bottles of medications with warning stickers and information

We have been writing about the dangers of drug interactions for over 40 years. We assumed that when computers entered the scene doctors would check for dangerous drug combinations before prescribing a new medicine. We also believed that pharmacists would be the safety net and catch any deadly drug interaction that fell through the prescribing cracks. We were wrong on both counts. This reader shares a tragic story.

A Deadly Drug Interaction Between Lisinopril and Trimethoprim

Q. My husband had a cardiac arrest and died 20 days after being prescribed trimethoprim for an infection. He was already taking lisinopril to control his blood pressure.

The post-mortem concluded he had plaque in two of his cardiac arteries and had suffered a heart attack. There was no mention of a possible deadly drug interaction, although he had had no prior heart symptoms.

A Deadly Drug Interaction That Should NEVER Happen!

A. The potentially life-threatening interaction of trimethoprim with an ACE inhibitor such as lisinopril or enalapril is under-recognized. This antibiotic (trimethoprim) is often prescribed in combination with sulfamethoxazole to treat common infections. This combo is called co-trimoxazole, SMZ-TMP or TMP-SMX (Bactrim, Septra).

Millions take ACE Inhibitors and ARBs:

According to our calculations, 60 million Americans take ACE inhibitors or ARBs. That amounts to over 240 million prescriptions for these drugs. Eight million people take the antibiotic trimethoprim plus sulfamethoxazole. With so many people taking these kinds of meds interactions are inevitable.

Imagine this scenario. Someone taking lisinopril develops a urinary tract infection. The doctor or nurse practitioner prescribes TMP-SMX to clear up the infection. No one bothers to read the warnings. The result could be a deadly drug interaction that no one recognizes.

How Does This Deadly Drug Interaction Occur?

All ACE inhibitors and ARBs like valsartan or losartan can interact with this antibiotic to raise potassium to lethal levels (BMJ, Oct. 30, 2014).  Too much potassium can cause cardiac arrest that is hard to distinguish from a heart attack.

Other symptoms of excess potassium (hyperkalemia) include irregular heart rhythms, tingling or numbness in the lips, feet or fingers, breathing difficulties, fatigue, weakness, slow pulse and mental confusion.

Most drug interaction references say monitor potassium when prescribing or dispensing an ACEi, or an ARB plus the antibiotic SMZ-TMP or TMP-SMX. The trouble is that most people are not monitored closely for potassium. Levels can rise so quickly that no health professional could catch this deadly drug interaction in time.

Protect Yourself and Those You Love!

We have written extensively about this and other deadly interactions in our book, Top Screwups. To protect yourself, you may want to check our top 11 tips for preventing dangerous drug interactions, pages 108-110.

The book is available at your local library or at To order by mail, please send $15 plus $4 postage and handling to:

  • Graedons’ People’s Pharmacy, Dept. TSDM
  • PO Box 52027
  • Durham, NC 27717-2027

Share your own drug interaction story below in the comment section

Get The Graedons' Favorite Home Remedies Health Guide for FREE

Join our daily email newsletter with breaking health news, prescription drug information, home remedies AND you'll get a copy of our brand new full-length health guide — for FREE!

  1. JF

    jf…..what about negative inter actions between herbs and herbal supplements.? is there info one should be made awear of?

  2. Kaye

    I was put on Doxycycline for a month (ended 6/30) due to an exacerbation of peripheral neuropathy symptoms resulting from the bite in 2012. I take LoSartan daily. I’ve been experiencing many of the symptoms you mentioned in the antibiotic/BP reaction. Do these two meds interact in a similar way?

  3. Ron
    Fredericksburg VA

    WOW! HOLY S–T I was taking Bactrim for a urinary infection last year. but I also take losartan on a daily basis im surprised my physician did not catch that one.. as they have all the records of medications I take. many years ago a leader in my trade group said (quote) you ae the guardian of your own welfare…… that quotation had nothing to do with medicine but in so many ways it is true. doctors really can screw up badly, even now with a laptop full of your medical info right in front of them THANKS to you folks for this article. I can see I will have to be more diligent in the future

    • Sara
      North Carolina

      Doctors should be required to read the People’s Pharmacy Newsletter!!!

