Increasing evidence supports the hypothesis that podocyte injury can result from a single causative agent or a combination of multiple factors acting with complex mechanisms, making multifactoriality relevant in the pathophysiology of these disorders. Medications cause approximately 20% of community- and hospital-acquired episodes of acute kidney injury (AKI), and among older adults, the incidence of drug-induced nephrotoxicity is as high as 66% 
. Medications have the capacity to damage cells within all compartments of the kidney. Tubulointerstitial injury is most commonly mentioned, whereas less attention has been paid to glomerular injury. However, recent advances in the study of glomerular physiology and metabolism have increased this understanding of the pathogenesis of drug-induced glomerular disease. In the glomerulus, both the cells and the subepithelial space can be affected. The podocytes, the endothelial cells and the mesangial cells can be affected. There are four major mechanisms of glomerular toxicity: cytotoxic or charge-related injury to the filtration barrier, toxicity related to accumulation of a xenobiotic within the glomerular compartment based on pharmacologic or off-target activity, glomerulosclerosis and immune-mediated injury 
. Drug-induced podocytopathies typically include minimal-change disease (MCD) and focal segmental glomerulosclerosis (FSGS), which are clinically manifested with proteinuria and nephrotic syndrome with or without AKI. Known representatives from the literature are pamidronate, IFN, TKIs, lithium, NSAIDs, quinolones, rifampicin, ipilimumab, nivolumab and pembrolizumab for MCD and tyrosine kinase inhibitors (TKIs), sirolimus, pamidronate, anabolic steroids, lithium, IFN and nivolumab for FSGS 
. Endothelial cell injury appears as thrombotic microangiopathy, clinically characterized by microangiopathic hemolytic anemia. Therapeutic agents affecting endothelial cells include gemcitabine, mitomycin C, calcineurin inhibitors, sirolimus, everolimus, IFN, vincristine, opioids, proteasome inhibitors, valproic acid, IVIg, quinine, IFN, thienopyridines, oxaliplatin, quetiapine, gemcitabine, penicillin and sulfisoxazole 
. Mesangial cell injury emerges as glomerulosclerosis and IgA nephropathy, with common examples being vancomycin, carbamazepine, ceftriaxone, metronidazole, cyclosporine, acetaminophen, amiodarone, furosemide, nivolumab, ipilimumab and pembrolizumab 
. Subepithelial-space injury, caused by medications such as gold, penicillamine, captopril, NSAIDs, gefitinib, nivolumab, adalimumab, celecoxib and lithium, is manifested as membranous nephropathy (MN) 
2. Case 1 Description: MCD Associated with Tamoxifen
A 49-year-old female presented in 2017 with 1-week history of peripheral edema, increase in body weight up to 10 kg and intermittent unilateral lumbar pain. Her past medical history was significant for hepatitis B infection; rheumatoid arthritis diagnosed 12 years prior to presentation, treated with methotrexate and steroids for four years and adalimumab for two more years; and in situ breast carcinoma 6 years prior to presentation, for which she had surgical excision and radiotherapy and was on tamoxifen afterwards. She was not on any NSAIDs. Physical examination revealed bilateral pitting leg edema up to the thighs and reduced air entry bibasally. Her blood pressure was 117/70 with 64 pulses, without any orthostatic signs. Laboratorial findings were remarkable for nephrotic-range proteinuria (9.7 g/24 h) without microscopic hematuria, eosinophiluria or aseptic pyuria; low serum albumin (1.6 g/dL); and hyperlipidemia (total cholesterol 459 mg/dL, triglycerides 282 mg/dL, low high-density lipoprotein 322 mg/dL). Hemoglobin, white blood cells including eosinophils, C-reactive protein (CRP) and renal and hepatic function were normal. Serum protein electrophoresis was normal, and no monoclonal component was detected on immunofixation. Serum-free light chains, complement compounds (C3 and C4), and serological tests all were normal. Blood and urine cultures were negative. Hepatitis B surface antigen and anti-HBc were positive, and anti-hepatitis C virus and anti-HIV antibodies were negative. Thyroid hormones and CA15-3 were within normal limits. Echocardiogram and renal ultrasound were negative.
