3.9 Sulfonamides

Open Resources for Nursing (Open RN)

Sulfonamides are one of the oldest broad-spectrum antimicrobial agents that work by competitively inhibiting bacterial metabolic enzymes needed for bacterial function.

Indications: Sulfonamides are used to treat urinary tract infections, otitis media, acute exacerbations of chronic bronchitis, and travelers’ diarrhea.

Mechanism of Action: This mechanism of action provides bacteriostatic inhibition of growth against a wide spectrum of gram-positive and gram-negative pathogens.

Specific Administration Considerations: Allergic reactions to sulfonamide medications are common and, therefore, patients should be monitored carefully for adverse effects including delayed hypersensitivity reactions. Sulfonamide medications increase the risk of crystalluria that can cause kidney stones or decreased kidney function; therefore, patients should increase their water intake while taking these medications.[1]

Patient Teaching & Education: The patient should receive education to complete the full prescribed dose of medications and take measures to not skip doses.  If a dose is missed, the patient should take the missed dose as soon as possible unless it is near the next dosing time.  The medication can cause increased photosensitivity, and patients should be educated to use sunscreen and protective clothing with sun exposure.  The patient should also report any rash, sore throat, fever, or mouth sores that might occur.  Unusual bleeding or bruising should also be reported to the provider.  If patients are receiving prolonged therapy, they may require platelet count monitoring.[2]

Now let’s take a closer look at the medication grid for trimethoprim-sulfamethoxazole in Table 3.9.[3]

Table 3.9 Sulfonamides Medication Grid

Administration Considerations
Therapeutic Effects
Side/Adverse Effects
Sulfonamides trimethoprim – sulfamethoxazole Check for allergies

Dose adjustment for renal impairment

Administer PO with 8 oz of water

Monitor urine output and for cloudiness or crystals

Do not administer IM

Use cautiously with cardiac antidysrhythmics

Use cautiously with oral antidiabetics; may increase hypoglycemic effects. Monitor glucose level carefully

Use cautiously with anticoagulant medications such as warfarin; may increase risk of bleeding. Monitor INR and patient for signs of bleeding

Monitor for systemic signs of infection:



Monitor actual site of infection

Monitor culture results, if obtained


Sulfonamides, including sulfonamide-containing products such as sulfamethoxaole /trimethoprim, should be discontinued at the first appearance of skin rash of any sign of adverse reaction


Critical Thinking Activity 3.9a

Using the above grid information, consider the following clinical scenario question:

A nurse is caring for an elderly diabetic patient who has been prescribed trimethoprim-sulfamethoxazole for a urinary tract infection.  What nursing interventions will be implemented prior to medication administration?

Note: Answers to the Critical Thinking activities can be found in the “Answer Key” sections at the end of the book.

  1. This work is a derivative of Microbiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/microbiology/pages/1-introduction
  2. uCentral from Unbound Medicine. https://www.unboundmedicine.com/ucentral
  3. Daily Med, https://dailymed.nlm.nih.gov/dailymed/index.cfm, used for hyperlinked medications in this module. Retrieved June 27, 2019


Icon for the Creative Commons Attribution 4.0 International License

Nursing Pharmacology Copyright © 2020 by Open Resources for Nursing (Open RN) is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

Share This Book