  4. Nancy P M
    North Carolina

    New conversation: Have been having bad leg cramps that wake me up at night. I’ve read that lack of magnesium causes them.

    Could something like milk of magnesia tablets taken in small amounts help with this?

    I have used your other recommendations (tonic water, soap under the sheets, etc.) in the past, and they are very effective. However it seems at age 85 with bp and afib meds already, I should not just run to the store and buy over the counter magnesium.

  5. Minnie
    Sumter, S. C.

    I enjoy the information I learned listening to the program on Saturday Morning.
    Thank you for the medical facts that., we don’t have access to. Not only do I listen I actually put some of them to practice. Plus I share the information with my family and friends. Thank you.

    • Sara
      North Carolina

      You are so correct, Minnie! I tell everyone, even people I do not know, about the People’s Pharmacy and their newsletter. They are truly a wonder and so caring, and providing much more information than our doctors even know about! I even tell the personnel at Duke University Medical Hospital, where I am getting three day Chemo treatments every third week, that they should subscribe to the People’s Pharmacy’s free Newsletter!

    • Linda
      Tacoma WA USA

      I use inexpensive glycerin, and rub it in to my calves and feet nightly. It works beautifully for me.

  6. Georgie

    I believe Doctors don’t really know in many cases of drug reactions of any kind, with or without other drug involvement.

    And, pharmacists are pressured to fill scripts quickly, I do not think they really monitor interactions.

    Then, like myself, all my maintenance drugs come by mail. so, if I buy a script for instance, for short term use, local pharmacist really is not to blame as he probably does not know of my maintenance drug, thus possible problem if Primary Care Dr. did not catch it.

    I try, by computer, to monitor my drugs before I take a new one. It helps as I have learned.

  7. ray

    I have been with my dr over 15 yrs. my cholestrol was high and increased my lisinopril (bp). I thought she was wrong. I google it, and ask 2 different pharmist to confirm.

    I called her back and she said she had made an error on which med to increase. Also one of my meds increases the effect of lisinopril. I trust my dr, but its best to research your meds also.

  8. Lily

    That was tragic and totally avoidable It really annoys me when medics dish out these drugs and do not take 5 to consider interactions or previous health conditions I personally have heart problems yet on several occasions I was given antibiotics that are black boxed and even the pharmacist missed it! I think when it comes to ace inhibitors medics need to consider stopping them for a couple of days if possible and also drug companies need to high light these interactions on the outside of the packages

  9. Carol
    Wake Forest NC

    Why isn’t an online program available to all medical people licensed to prescribe medication that would use a patient’s current list of medications to indicate contraindications with whatever drug is being considered to be prescribed.

    I feel that physicians, PAs, NPs and any other medical personnel involved in providing patient care have an obligation to be involved and up to date with RX effects and interactions of any and all medications each would prescribe.

    It is obviously not being addressed by the package warnings accompanying prescriptions.

  10. Jane

    What I do know is that Lisinopril is a dangerous drug. I was on it for a while and when I developed an itch on my lip my doctor immediately took me off it.

    People literally drop dead after taking it for a while.

    Please just google something like “Is Lisinopril a dangerous drug” and see for yourself. How the FDA lets this stay on the market can only be due to their being paid off maybe? I don’t trust Lisinopril or the FDA.

  11. Carl and Pat V

    Just wonder if potassium from bananas would be too much combined with different prescriptions, can cause problems. My husband has a valve issue and has received a clip on the leak.

    He take water pills and baby aspirin, and has been advised to eat a
    banana, because the large one has at least 550 mg. potassium.

    Sometimes he eats two, morning and evening.

  12. Sally

    Thank you for continuing to write about the deadly interaction between SMZ-TMP because you may have saved my husband’s life! If only doctors and pharmacists would read your articles. You wrote about such a reaction many years ago, and, at that time, I alerted my elderly friends to be aware.

