Kidney Function in Seniors: What Changes and How Medications Affect It

When you get older, your kidney function in seniors, the natural decline in how well kidneys filter waste and balance fluids as you age isn't just a normal part of aging—it's a silent risk factor for dangerous drug reactions. Your kidneys shrink, blood flow drops, and filtering slows down. By age 70, most people have lost 30-50% of their kidney function compared to when they were 30. That means drugs like methotrexate, a drug used for autoimmune diseases and cancer that builds up in the body if kidneys can't clear it or NSAIDs, common painkillers like ibuprofen that can reduce blood flow to the kidneys stick around longer and hit harder. This isn't theory—it's why older adults are 3x more likely to end up in the hospital from drug-related kidney problems.

Many seniors take multiple meds at once, and that’s where things get risky. A painkiller for arthritis, a diuretic for swelling, and a blood pressure pill might all affect the same kidneys. The renal toxicity, kidney damage caused by drugs or their interactions from mixing NSAIDs with methotrexate isn’t rare—it’s well-documented. Even something as simple as a daily aspirin can raise drug levels in the blood if your kidneys aren’t filtering properly. And here’s the catch: you might not feel a thing until it’s too late. No pain, no swelling, no warning. Just a blood test showing creatinine has crept up. That’s why knowing your kidney numbers matters more than ever after 65.

What you can do? Ask your doctor for a simple eGFR test—it’s not a fancy scan, just a blood test that tells you how well your kidneys are working. If your number is below 60, your drug doses may need adjusting. Avoid long-term NSAIDs unless absolutely necessary. Watch for signs like swelling in your ankles, fatigue, or urinating less. And if you’re on methotrexate, lithium, or any drug with a narrow therapeutic index, regular monitoring isn’t optional—it’s life-saving. The posts below break down exactly which medications are most risky, how to spot trouble early, and what alternatives actually work without putting extra strain on your kidneys. You don’t need to guess. You just need to know what to ask for.