Our aging population is frequently prescribed drugs, drugs, and then more drugs! As hospitalists, we are often called upon to manage the complications these medications can produce.
In some cases, the diagnosis and treatment is straightforward, such as the patient with atrial fibrillation on chronic warfarin who presents with tarry stools and an INR of 12. Even, most medical students would feel comfortable making the diagnosis of warfarin toxicity causing a GI hemorrhage. However, there are many esoteric cases. Sometimes more than one issue is contributing to the problem at hand, and it can be very easy to focus on the forest and overlook the trees.
By Dr. A. Maria Hester
The other day, I listened to an Audio Digest CD on rhabdomyolysis, presented by Dr. Derek M. Fine of the nephrology division at Johns Hopkins University, Baltimore. I see rhabdomyolysis on a regular basis and thought there was almost always a simple explanation, but he made me think about this potentially fatal illness differently.
For instance, we typically see cases such as an otherwise healthy 70 year-old who trips and falls and breaks a hip. A day or two later, his daughter stops by and finds him on the floor. He is rushed to the hospital and found to have a creatinine phosphokinase of 20,000 and an elevated creatinine. That one is simple. But how often do we see seniors with chronic medical conditions? Very commonly! And that’s where the esoteric can hide:
Dr. Fine presented a case of a 64-year-old woman who presented with weakness and acute kidney injury. She had hypertension, peptic ulcer disease, and hypercholesterolemia. She was being treated with diltiazem for her high blood pressure, and simvastatin for her high cholesterol, two very commonly prescribed medications. After receiving a diagnosis of H. pylori, her physician started her on clarithromycin. Close to a week later, she presented in fulminant rhabdomyolysis. Simvastatin, clarithromycin, and diltiazem all use a common cytochrome (CYP3A4), and it was likely the combination of these drugs that contributed to her renal failure.
With so many Americans with both high blood pressure and high cholesterol, it is not surprising that patients are often prescribed a nondihydropyridine calcium channel blocker, such as diltiazem or verapamil, for blood pressure control and a statin to lower cholesterol levels. Unfortunately, according to Dr. Fine’s presentation, one study showed up to a 100-fold elevation of lovastatin in the blood simply by adding diltiazem. Such statin interactions are well documented for a range of medications, including Coumadin, and certain macrolides and calcium antagonists. (Circulation 2004;109:III-50-7).
To complicate matters even further, some of the older, cheaper, generic options for managing blood pressure, such as diltiazem and verapamil, are the main culprits in these scenarios. Likewise, lovastatin and simvastatin, also generic statins, are more likely to interact to cause rhabdomyolysis than are some of the newer, more popular alternatives, such as rosuvastatin and atorvastatin. Fortunately, pravastatin, also available in a generic form, is less likely to cause rhabdomyolysis, so it’s worth thinking about when selecting a new statin for our patients, Dr. Fine says.
The lesson for hospitalists is that we can decrease the chance of a deadly interaction by plugging the drugs we intend to use into one of the many available drug interaction tools, such as the one from Up to Date, especially when we plan to discharge a patient on new medications.
What we can teach our patients is that they, too, can research potential drug interactions online or simply by using the same pharmacy for all prescriptions and asking the pharmacist to check for dangerous mixes.
Dr. Hester is a hospitalist with Baltimore-Washington Medical Center in Glen Burnie, Md., who has a passion for empowering patients to partner in their health care. She reports having no conflicts of interest.