atrophy) - Renal papilla sloughing (may be seen as filling defect in pelvis on IVP—seldom done now)

Biopsy (rarely needed): - Histology: Chronic TIN, tubular atrophy, interstitial fibrosis; papillary necrosis (if sampled) - No glomerular disease (distinguishes from glomerulonephritis)

Diagnostic algorithm: 1. History of chronic analgesic use (often understated by patients—ask directly) 2. Imaging findings (CT “bumpy kidney,” ring sign) 3. Urinalysis: minimal proteinuria (usually <1 g/day; heavy proteinuria suggests glomerular disease) 4. Exclusion of other causes: Normal immunology, no glomerular IgA/IgM deposits on biopsy

Management

1. Discontinue all NSAIDs and aspirin immediately
2. Treat hypertension: ACEi/ARB preferred (renal protection)
3. Monitor renal function: Slow Cr decline expected but may stabilize off NSAIDs
4. Manage UTIs: Culture-directed antibiotics; prophylaxis if recurrent (though culture-negative dysuria often unresponsive to antibiotics)
5. Screen for urothelial malignancy: Analgesic nephropathy ↑ risk of renal cell carcinoma and urothelial cancer (TCC)
   • Annual urine cytology if feasible
   • Annual renal ultrasound or CT
   • Low threshold for hematuria evaluation
6. Renal replacement therapy: As needed when ESRD reached

Prognosis

• CKD progression: Variable; some stabilize, others progress to ESRD
• Malignancy: 1–5% develop renal cell carcinoma or urothelial malignancy (cumulative risk over decades)
• Outcomes post-discontinuation: Renal function rarely improves dramatically; primary goal = halt progression

Epidemiology

Use: Lithium carbonate for bipolar disorder maintenance (decades of use in stable patients)

Prevalence: 20–40% of long-term lithium users have eGFR <60; ~7% progress to ESRD

Mechanisms of Lithium Nephrotoxicity

1. Nephrogenic Diabetes Insipidus (NDI)—Early/Reversible: - Mechanism: Lithium accumulation in collecting duct principal cells → inhibits vasopressin (V2) receptor signaling → ↓ aquaporin-2 water channel expression - Result: Polyuric state (6–12 L/day); polydipsia compensation - Timeline: Develops within weeks–months of initiation - Reversibility: 50% improve with lithium discontinuation; partial improvement common

2. Chronic Kidney Disease—Late/Progressive: - Mechanism: Chronic lithium exposure → interstitial fibrosis, tubular atrophy, glomerulosclerosis - Histology: TIN with cystic dilation of distal tubules; possible glomerular changes - Timeline: Develops over years of chronic therapy - Reversibility: Often irreversible (progressive even after discontinuation)

Clinical Presentation

Early phase (months): - Polyuria: 6–10 L/day (vs. normal 1–2 L/day) - Polydipsia: Compensatory increased fluid intake - Urine specific gravity: Low (<1.010; normally 1.010–1.030) - Renal function: Usually normal Cr initially

Late phase (years): - CKD progression: ↑ Cr over years despite normal urine output (drinking enough to maintain urine output) - Hypertension: Often develops - Hyperparathyroidism: Lithium ↑ PTH secretion; additive to CKD mineral bone disease - Hematuria: Possible (from cyst hemorrhage)

Diagnosis

Clinical context key: - History: Years of lithium use for bipolar disorder - NDI: Polyuria + low urine SG + normal Cr = early lithium effect - CKD: ↑ Cr + polyuria (or inability to concentrate urine) = chronic lithium nephropathy

Imaging: - Ultrasound: Microcysts in medulla/papilla (classic but not pathognomonic) - CT: Cystic changes in renal medulla

Biopsy (rarely needed): - Histology: TIN, tubular atrophy, cysts in medulla

Laboratory: - Serum lithium level: Therapeutic 0.6–1.2 mmol/L; levels >1.5 → ↑ toxicity risk - Urine osmolality: Low (osmotic diuresis pattern; unable to concentrate) - Serum sodium: May be high (dehydration from polyuria)

Management

1. Lithium dose optimization: - Maintain lowest effective therapeutic level (0.6–0.8 mmol/L vs. 1.0–1.2) - Once-daily dosing: More stable levels; ↓ peak toxicity than BID dosing - Therapeutic drug monitoring: Baseline, then every 3–6 months

2. Nephrology referral: - eGFR <60 or Cr rise: Consider alternative mood stabilizer (valproic acid, lamotrigine, atypical antipsychotics) - NDI without renal dysfunction: Continue lithium (renal function usually preserved) - Progressive CKD: Strongly consider discontinuation if alternatives available

