One of the things I enjoy about this site is learning from the donations of others. Here’s an excellent case of trimethoprim and hyperkalemia. If you have an interesting case study to share that can help educate healthcare professionals, please contact me. Here’s the case.
MP is a 77 year old male presenting to the emergency department with a chief complaint of weakness. MP has multiple comorbidities, including hypertension, coronary artery disease, type II diabetes, and pulmonary hypertension. His chronic medications include:
- Metoprolol succinate
- Aspirin 81mg
- Nitroglycerin sublingual
Also, of note MP was started on sulfamethoxazole/trimethoprim (Bactrim®) 5 days prior to presentation for a sinus infection.
Pertinent vitals signs and initial findings include a heart rate of 43 beats/minute and prominent T waves per the electrocardiogram.
Pertinent initial labs include: Potassium of 7.3 meq/L, sodium of 125 meq/L, and a digoxin level of 1.2. MP was successfully treated for hyperkalemia and was able to be discharged from the hospital a couple days later after multiple medication adjustments, the primary one being stopping sulfamethoxazole/trimethoprim.
Multiple medications were contributing to the lab abnormalities and likely peaked with the addition of sulfamethoxazole/trimethoprim. Digoxin, spironolactone, and lisinopril (as well as all ACE inhibitors and angiotensin receptor blockers) are known to increase serum potassium levels. Trimethoprim has been found to reduce renal potassium excretion via a similar mechanism as the potassium sparing diuretic amiloride.
This drug interaction needs to be taken seriously. In patients chronically taking a medication known to increase potassium and in whom an antibiotic is needed (for an indication that sulfamethoxazole/trimethoprim could be used), the clinician should consider an alternative agent.
It must also be noted that this drug interaction (sulfamethoxazole/trimethoprim and either an ACE inhibitor or ARB) has been associated with an increased risk of sudden death in a recent population-based, nested, case-control study.
Donated by Joel Van Heukelom PharmD – You can find him on Twitter @
Looking for more useful clinical medication content? Check out the 30 medication mistakes, from my everyday practice as a pharmacist.
Reference: Fralick M, Macdonald EM, Gomes T, et al. Co-trimoxazole and sudden death in patients receiving inhibitors of renin-angiotensin system: population based study. BMJ. 2014;349:g6196 doi: 10.1136/bmj.g6196.