Commonly prescribed drugs have dangerous interactions
Fifty years ago, Joe Graedon wrote this in the book, “The People’s Pharmacy:” “Drug interactions are the Achilles heel of the medical profession. The laws of nature no longer hold true. This is a crazy world where one plus one equals three, where down may very well be up and surely pigs have wings. In fact, mixing medicines is very much like playing Russian roulette. You never know when a particular combination will produce a lethal outcome.”
In those days, there were no computer programs to warn prescribers about dangerous drug combinations. These days, prescribers and dispensers rely on digital systems to double-check for hazardous combinations. No thinking is required. But when humans rely upon computers to make life-and-death decisions, it can sometimes end badly.
Physicians, nurse practitioners, physician associates and pharmacists are incredibly busy these days. We frequently hear from clinicians that they feel like they are on a conveyor belt rushing from one patient to another. They may not have much time to talk about drug side effects or warn about potentially serious interactions.
There is also the “cry wolf ” phenomenon. Prescribers get so many computerized warnings that they tend to ignore many of them. There is even a name for this phenomenon: “alert fatigue.” Pharmacists, too, see digital alerts so often that they frequently override the software-generated drug interaction flags.
We commonly hear from health professionals that they only override what seems like minor incompatibility reactions. But here is an example of a deadly interaction that could easily be ignored.
Lisinopril and losartan are blood pressure (BP) medications. They are among the most prescribed drugs in the country. About 34 million Americans take one of these drugs. Both preserve potassium in the body. If one of these patients were to develop a urinary tract infection (UTI), it is entirely possible that an antibiotic would be prescribed. About 5 million prescriptions are written annually for co-trimoxazole (sulfamethoxazole + trimethoprim, aka Bactrim, Septra), many for UTIs.
The drug interaction checker that we often use lists 75 medications that are “contraindicated” or should be avoided if someone is prescribed co-trimoxazole. They include both lisinopril and losartan because the combination can lead to life-threatening potassium buildup and fatal heart rhythms (BMJ, Oct. 30, 2014). We worry that if health care professionals override the warnings against combining these familiar drugs, the outcome could be catastrophic.
The diabetes drug metformin is taken by more than 20 million Americans. It helps control blood sugar. But metformin can also interact with dozens of other drugs. The Food and Drug Administration requires a black box warning for prescribers about a dangerous condition called lactic acidosis. The antiseizure medicine topiramate (Topamax) increases the risk of this potentially deadly problem.
Some statins, such as lovastatin or simvastatin, can interact with the commonly prescribed blood pressure medicine amlodipine. This combination could increase the risk of life-threatening muscle breakdown (rhabdomyolysis) and kidney failure. As a result, prescribers are supposed to limit the statin dose to 20 milligrams for patients taking amlodipine.
These examples should serve to alert both providers and patients to take drug interactions seriously. Ignoring warnings could be deadly.
In their column, Joe and Teresa Graedon answer letters from readers. Write to them in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email them via their website: www.PeoplesPharmacy.com. Their newest book is “Top Screwups Doctors Make and How to Avoid Them.”