What they are
ACE inhibitors and ARBs are two related classes of medication that work on the renin-angiotensin-aldosterone system (RAAS), the hormonal pathway that regulates blood pressure and fluid balance.
- ACE inhibitors (Angiotensin-Converting Enzyme inhibitors): block the enzyme that produces angiotensin II, a potent constrictor of blood vessels. Common examples: lisinopril, ramipril, enalapril, benazepril.
- ARBs (Angiotensin Receptor Blockers): block the receptor where angiotensin II acts. Common examples: losartan, valsartan, irbesartan, olmesartan.
Both classes lower blood pressure by similar amounts, and both protect kidney function in similar ways.
How they help kidneys
In the kidney, angiotensin II constricts the small blood vessels at the exit of the glomerulus (efferent arterioles), which raises pressure inside the filter. Over time this high pressure damages the filter and accelerates protein leakage. ACE inhibitors and ARBs reduce this pressure, lowering protein loss and slowing the rate of kidney function decline.
This is why these medications are first-line for:
- Patients with diabetes and any albuminuria (protein in the urine)
- Patients with CKD and proteinuria
- Patients with hypertension and CKD
- Patients with heart failure (regardless of kidney status)
Who should not take them
ACE inhibitors and ARBs are not appropriate for:
- Patients with bilateral renal artery stenosis (severe narrowing of arteries to both kidneys)
- Patients with a history of angioedema (severe swelling reaction)
- Patients with very high potassium that cannot be controlled
- Pregnant patients (they cause harm to the fetus)
Common side effects
- Dry, persistent cough — occurs in 5–10% of patients on ACE inhibitors but rarely on ARBs. Switching to an ARB usually resolves the cough.
- High potassium (hyperkalemia) — these medications mildly retain potassium. Often manageable with diet or potassium binders.
- Dizziness or low blood pressure — especially when first starting or when dehydrated.
- Mild creatinine rise — a small initial increase in serum creatinine (up to about 30%) is expected and often signals the medication is working. Larger rises require evaluation.
- Angioedema (rare): sudden swelling of the lips, tongue, or throat. Stop the medication and seek emergency care.
Monitoring
After starting an ACE inhibitor or ARB, your nephrologist or primary care doctor will typically check blood pressure, serum creatinine, and potassium within 1–2 weeks. After that, monitoring is usually every 3–6 months or sooner if doses change.
When to stop temporarily
In certain situations — acute illness with severe vomiting or diarrhea, before contrast imaging in some cases, or with major surgery — it may be wise to hold these medications temporarily. Always discuss with your doctor; do not stop on your own.