Losartan with Trimethoprim Interaction Details

Brand Names Associated with Losartan

Brand Names Associated with Trimethoprim

Medical Content Editor Dr. Brian Staiger, PharmD
Last updated Nov 05, 2023

Interaction Effect

Increased risk of hyperkalemia

Interaction Summary

Coadministration of trimethoprim with drugs known to induce hyperkalemia, including potassium-sparing agents, may result in increased risk of hyperkalemia. In a population based, nested, case-control study (N=165,754), sulfamethoxazole/trimethoprim was found to be 12 times more likely to cause hyperkalemia in elderly patients than amoxicillin . Two cases of hyperkalemia have been reported in patients who were taking trimethoprim/sulfamethoxazole concomitantly with an ACE inhibitor. If coadministration of trimethoprim with a potassium-sparing drug is necessary, close monitoring of serum potassium is warranted in such patients .

Severity

Major

Onset

Unspecified

Evidence

Theoretical

How To Manage Interaction

Concomitant use of trimethoprim with drugs known to induce hyperkalemia, including potassium-sparing agents, may result in increased risk of hyperkalemia. Closely monitor serum potassium in patients who are coadministered trimethoprim with a potassium-sparing drug.

Mechanism Of Interaction

Additive effects of hyperkalemia

Literature Reports

A) In a population based, nested, case-control study of patients aged 66 years or older administered spironolactone, 6903 of 165,754 patients were admitted to the hospital for hyperkalemia. Among them, 161 were admitted within 14 days of receiving sulfamethoxazole/trimethoprim. Primary analysis revealed an increased risk of hospital admission for hyperkalemia in patients administered sulfamethoxazole/trimethoprim and spironolactone compared with matching controls. An adjusted analysis shown that patients admitted with hyperkalemia were 12.4 times more likely to have received a prescription for sulfamethoxazole/trimethoprim than amoxicillin. In addition, a higher risk of hospital admission was associated with a double-strength formulation of sulfamethoxazole/trimethoprim when compared with single-strength tablets (13.5 vs 9.7-fold increased risk). Analysis also determined, based on the population attributable fraction, that approximately 60% of all hyperkalemia cases in older patients treated with antibiotics for urinary infection would not have taken place if sulfamethoxazole/trimethoprim was not prescribed .

B) Hyperkalemia levels greater than 7 mEq/L associated with azotemia (BUN 33 mg/dL, serum creatinine 3.3 mg/dL) was noted 20 days after addition of trimethoprim-sulfamethoxazole for mild acute pyelonephritis to a stable, 3-year regimen of quinapril 20 mg daily in a 74-year-old man being treated for hypertension. The patient was asymptomatic; an ECG did not reflect classic signs of hyperkalemia. Drug withdrawal and specific treatment for hyperkalemia, including insulin, dextrose, sodium polystyrene sulfonate, and calcium, was required, with resolution over 36 hours. Nifedipine was substituted for blood pressure control .

C) A 40-year-old woman with double lung transplantation developed a pneumocystis carinii infection 1 year post-transplant. Medications she was stabilized on included enalapril 30 mg daily. High dose trimethoprim-sulfamethoxazole therapy (20 mg/kg/day and 100 mg/kg/day) was instituted. After 9 days of concurrent therapy with trimethoprim-sulfamethoxazole and enalapril, the patient's potassium level reached 6.8 mmol/L. Both medications were discontinued and the patient required treatment for her hyperkalemic condition .

Losartan Overview

• Losartan is used alone or in combination with other medications to treat high blood pressure. Losartan is also used to decrease the risk of stroke in people who have high blood pressure and a heart condition called left ventricular hypertrophy (enlargement of the walls of the left side of the heart). Losartan may not decrease the risk of stroke in African Americans who have these conditions. This medication is also used to treat kidney disease in people who have type 2 diabetes (condition in which the body does not use insulin normally and therefore cannot control the amount of sugar in the blood) and high blood pressure. Losartan is in a class of medications called angiotensin II receptor antagonists. It works by blocking the action of certain natural substances that tighten the blood vessels, allowing the blood to flow more smoothly and the heart to pump more efficiently.

• High blood pressure is a common condition, and when not treated it can cause damage to the brain, heart, blood vessels, kidneys, and other parts of the body. Damage to these organs may cause heart disease, a heart attack, heart failure, stroke, kidney failure, loss of vision, and other problems. In addition to taking medication, making lifestyle changes will also help to control your blood pressure. These changes include eating a diet that is low in fat and salt, maintaining a healthy weight, exercising at least 30 minutes most days, not smoking, and using alcohol in moderation.

Trimethoprim Overview

• Trimethoprim eliminates bacteria that cause urinary tract infections. It is used in combination with other drugs to treat certain types of pneumonia. It also is used to treat traveler's diarrhea. Antibiotics will not work for colds, flu, or other viral infections.

• This medication is sometimes prescribed for other uses; ask your doctor or pharmacist for more information.

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Definitions

Severity Categories

Contraindicated

These drugs, generally, should not be used together simultaneously due to the high risk of severe adverse effects. Combining these medications can lead to dangerous health outcomes and should be strictly avoided unless otherwise instructed by your provider.

Major

This interaction could result in very serious and potentially life-threatening consequences. If you are taking this drug combination, it is very important to be under close medical supervision to minimize severe side effects and ensure your safety. It may be necessary to change a medication or dosage to prevent harm.

Moderate

This interaction has the potential to worsen your medical condition or alter the effectiveness of your treatment. It's important that you are monitored closely and you potentially may need to make adjustments in your treatment plan or drug dosage to maintain optimal health.

Minor

While this interaction is unlikely to cause significant problems, it could intensify side effects or reduce the effectiveness of one or both medications. Monitoring for changes in symptoms and your condition is recommended, and adjustments may be made if needed to manage any increased or more pronounced side effects.

Onset

Rapid: Onset of drug interaction typically occurs within 24 hours of co-administration.

Delayed: Onset of drug interaction typically occurs more than 24 hours after co-administration.

Evidence

Level of documentation of the interaction.

Established: The interaction is documented and substantiated in peer-reviewed medical literature.

Theoretical: This interaction is not fully supported by current medical evidence or well-documented sources, but it is based on known drug mechanisms, drug effects, and other relevant information.

How To Manage The Interaction

Provides a detailed discussion on how patients and clinicians can approach the identified drug interaction as well as offers guidance on what to expect and strategies to potentially mitigate the effects of the interaction. This may include recommendations on adjusting medication dosages, altering the timing of drug administration, or closely monitoring for specific symptoms.

It's important to note that all medical situations are unique, and management approaches should be tailored to individual circumstances. Patients should always consult their healthcare provider for personalized advice and guidance on managing drug interactions effectively.

Mechanism Of Interaction

The theorized or clinically determined reason (i.e., mechanism) why the drug-drug interaction occurs.

Disclaimer: The information provided on this page is for informational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional regarding your specific circumstances and medical conditions.

Where Does Our Information Come From?

Information for our drug interactions is compiled from several drug compendia, including:

• Gold Standard Drug Database
• Micromedex
• Lexicomp
• DrugBank

The prescribing information for each drug, as published on DailyMED, is also used. 

Individual drug-drug interaction detail pages contain references specific to that interaction. You can click on the reference number within brackets '[]' to see what reference was utilized.

The information posted is fact-checked by HelloPharmacist clinicians and reviewed quarterly.