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Can bactrim cause urinary retention?

Can bactrim cause urinary retention?

Navin Khosla NowPatientGreen tick
Created on 4 Jul 2024
Updated on 16 Jul 2024

Bactrim or Septra, is a widely prescribed antibiotic used to treat a variety of bacterial infections, including urinary tract infections (UTIs). While this medication is considered safe, it does have the potential to cause urinary retention, a condition where the bladder is unable to empty. Here, we will explore the reasons behind why this may happen.

What is urinary retention?

Urinary retention is a condition characterized by the inability to empty the bladder, resulting in a buildup of urine. This can lead to a feeling of incomplete bladder emptying, difficulty starting urination, a weak urine stream, and frequent or urgent urination.

Urinary retention can be either acute or chronic, where the condition persists over a more extended period. Acute urinary retention is a medical emergency, requiring prompt intervention to prevent serious side effects, such as bladder damage, kidney damage, and life-threatening infections.

What is Bactrim?

Bactrim is an antibiotic containing sulfamethoxazole and trimethoprim. It has a wide range of uses in the treatment and prevention of bacterial infections. Its can be used to treat various conditions including:

  • Urinary tract infections

Bactrim (trimethoprim-sulfamethoxazole) is commonly used for the treatment of urinary tract infections caused by Escherichia coli, Enterobacter species, Klebsiella species, Morganella morganii, Proteus mirabilis, and Proteus vulgaris.

  • Acute otitis media

In pediatric patients, Bactrim can be used for the treatment of acute otitis media caused by Streptococcus pneumoniae or Haemophilus influenzae.

Bactrim may be used for the treatment of Acute exacerbations of chronic bronchitis due to Streptococcus pneumoniae or Haemophilus influenzae.

  • Shigellosis

Bactrim can be used for the treatment of enteritis caused by Shigella flexneri and Shigella sonnei.

  • Pneumocystis jirovecii pneumonia

Bactrim is a treatment option for Pneumocystis jirovecii pneumonia and for prophylaxis against this infection in immunosuppressed individuals.

  • Traveler’s diarrhea

Bactrim can be used for the treatment of traveler’s diarrhea due to enterotoxigenic Escherichia coli.

Despite its widespread use, Bactrim is not without its contraindications and warnings.


Bactrim is contraindicated in the following situations:

  • Known hypersensitivity to trimethoprim or sulfonamides
  • History of drug-induced immune thrombocytopenia with use of trimethoprim and/or sulfonamides
  • Megaloblastic anemia due to folate deficiency
  • Patients less than 2 months of age
  • Severe renal insufficiency when renal function status cannot be monitored
  • Concomitant administration with dofetilide

Warnings and precautions

Warnings and precautions, include:

  • Embryofetal toxicity and an increased risk of congenital malformations
  • Severe allergic reactions, fulminant hepatic necrosis, agranulocytosis, aplastic anemia, and other life-threatening conditions
  • Hyperkalemia, hyponatremia, and other electrolyte disturbances, especially in patients with underlying disorders or concomitant medication use

Drug interactions

Drug interactions with Bactrim include:

Healthcare providers must consider these drug interactions and monitor patients when prescribing Bactrim in conjunction with other medications.

Sulfamethoxazole and trimethoprim are inhibitors of bacterial growth. The use of Bactrim has been shown to develop urinary retention in some patients. This is believed to be related to the mechanisms of action of the individual components of Bactrim.

Sulfamethoxazole and urinary retention

Sulfamethoxazole is a sulfonamide antibiotic. Some sulfonamides have been linked with the formation of crystalline deposits in the urinary tract, which can potentially block the flow of urine, leading to urinary retention.

Trimethoprim and urinary retention

Trimethoprim is known to inhibit the enzyme dihydrofolate reductase, which is involved in making folic acid. This can change the urinary environment and encourage crystals or stones to form that can obstruct urine flow.

Synergistic effects

The individual effects of sulfamethoxazole and trimethoprim on the urinary system can be boosted increasing the risk of urinary retention. Crystalline deposits and potential changes in the urinary environment can create a perfect environment for this side effect.

Risk factors

Certain factors may increase the risk of urinary retention occurring:

Underlying urological conditions

Patients with pre-existing urological conditions, such as benign prostatic hyperplasia (BPH), neurogenic bladder, or previous urinary tract surgeries, may be at a higher risk of developing urinary retention, making the urinary system more sensitive to the potential adverse effects of Bactrim.

Dehydration and metabolic abnormalities

Dehydration, metabolic disorders, or use of certain medications together, may alter the composition and pH of the urine and increase the risk of crystal formation and urinary retention in patients taking Bactrim.

Repeated Bactrim exposure

Patients who need prolonged or repeat courses of Bactrim may be at a greater risk of developing urinary retention.

Elderly patients

Older adults may be more susceptible to Bactrim-induced urinary retention due to age-related changes in the urinary system.


The primary symptom of Bactrim-induced urinary retention is the inability to fully empty the bladder, leading to a feeling of incomplete voiding, frequent urination, and a feeling of pressure or discomfort in the lower abdomen. In more severe cases, patients may experience acute urinary retention, characterized by a complete inability to urinate.

Diagnosing Bactrim-induced urinary retention involves a combination of patient history, physical examination, and diagnostic imaging. Healthcare providers may order imaging tests, such as abdominal X-rays or computed tomography (CT) scans, to detect urinary stones or other obstructions.

Treatment options

  • Discontinuation of Bactrim: Discontinue the medication, if possible, and transition to an alternative antibiotic that does not carry the same risk
  • Urologic intervention: Drain the bladder to relieve the obstruction and prevent complications. This may involve the use of a catheter
  • Fluid intake and hydration: This can help to dilute the urine and reduce the risk of crystal formation
  • Addressing underlying conditions: Such as benign prostatic hyperplasia or metabolic disorders
  • Supportive care: Hydration, pain management, and the use of alpha-blocker medications to facilitate bladder emptying
  • Preventive strategies: Maintaining adequate hydration, and adjusting dietary intake


Patients taking Bactrim should be closely monitored for the development of this adverse effect. Regular follow-up visits, routine imaging, and open communication are crucial to identify and manage Bactrim-induced urinary retention.

Balancing the risks and benefits of Bactrim

Healthcare professionals must weigh the benefits against the risks of urinary retention, particularly in patients with pre-existing urologic conditions or a history of recurrent UTIs. Alternative antibiotic options may be considered to minimize the risk.


Bactrim-induced urinary retention is a rare but significant adverse effect, especially in individuals with underlying risk factors. By understanding and recognizing the warning signs, and knowing how to avoid it from happening, healthcare teams can reduce the risks and ensure the safe and effective use of this antibiotic.


Medical Disclaimer

NowPatient has taken all reasonable steps to ensure that all material is factually accurate, complete, and current. However, the knowledge and experience of a qualified healthcare professional should always be sought after instead of using the information on this page. Before taking any drug, you should always speak to your doctor or another qualified healthcare provider.

The information provided here about medications is subject to change and is not meant to include all uses, precautions, warnings, directions, drug interactions, allergic reactions, or negative effects. The absence of warnings or other information for a particular medication does not imply that the medication or medication combination is appropriate for all patients or for all possible purposes.

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