ARBs and Your Kidneys
I am a 66-year-old female with type 2 diabetes. My A1C was less than 6 without medication. My microalbumin is less than 3. I had a problem with my ACE inhibitor: a side effect of constant dry coughing. Recently, my blood pressure has been high, so I started taking Norvasc, which brought my blood pressure down below 110/70. I have been told Cozaar, an ARB, will protect the kidneys. Would you explain the mechanism of how ARBs affect the kidneys? Is there an added benefit to being on an ARB even though Norvasc keeps my blood pressure down? If so, what is the optimum dose of Cozaar to protect the kidneys? My cardiologist said a higher dose is better. Esther Yoo, MD, Shavano Park, Texas
Craig Williams, PharmD, responds: Angiotensin receptor blockers (ARBs) and angiotensin- converting enzyme inhibitors (ACEIs) have special effects that protect the kidneys in a way other blood pressure-lowering medicines don't. ARBs and ACEIs achieve this through reducing the effects of the hormone angiotensin 2.
In the kidneys, angiotensin 2 constricts the blood vessels in an especially harmful way, which results in an elevated blood pressure in the kidney that is often more severe than elevations in systemic blood pressure (what we measure with the cuff on the arm). In fact, damage to the blood vessels in the kidney and elevated kidney blood pressure can occur before any elevation in the blood pressure you typically measure. To watch for this early damage, we monitor for protein in the urine (proteinuria). You mentioned that the amount of protein in your urine (your microalbumin) is normal (anything less than 3 mg/dl or 30 µg/ml is considered normal). That is very good. The numbers that you describe (blood pressure of 110/70 and normal proteinuria) are at their goals.
In general, both the National Kidney Foundation and the American Diabetes Association agree that patients with an elevated blood pressure or abnormal proteinuria should be on an ACEI or ARB, with a goal of reducing proteinuria and achieving a blood pressure of less than 130/80 mmHg. While higher than normal doses of either class of medicine can have a greater effect on lowering proteinuria and may be needed to achieve blood pressure goals, it is not clear there are benefits to those higher doses if blood pressure and proteinuria are already at goal on standard doses.
In general, ACEIs and ARBs should be used in at least standard doses to achieve blood pressure goals and to lower proteinuria. Side effects to watch for at normal or higher doses are hypotension (low blood pressure), an elevated amount of potassium in the blood, and, as you noted, a dry cough with an ACEI. A condition called angioedema can also occur with ACEI and it can also happen with an ARB in patients who experienced it with an ACEI. Angioedema is characterized by swelling or edema around the face and neck.
Despite how good ACEI and ARB medications sound, that doesn't mean that every patient with diabetes should be on one. While some experts like to debate this point, patients with diabetes who have a normal untreated blood pressure and normal proteinuria can be safely followed without being put on an ACEI or ARB. If so, it is important to have good medical supervision so that therapy can be started if either risk factor appears. Your doctor should check your blood pressure and screen for proteinuria at least once a year.