A 70-year-old man with osteoarthritis and hypertension is taking irbesartan and hydrochlorothiazide. He starts regular ibuprofen for knee pain and 2 weeks later presents with lethargy and rising creatinine from 95 to 185 µmol/L. Blood pressure is 105/60 mmHg and he appears volume depleted. What is the most likely mechanism of his kidney injury?