They can. But they can also protect your kidneys. Confused? I’m not surprised! This is a subject that many doctors also find confusing.
Why your kidneys?
Firstly, why should your kidneys be damaged at all? Think of them as a pair of very fine sieves. These sieves filter your blood, removing waste and producing urine. If there is no pressure pushing your blood through the sieve then nothing gets filtered. Your kidneys also don’t get enough blood for themselves to stay healthy. This is how some blood pressure medications can cause harm to the kidneys. But too much pressure and the sieve itself is damaged. This is how untreated high blood pressure can damage the kidneys.
Just the right amount of pressure
So, your kidneys are quite sensitive when it comes to blood pressure – either too high or too low causes problems. Your kidneys are therefore protected by reducing high blood pressure, but if it is lowered too far they can also run into trouble. It is uncommon to lower blood pressure so far that your kidneys no longer get enough pressure BUT there is a particular class of blood pressure medication that deserves further consideration in this respect.
ACE inhibitors and ARBs
These drugs include Ramipril, Lisinopril, Enalapril, Perindopril and Losartan, Irbesartan, Candesartan respectively. Although they lower your blood pressure, they have a particularly strong effect on lowering the pressure in the kidneys. This means they are more protective of your kidneys than other blood pressure medications if you have high blood pressure.
But, it also means it is easier to overshoot and lower the pressure in the kidneys too far. This is why people who take these drugs should have an annual blood test and also a blood test whenever the dose is increased to measure their kidney function. The benefits certainly outweigh the risks though – with adequate monitoring they are one of the best types of blood pressure medication thanks to their extra kidney protection.
Blood test confusion
I’m afraid there’s an additional bit of complexity to throw in here. The blood test that we use to measure kidney function is affected by the ACE inhibitor and ARB drugs. That means that when we are monitoring your kidney health with a blood test we have to take this into account.
After starting one of these drugs, up to a 25% drop in the blood test we use to measure kidney function is considered acceptable. Remember this is NOT because they are harming your kidneys, more that it shows that the drugs are working as anticipated to reduce the pressure in the kidneys.
So, it is true that blood pressure medications can harm your kidneys if not properly monitored. But used correctly, they will actually protect your kidneys from the damaging effect of high blood pressure.
Small disclaimer: It will probably be of no surprise to learn that this is a simplified version of events! For those that are interested, the situation is complicated further by the fact that your kidneys produce a hormone which regulates your blood pressure, so entangling the situation even further.