3. Renal protective measures: - ACEi/ARB: If hypertensive or CKD (standard CKD management) - Hydration: Encourage adequate fluid intake (prevent dehydration-induced Cr rise) - NSAIDs: Absolutely avoid (synergistic nephrotoxicity) - Thiazide diuretics: Avoid (↑ lithium reabsorption → toxicity) - Monitor renal function: Baseline Cr, then annually if stable; more frequently if CKD present

4. Management of NDI: - Thiazide diuretics: Paradoxically ↓ polyuria (mechanism: mild volume depletion → ↑ proximal reabsorption) - NSAIDs: ↓ Polyuria (block prostaglandin; ↓ solute-free water clearance) but caution with renal dysfunction - Low sodium diet: ↓ Urine output (decrease solute load) - Amiloride: Specific K⁺-sparing diuretic blocking lithium entry into collecting duct cells; potent NDI treatment (5 mg BID; monitor K⁺)

5. Phosphate binders and PTH management: - Hyperparathyroidism: Lithium directly stimulates PTH secretion - Monitor: Baseline PTH, Ca²⁺; then annually - Treat: Aggressive CKD mineral bone disease management (phosphate binders, active vitamin D, calcimimetic if indicated)

Prognosis

• NDI: 50% reversible on discontinuation; degree of reversal variable
• Progressive CKD: Often continues despite lithium discontinuation (cumulative injury)
• ESRD: 5–10% of chronic lithium users progress to dialysis-dependent ESRD

Exposure Sources

• Occupational: Battery manufacturing, smelting, welding, lead-based paint (now restricted in US)
• Environmental: Contaminated water supplies (Flint, MI example); soil in older urban areas
• Recreational: Ammunition, lead-containing glassware (occasional exposures)

Mechanism

Lead bioaccumulation in kidneys: 1. Tubular reabsorption: Lead binds tubular protein → intracellular accumulation 2. Proximal tubule effects: ↓ Na⁺-glucose cotransport → Fanconi syndrome (rare) 3. Chronic effect: TIN, fibrosis, glomerulosclerosis (unclear mechanism)

Clinical Presentation

Acute lead poisoning (rare in chronic exposure): - Abdominal colic: Severe pain (classic “saturnine colic”) - Neuropathy: Wrist drop (motor nerve affected); sensory less common - Encephalopathy: Confusion, headache (severe poisoning)

Chronic lead nephropathy (more common in modern era): - Slowly progressive CKD: ↑ Cr over years from occupational/environmental exposure - Hypertension: Common; often ↑ BP before renal dysfunction evident - Gout: Lead impairs uric acid excretion → hyperuricemia → gout (classic finding in lead exposure) - Urinalysis: Usually normal (minimal proteinuria, no hematuria) - Absence of systemic signs (differs from acute poisoning)

Diagnosis

Blood lead level (BLL): - Normal: <10 µg/dL (CDC 2021 recommendation for safety threshold) - Occupational exposure: 10–50+ µg/dL (OSHA permissible 50 µg/dL but toxicity occurs <50) - Historical context: Many with CKD + lead exposure have BLL measured decades ago (not current) - Note: BLL reflects recent exposure; bone lead (x-ray fluorescence) reflects cumulative burden (not routinely available)

Diagnosis approach: 1. Occupational/environmental history: Direct question about lead exposure 2. Clinical clue: Hypertension + gout + slowly progressive CKD + normal urinalysis 3. BLL measurement: If history suggestive 4. Urine lead: Less useful; not standardized 5. Biopsy (rarely performed): Shows TIN; no specific lead-induced pattern

Management

1. Lead exposure elimination: Occupational exposure abatement; home water lead testing/remediation
2. Renal protective therapy: ACEi/ARB (standard CKD management); especially important if hypertensive
3. Gout management: Allopurinol or febuxostat for uric acid control
4. Renal function monitoring: Baseline Cr, then annually; more frequent if CKD present
5. Chelation therapy: Controversial in chronic low-level exposure
   • Not recommended for asymptomatic chronic exposure (limited evidence for benefit; toxicity risk of chelating agents)
   • Reserved for: Acute poisoning or severe symptomatic toxicity (neuropathy, encephalopathy)
   • Agent: Dimercaprol (BAL), EDTA, or DMSA (succimer)

Exposure

• Occupational: Nickel-cadmium batteries, plating, soldering, welding
• Environmental: Tobacco smoke, contaminated foods
• Consumer products: Some paints, pigments

Mechanism

Cadmium accumulation: - Absorption: GI (dietary) > pulmonary (occupational) - Renal handling: Glomerular filtration followed by tubular reabsorption - Intracellular binding: Metallothionein-cadmium complex - Chronic toxicity: Tubular damage, proteinuria (low molecular weight), TIN

