Swollen Ankles and a Painkiller
Mrs. B is 58 and has high blood pressure and type 2 diabetes. She visits a pharmacy because her ankles have become swollen over two weeks and her urine looks frothy. Her current prescription is amlodipine 5 mg daily and metformin 500 mg twice daily. For knee osteoarthritis she has been taking ibuprofen 400 mg three times a day for the past month, bought without a prescription. A recent clinic record shows blood pressure 156/94 mmHg, creatinine 150 µmol/L, eGFR 46 mL/min/1.73 m², and a urine albumin-to-creatinine ratio of 45 mg/mmol. She has gained 2 kg and reports passing less urine than usual, though she says she drinks only about 1 L of fluid daily. She asks whether the ibuprofen is causing the swelling and whether she should stop it and take a 'water tablet' instead.
1. Explain how the kidney normally adjusts water and salt loss, and use the data to explain why Mrs. B has swollen ankles and reduced urine output.
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The kidney filters plasma at the glomerulus and then reabsorbs most of the filtered water, sodium, and glucose in the tubules. Fine control of sodium reabsorption, especially in the distal tubule and collecting duct, determines how much water is retained or lost. Albumin should normally stay in the blood because it is too large to be filtered; its presence in urine signals glomerular damage.
Mrs. B's eGFR of 46 mL/min/1.73 m² is below normal, and the albumin-to-creatinine ratio of 45 mg/mmol confirms protein leakage. With reduced filtration and tubular injury, the kidney is less able to excrete sodium and water efficiently. The result is extracellular fluid accumulation, which appears as ankle swelling and a 2 kg weight gain. Her low fluid intake of about 1 L per day does not protect her: the kidney may still retain sodium and water because of reduced perfusion, diabetes-related damage, and the effect of ibuprofen.
The frothy urine is consistent with proteinuria, not with a simple water imbalance. The reduced urine volume is therefore a warning sign of reduced kidney function, not evidence that she simply needs more fluid or a diuretic.
2. Judge whether continuing ibuprofen is appropriate and explain the trade-off. What should the pharmacist advise?
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Continuing ibuprofen at 400 mg three times daily is not appropriate without prescriber review. Ibuprofen is a non-steroidal anti-inflammatory drug that inhibits prostaglandin synthesis. In the kidney, prostaglandins help keep the afferent arteriole dilated when renal blood flow is reduced. Blocking them can lower glomerular filtration further, cause sodium and water retention, raise blood pressure, and precipitate acute kidney injury. Mrs. B already has reduced eGFR, proteinuria, hypertension, and diabetes, so she is at higher risk.
The trade-off is that ibuprofen may be relieving her knee pain, but the cost is potential irreversible loss of kidney function. She should not simply stop a medicine and start a 'water tablet' on her own: a diuretic could worsen dehydration or electrolyte imbalance, especially if her fluid intake is low.
The pharmacist should advise her to stop ibuprofen only under medical direction, contact the prescriber the same day, and ask for a safer pain-management plan. Blood pressure, creatinine, and urine protein should be rechecked. The reasoning is that the swollen ankles and reduced urine output are plausible drug-related renal effects, and the safer judgement is to protect the kidney while treating the pain by another route.