VentralinkVentralink Medication Education Series
ACE Inhibitors & ARBs • Article 5 of 6
Saving Your Kidneys
How ACE Inhibitors and ARBs Protect Against Diabetic Kidney Disease
Why Your Doctor Prescribes Lisinopril, Losartan, or Irbesartan to Slow Kidney Damage from Diabetes
Key Takeaways
- Diabetes is the leading cause of kidney failure in the United States
- ACE inhibitors and ARBs protect your kidneys beyond just lowering blood pressure—they slow the disease itself
- Starting these medications early can reduce your risk of needing dialysis by 20-30%
- Both drug classes work equally well—if one causes side effects, the other is a good alternative
Why Diabetes Damages Kidneys
Your kidneys filter your blood. Think of them as very fine strainers. Every day, they clean about 50 gallons of blood—removing waste while keeping important things like protein in your body.
When you have diabetes, high blood sugar slowly damages the tiny blood vessels in these filters. Over time, the filters become leaky. Protein that should stay in your blood starts spilling into your urine. This protein leak is often the first warning sign of kidney trouble.
The Warning Signs
Microalbuminuria means small amounts of protein are leaking into your urine. This is the early stage—damage is happening, but your kidneys still work well. Macroalbuminuria (also called overt nephropathy) means larger amounts are leaking. Without treatment, this often leads to kidney failure within 10-15 years.
The scary part? You usually feel fine during this process. By the time you notice symptoms—swelling in your legs, tiredness, changes in urination—significant damage has already occurred. That's why regular testing is so important if you have diabetes.
How These Medications Protect Your Kidneys
Remember the renin-angiotensin system we discussed in Article 1? This hormone system does more than control blood pressure. In your kidneys, angiotensin II causes a specific problem: it squeezes the blood vessels leaving your kidney filters harder than the ones entering them.
This creates extra pressure inside the filters—like putting your thumb over a garden hose. In the short term, this keeps your kidneys working despite damage. But over months and years, the extra pressure causes more harm. The filters scar and fail faster.
What ACE Inhibitors and ARBs Do
These medications relax that squeeze on the vessels leaving your kidney filters. This lowers the pressure inside the filters, giving them a chance to heal instead of being damaged further. The protection happens even when blood pressure doesn't drop much—it's a direct effect on the kidney itself.
The Evidence: Landmark Clinical Trials
Three major trials proved that blocking the renin-angiotensin system protects diabetic kidneys. Together, they changed how doctors treat this condition.
The Captopril Study (1993) — Type 1 Diabetes
409 patients with Type 1 diabetes and kidney damage • Captopril vs. placebo • 3 years of follow-up
This was the study that started it all. Patients already had protein in their urine and some kidney damage. The question: could captopril (an ACE inhibitor) protect their remaining kidney function?
The combined risk of death, dialysis, or transplant was cut nearly in half. Importantly, the benefit was independent of blood pressure—patients on captopril did better even when their blood pressure was similar to those on placebo.
RENAAL Trial (2001) — Type 2 Diabetes
Reduction of Endpoints in NIDDM with the Angiotensin II Antagonist Losartan
1,513 patients with Type 2 diabetes and nephropathy • Losartan vs. placebo • Average 3.4 years
Type 2 diabetes is far more common than Type 1. Would an ARB (losartan) work in these patients? RENAAL provided the answer.
Losartan also reduced the risk of kidney function declining sharply by 25%. The researchers estimated that for every 100 patients treated for 4 years, losartan would prevent 8-19 patients from needing dialysis, depending on how advanced their kidney disease was at the start.
IDNT Trial (2001) — Type 2 Diabetes, Comparing to Calcium Channel Blocker
Irbesartan Diabetic Nephropathy Trial
1,715 patients with Type 2 diabetes and nephropathy • Irbesartan vs. amlodipine vs. placebo • 2.6 years
This trial asked a crucial question: is the kidney protection just from lowering blood pressure, or is there something special about blocking angiotensin? They compared an ARB (irbesartan) to a calcium channel blocker (amlodipine)—a different type of blood pressure medication.
Both medications lowered blood pressure similarly. But only irbesartan protected the kidneys. Amlodipine performed no better than placebo for kidney outcomes. This proved that the benefit comes from blocking angiotensin specifically, not just from lowering blood pressure.
Type 1 vs. Type 2 Diabetes: Same Story, Same Solution
Type 1 Diabetes
- Captopril Study proved ACE inhibitors work
- 48% reduction in serious kidney decline
- Benefits last for years after study ended
Type 2 Diabetes
- RENAAL and IDNT proved ARBs work
- 20-28% reduction in progression to dialysis
- Protection beyond blood pressure lowering
The Bottom Line for Your Kidneys
If you have diabetes and:
- • Protein in your urine (microalbuminuria or macroalbuminuria)
- • High blood pressure
- • Any sign of kidney function decline
...an ACE inhibitor or ARB should be part of your treatment plan. These medications can:
- • Slow the progression of kidney disease by 20-50%
- • Reduce protein leakage in urine
- • Delay or prevent the need for dialysis
- • Provide protection even if your blood pressure is already well-controlled