Medicine for the Outdoors
Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Trimethoprim-Sulfamethoxazole and Drug Interaction

Urinary tract (bladder or kidney) infections are common in all age groups. Many antibiotics are used and are effective to treat these infections. In the overwhelming majority of cases, there aren’t any problems with prescribing antibiotics. However, there is the occasional allergic or adverse reaction.

In elders or persons suffering from other illnesses, there’s another factory to consider, namely, the possibility of a drug-drug interaction. If a person is already taking (many) medications, then any new drug can create an interaction, which is usually manifested by an abnormality in blood chemistry, or accentuation or blunting of a particular drug effect. For instance, anticoagulant drugs (“blood thinners”) may be rendered more potent, or a heart medication might be less effective because of a drug-drug interaction. Occasionally, a drug-drug interaction can be frankly dangerous, such as when it predisposes to a dangerous heart rhythm.

An antibiotic commonly used to treat urinary tract infections is trimethoprim-sulfamethoxazole (TMP-SMX). It’s also used to treat methicillin-resistant Staphylococcus aureus (MRSA) infections. Normally, one wouldn’t think twice about using this drug, but this approach should be re-examined. As noted by the American Society of Nephrology, persons taking a class of drugs known as “beta blockers,” commonly used to treat high blood pressure and certain heart conditions, who also take TMP-SMX, may develop dangerously high levels of potassium in their blood. So, another antibiotic, such as a cephalosporin or amoxicillin, should be selected.

Drug interactions are pervasive, because we all take so many medications. Be sure to discuss this possibility with your medical professional any time you are prescribed a new medication, or decide yourself to take a pharmaceutical remedy, including naturopathic remedies.


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About the Author

Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.