    Little did I know that my 79-year-old husband would fall victim to such a prescription interaction last year when our elderly internist prescribed a high dose of 800 mg/160mg twice a day of SMZ-TMP for 14 days in treatment of pneumonia. We have known that he does not keep up with updates in many areas of medicine.

    Remembering the possibility of this deadly interaction from your articles, I immediately alerted his cardiologist who ran blood tests which determined he was suffering from dehydration and moderate loss of kidney function with a GFR level of 48 placing him in Stage three chronic kidney disease because he also was daily taking 100 mg of Losartan. His cardiologist said to discontinue the diuretic to avoid hyperkalemia and my husband also stopped at only 10 tablets of SMZ-TMP. When our internist saw the blood test results, he said, “These results must be wrong.”

    I don’t know how many times I share your many articles with our cardiologist who actually reads them which makes for a good team relationship. Our internist never reads anything we give him with the comment, “It depends upon who you listen to,” who most likely are pharmaceutical reps.

    Keep up the good work in making us good health advocates for our own protection!

  13. Mary Jewell B

    You sure do have to do your homework in all situations when you are taking medications. I have become more and more informed reading your letters.

  14. RayLin S

    I am allergic to Sulfa drugs – and yet, pharmacies, using computers, have filled prescriptions that contain sulfa. The last time almost killed me as I went comatose.

    Walmart was the only pharmacy that refused to fill a prescription due to Sulfa. Was a life saver.

  15. shirley

    Lots of cranberry juice and water is a better alternative to clearing up a urinary tract infection and eating two bananas a day with lots of other produce and exercise is a better way to keep blood pressure down. Drug side effects and interactions are widespread, dangerous and hard to keep up with even for careful consumers, doctors and pharmacists.

  16. Jackie H

    I am taking Losartan and carvedilol, and I have been having a lot of night mares and mental problems. Has anyone else had this problem when taking the two together

  17. Don

    Can you name a good web site where we can put in the drugs we are taking and see if there any drug interactions?
    Don R

    • Sally

      I have found to be a reliable resource for drug information and reactions with other medications. Our pharmacist also says it is a dependable site.

  18. May

    I was given Bactrim for a UTI despite being on an ARB. I called the doctor’s office, and was prescribed a different antibiotic, but I was the one who had to catch this. I have no confidence that it was not done to someone else the next day. The pharmacist essentially told me it was not his job to catch this and did not seem to even be aware of the problem.

    My mother is in a nursing unit in another state. The same thing happened to her. I was the one who had to intervene. The medical personnel did not seem concerned when I went to them with a printout in hand about the issue. Again I have no confidence that they learned anything. I suspect they regarded me as a pest.

  19. patty

    I have noticed a trend nowadays for antibiotics to prescribed as a combo with another drug. One pill with two drugs. Why is this? What is the endgame. I think the extra drugs with the antibiotic is overkill.Literally.

  20. Denise
    Tampa, Florida

    I developed serotonin syndrome after being prescribed Effexor and Buspar. When I was given 3 different antibiotics bc they thought I had pneumonia I developed serious negative reactions that put me in the ER 3 times. After 4 months of getting progressively illl and missed diagnosis several times I stumbled on serotonin syndrome.

    I had every symptom. My primary doctor got snooty to me bc I suggested it. Finally my prescribing psychiatrist realized that’s indeed what I have.

    Six months out of my life were taken from me because my doctor didn’t heed those warnings. If I wasn’t able to self diagnose I would be in a coma by now or dead.

What Do You Think?

We invite you to share your thoughts with others, but remember that our comment section is a public forum. Please do not use your full first and last name if you want to keep details of your medical history anonymous. A first name and last initial or a pseudonym is acceptable. Advice from other commenters on this website is not a substitute for medical attention. Do not stop any medicine without checking with the prescriber. Stopping medication suddenly could result in serious harm. We expect comments to be civil in tone and language. By commenting, you agree to abide by our commenting policy and website terms & conditions. Comments that do not follow these policies will not be posted. Learn how your comment data is processed.

Your cart

Shipping and discount codes are added at checkout.