Clinical Presentation

Acute exposure (rare): - GI symptoms: Nausea, vomiting, diarrhea - Respiratory: Dyspnea, wheezing (if inhaled)

Chronic exposure: - Early: Low molecular weight proteinuria (β₂-microglobulin, lysozyme) without ↑ Cr - Late: Progressive proteinuria, ↑ Cr, CKD - Associated findings: Bone disease (Cd also affects calcium metabolism; osteomalacia, osteoporosis); renal stones possible - “Itai-itai disease”: Historical endemic poisoning in Japan (Cd-contaminated rice); severe bone disease + renal dysfunction

Diagnosis

Urine cadmium: - 24-hr urine Cd or spot urine Cd/Cr ratio - Threshold for concern: >5 µg/L or >5 µg/g Cr - Interpretation: Reflects recent exposure (days–weeks)

Chelation challenge test (research only): - Not recommended for clinical diagnosis

Management

1. Exposure elimination: Occupational abatement
2. Renal protection: ACEi/ARB (standard CKD therapy)
3. Calcium/vitamin D supplementation: If bone disease present
4. Monitoring: Cr, Alb/protein, bone health annually
5. Chelation: Not recommended for chronic asymptomatic exposure

Epidemiology and Exposure

Source: Traditional Chinese medicines (TCM) containing Aristolochia species

History: - Discovered: 1990s (Belgium) — 100+ patients with rapidly progressive CKD; retrospective link to Aristolochia-containing weight-loss herbs - Mechanism revealed: Aristolochic acid (AA) — direct DNA carcinogen - Global prevalence: Taiwan, Balkans (historically); now rare in regions with product restrictions

Mechanism

Aristolochic acid (AA) toxicity: 1. Metabolic activation: Hepatic N-acetylation of AA → reactive intermediate 2. DNA binding: Covalent AA-DNA adducts → mutations 3. Tubular toxicity: Proximal tubule apoptosis → necrosis 4. Uroepithelial mutagenesis: ↑ Risk urothelial carcinoma (urothelial cancer, upper urinary tract) 5. Inflammation: TIN development

Clinical Presentation

Typically rapid, severe progression: - CKD development: Months to a few years of exposure (faster than most toxic nephropathies) - Proteinuria: Usually <1 g/day (tubular pattern) - Anemia: Often severe; disproportionate to renal dysfunction - Risk of ESRD: ~50% progress to ESRD within 3–5 years of diagnosis - Urothelial cancer: 10–20% develop TCC (ureter, bladder, rarely renal pelvis)

Diagnosis

Clinical clues: - History of TCM use (specifically weight-loss supplements or unexplained TCM exposure) - Rapidly progressive CKD out of proportion to UA findings - Severe anemia relative to GFR decline - Normal immunology, UA bland (excludes glomerulonephritis)

Imaging: - CT/ultrasound: Renal atrophy, normal size to slightly small kidneys - Upper tract imaging (IVP, CT urography): Screen for urothelial malignancy

Biopsy (if performed): - Histology: TIN, tubular atrophy, interstitial fibrosis - No glomerular disease

AA-DNA adduct testing: Research only; not clinically available in most centers

Management

1. Discontinue TCM containing Aristolochia immediately
2. Monitor renal function closely: Monthly Cr initially; progression may continue despite cessation (cumulative injury)
3. ACEi/ARB therapy: Renal protection (standard CKD management)
4. Urothelial surveillance: Critical
   • Baseline imaging: CT/ultrasound + CT urography or IVP (evaluate upper urinary tract)
   • Annual follow-up: Imaging + urine cytology for malignancy screening
   • Low threshold for hematuria investigation: Any hematuria → imaging
   • Note: Upper urothelial cancers (ureter, renal pelvis) more common than bladder; require aggressive surveillance
5. Renal replacement therapy: As needed

Prognosis

• Progressive: Most progress to ESRD within 3–5 years
• Malignancy: Annual risk ~1–2% TCC; cumulative 10–20% lifetime
• Monitoring: Long-term surveillance even on dialysis (malignancy risk persists)

Silica-Associated Nephropathy

Exposure: Mining, sandblasting, foundry work, stonemasonery

Mechanism: Chronic inhalation → silica accumulation → immune complex deposition (mimics glomerulonephritis); TIN also reported

Clinical: Slowly progressive CKD; proteinuria variable

Diagnosis: Occupational history + imaging/biopsy findings; serology often positive (ANA, ANCA) mimicking autoimmune disease

Management: Occupational cessation; standard CKD therapy

Asbestos-Associated Nephropathy

Exposure: Insulation, construction trades

Mechanism: Chronic inflammation; uncertain exact pathway

Clinical: Slowly progressive CKD; asbestos typically affects lungs (more clinically significant than kidney)

Management: Occupational cessation; lung health monitoring