A kidney biopsy was performed, and fourteen glomeruli were obtained. One had glomerulosclerotic appearance, with the rest having normal size without hypercellularity, slightly thickened capillary walls and normal mesangium (Figure 1). Glomerular basement membrane (GBM) was normal. Tubular atrophy and interstitial fibrosis were presented in 20% of renal parenchyma. Slight arteriosclerosis was documented. Congo red staining was negative. Immunofluorescence was negative. Electron microscopy revealed loss of podocyte foot processes with microvilli (Figure 2).
Figure 1. Light microscopy: glomeruli were unremarkable.
Figure 2. Electron microscopy: podocyte activation and foot processes effacement (blue arrows) with microvilli transformation, without substantial immune-complex deposits in glomerular basement membranes or mesangium.
To exclude secondary causes associated with MCD, a total-body computed tomography was performed with no findings.Thyroid ultrasound showed only increased generalized vasculature, and breast magnetic tomography, gastroscopy and colonoscopy were normal. The patient was also evaluated by an endocrinologist and was started on thyroxine 50 mcg, while oncology consultation was negative for breast cancer exacerbation or any new cancer development. Exclusion of all other causes led to tamoxifen discontinuation with gradual but significant improvement of proteinuria, ending in complete resolution of nephrotic syndrome within 3 weeks of cessation.
3. Case 2 Description: MCD Associated with D-Penicillamine
A 46-year-old female presented with nephrotic syndrome associated with new-onset significant peripheral edema and 1-day history of left-sided pleuritic chest pain. Her past medical history was significant for latent tuberculosis (positive Mantoux test), hypothyroidism for almost 10 years and a 6-month history of scleroderma associated with Raynaud’s phenomenon, fingertip ulcers, generalized weakness and skin telangiectasis. Medications at presentation included isoniazid, thyroxine, methylprednisolone at 8 mg per day, recently started (5 months prior to presentation) D-penicillamine (200 mg twice per day) and bosentan (dual endothelin receptor antagonist) for the last 3 days prior to presentation. She was not on any NSAIDs.
On physical examination, she exhibitedbilateral pitting leg edema, reduced air entry on the left base and scleroderma-like changes, with ulcers on both hands. Laboratory findings showed nephrotic-range proteinuria (24 g/24 h) with microscopic hematuria (RBCs 4-5 per hpf), low serum albumin (2 g/dL) and hyperlipidemia (total cholesterol 338 mg/dL, triglycerides 156 mg/dL, low high-density lipoprotein 187 mg/dL). Urinalysis was negative for white cells and white-cell casts. Hematological profile, CRP and renal, hepatic and thyroid function were normal. Human immunodeficiency virus (HIV) and hepatitis screen were negative. A kidney biopsy was scheduled and D-penicillamine was withheld, as it was associated with new-onset nephrotic syndrome. Furthermore, methylprednisolone dose was increased to 32 mg/day. Discontinuation of D-penicillamine in combination with glucocorticoids therapy resulted in significant decrease in proteinuria, which ended up in normal range within the next 15 days. Despite decrease in proteinuria, the kidney biopsy was carried out, showing 55 glomeruli with normal size and mesangium without hypercellularity (Figure 3). GBM was normal. Tubular atrophy and interstitial fibrosis were present in 15% of renal parenchyma. Slight arteriosclerosis of the large vessels was documented. Immunofluorescence was negative. A diagnosis of a recently depressed MCD was made, as confirmed by electron microscopy (Figure 4).
Figure 3. Light microscopy: glomeruli showed no essential changes.
Figure 4. Electron microscopy: diffuse foot processes effacement (blue arrows) with microvilli transformation; no immune-complex deposits were found. Magnification: 2200×.
