Amiloride in Nephrotic Syndrome

Inclusion Criteria: 1. Acute nephrotic syndrome with proteinuria \> 3 g/day and formation of edema. 2. Age ≥ 18 years at the time of signing the informed consent. 3. Understand and voluntarily sign an informed consent document prior to any study related assessments/procedures. 4. Ability to adhere to the study visit schedule and other protocol requirements. 5. Use of adequate thrombosis prophylaxis due to the increased risk of thrombosis in nephrotic syndrome and the expected fluctuations in volume balance during study participation. 6. Subject (male or female) is willing to use highly effective methods of contraception according to the "Clinical trial fertility group" recommendations. 7. Female Patients of childbearing potential (WOCBP) must agree to pregnancy testing before inclusion in the study. 8. Female Patients must agree to abstain from breastfeeding during study participation and 28 days after study drug discontinuation. 9. All subjects must agree not to share medication. Exclusion Criteria: 1. Severe reduction of kidney function: Creatinine clearance or calculated GFR \< 30 mL/min/1.73m² or acute kidney injury KDIGO stage 2 or 3 or anuria. 2. Hypovolemia or dehydration. 3. Uncontrolled diabetes mellitus. 4. Hypotension, systolic blood pressure \< 90 mmHg. 5. Hyperkalemia, plasma potassium concentration \> 4.8 mmol/l. 6. Hypokalemia, plasma potassium concentration \< 3.3 mmol/l. 7. Hyponatremia, plasma sodium concentration \< 128 mmol/l. 8. Hypercalcemia, ionized calcium \> 2.0 mmol/l or total albumin corrected calcium \> 3.0 mmol/l. 9. Signs of cardiac decompensation (orthopnoe, dyspnoe NYHA IV). 10. Hepatic coma or precoma. 11. Symptoms of gout. 12. Current therapy with potassium-sparing diuretics (e.g. spironolactone) or potassium supplements. 13. Women during pregnancy and lactation. 14. History of hypersensitivity to the investigational medicinal product, comparator or co-medication or to any drug with similar chemical structure or to any excipient present in the pharmaceutical form of the investigational medicinal product, comparator or co-medication. 15. Any other clinical condition that would jeopardize the patient's safety while participating in this clinical trial. 16. Active participation in other clinical trials or observation period of competing trials.