For men, creatinine clearance = ((140- Age) * IBW) / (72 * SCr) For women, creatinine clearance = ((140- Age) * IBW * 0.85) / (72 * SCr) Where Age is in years, IBW is ideal body weight in kilograms, and SCr is serum creatinine in mg/dl.

(For algebraically-challenged and for anyone wanting help in calculating results of these complicated equations, please visit this creatinine clearance calculator: www.medicationadvisor.com/creatinine/creatinine.asp.)

Now once you run this a few times, you’ll find that creatinine clearance for young healthy people is about 100 ml/min (we’ll just leave off “ml/min” part from now on).

And, dead people have a creatinine clearance of about 0, depending on how healthy they are.

Everyone else falls somewhere in between.

(Now someone in back of room is saying, “I just ran this on myself and I have a creatinine clearance of 150”. Well aren’t you special? In fact, young good-looking people can have creatinine clearances of 130, 140, or more…but it doesn’t do a whole lot of good since 100 is perfectly acceptable. In fact, it’s just another case of overachiever overkill.)

Now, if someone has a creatinine clearance of 80, that means that they have about…..80% kidney function.

And, if someone has a creatinine clearance of 50, that means that they have about…..50% kidney function. (Are you following all of this?)

Many drugs that are eliminated by kidney will require moderate dosage reductions once a patient’s renal function is in 40-60 range. Patients in 20-40 range will typically require very large reductions in dose.

And, patients who are in “less than 20” range will often need HUGE dosage reductions for medications eliminated by kidney (or better yet, they’ll need to take medications that are removed by some other organ altogether...if such an alternative is available).

One last tidbit to consider. Renal function declines as people age. No getting around that. But, rate of decline is different for different people. By time you’re 50 years old, there is a reasonable chance you’ll have moderate renal function (or worse)…by time you’re 80, you’ll almost certainly have some important degree of renal impairment…and you probably won’t even know it or feel it.

Now that you know more renal physiology than you ever, EVER wanted to know…let’s get back to main thread of this article…medication safety.

If you (or a loved one) are at risk for having decreased kidney function (and I’ll tell you who such folks are in just a second), you need to step up to plate and get a handle on this issue (because there is a very good chance that your physician and pharmacist either didn’t have renal function data or didn’t consider it when coming up with a dosage for you).

Here are steps I recommend for everyone taking prescription or over-the-counter medications:

1)For everyone: If you have access to results of a recent serum creatinine test (it is probably part of your annual physical and you may have gotten a copy), memorize it or write it down and then say to your physician or pharmacist when you get a medication, “Say, I think my serum creatinine is about X. So, does this medication need any dosage adjustment in order to be safe for me?

2)If you are in one of following categories, you should expect your physician and pharmacist to have considered your renal function before dosing a medication:

known kidney disease; age greater than 50; history or heart attack, angina, stroke, or other artery blockages; history of diabetes (any type); history of high blood pressure; prior exposure to chemotherapy drugs; prior prolonged exposure to IV antibiotics; frequent use of pain medications (especially non-steroidal anti-inflammatory drugs, but others as well).

So you might say to your physician or pharmacist, “Is this drug removed by kidney, because I have condition X that could decrease kidney function and I just want to be safe.” If drug is removed by kidney, you might also ask physician or pharmacist to tell you what your serum creatinine is…and if he or she does not have this information, a big red flag should be going up in your head.

3)If you are not in one of categories in question 2 and you don’t have a serum creatinine available, don’t worry. You’re probably safe. But you may want to ask your physician if there is a serum creatinine in your chart and if so, what it is.

4)If you are on dialysis of any sort, serum creatinine is not all that useful for dosing medications. Just make sure your physician and pharmacist are aware that you are on dialysis and perhaps ask, “Now is this usual dose for someone on dialysis?”

These are some of steps I hope you will consider next time you get a prescription or over-the-counter medication so you can be sure that that you (or your loved one) are getting right dose.

In this series, we are going to take a close look at processes that cause medication errors (some things that your physician and pharmacist may not even want you to know) and what steps you can specifically take to make sure that you and your love ones are protected from this hazard.

Ten years ago, your ability to get current, objective, reliable information on your medications in a quick and easy way was practically non-existent. It probably would have involved a trip to library and required considerable knowledge about pharmacology to get answers.

Today, that’s not case. There is a host of on-line tools, databases, and resources that allow you to learn information about medications that even your physician and pharmacist may not know.

We’re going to talk about them, show you were to go, tell you key things you need to know about medications, expose some myths, and let you know questions you should be asking. It’s not as hard as it may seem.

In fact, you need to become final line of defense in battle against medication errors.

Throughout, we are going to give you some key rules that should guide your defense.

So, Rule Number 1. Trust, but verify. Never assume that medication you have received is right medication for you or that it is dosed correctly for you. Specifically, you should check:

•the name of patient on bottle; •the name of doctor on bottle; •the name of medication (and cross check it to be sure that it treats a disease or problem you actually have…there are lots of look-alike/sound-alike drug names out there); •the dose (from an independent source…to make sure that it is a plausible dose for you); •the “route” (to make sure, for example, that eye drops are being prescribed for eye, and not mouth, or ear…amazingly injuries from drug misplacement occur all time); •the expiration date.

We’ll talk about some specific resources that will help with each of these throughout this series.

The result, we hope, will be piece of mind to know that you and your family are getting your 7 rights:

•right drug; •right patient; •right dose; •right time; •right route; •right reason; •right documentation.

Right on!

© 2004 Timothy McNamara, MD, MPH