4. Case 3 Description: D-Penicillamine-Associated MCD
A 75-year-old female was referred to the clinic by her treating rheumatologist in 2012, with 15-day history of lower limb and bilateral eyelid edema. Her past medical history included osteopenia, osteoarthritis and 1-year history of scleroderma and Raynaud’s phenomenon, for which she was given D-penicillamine and bosentan. Other medications included risedronate, atorvastatin, enalapril, rabeprazole and low molecular heparin. She was not on any NSAIDs. On physical examination, she had bilateral pitting leg edema and eyelid edema. Laboratory findings showed nephrotic-range proteinuria (6.4 g/24 h) without microscopic hematuria, low serum albumin (2 g/dL) and hyperlipidemia (total cholesterol 400 mg/dL, triglycerides 265 mg/dL, low high-density lipoprotein 280 mg/dL). Urine sediment was negative for eosinophils and white-cell casts. Hematological profile including eosinophils, CRP and renal, hepatic and thyroid function, were normal. Immunologic profile was normal except for antinuclear antibodies (ANA >1:640). Screening for HIV and hepatitis was negative. Cessation of D-penicillamine was followed by gradual but significant improvement of nephrotic syndrome until complete resolution, i.e., proteinuria reduced to normal range within the next 10 days, which remains normal up to the present. The kidney biopsy revealed 26 glomeruli of normal size without hypercellularity, with only 2 of them having chronic lesions (sclerosis).The mesangium and GBMwere normal. Tubular atrophy and interstitial fibrosis were present in 15% of renal parenchyma. Arterioles were documented with mild partial segmental hyalinosis and thickening of inner wall. There were not any onion-skin-like changes scleroderma related in vasculature. Immunofluorescence was negative. The diagnosis was MCD, as widespread foot processes effacement was found by electron microscopy.
5. Case 4 Description: Pembrolizumab-Axitinib-Induced MCD
A 74-year-old man presented in 2020 with nephrotic syndrome and acute kidney injury (serum creatinine 5.8 mg/dL from 1.8 mg/dL baseline creatinine), which was found during workup for generalized weakness. His past medical history included renal cell carcinoma (RCC) with left nephrectomy (7 months before admission) on combined therapy with axitinib (tyrosine kinase inhibitor–anti-VEGF) and an ICPI pembrolizumab administered intravenously every 3 weeks. He also had asymptomatic rheumatoid arthritis (not on treatment) and hypertension on amlodipine.
Physical examination was significant for revealed bilateral pitting leg edema. Laboratory findings were remarkable for nephrotic-range proteinuria (18 g/24 h) without microscopic hematuria or eosinophiluria, low serum albumin (1.9 g/dL), hyperlipidemia (total cholesterol 467 mg/dL, triglycerides 342 mg/dL) and raised creatinine (5.8 mg/dL). Serum protein electrophoresis showed elevated a2 proteins, but all the rest of the immunological tests were normal. Hemoglobin, white blood cells including eosinophils, CRP and hepatic function were normal. Hepatitis screen showed previous HBV infection. Echocardiogram was normal. The kidney biopsy specimen included only four glomeruli, which had normal size, without any glomerulosclerotic appearance or hypercellularity. Mesangium appeared with mild hypercellularity. Tubular interstitial necrosis in connection with acute interstitial nephritis was present, as diagnosed from tubular dilatation, flattened tubular epithelial cells and edema, and lymphocyte infiltration and tubulitis. GMB was normal. Slight arteriosclerosis was documented. Congo red staining was negative. Immunofluorescence showed IgM+2, IgA trace, C3+1 and L light chain +1. The histological findings were suggestive of tubular interstitial necrosis, acute interstitial nephritis and MCD (Figure 5). The sample was inadequate for electron microscopy.
Figure 5. Light microscopy: acute tubular injury, in association with tubulointerstitial nephritis, as manifested by the aggregations of lymphocytes and monocytes into the interstitium (blue arrows), while glomeruli showed no abnormalities. Magnification: H&E 200×.
Chemotherapy and immunotherapy were discontinued, and oral glucocorticoids (prednisolone 1 mg/kg) were started, with significant improvement of kidney function and proteinuria and complete remission after 3 months. However, three months after his hospital discharge, while on complete remission, he was restarted on another type of VEGF inhibitor (pazopanib) by the treating oncologist, leading to relapse of nephrotic syndrome nearly 1 month post treatment initiation. A new course of glucocorticoids was given, and pazopanib was discontinued. Two months later, immunosuppression was switched to cyclosporine and glucocorticoids were discontinued, due to adverse reactions. A partial remission was achieved 3 months post pazopanib discontinuation.