New research suggests that the antibiotic Primsol may not be the best treatment option for urinary tract infections, due to a risk of kidney injury and the development of dangerously high levels of potassium. 

While the antibiotic has been used mainly as a urinary tract infection treatment for decades, a study published last week in the medical journal The BMJ raises questions about this practice.

Primsol (trimethoprim) has been a commonly used antibiotic since the 1960s. It is available in generic form and is primarily used to treat urinary tract infections. It is also used to treat middle ear infections, pneumonia and Traveler’s diarrhea.

In this new study, researchers from the U.K. looked at data on more than 178,000 individuals age 35 and over who were treated for urinary tract infections (UTIs) from April 1997 to September 2015. The subjects were treated with either Primsol, Cipro, Macrobid, amoxicillin or cefalexin. The drugs were used to treat more than 400,000 episodes of UTI during that time period among the subjects.

According to the findings, Primsol carried a 72% increased risk of acute kidney injury, and Cipro carried a nearly 50% increased risk, when compared to the other antibiotics. Additionally, Primsol more than doubled the risk of hyperkalemia; high levels of potassium which can cause muscle pain, numbness, abnormal heart rates, cardiac arrest and death.

Researchers determined that Primsol use resulted in two cases of additional incidents of acute kidney injury per 1,000 UTIs treated, and one to two additional cases of hyperkalemia, when compared to amoxicillin, which researchers used as a baseline.

However, the findings indicated there was no increased risk of death associated with Primsol, compared to the use of the other antibiotics, unless the patients were also taking renin-angiotensin system blockers, a class of drugs used to treat hypertension, in which case there was a slightly higher risk of death.

“Trimethoprim is associated with a greater risk of acute kidney injury and hyperkalaemia compared with other antibiotics used to treat UTIs, but not a greater risk of death,” the researchers concluded. “The relative risk increase is similar across population groups, but the higher baseline risk among those taking renin-angiotensin system blockers and potassium-sparing diuretics translates into higher absolute risks of acute kidney injury and hyperkalaemia in these groups.”

Tags: Acute Kidney Injury, Amoxicillian, Antibiotics, Cipro, Hyperkalemia, Primsol, Urinary Tract Infection