Tubulointerstitial Disease and Nephrotoxicity — Advanced

This presentation is classical for drug-induced acute interstitial nephritis (AIN): recent new drug exposure, fever, rash, eosinophilia, pyuria and white-cell casts with rapid rise in creatinine. The first and immediate step is to stop the offending drug. In cases with severe or rapidly progressive renal impairment (large creatinine rise over days, oligo/anuria or failure to improve after withdrawal) early systemic corticosteroids are indicated and are associated with improved renal recovery. Immediate renal biopsy is not required in every case if clinical picture is typical and there are no contraindications to empiric steroids; biopsy is reserved for atypical presentations, diagnostic uncertainty, or where steroid therapy is being considered but diagnosis is unclear. Empiric antibiotics without evidence of infection are inappropriate. Haemodialysis is only indicated for standard indications (refractory hyperkalaemia, severe acidosis, volume overload, uremic complications) and is not first‑line purely to treat AIN.

Aminoglycosides are taken up by proximal tubular epithelial cells and accumulate in lysosomes and mitochondria, causing oxidative and mitochondrial injury that results in proximal tubular cell dysfunction and acute tubular necrosis (ATN). They are not primarily associated with immune complex glomerulonephritis, allergic interstitial nephritis, haemolysis-related pigment nephropathy, or systemic hypotension as the main mechanism. Clinical features include non-oliguric AKI, rising creatinine typically after several days of therapy, and granular casts on urine microscopy.

For patients at increased risk of contrast‑associated AKI (eg markedly reduced eGFR), the most evidence-supported preventive strategy is adequate intravascular volume expansion with isotonic crystalloid (normal saline) commenced before and continued after contrast exposure. Routine use of N‑acetylcysteine has conflicting evidence and is no longer uniformly recommended as a sole preventive strategy. Calcium channel blockers are not indicated to prevent contrast nephropathy. Saying no measures are required is inappropriate in a high-risk patient. Oral bicarbonate has been evaluated in trials with inconsistent benefit compared with saline and is not established as uniformly superior.

In myeloma cast nephropathy the priority is rapid reduction of circulating free light chains by effective anti‑myeloma therapy (commonly a bortezomib‑based regimen) as the key intervention to improve renal recovery. Renal replacement therapy may be required for standard indications but does not treat the underlying pathology by itself. The role of plasma exchange is unproven and not routinely recommended; it may remove some light chains but trials have not shown consistent benefit. Diuretics do not address the cause and may worsen renal perfusion if overused. Corticosteroids alone are insufficient without definitive myeloma-directed therapy.

dRTA is due to impaired distal acidification leading to reduced urinary NH4+ excretion; the urine anion gap (Na+ + K+ − Cl−) is typically positive (or less negative) indicating low urinary ammonium, which supports RTA. A negative urine anion gap would indicate appropriate urinary ammonium excretion (eg diarrhoea). Albuminuria in the nephrotic range is not a feature of primary RTA. Fractional sodium excretion and urinary beta2‑microglobulin are not diagnostic for dRTA; beta2‑microglobulin may rise in proximal tubular disease, and fractional sodium excretion is a marker used in AKI assessment, not for diagnosing dRTA.

Chronic analgesic nephropathy (typically from long-term combined analgesic use, especially phenacetin historically and some NSAIDs) is characterised by papillary necrosis and chronic tubulointerstitial nephritis with interstitial fibrosis and progressive renal impairment; tubular dysfunction and chronic kidney disease are common. It does not typically present with nephrotic‑range proteinuria or crescentic GN. Isolated haematuria without progressive GFR loss is not typical; acute tubular necrosis after a single paracetamol dose is not the usual mechanism of chronic analgesic nephropathy.

Immune checkpoint inhibitors can cause acute interstitial nephritis. The recommended immediate action is to withhold the offending immunotherapy and start systemic corticosteroids for significant renal injury (moderate to severe AKI). Urgent biopsy may be helpful in atypical cases or before prolonged immunosuppression if the diagnosis is uncertain, but it is not mandatory before initiating steroids when the clinical picture is typical. Continuing the drug risks further renal injury; dialysis is reserved for standard renal indications; cyclophosphamide is not first‑line therapy for this toxicity.

Lead nephropathy preferentially affects the proximal tubules and can cause a Fanconi-like proximal tubulopathy with impaired reabsorption: glycosuria despite normoglycaemia, phosphate wasting, aminoaciduria and bicarbonate loss. Heavy orthostatic proteinuria or selective albuminuria are glomerular patterns and not characteristic of proximal tubule toxin-induced dysfunction. Isolated glucosuria that resolves with glycaemic control indicates diabetic glucosuria rather than tubular dysfunction.

Secondary oxalate nephropathy (eg from massive vitamin C intake) can cause intratubular crystal deposition and AKI. Immediate steps include stopping the offending agent, supportive care and when standard indications for renal replacement therapy (refractory hyperkalaemia, acidosis, volume overload, uremia) exist, urgent dialysis is appropriate — it can also help remove small molecules and manage complications while renal recovery is assessed. Fomepizole is used for ethylene glycol poisoning to prevent oxalate formation and is not indicated for vitamin C–induced oxalate nephropathy. Intravenous calcium is not an appropriate treatment to manage intrarenal oxalate crystals. Corticosteroids have no proven role acutely for crystal-induced tubular obstruction. Potassium citrate may be used chronically to reduce stone risk but is not the immediate treatment for severe AKI.

When there is progressive AKI of uncertain aetiology despite stopping a suspected offending drug, or when there is diagnostic uncertainty that will change management (for example to decide on immunosuppression), a renal biopsy is indicated to establish the histological diagnosis (eg AIN vs ATN vs other). Continuing conservative management risks further irreversible injury if the process is treatable. Empirical high‑dose corticosteroids without histological confirmation may be reasonable in some clear-cut cases but is not appropriate when the diagnosis is uncertain and a biopsy will influence treatment. Empirical antibiotics are not indicated without evidence of infection. Transplant referral is inappropriate at this stage.